fix: add the two includes clang-tidy reported as missing

misc-include-cleaner on the changed lines:
  TextureLibrary.cpp uses DecodedHeightTexture, which only reached it through
  TextureLibrary.hpp; it now includes libslic3r/TextureDisplacement.hpp itself.
  The contrast test uses std::not_equal_to, so <functional>.

src/libslic3r/TextureDisplacement.cpp

@@ -157,12 +157,33 @@ struct SmoothedTextureCache
     {
         std::weak_ptr<const std::vector<unsigned char>> source;
         float                                           smoothing = 0.f;
+        // Part of the key, not of the result: smoothing is applied *after* the panel's adjustments, so a
+        // blur computed over one set of adjustments is not the blur another set would give.
+        TextureAdjustments                              adjust;
         DecodedHeightTexture                            texture;
     };
     std::mutex                                   mutex;
     std::unordered_map<const void *, Entry>      entries;
 };
 SmoothedTextureCache g_smoothed_texture_cache;
+
+// The adjusted copy, cached between the raw decode and the smoothed one. Needed for the same reason the
+// smoothed cache is: while a slider in the image-adjustment panel moves, the thumbnail, the shaded
+// preview's height and colour textures, the UV editor backdrop and the displacement preview job all ask
+// for the same (image, adjustments) pair within one frame, and each of them running a full-size resample
+// of its own is what would make the panel unusable on a large texture.
+struct AdjustedTextureCache
+{
+    struct Entry
+    {
+        std::weak_ptr<const std::vector<unsigned char>> source;
+        TextureAdjustments                              adjust;
+        DecodedHeightTexture                            texture;
+    };
+    std::mutex                              mutex;
+    std::unordered_map<const void *, Entry> entries;
+};
+AdjustedTextureCache g_adjusted_texture_cache;
 } // namespace
 
 namespace {
@@ -338,6 +359,34 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
         entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), result };
     }
 
+    // The image-adjustment panel's live edits, on top of the decode and before the smoothing. Before,
+    // because `preview_adjust` is an edit to the image while `smoothing` is a live low-pass over whatever
+    // the image is - the same order the panel presents them in, and the same order a commit bakes in.
+    //
+    // Nothing applies here once the panel has closed: it resets preview_adjust to identity, and identity
+    // is a no-op that costs one comparison.
+    if (!layer.preview_adjust.identity()) {
+        bool have_adjusted = false;
+        {
+            std::lock_guard<std::mutex> lock(g_adjusted_texture_cache.mutex);
+            auto it = g_adjusted_texture_cache.entries.find(key);
+            if (it != g_adjusted_texture_cache.entries.end() && it->second.adjust == layer.preview_adjust &&
+                it->second.source.lock() == layer.image_data) {
+                result        = it->second.texture;
+                have_adjusted = true;
+            }
+        }
+        if (!have_adjusted) {
+            result = apply_texture_adjustments(result, layer.preview_adjust);
+            std::lock_guard<std::mutex> lock(g_adjusted_texture_cache.mutex);
+            auto &entries = g_adjusted_texture_cache.entries;
+            for (auto it = entries.begin(); it != entries.end();)
+                it = it->second.source.expired() ? entries.erase(it) : std::next(it);
+            entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data),
+                             layer.preview_adjust, result };
+        }
+    }
+
     // Smoothing radius scales with the texture so the same slider value blurs the same *fraction* of
     // the image whatever resolution it came in at, and stays continuous in the slider - see
     // smooth_height_pixels(). The cap is a cost limit, not part of the mapping: the blur is
@@ -348,7 +397,7 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
             std::lock_guard<std::mutex> lock(g_smoothed_texture_cache.mutex);
             auto it = g_smoothed_texture_cache.entries.find(key);
             if (it != g_smoothed_texture_cache.entries.end() && it->second.smoothing == layer.smoothing &&
-                it->second.source.lock() == layer.image_data)
+                it->second.adjust == layer.preview_adjust && it->second.source.lock() == layer.image_data)
                 return it->second.texture;
         }
         const float span   = 0.05f * float(std::min(result.width, result.height));
@@ -372,12 +421,70 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
         auto &entries = g_smoothed_texture_cache.entries;
         for (auto it = entries.begin(); it != entries.end();)
             it = it->second.source.expired() ? entries.erase(it) : std::next(it);
-        entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), layer.smoothing, result };
+        entries[key] = { std::weak_ptr<const std::vector<unsigned char>>(layer.image_data), layer.smoothing,
+                         layer.preview_adjust, result };
     }
     return result;
 }
 
 namespace {
+// Fraction of the short side that TextureAdjustments::blur == 1 blurs over, and the cost cap on it.
+// Deliberately the same pair decode_height_texture() uses for the Smoothing slider - see
+// adjustment_blur_radius().
+constexpr float SOURCE_BLUR_SPAN   = 0.05f;
+constexpr float SOURCE_BLUR_MAX_PX = 48.f;
+
+// Radius of the unsharp mask's blurred reference, in texels. Small and only mildly resolution-dependent:
+// a sharpen is meant to act on the finest detail the image holds, so its radius tracks the texel grid
+// rather than the picture's size. 1024x1024 gives ~2 texels, the usual photo-editor default.
+float unsharp_radius(int width, int height)
+{
+    return std::max(1.f, 0.002f * float(std::min(width, height)));
+}
+
+// Brightness as a *lift* toward white (or toward black) rather than an additive offset: positive b maps
+// v to v + b*(1 - v), negative to v*(1 + b). Both reach the endpoint exactly at |b| == 1 while staying
+// monotonic and non-clipping in between, which an additive shift does not - it drives a whole region to
+// a flat 255 and, because this image is also the height map, that region bakes as flat relief rather
+// than as bright relief. Keeping the curve injective keeps the detail in it.
+float apply_brightness(float v, float b)
+{
+    return b >= 0.f ? v + b * (1.f - v) : v * (1.f + b);
+}
+
+// Contrast about the 0.5 pivot. Gain is 1/(1-c) going up (c == 1 would be an infinite-slope threshold, so
+// the caller's clamp keeps it finite) and 1+c going down, reaching a flat mid-grey at c == -1.
+float apply_contrast(float v, float c)
+{
+    const float gain = c >= 0.f ? 1.f / std::max(1e-3f, 1.f - c) : 1.f + c;
+    return (v - 0.5f) * gain + 0.5f;
+}
+
+// Blur then sharpen one 8-bit channel in place. Shared by the grayscale path and by each of a colour
+// image's three channels, so every channel gets the identical spatial treatment and a colour image's
+// hue cannot shift just because its channels were filtered differently.
+void adjust_channel_spatial(std::vector<uint8_t> &channel, int width, int height, float blur, float sharpness)
+{
+    if (blur > 0.f)
+        smooth_height_pixels(channel, width, height, adjustment_blur_radius(blur, width, height));
+
+    if (sharpness <= 0.f)
+        return;
+
+    // Unsharp mask: push each texel away from its local average by `amount` times the difference. The
+    // blurred reference is a copy, so the sharpen reads the un-sharpened neighbourhood everywhere rather
+    // than its own partly-written output.
+    std::vector<uint8_t> base = channel;
+    smooth_height_pixels(base, width, height, unsharp_radius(width, height));
+    const float amount = 1.5f * std::clamp(sharpness, 0.f, 1.f);
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, channel.size()), [&](const tbb::blocked_range<size_t> &r) {
+        for (size_t i = r.begin(); i < r.end(); ++i) {
+            const float v = float(channel[i]) + amount * (float(channel[i]) - float(base[i]));
+            channel[i]    = uint8_t(std::lround(std::clamp(v, 0.f, 255.f)));
+        }
+    });
+}
+
 struct TextureDetailCache
 {
     std::mutex mutex;
@@ -386,6 +493,150 @@ struct TextureDetailCache
 TextureDetailCache g_texture_detail_cache;
 } // namespace
 
+float adjustment_blur_radius(float blur, int width, int height)
+{
+    if (blur <= 0.f || width <= 0 || height <= 0)
+        return 0.f;
+    const float span = SOURCE_BLUR_SPAN * float(std::min(width, height));
+    return std::clamp(blur, 0.f, 1.f) * std::min(span, SOURCE_BLUR_MAX_PX);
+}
+
+DecodedHeightTexture downscale_height_texture(const DecodedHeightTexture &src, int max_px)
+{
+    if (src.empty() || max_px <= 0 || (src.width <= max_px && src.height <= max_px))
+        return src;
+
+    const int  scale = std::max(1, (std::max(src.width, src.height) + max_px - 1) / max_px);
+    const int  w     = std::max(1, src.width / scale);
+    const int  h     = std::max(1, src.height / scale);
+    const bool color = src.has_color();
+
+    DecodedHeightTexture out;
+    out.width  = w;
+    out.height = h;
+    out.pixels.resize(size_t(w) * size_t(h));
+    if (color)
+        out.rgb.resize(size_t(w) * size_t(h) * 3);
+
+    tbb::parallel_for(tbb::blocked_range<int>(0, h), [&](const tbb::blocked_range<int> &r) {
+        for (int y = r.begin(); y < r.end(); ++y)
+            for (int x = 0; x < w; ++x) {
+                // The source block this destination texel covers. The max() keeps the block non-empty
+                // when rounding would otherwise collapse it.
+                const int x0 = x * src.width / w, x1 = std::max(x0 + 1, (x + 1) * src.width / w);
+                const int y0 = y * src.height / h, y1 = std::max(y0 + 1, (y + 1) * src.height / h);
+                uint32_t  sum_h = 0, sum_c[3] = { 0, 0, 0 }, n = 0;
+                for (int sy = y0; sy < y1 && sy < src.height; ++sy)
+                    for (int sx = x0; sx < x1 && sx < src.width; ++sx, ++n) {
+                        const size_t si = size_t(sy) * size_t(src.width) + size_t(sx);
+                        sum_h += src.pixels[si];
+                        if (color)
+                            for (int c = 0; c < 3; ++c)
+                                sum_c[c] += src.rgb[si * 3 + size_t(c)];
+                    }
+                const size_t di = size_t(y) * size_t(w) + size_t(x);
+                out.pixels[di]  = n > 0 ? uint8_t(sum_h / n) : 0;
+                if (color)
+                    for (int c = 0; c < 3; ++c)
+                        out.rgb[di * 3 + size_t(c)] = n > 0 ? uint8_t(sum_c[c] / n) : 0;
+            }
+    });
+    return out;
+}
+
+DecodedHeightTexture apply_texture_adjustments(const DecodedHeightTexture &src, const TextureAdjustments &adj)
+{
+    DecodedHeightTexture out = src;
+    if (src.empty() || adj.identity())
+        return out;
+
+    const int    w = out.width;
+    const int    h = out.height;
+    const size_t n = size_t(w) * size_t(h);
+
+    const float brightness = std::clamp(adj.brightness, -1.f, 1.f);
+    // Short of 1, so apply_contrast()'s gain stays finite; at this value it is already a 1000x slope,
+    // i.e. a threshold in all but name.
+    const float contrast   = std::clamp(adj.contrast, -1.f, 0.999f);
+    const float blur       = std::clamp(adj.blur, 0.f, 1.f);
+    const float sharpness  = std::clamp(adj.sharpness, 0.f, 1.f);
+
+    // The tonal pass: a 256-entry lookup table, because brightness and contrast are the same scalar
+    // curve for every texel and every channel. Building it once beats evaluating two curves a few
+    // million times, and it is what keeps this pass off the panel's critical path.
+    std::array<uint8_t, 256> tone{};
+    for (int i = 0; i < 256; ++i) {
+        float v = float(i) / 255.f;
+        v       = apply_brightness(v, brightness);
+        v       = apply_contrast(v, contrast);
+        tone[size_t(i)] = uint8_t(std::lround(std::clamp(v, 0.f, 1.f) * 255.f));
+    }
+
+    if (!out.has_color()) {
+        // Grayscale: one channel, and hue has nothing to turn.
+        tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
+            for (size_t i = r.begin(); i < r.end(); ++i)
+                out.pixels[i] = tone[out.pixels[i]];
+        });
+        adjust_channel_spatial(out.pixels, w, h, blur, sharpness);
+        return out;
+    }
+
+    // Colour: tone each channel through the same table, then rotate the hue about the luminance axis.
+    //
+    // The rotation is feColorMatrix's hueRotate matrix (SVG filters), which holds Rec.709 luma fixed.
+    // The height below is taken with decode_height_texture()'s Rec.601 coefficients instead, so a hue
+    // turn is not perfectly height-neutral - a few levels at full saturation. Reconciling the two would
+    // mean a different rotation than every other tool's, which is the worse trade: the user is watching
+    // the colour, and the height follows the colour by construction either way.
+    const float  theta = adj.hue_deg * float(M_PI) / 180.f;
+    const float  c     = std::cos(theta);
+    const float  s     = std::sin(theta);
+    const float  m[9]  = {
+        0.213f + c * 0.787f - s * 0.213f, 0.715f - c * 0.715f - s * 0.715f, 0.072f - c * 0.072f + s * 0.928f,
+        0.213f - c * 0.213f + s * 0.143f, 0.715f + c * 0.285f + s * 0.140f, 0.072f - c * 0.072f - s * 0.283f,
+        0.213f - c * 0.213f - s * 0.787f, 0.715f - c * 0.715f + s * 0.715f, 0.072f + c * 0.928f + s * 0.072f,
+    };
+    const bool turn_hue = adj.hue_deg != 0.f;
+
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
+        for (size_t i = r.begin(); i < r.end(); ++i) {
+            const float rr = float(tone[out.rgb[i * 3]]);
+            const float gg = float(tone[out.rgb[i * 3 + 1]]);
+            const float bb = float(tone[out.rgb[i * 3 + 2]]);
+            const float nr = turn_hue ? m[0] * rr + m[1] * gg + m[2] * bb : rr;
+            const float ng = turn_hue ? m[3] * rr + m[4] * gg + m[5] * bb : gg;
+            const float nb = turn_hue ? m[6] * rr + m[7] * gg + m[8] * bb : bb;
+            out.rgb[i * 3]     = uint8_t(std::lround(std::clamp(nr, 0.f, 255.f)));
+            out.rgb[i * 3 + 1] = uint8_t(std::lround(std::clamp(ng, 0.f, 255.f)));
+            out.rgb[i * 3 + 2] = uint8_t(std::lround(std::clamp(nb, 0.f, 255.f)));
+        }
+    });
+
+    // The spatial pass wants one channel at a time (smooth_height_pixels() is a single-channel blur, and
+    // reusing it is what keeps this consistent with Smoothing), so de-interleave, filter, re-interleave.
+    if (blur > 0.f || sharpness > 0.f) {
+        std::vector<uint8_t> channel(n);
+        for (int ch = 0; ch < 3; ++ch) {
+            for (size_t i = 0; i < n; ++i)
+                channel[i] = out.rgb[i * 3 + size_t(ch)];
+            adjust_channel_spatial(channel, w, h, blur, sharpness);
+            for (size_t i = 0; i < n; ++i)
+                out.rgb[i * 3 + size_t(ch)] = channel[i];
+        }
+    }
+
+    // Height is the luminance of the colour that came out, not the toned luminance of the colour that
+    // went in: the two differ once hue rotation or a per-channel clamp has moved the channels around,
+    // and a height that disagrees with the colour it is stored next to is the bug this avoids.
+    tbb::parallel_for(tbb::blocked_range<size_t>(0, n), [&](const tbb::blocked_range<size_t> &r) {
+        for (size_t i = r.begin(); i < r.end(); ++i)
+            out.pixels[i] = uint8_t(std::lround(0.299 * out.rgb[i * 3] + 0.587 * out.rgb[i * 3 + 1] +
+                                                0.114 * out.rgb[i * 3 + 2]));
+    });
+    return out;
+}
+
 TextureDetail analyze_texture_detail(const TextureDisplacementLayer &layer)
 {
     TextureDetail out;

src/libslic3r/TextureDisplacement.hpp

@@ -154,6 +154,38 @@ struct TextureIsland
 // chart to its true mm area, so a freshly unwrapped patch has uniform texel density to begin with.
 void average_island_scales(std::vector<TextureIsland> &islands);
 
+// Photo-style adjustments to a layer's source image, as the gizmo's image-adjustment panel sets them.
+//
+// These are *not* layer parameters: nothing here is stored on TextureDisplacementLayer and nothing here is
+// re-applied at bake time. The panel applies them once, to the image, and the result becomes the layer's
+// image - so the adjusted pixels feed the colour and the displacement together, and a brightness change
+// really does change the relief. That is the intended behaviour: one image, one source of truth, rather
+// than a second set of knobs the bake would have to replay in the right order.
+//
+// Contrast with TextureDisplacementLayer::smoothing, which *is* a layer parameter applied on every decode:
+// `blur` here is a destructive edit of the image, `smoothing` is a live low-pass over whatever the image is.
+struct TextureAdjustments
+{
+    float brightness = 0.f; // [-1, 1]; 0 unchanged, -1 black, +1 white
+    float contrast   = 0.f; // [-1, 1]; 0 unchanged, -1 flat mid-grey, +1 hard threshold
+    float sharpness  = 0.f; // [0, 1];  0 unchanged. Unsharp-mask amount
+    float blur       = 0.f; // [0, 1];  0 unchanged. Fraction of SOURCE_BLUR_SPAN, as `smoothing` is
+    float hue_deg    = 0.f; // [-180, 180]; 0 unchanged. No effect on a grayscale image - grey has no hue
+
+    bool identity() const
+    {
+        return brightness == 0.f && contrast == 0.f && sharpness == 0.f && blur == 0.f && hue_deg == 0.f;
+    }
+    // Exact equality, which is what is wanted: these come straight off sliders, and the question asked of
+    // them is "is this still the value the preview on screen was computed from", not "are these close".
+    bool operator==(const TextureAdjustments &o) const
+    {
+        return brightness == o.brightness && contrast == o.contrast && sharpness == o.sharpness &&
+               blur == o.blur && hue_deg == o.hue_deg;
+    }
+    bool operator!=(const TextureAdjustments &o) const { return !(*this == o); }
+};
+
 // One texture asset plus its projection/displacement parameters. Several layers may be painted
 // onto overlapping areas of the same volume: their displacements are combined per vertex, in slot
 // order, each layer folding into the total via its own TextureBlendMode (see
@@ -293,6 +325,18 @@ struct TextureDisplacementLayer
     // for the boundary to be drawn on.
     bool color_enabled = false;
 
+    // Live, unsaved image adjustments from the gizmo's image-adjustment panel, applied by
+    // decode_height_texture() on top of the decoded image - so while the panel is open the relief, the
+    // colour, the thumbnails and the bake all see the adjusted image, and moving a slider really does
+    // change the displacement. See TextureAdjustments.
+    //
+    // Deliberately *not* serialized, by either save()/load() here or the .3mf: it is the state of an open
+    // editor, not a property of the layer. The panel resets it when it closes, and "Save as copy" resolves
+    // it by writing a new image and pointing the layer at that - which is the only way an adjustment
+    // becomes permanent. A project saved mid-adjustment therefore stores the unadjusted image, which is
+    // the honest answer: nothing was committed.
+    TextureAdjustments preview_adjust;
+
     bool empty() const { return !image_data || image_data->empty(); }
 
     template<class Archive> void save(Archive &ar) const
@@ -489,6 +533,36 @@ DecodedHeightTexture decode_height_texture(const TextureDisplacementLayer &layer
 // texture - cheap enough to ask every frame. Smoothing does not change it, so the raw decode is what is read.
 bool height_texture_has_color(const TextureDisplacementLayer &layer);
 
+// Applies `adj` to `src` and returns the result; `src` is left alone. An empty `src`, or an identity
+// `adj`, gives back a copy.
+//
+// Order is tonal, then spatial: brightness, contrast and hue per texel first, then blur, then sharpness.
+// Sharpness last is what lets the two spatial knobs be used together - blur to kill speckle, then
+// sharpness to put the real edges back - instead of the blur simply undoing the sharpen.
+//
+// Grayscale in, grayscale out (`rgb` stays empty): promoting a grey image to RGB would hand the layer's
+// colour feature a row of identical greys to "colour" the model with, and triple the stored PNG for it.
+// For a colour image the height is recomputed as the luminance of the *adjusted* colour, with
+// decode_height_texture()'s own coefficients, so the relief and the colour can never drift apart.
+DecodedHeightTexture apply_texture_adjustments(const DecodedHeightTexture &src, const TextureAdjustments &adj);
+
+// Blur radius, in texels, that TextureAdjustments::blur == 1 means on a `min(width, height)`-sized image:
+// the same 5%-of-the-short-side span the Smoothing slider uses, under the same 48-texel cost cap, so the
+// two controls bite at the same rate and a user moving between them is not surprised.
+float adjustment_blur_radius(float blur, int width, int height);
+
+// Box-filters `src` down so neither side exceeds `max_px`, preserving aspect; never upscales, and
+// returns a copy when it already fits. Colour and height are filtered the same way, and the height
+// stays the height - it is not recomputed from the filtered colour, because a box filter is linear and
+// luminance is linear in the channels, so the two agree already.
+//
+// This is what lets the adjustment panel's live preview cost depend on the size of the box it is drawn
+// in rather than on the size of the image: adjusting a downscaled copy per slider frame, and the
+// full-size image only once, on commit. A box filter (rather than a plain decimation) is the point -
+// these textures are high-frequency by nature, and dropping texels would alias the preview into
+// showing detail the adjustment is not actually producing.
+DecodedHeightTexture downscale_height_texture(const DecodedHeightTexture &src, int max_px);
+
 // Maps a linear RGB colour in [0, 1] to an index into the caller's palette, or -1 for "no colour".
 //
 // Deliberately a callback rather than a function here: matching a colour to a filament is a

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.cpp

@@ -43,6 +43,7 @@
 #include <cstdint>
 #include <functional>
 #include <chrono>
+#include <future>
 #include <cstdio>
 #include <glad/gl.h>
 #include <imgui.h>
@@ -120,6 +121,14 @@ constexpr int THUMBNAIL_MAX_PX = 128;
 // blur of it - which is what made Fast look flatter and softer than the result it was previewing.
 constexpr int HEIGHT_TEX_MAX_PX = 2048;
 
+// Size the image-adjustment panel's live preview is computed and uploaded at. The panel draws the image
+// in a box about 240 px wide, so there is nothing to show above this - and the preview is recomputed on
+// every slider move, which is what makes its cost worth bounding. Measured on a 1024x1024 with every
+// knob engaged, a full-size pass is 13-19 ms grayscale / 40-60 ms in colour (130-190 ms at 2048 in
+// colour); the same pass on a 384 px copy is 3-4 ms / 9-12 ms, and it runs off the UI thread besides.
+// The full-size image is only ever adjusted once, on commit.
+constexpr int ADJUST_PREVIEW_MAX_PX = 384;
+
 // How many rings of vertex-adjacent triangles either side of the paint's edge join the border refine
 // band (see collect_paint_region()). Two is enough to grade the size change without the band's own
 // cost growing to matter: it is a ring around a perimeter, not an area.
@@ -525,6 +534,10 @@ void GLGizmoTextureDisplacement::on_shutdown()
     // progress poll, and its completion handler then finds nothing to do.
     m_preview_generation->fetch_add(1);
     m_preview_job_pending = false;
+    // The adjustment panel holds a full-size decode of its layer's image, which is the largest thing
+    // here; a closed gizmo should not keep it alive. Discards the edit, as closing the gizmo on an open
+    // panel implies.
+    close_image_adjust();
     // The palette caches hold the last volume's images; a closed gizmo should not keep them alive.
     m_palette_cache.clear();
     m_palette_quantizer      = nullptr;
@@ -2450,9 +2463,12 @@ void GLGizmoTextureDisplacement::update_uv_editor()
     // before, and independently of, the unwrap - the texture belongs on screen before anything is unwrapped - and
     // only when the choice, the layer's image or its smoothing changed, because the height image is large.
     const UVBackground desired_bg = (m_uv_check_mode == UVCheckMode::Checker) ? UVBackground::Checker : UVBackground::Height;
-    const bool bg_smoothing_changed = (desired_bg == UVBackground::Height) && (m_uv_editor_bg_smoothing != layer->smoothing);
+    const bool bg_smoothing_changed = (desired_bg == UVBackground::Height) &&
+                                      (m_uv_editor_bg_smoothing != layer->smoothing ||
+                                       !(m_uv_editor_bg_adjust == layer->preview_adjust));
     if (desired_bg != m_uv_editor_bg || layer->image_data.get() != m_uv_editor_bg_image || bg_smoothing_changed) {
         m_uv_editor_bg_smoothing = layer->smoothing;
+        m_uv_editor_bg_adjust    = layer->preview_adjust;
         m_uv_editor_bg_image     = layer->image_data.get();
         m_uv_editor_bg           = desired_bg;
         if (desired_bg == UVBackground::Checker) {
@@ -3678,7 +3694,7 @@ void GLGizmoTextureDisplacement::ensure_panel_icons()
         "menu_obj_sphere.svg", "menu_obj_cube.svg", "menu_obj_cylinder.svg", "texture_displacement_map_unwrap.svg",
         "texture_displacement_map_view.svg", "texture_displacement_tile_repeat.svg", "menu_mirror_x.svg",
         "texture_displacement_adjust.svg", "canvas_drag.svg", "texture_displacement_move_up.svg",
-        "texture_displacement_move_down.svg", "texture_displacement_drag.svg",
+        "texture_displacement_move_down.svg", "texture_displacement_drag.svg", "cog.svg",
         "texture_displacement_select_all.svg", "texture_displacement_erase_all.svg",
     };
     std::vector<std::string> paths;
@@ -3982,6 +3998,321 @@ void GLGizmoTextureDisplacement::render_texture_library_popup(const ImVec2 &pane
         m_picker_open_request = true;
     }
 }
+bool GLGizmoTextureDisplacement::load_image_adjust_source(const TextureDisplacementLayer &layer)
+{
+    if (layer.empty())
+        return false;
+
+    // The *raw* image: neither the layer's Smoothing nor the panel's own preview_adjust, so what the
+    // sliders act on is always the image as it is actually stored rather than the last preview of it.
+    // Without clearing preview_adjust here the adjustment would compound on itself every reload.
+    TextureDisplacementLayer raw = layer;
+    raw.smoothing                = 0.f;
+    raw.preview_adjust           = TextureAdjustments{};
+
+    DecodedHeightTexture decoded = decode_height_texture(raw);
+    if (decoded.empty())
+        return false;
+
+    m_adjust_source         = std::move(decoded);
+    m_adjust_preview_source = downscale_height_texture(m_adjust_source, ADJUST_PREVIEW_MAX_PX);
+    m_adjust_source_image   = layer.image_data.get();
+    // The unadjusted image, so the box is filled now rather than one background pass later. Pairing it
+    // with an identity `shown` is what makes update_image_adjust_preview() relaunch for the sliders'
+    // current values against the new source instead of deciding it is already showing them.
+    m_adjust_preview_shown = TextureAdjustments{};
+    m_adjust_preview_tex   = upload_height_thumbnail(m_adjust_preview_source, ADJUST_PREVIEW_MAX_PX);
+    m_adjust_preview_valid = m_adjust_preview_tex != nullptr;
+    return true;
+}
+
+void GLGizmoTextureDisplacement::open_image_adjust(const TextureDisplacementLayer &layer)
+{
+    if (layer.empty() || layer.slot < 0)
+        return;
+
+    close_image_adjust(); // reverts and clears any previous panel
+
+    if (!load_image_adjust_source(layer))
+        return;
+
+    m_adjust           = TextureAdjustments{};
+    m_adjust_applied   = TextureAdjustments{};
+    m_adjust_slot      = layer.slot;
+    const ModelVolume *mv = texture_volume();
+    m_adjust_volume_id = mv != nullptr ? mv->id().id : 0;
+}
+
+void GLGizmoTextureDisplacement::close_image_adjust()
+{
+    // Revert the layer's live adjustment. Every exit that reaches here is a discard: a commit resets
+    // preview_adjust itself, before pointing the layer at the file that already carries the edit, so this
+    // cannot undo a committed adjustment.
+    //
+    // Found by the id recorded when the panel opened rather than through texture_volume(), which answers
+    // for the *current* selection. One of the ways to get here is the selection having moved on, and
+    // reverting the newly selected object's layer instead would both miss the adjustment that is still
+    // live on the original volume and clear one the user never touched.
+    bool reverted = false;
+    if (m_adjust_slot >= 0 && m_adjust_volume_id != 0)
+        for (ModelObject *mo : wxGetApp().model().objects) {
+            for (ModelVolume *mv : mo->volumes) {
+                if (mv->id().id != m_adjust_volume_id)
+                    continue;
+                for (TextureDisplacementLayer &l : mv->texture_displacement_layers)
+                    if (l.slot == m_adjust_slot && !l.preview_adjust.identity()) {
+                        l.preview_adjust = TextureAdjustments{};
+                        reverted         = true;
+                    }
+            }
+        }
+
+    // std::async's future blocks here until the pass finishes. That is a few milliseconds on an image
+    // this small, and the alternative - a detached thread writing into the members of a closed panel -
+    // is worse.
+    if (m_adjust_preview_job.valid())
+        m_adjust_preview_job.wait();
+    m_adjust_preview_job = {};
+
+    m_adjust_slot           = -1;
+    m_adjust                = TextureAdjustments{};
+    m_adjust_applied        = TextureAdjustments{};
+    m_adjust_source         = DecodedHeightTexture{};
+    m_adjust_preview_source = DecodedHeightTexture{};
+    m_adjust_source_image   = nullptr;
+    m_adjust_volume_id      = 0;
+    m_adjust_preview_tex.reset();
+    m_adjust_preview_valid = false;
+
+    // Only while the gizmo is up: on_shutdown() also comes through here, and rebuilding a preview for a
+    // gizmo that is closing would be work for a model nobody is looking at. The reverted layer data is
+    // what matters there, and that is already done above.
+    if (reverted && m_state == On) {
+        rebuild_preview();
+        m_parent.set_as_dirty();
+    }
+}
+
+void GLGizmoTextureDisplacement::update_image_adjust_preview()
+{
+    if (m_adjust_preview_source.empty())
+        return;
+
+    // Collect a finished pass. wait_for(0) rather than get() outright: this runs inside the frame, and
+    // blocking on the worker here would hand back to the UI thread the very stall the worker exists to
+    // spare it.
+    if (m_adjust_preview_job.valid() &&
+        m_adjust_preview_job.wait_for(std::chrono::seconds(0)) == std::future_status::ready) {
+        const DecodedHeightTexture adjusted = m_adjust_preview_job.get();
+        m_adjust_preview_job                = {};
+        if (std::unique_ptr<GLTexture> tex = upload_height_thumbnail(adjusted, ADJUST_PREVIEW_MAX_PX)) {
+            m_adjust_preview_tex   = std::move(tex);
+            m_adjust_preview_shown = m_adjust_preview_running;
+            m_adjust_preview_valid = true;
+        }
+    }
+
+    // One pass at a time: whatever the sliders did while it ran is picked up by the next launch, so a
+    // drag collapses to the value the sliders ended on instead of queuing one pass per frame.
+    if (!m_adjust_preview_job.valid() && m_adjust != m_adjust_preview_shown) {
+        m_adjust_preview_running = m_adjust;
+        // Captured by value: the pass must not read members the UI thread goes on editing while it runs.
+        m_adjust_preview_job = std::async(std::launch::async,
+                                          [src = m_adjust_preview_source, adj = m_adjust_preview_running] {
+                                              return apply_texture_adjustments(src, adj);
+                                          });
+    }
+
+    // A pass in flight has no other way to get its result on screen: without a redraw request the canvas
+    // can sit idle, and the preview would only catch up on the next unrelated frame.
+    if (m_adjust_preview_job.valid())
+        m_parent.set_as_dirty();
+}
+
+void GLGizmoTextureDisplacement::commit_image_adjust(TextureDisplacementLayer &layer)
+{
+    if (m_adjust_source.empty() || m_adjust.identity()) {
+        // Nothing was changed, so there is nothing to save.
+        close_image_adjust();
+        return;
+    }
+
+    // The full-size pass, once: 13-19 ms grayscale / 40-60 ms colour on a 1024x1024 with every knob
+    // engaged. Run on the UI thread deliberately, unlike the live preview: this is a single click, and the
+    // rebuild that follows it - a CPU mesh displacement of the painted patch - is already an order of
+    // magnitude more work, synchronously, so moving only this off the thread would buy nothing a user
+    // could perceive.
+    const DecodedHeightTexture adjusted = apply_texture_adjustments(m_adjust_source, m_adjust);
+
+    std::string                              error;
+    const std::string                        stem  = layer.name.empty() ? std::string("texture") : layer.name;
+    const std::optional<TextureLibraryEntry> entry = save_texture_to_library(adjusted, stem, error);
+    if (!entry) {
+        show_error(nullptr, error);
+        return; // the panel stays open, and the layer keeps the live adjustment: the edit is not lost
+    }
+
+    // Cleared *before* the layer is pointed at the new file, and this ordering is the whole correctness of
+    // the commit: the saved image already has the adjustment baked into its pixels, so leaving
+    // preview_adjust set would apply brightness, contrast and the rest a second time on top of itself.
+    layer.preview_adjust = TextureAdjustments{};
+    // set_layer_texture() does the rest - the name, the recently-used ordering, a fresh image_data buffer
+    // (which is what invalidates every cache keyed by the old pointer), the undo snapshot and the rebuild.
+    set_layer_texture(layer, *entry);
+
+    close_image_adjust();
+}
+
+void GLGizmoTextureDisplacement::render_image_adjust_window(const ImVec2 &panel_min, const ImVec2 &panel_max)
+{
+    if (m_adjust_slot < 0)
+        return;
+
+    ModelVolume *mv = texture_volume();
+    // A different volume is selected than the one this panel was opened on. Slots are numbered per
+    // volume, so looking m_adjust_slot up here would find an unrelated layer rather than nothing.
+    if (mv == nullptr || mv->id().id != m_adjust_volume_id) {
+        close_image_adjust();
+        return;
+    }
+
+    TextureDisplacementLayer *layer = nullptr;
+    for (TextureDisplacementLayer &l : mv->texture_displacement_layers)
+        if (l.slot == m_adjust_slot)
+            layer = &l;
+    if (layer == nullptr) {
+        // The layer went away under the panel (removed, or merged away by an undo).
+        close_image_adjust();
+        return;
+    }
+
+    // The layer's image can be swapped from the texture picker while this panel is open - the panel is a
+    // window now, so the rest of the gizmo stays usable behind it. Re-read the source when that happens,
+    // keeping the slider positions: the user is adjusting this layer, and the 3D view has already moved to
+    // the new image (decode_height_texture() reads layer.image_data, which changed), so re-reading here is
+    // also what keeps the panel's photo and the model showing the same thing.
+    if (layer->image_data.get() != m_adjust_source_image && !load_image_adjust_source(*layer)) {
+        close_image_adjust(); // the new image cannot be decoded; nothing left to adjust
+        return;
+    }
+
+    const float img_w = std::round(m_imgui->scaled(16.f));
+    const float gap   = m_imgui->scaled(0.5f);
+    // Placed beside the panel on first appearance only, and left wherever the user drags it after that -
+    // it is a window, not a popup, so its position is theirs to keep.
+    const float win_w = img_w + 2.f * ImGui::GetStyle().WindowPadding.x;
+    const bool  left  = panel_min.x - gap - win_w >= 0.f;
+    ImGui::SetNextWindowPos(ImVec2(left ? panel_min.x - gap - win_w : panel_max.x + gap,
+                                   panel_min.y + m_imgui->scaled(4.f)), ImGuiCond_Appearing);
+
+    bool keep_open = true;
+    if (!ImGui::Begin((_u8L("Adjust image") + "##texture_adjust").c_str(), &keep_open,
+                      ImGuiWindowFlags_AlwaysAutoResize | ImGuiWindowFlags_NoCollapse)) {
+        ImGui::End();
+        if (!keep_open)
+            close_image_adjust();
+        return;
+    }
+
+    // Collect a finished pass and start one for the current slider values before the image is drawn, so
+    // the newest available result is what lands on screen this frame.
+    update_image_adjust_preview();
+
+    // The photo itself, at the image's own aspect so a non-square texture is not stretched.
+    const float aspect = m_adjust_source.height > 0 ? float(m_adjust_source.width) / float(m_adjust_source.height) : 1.f;
+    const float img_h  = std::round(img_w / std::max(0.05f, aspect));
+    if (m_adjust_preview_valid && m_adjust_preview_tex)
+        ImGui::Image((ImTextureID) (intptr_t) m_adjust_preview_tex->get_id(), ImVec2(img_w, img_h));
+    else
+        ImGui::Dummy(ImVec2(img_w, img_h));
+
+    // The label column is sized off the widest of the five labels, so the tracks line up whatever the
+    // translation does to their lengths.
+    float label_w = 0.f;
+    for (const wxString &l : { _L("Brightness"), _L("Contrast"), _L("Sharpness"), _L("Blur"), _L("Hue") })
+        label_w = std::max(label_w, ImGui::CalcTextSize(into_u8(l).c_str()).x);
+    label_w += m_imgui->scaled(1.2f);
+    // An explicit track width rather than a fill-to-the-right one: this window is AlwaysAutoResize, so its
+    // width comes from its content, and an item asking for "whatever is left" would make the width depend
+    // on itself. The image above sets the content width, and the sliders match it.
+    const float slider_w = std::max(m_imgui->scaled(4.f), img_w - label_w);
+
+    const auto row = [&](const char *id, const wxString &label, float *v, float v_min, float v_max,
+                         const char *format, bool enabled, const std::string &tip) {
+        const float x0 = ImGui::GetCursorPosX();
+        ImGui::AlignTextToFramePadding();
+        m_imgui->text(label);
+        ImGui::SameLine();
+        ImGui::SetCursorPosX(std::max(ImGui::GetCursorPosX(), x0 + label_w));
+        ImGui::SetNextItemWidth(slider_w);
+        m_imgui->disabled_begin(!enabled);
+        ImGui::SliderFloat(id, v, v_min, v_max, format, ImGuiSliderFlags_AlwaysClamp);
+        m_imgui->disabled_end();
+        // Only on an enabled row: a disabled item does not report hover, so a tooltip on one would never
+        // be shown. What has to be said about a disabled slider is written out below it instead.
+        if (enabled && !tip.empty() && ImGui::IsItemHovered())
+            m_imgui->tooltip(tip, ImGui::GetFontSize() * 20.f);
+    };
+
+    row("##adj_brightness", _L("Brightness"), &m_adjust.brightness, -1.f, 1.f, "%.2f", true, {});
+    row("##adj_contrast", _L("Contrast"), &m_adjust.contrast, -1.f, 1.f, "%.2f", true, {});
+    row("##adj_sharpness", _L("Sharpness"), &m_adjust.sharpness, 0.f, 1.f, "%.2f", true,
+        _u8L("Brings out the finest detail in the image. Applied after Blur, so the two can be used "
+             "together: blur away the speckle, then sharpen the edges that remain."));
+    row("##adj_blur", _L("Blur"), &m_adjust.blur, 0.f, 1.f, "%.2f", true,
+        _u8L("Blurs the image itself. The layer's own Smoothing slider softens the relief without altering "
+             "the image, and is the one to reach for first."));
+    // Grey has no hue to turn, and the shipped library is grayscale - so on most textures this is a
+    // slider that would visibly do nothing. Disabled with the reason given, rather than hidden.
+    const bool has_color = m_adjust_source.has_color();
+    row("##adj_hue", _L("Hue"), &m_adjust.hue_deg, -180.f, 180.f, "%.0f°", has_color, {});
+    if (!has_color) {
+        ImGui::PushTextWrapPos(ImGui::GetCursorPosX() + img_w);
+        ImGui::TextDisabled("%s", _u8L("This texture is grayscale, so it has no hue to shift.").c_str());
+        ImGui::PopTextWrapPos();
+    }
+
+    if (m_imgui->button(_L("Reset")))
+        m_adjust = TextureAdjustments{};
+
+    // Hand the sliders to the layer, which is what puts the adjusted image in front of the displacement:
+    // decode_height_texture() applies preview_adjust, so the relief, the colour and the thumbnails all
+    // follow from here. Written every frame rather than only on a change, so an undo snapshot or a
+    // reselection that resets the layer cannot leave the model showing an adjustment the panel has moved
+    // on from.
+    layer->preview_adjust = m_adjust;
+    if (m_adjust != m_adjust_applied) {
+        m_adjust_applied = m_adjust;
+        // Marked dirty rather than rebuilt here: the panel's own flag is consumed by the main panel's
+        // "rebuild once the mouse is released" rule, so dragging a slider recomputes the displacement
+        // once, on release, instead of on every frame of the drag. That is what keeps the UI responsive
+        // while a full-size resample and a mesh displacement happen behind it.
+        m_preview_params_dirty = true;
+        // This window is drawn after the block that consumes that flag, so the rebuild happens on a later
+        // frame - which means there has to *be* one. Cheap insurance: a slider release that generated no
+        // further canvas event would otherwise leave the flag set and the model unchanged until something
+        // unrelated redrew.
+        m_parent.set_as_dirty();
+    }
+
+    ImGui::Separator();
+    m_imgui->text_wrapped(_u8L("The model updates when you release a slider. Save as copy writes the "
+                               "adjusted image to your texture library and points this layer at it."), img_w);
+
+    const bool cancel = m_imgui->button(_L("Cancel"));
+    ImGui::SameLine();
+    // Nothing to save until a slider has actually moved.
+    m_imgui->disabled_begin(m_adjust.identity());
+    const bool as_copy = m_imgui->button(_L("Save as copy"));
+    m_imgui->disabled_end();
+
+    ImGui::End();
+
+    if (cancel || !keep_open)
+        close_image_adjust();
+    else if (as_copy)
+        commit_image_adjust(*layer);
+}
 
 void GLGizmoTextureDisplacement::remove_texture_layer(int slot)
 {
@@ -4040,6 +4371,7 @@ void GLGizmoTextureDisplacement::swap_layer_slots(int slot_a, int slot_b)
     std::swap(m_thumbnails[a], m_thumbnails[b]);
     std::swap(m_thumbnail_source[a], m_thumbnail_source[b]);
     std::swap(m_thumbnail_smoothing[a], m_thumbnail_smoothing[b]);
+    std::swap(m_thumbnail_adjust[a], m_thumbnail_adjust[b]);
     std::swap(m_layer_expanded[a], m_layer_expanded[b]);
     if (m_active_layer_slot == slot_a)
         m_active_layer_slot = slot_b;
@@ -5303,7 +5635,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
 
     const size_t slot = size_t(layer.slot);
     if (m_thumbnails[slot] && m_thumbnail_source[slot] == layer.image_data.get() &&
-        m_thumbnail_smoothing[slot] == layer.smoothing)
+        m_thumbnail_smoothing[slot] == layer.smoothing && m_thumbnail_adjust[slot] == layer.preview_adjust)
         return m_thumbnails[slot].get();
 
     // Reuses the already-decoded, already-cached grayscale pixels (see decode_height_texture()'s
@@ -5317,6 +5649,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_thumbnail(const TextureDisplace
     m_thumbnails[slot]          = std::move(texture);
     m_thumbnail_source[slot]    = layer.image_data.get();
     m_thumbnail_smoothing[slot] = layer.smoothing;
+    m_thumbnail_adjust[slot]    = layer.preview_adjust;
     return m_thumbnails[slot].get();
 }
 
@@ -5324,7 +5657,8 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_color_texture(const TextureDisp
 {
     if (layer.empty() || !layer.color_enabled)
         return nullptr;
-    if (m_color_tex && m_color_tex_source == layer.image_data.get() && m_color_tex_smoothing == layer.smoothing)
+    if (m_color_tex && m_color_tex_source == layer.image_data.get() && m_color_tex_smoothing == layer.smoothing &&
+        m_color_tex_adjust == layer.preview_adjust)
         return m_color_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_color_texture(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
@@ -5336,6 +5670,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_color_texture(const TextureDisp
     m_color_tex           = std::move(texture);
     m_color_tex_source    = layer.image_data.get();
     m_color_tex_smoothing = layer.smoothing;
+    m_color_tex_adjust    = layer.preview_adjust;
     return m_color_tex.get();
 }
 
@@ -5346,7 +5681,8 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
 
     // One slot, not one per layer: the preview shader only ever shades the *active* layer, so a single
     // full-resolution upload is enough and the VRAM cost stays at one texture rather than eight.
-    if (m_height_tex && m_height_tex_source == layer.image_data.get() && m_height_tex_smoothing == layer.smoothing)
+    if (m_height_tex && m_height_tex_source == layer.image_data.get() && m_height_tex_smoothing == layer.smoothing &&
+        m_height_tex_adjust == layer.preview_adjust)
         return m_height_tex.get();
 
     std::unique_ptr<GLTexture> texture = upload_height_thumbnail(decode_height_texture(layer), HEIGHT_TEX_MAX_PX);
@@ -5356,6 +5692,7 @@ GLTexture *GLGizmoTextureDisplacement::get_layer_height_texture(const TextureDis
     m_height_tex           = std::move(texture);
     m_height_tex_source    = layer.image_data.get();
     m_height_tex_smoothing = layer.smoothing;
+    m_height_tex_adjust    = layer.preview_adjust;
     return m_height_tex.get();
 }
 
@@ -6412,7 +6749,7 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                 ImGui::SameLine();
 
                 const std::string not_painted = _u8L("not painted");
-                const float right_w = (painted ? 0.f : ImGui::CalcTextSize(not_painted.c_str()).x + gap_s) + 3.f * frame_h + 2.f * gap_s;
+                const float right_w = (painted ? 0.f : ImGui::CalcTextSize(not_painted.c_str()).x + gap_s) + 4.f * frame_h + 3.f * gap_s;
                 const float name_w  = std::max(frame_h, ImGui::GetWindowContentRegionMax().x - card_pad - ImGui::GetCursorPosX() - gap_s - right_w);
                 ImGui::PushStyleColor(ImGuiCol_HeaderHovered, ImVec4(orca.x, orca.y, orca.z, 0.2f));
                 ImGui::PushStyleColor(ImGuiCol_HeaderActive, ImVec4(orca.x, orca.y, orca.z, 0.35f));
@@ -6426,6 +6763,16 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
                     ImGui::SameLine();
                     ImGui::TextDisabled("%s", not_painted.c_str());
                 }
+                // Between the name and the order arrows: it acts on the image the name refers to, so it
+                // belongs with the name rather than with the controls that reorder the stack.
+                ImGui::SameLine();
+                m_imgui->disabled_begin(busy || layer.empty());
+                if (icon_button(613 + layer.slot, "cog.svg", frame_h, _L("Adjust image"),
+                                _u8L("Brightness, contrast, sharpness, blur and hue, shown on the image and on the "
+                                     "model as you set them. Save as copy writes the result to your texture library "
+                                     "and points this layer at it.")))
+                    open_image_adjust(layer);
+                m_imgui->disabled_end();
                 ImGui::SameLine();
                 m_imgui->disabled_begin(busy || li == 0);
                 if (icon_button(611, "texture_displacement_move_up.svg", frame_h, _L("Move up"), _L("Move up - applied earlier"))) {
@@ -7225,10 +7572,15 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         set_active_layer(m_picker_slot);
 
     // In this window's scope, where the popup's open request and the popup itself share one ID stack.
+    ImVec2 panel_rect_min, panel_rect_max;
     {
         const ImVec2 win_min = ImGui::GetWindowPos();
         const ImVec2 win_sz  = ImGui::GetWindowSize();
         render_texture_library_popup(win_min, ImVec2(win_min.x + win_sz.x, win_min.y + win_sz.y));
+        // Only recorded here. The image-adjustment panel is a top-level window rather than a popup, so it
+        // cannot be begun inside this one; it is drawn after GizmoImguiEnd() below.
+        panel_rect_min = win_min;
+        panel_rect_max = ImVec2(win_min.x + win_sz.x, win_min.y + win_sz.y);
     }
 
     // ImGui sliders report "changed" continuously on every frame while being dragged, not just once on
@@ -7465,6 +7817,11 @@ void GLGizmoTextureDisplacement::on_render_input_window(float x, float y, float
         m_parent.request_extra_frame();
     }
     GizmoImguiEnd();
+
+    // Outside the gizmo's window, because it is a window of its own: a floating, non-modal panel that
+    // leaves the 3D view live so the relief can be watched while the sliders move. No-op when closed.
+    render_image_adjust_window(panel_rect_min, panel_rect_max);
+
     ImGuiWrapper::pop_toolbar_style();
 
     // Drawn last, over everything, via the foreground draw list: the +/- add-remove sign next to the 3D

src/slic3r/GUI/Gizmos/GLGizmoTextureDisplacement.hpp

@@ -23,6 +23,7 @@
 #include "libslic3r/Point.hpp"
 #include <imgui.h>
 #include <map>
+#include <future>
 #include <memory>
 #include <optional>
 #include "slic3r/GUI/Gizmos/GLGizmoBase.hpp"
@@ -399,6 +400,68 @@ private:
     void set_layer_texture(TextureDisplacementLayer &layer, const TextureLibraryEntry &entry);
     void import_custom_texture(TextureDisplacementLayer &layer);
 
+    // ---- The image-adjustment panel ----
+    //
+    // Brightness/contrast/sharpness/blur/hue over one layer's image, shown on the image itself and
+    // updating as the sliders move. What it produces is not a set of layer parameters: it replaces the
+    // layer's *image*, so the adjusted pixels feed the colour and the displacement together and a
+    // brightness change moves the relief too (see TextureAdjustments).
+    //
+    // An ordinary floating window rather than a popup, and deliberately so. A popup dims the canvas
+    // behind it and closes on any click outside itself, which between them make it impossible to watch the
+    // relief change on the model - which is the whole point of adjusting the image here rather than in an
+    // image editor. A window leaves the 3D view live, clickable and orbitable while the panel is open.
+    void render_image_adjust_window(const ImVec2 &panel_min, const ImVec2 &panel_max);
+    // Opens the panel for `layer`, decoding its image into m_adjust_source. Sliders never re-decode
+    // the PNG.
+    void open_image_adjust(const TextureDisplacementLayer &layer);
+    // Reads `layer`'s stored image into the panel's source buffers and records which image it came from.
+    // Called when the panel opens and again whenever the layer's image is swapped under it, which is why
+    // it leaves the slider values alone. False when the image cannot be decoded.
+    bool load_image_adjust_source(const TextureDisplacementLayer &layer);
+    // Resolves the panel: writes the adjusted image into the user's texture library as a new file and
+    // points `layer` at it, which is the only way an adjustment becomes permanent. Closes the panel.
+    void commit_image_adjust(TextureDisplacementLayer &layer);
+    // Closes the panel and reverts the layer's live preview_adjust to identity, so every exit that is not
+    // a commit - Cancel, the window's close button, the gizmo closing - leaves the layer as it was found.
+    void close_image_adjust();
+    // Collects a finished preview and starts one for the current slider values. One at a time, so a drag
+    // coalesces into "whatever the sliders last said" instead of a queue of superseded frames.
+    void update_image_adjust_preview();
+
+    int                m_adjust_slot = -1; // the layer the panel is open for; -1 when closed
+    TextureAdjustments m_adjust;           // what the sliders currently say
+    // What the layer's live preview_adjust was last set from, so a slider move can be told from a frame in
+    // which nothing happened and only the former asks the displacement to be recomputed.
+    TextureAdjustments m_adjust_applied;
+
+    // The layer's image as it was when the panel opened, and a small copy of it. The sliders are applied
+    // to the small copy for the live preview and to the full-size one exactly once, on commit. Measured on
+    // a 1024x1024 with every knob engaged, a full-size pass costs 13-19 ms grayscale and 40-60 ms in
+    // colour (130-190 ms at 2048 in colour) - far too much to repeat per slider frame. The same pass on a
+    // 384 px copy is 3-4 ms / 9-12 ms, and that is all the preview box can show anyway.
+    DecodedHeightTexture m_adjust_source;
+    DecodedHeightTexture m_adjust_preview_source;
+    // Which image_data the two buffers above were decoded from, so the panel can notice the layer's image
+    // being swapped from the texture picker while it is open and re-read it. Compared, never dereferenced.
+    const void          *m_adjust_source_image = nullptr;
+    // And which volume the panel was opened on. Slot numbers are per volume, so without this a change of
+    // selection would silently rebind the open panel to whichever layer happens to hold the same slot on
+    // the newly selected object - a different image, under a panel the user opened for this one.
+    size_t               m_adjust_volume_id = 0;
+    // The preview image on screen, re-uploaded whenever a background pass finishes.
+    std::unique_ptr<GLTexture> m_adjust_preview_tex;
+
+    // The live preview runs on its own thread rather than on the UI thread or on the plater's job
+    // worker. Not the UI thread because even the small pass is milliseconds and this runs while a slider
+    // is being dragged; not the job worker because that is a single FIFO shared with Bake and the
+    // displacement preview (see queue_preview_job()), where a per-frame image filter would sit behind -
+    // and delay - multi-second mesh work.
+    std::future<DecodedHeightTexture> m_adjust_preview_job;
+    TextureAdjustments                m_adjust_preview_running; // what the in-flight pass is computing
+    TextureAdjustments                m_adjust_preview_shown;   // what m_adjust_preview_tex holds
+    bool                              m_adjust_preview_valid = false;
+
     // Paint / Erase, from the panel. See get_left_button_state_type().
     bool m_erase_mode = false;
     // Per slot: whether the layer's card shows every setting or only Depth, Tile size and Rotation.
@@ -878,6 +941,7 @@ private:
     enum class UVBackground { None, Height, Checker };
     UVBackground m_uv_editor_bg = UVBackground::None;
     float        m_uv_editor_bg_smoothing = -1.f; // smoothing the height backdrop was uploaded at
+    TextureAdjustments m_uv_editor_bg_adjust;        // and the live image adjustment it was uploaded at
     const void  *m_uv_editor_bg_image     = nullptr; // the layer image it was uploaded from
     // Per-chart distortion heatmap colour for the UV pane (#7/#14), computed once when the unwrap is
     // re-solved (relative stretch doesn't change when islands are merely moved), fed to the canvas only
@@ -921,6 +985,10 @@ private:
     std::array<const void *, TEXTURE_DISPLACEMENT_MAX_LAYERS>               m_thumbnail_source{};
     // The smoothing each cached thumbnail was built at, so a smoothing change re-uploads it.
     std::array<float, TEXTURE_DISPLACEMENT_MAX_LAYERS>                      m_thumbnail_smoothing{};
+    // And the live image adjustment each was built at, so moving a slider in the image-adjustment panel
+    // re-uploads it. Part of the key for the same reason smoothing is: preview_adjust changes the pixels
+    // decode_height_texture() hands back, and every one of these textures is a copy of those pixels.
+    std::array<TextureAdjustments, TEXTURE_DISPLACEMENT_MAX_LAYERS>          m_thumbnail_adjust{};
 
     // Full-resolution height texture for the preview shader, keyed the same way (see
     // get_layer_height_texture()). A smoothing change re-uploads it, so the fast preview shows the
@@ -928,12 +996,14 @@ private:
     std::unique_ptr<GLTexture> m_height_tex;
     const void                *m_height_tex_source    = nullptr;
     float                      m_height_tex_smoothing = -1.f;
+    TextureAdjustments         m_height_tex_adjust;
 
     // The same, for the layer's *colour*, which the fast preview quantizes per fragment so it shows
     // the image at texel resolution rather than at the mesh's. Null for a grayscale texture.
     std::unique_ptr<GLTexture> m_color_tex;
     const void                *m_color_tex_source    = nullptr;
     float                      m_color_tex_smoothing = -1.f;
+    TextureAdjustments         m_color_tex_adjust;
 
     // Library textures the picker has shown at least once, keyed by file path (see LibraryTexture).
     std::map<std::string, LibraryTexture> m_library_textures;

src/slic3r/GUI/TextureLibrary.cpp

@@ -27,6 +27,7 @@
 #include <wx/mstream.h>
 
 #include "libslic3r/PNGReadWrite.hpp"
+#include "libslic3r/TextureDisplacement.hpp"
 #include "libslic3r/Utils.hpp"
 
 #include "libslic3r/AppConfig.hpp"
@@ -158,6 +159,28 @@ bool encode_png_bytes(const wxImage &image, std::vector<unsigned char> &out, std
                                   : encode_gray_png_bytes(image, out, error);
 }
 
+// A wxImage over decoded pixels, so the encoders above can be reached from an in-memory image as well as
+// from a file. Grayscale is expanded to the three equal channels wxImage always stores, which is what
+// image_has_color() then reads as "no colour" - so a grey image still encodes as a grayscale PNG.
+//
+// `scratch` holds the pixel buffer: the wxImage is constructed over it without taking ownership, so it
+// has to outlive every use of the returned image.
+wxImage image_from_decoded(const DecodedHeightTexture &image, std::vector<unsigned char> &scratch)
+{
+    if (image.empty())
+        return wxImage();
+
+    const size_t n = size_t(image.width) * size_t(image.height);
+    scratch.resize(n * 3);
+    if (image.has_color())
+        scratch.assign(image.rgb.begin(), image.rgb.end());
+    else
+        for (size_t i = 0; i < n; ++i)
+            scratch[i * 3] = scratch[i * 3 + 1] = scratch[i * 3 + 2] = image.pixels[i];
+
+    return wxImage(image.width, image.height, scratch.data(), /* static_data */ true);
+}
+
 std::vector<unsigned char> read_file_bytes(const std::string &path)
 {
     std::ifstream ifs(path, std::ios::binary);
@@ -186,6 +209,42 @@ bool is_supported_height_map(const std::vector<unsigned char> &bytes)
 std::vector<TextureLibraryEntry> g_library;
 bool                             g_library_scanned = false;
 
+// Writes `bytes` into the user's own texture folder as `stem`.png, uniquified so an existing texture -
+// shipped-name collision, or a second edit of the same source - is never overwritten. Returns the new
+// file's library entry. Shared by import_texture_to_library() and save_texture_to_library(), which
+// differ only in where their bytes came from.
+std::optional<TextureLibraryEntry> write_user_texture(const std::vector<unsigned char> &bytes, const std::string &stem,
+                                                      std::string &error)
+{
+    const std::string user_dir = user_texture_dir();
+    if (user_dir.empty()) {
+        error = _u8L("Could not create the folder for imported textures.");
+        return std::nullopt;
+    }
+
+    boost::filesystem::path dest = boost::filesystem::path(user_dir) / (stem + ".png");
+    for (int i = 2; boost::filesystem::exists(dest); ++i)
+        dest = boost::filesystem::path(user_dir) / (stem + " (" + std::to_string(i) + ").png");
+
+    {
+        boost::nowide::ofstream ofs(dest.string(), std::ios::binary);
+        ofs.write(reinterpret_cast<const char *>(bytes.data()), std::streamsize(bytes.size()));
+        if (!ofs.good()) {
+            error = _u8L("Failed to save the imported texture.");
+            return std::nullopt;
+        }
+    }
+
+    texture_library(true); // pick the new file up
+    const std::string dest_str = dest.string();
+    for (const TextureLibraryEntry &e : g_library)
+        if (e.path == dest_str)
+            return e;
+
+    error = _u8L("Failed to save the imported texture.");
+    return std::nullopt;
+}
+
 // The user's own textures, most recently used first, kept in the app config. File names are stored rather
 // than paths so the order survives a moved data directory; '/' separates them because no platform allows
 // it inside a file name. Bounded so a long-lived config does not grow a line without end.
@@ -317,12 +376,6 @@ bool remove_user_texture(const std::string &path, std::string &error)
 
 std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &source_path, std::string &error)
 {
-    const std::string user_dir = user_texture_dir();
-    if (user_dir.empty()) {
-        error = _u8L("Could not create the folder for imported textures.");
-        return std::nullopt;
-    }
-
     wxImage image;
     if (!image.LoadFile(from_u8(source_path)) || !image.IsOk()) {
         error = _u8L("Could not load the selected image.");
@@ -333,30 +386,7 @@ std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &
     if (!encode_png_bytes(image, bytes, error))
         return std::nullopt;
 
-    // Never overwrite an existing texture (the user's or, if they picked the same name twice, their
-    // own earlier import) - uniquify instead.
-    const std::string       stem = boost::filesystem::path(source_path).stem().string();
-    boost::filesystem::path dest = boost::filesystem::path(user_dir) / (stem + ".png");
-    for (int i = 2; boost::filesystem::exists(dest); ++i)
-        dest = boost::filesystem::path(user_dir) / (stem + " (" + std::to_string(i) + ").png");
-
-    {
-        boost::nowide::ofstream ofs(dest.string(), std::ios::binary);
-        ofs.write(reinterpret_cast<const char *>(bytes.data()), std::streamsize(bytes.size()));
-        if (!ofs.good()) {
-            error = _u8L("Failed to save the imported texture.");
-            return std::nullopt;
-        }
-    }
-
-    texture_library(true); // pick the new file up
-    const std::string dest_str = dest.string();
-    for (const TextureLibraryEntry &e : g_library)
-        if (e.path == dest_str)
-            return e;
-
-    error = _u8L("Failed to save the imported texture.");
-    return std::nullopt;
+    return write_user_texture(bytes, boost::filesystem::path(source_path).stem().string(), error);
 }
 
 std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::string &path, std::string &error)
@@ -382,4 +412,21 @@ std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::s
     return std::make_shared<std::vector<unsigned char>>(std::move(converted));
 }
 
+std::optional<TextureLibraryEntry> save_texture_to_library(const DecodedHeightTexture &image, const std::string &stem,
+                                                           std::string &error)
+{
+    std::vector<unsigned char> scratch;
+    const wxImage              wx = image_from_decoded(image, scratch);
+    if (!wx.IsOk()) {
+        error = _u8L("The selected image is empty.");
+        return std::nullopt;
+    }
+
+    std::vector<unsigned char> bytes;
+    if (!encode_png_bytes(wx, bytes, error))
+        return std::nullopt;
+
+    return write_user_texture(bytes, stem.empty() ? std::string("texture") : stem, error);
+}
+
 } // namespace Slic3r::GUI

src/slic3r/GUI/TextureLibrary.hpp

@@ -6,6 +6,8 @@
 #include <string>
 #include <vector>
 
+#include "libslic3r/TextureDisplacement.hpp"
+
 namespace Slic3r::GUI {
 
 // One selectable height-map texture in the texture-displacement gizmo's texture picker.
@@ -57,6 +59,14 @@ std::optional<TextureLibraryEntry> import_texture_to_library(const std::string &
 // Returns nullptr with `error` set if the file cannot be read or decoded at all.
 std::shared_ptr<std::vector<unsigned char>> load_texture_image_data(const std::string &path, std::string &error);
 
+// Writes `image` into user_texture_dir() as a new PNG named after `stem` (uniquified if taken, so an
+// existing texture is never overwritten) and returns its library entry. The in-memory counterpart of
+// import_texture_to_library(), for an image that was edited rather than read off disk.
+//
+// Returns nullopt with `error` set on failure.
+std::optional<TextureLibraryEntry> save_texture_to_library(const DecodedHeightTexture &image, const std::string &stem,
+                                                           std::string &error);
+
 } // namespace Slic3r::GUI
 
 #endif // slic3r_TextureLibrary_hpp_

tests/libslic3r/test_texture_displacement.cpp

@@ -28,6 +28,7 @@
 
 #include <algorithm>
 #include <array>
+#include <functional>
 #include <cmath>
 #include <fstream>
 #include <limits>
@@ -2174,3 +2175,291 @@ TEST_CASE("whether a layer's texture has colour agrees with its decode", "[Textu
 
     CHECK_FALSE(height_texture_has_color(TextureDisplacementLayer{}));
 }
+
+// ---- Image adjustments (the gizmo's image-adjustment panel) ----------------------------------------
+
+// A grayscale ramp 0..255 across the width, so every input level is present exactly once per row and a
+// tonal curve can be read straight off the output.
+static DecodedHeightTexture make_gray_ramp(int w = 256, int h = 4)
+{
+    DecodedHeightTexture t;
+    t.width  = w;
+    t.height = h;
+    t.pixels.resize(size_t(w) * size_t(h));
+    for (int y = 0; y < h; ++y)
+        for (int x = 0; x < w; ++x)
+            t.pixels[size_t(y) * size_t(w) + size_t(x)] = uint8_t(x * 255 / std::max(1, w - 1));
+    return t;
+}
+
+// A one-texel checkerboard of 0 and 255 - the highest spatial frequency the grid can hold, which is what
+// a blur has to remove and a downscale has to average rather than drop.
+static DecodedHeightTexture make_gray_checkerboard(int w = 16, int h = 16)
+{
+    DecodedHeightTexture t;
+    t.width  = w;
+    t.height = h;
+    t.pixels.resize(size_t(w) * size_t(h));
+    for (int y = 0; y < h; ++y)
+        for (int x = 0; x < w; ++x)
+            t.pixels[size_t(y) * size_t(w) + size_t(x)] = ((x + y) % 2 == 0) ? 0 : 255;
+    return t;
+}
+
+static DecodedHeightTexture make_rgb_flat(uint8_t r, uint8_t g, uint8_t b, int w = 8, int h = 8)
+{
+    DecodedHeightTexture t;
+    t.width  = w;
+    t.height = h;
+    t.pixels.resize(size_t(w) * size_t(h));
+    t.rgb.resize(size_t(w) * size_t(h) * 3);
+    for (size_t i = 0; i < size_t(w) * size_t(h); ++i) {
+        t.rgb[i * 3]     = r;
+        t.rgb[i * 3 + 1] = g;
+        t.rgb[i * 3 + 2] = b;
+        t.pixels[i]      = uint8_t(std::lround(0.299 * r + 0.587 * g + 0.114 * b));
+    }
+    return t;
+}
+
+TEST_CASE("an adjustment that moves no slider returns the image unchanged", "[TextureDisplacement]")
+{
+    const DecodedHeightTexture src = make_gray_ramp();
+    const DecodedHeightTexture out = apply_texture_adjustments(src, TextureAdjustments{});
+    CHECK(out.width == src.width);
+    CHECK(out.height == src.height);
+    CHECK(out.pixels == src.pixels);
+    CHECK(TextureAdjustments{}.identity());
+}
+
+TEST_CASE("brightness reaches pure white and pure black only at the ends of its range", "[TextureDisplacement]")
+{
+    const DecodedHeightTexture src = make_gray_ramp();
+
+    TextureAdjustments up;
+    up.brightness = 1.f;
+    const DecodedHeightTexture white = apply_texture_adjustments(src, up);
+    CHECK(std::all_of(white.pixels.begin(), white.pixels.end(), [](uint8_t v) { return v == 255; }));
+
+    TextureAdjustments down;
+    down.brightness = -1.f;
+    const DecodedHeightTexture black = apply_texture_adjustments(src, down);
+    CHECK(std::all_of(black.pixels.begin(), black.pixels.end(), [](uint8_t v) { return v == 0; }));
+}
+
+TEST_CASE("brightness lifts the image without flattening it into a clipped plateau", "[TextureDisplacement]")
+{
+    // The reason brightness is a lift toward white rather than an additive offset: an offset would drive
+    // everything above mid-grey to a flat 255, and since this image is also the height map that region
+    // would bake as flat relief. Half a stop up must leave almost nothing at pure white.
+    const DecodedHeightTexture src = make_gray_ramp();
+    TextureAdjustments         adj;
+    adj.brightness = 0.5f;
+    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
+
+    REQUIRE(out.pixels.size() == src.pixels.size());
+    const size_t clipped = size_t(std::count(out.pixels.begin(), out.pixels.end(), uint8_t(255)));
+    CHECK(clipped * 100 < out.pixels.size()); // under 1%; an additive shift would clip half the ramp
+
+    // Every texel got brighter, and the curve stays ordered: brighter in means brighter out.
+    for (size_t i = 0; i < out.pixels.size(); ++i)
+        REQUIRE(out.pixels[i] >= src.pixels[i]);
+    for (int x = 1; x < out.width; ++x)
+        REQUIRE(out.pixels[size_t(x)] >= out.pixels[size_t(x - 1)]);
+}
+
+TEST_CASE("contrast at its lowest flattens the image to mid-grey and at its highest spreads it apart",
+          "[TextureDisplacement]")
+{
+    const DecodedHeightTexture src = make_gray_ramp();
+
+    TextureAdjustments flat;
+    flat.contrast = -1.f;
+    const DecodedHeightTexture grey = apply_texture_adjustments(src, flat);
+    // One value everywhere - the pivot. Which exact level that rounds to is not the point.
+    CHECK(std::adjacent_find(grey.pixels.begin(), grey.pixels.end(), std::not_equal_to<uint8_t>()) ==
+          grey.pixels.end());
+
+    TextureAdjustments hard;
+    hard.contrast = 1.f;
+    const DecodedHeightTexture split = apply_texture_adjustments(src, hard);
+    // A threshold about the pivot: the dark end of the ramp goes to black, the light end to white.
+    CHECK(split.pixels[0] == 0);
+    CHECK(split.pixels[size_t(split.width - 1)] == 255);
+}
+
+TEST_CASE("blur removes the finest detail and sharpness exaggerates an edge", "[TextureDisplacement]")
+{
+    // Blur: a one-texel checkerboard is the highest frequency the grid holds, so a blur has to collapse it
+    // toward its own mean. Measured as mean absolute deviation, which needs no assumption about the mean.
+    const DecodedHeightTexture checker = make_gray_checkerboard(32, 32);
+    const auto                 deviation = [](const DecodedHeightTexture &t) {
+        double mean = 0.;
+        for (uint8_t v : t.pixels)
+            mean += double(v);
+        mean /= double(t.pixels.size());
+        double dev = 0.;
+        for (uint8_t v : t.pixels)
+            dev += std::abs(double(v) - mean);
+        return dev / double(t.pixels.size());
+    };
+    TextureAdjustments blur;
+    blur.blur = 1.f;
+    CHECK(deviation(apply_texture_adjustments(checker, blur)) < 0.25 * deviation(checker));
+
+    // Sharpness: an unsharp mask pushes each side of a step further from the other, so the step
+    // overshoots - darker than the dark side just inside it, brighter than the bright side just inside.
+    DecodedHeightTexture step;
+    step.width  = 64;
+    step.height = 8;
+    step.pixels.assign(size_t(step.width) * size_t(step.height), 100);
+    for (int y = 0; y < step.height; ++y)
+        for (int x = step.width / 2; x < step.width; ++x)
+            step.pixels[size_t(y) * size_t(step.width) + size_t(x)] = 150;
+
+    TextureAdjustments sharp;
+    sharp.sharpness = 1.f;
+    const DecodedHeightTexture sharpened = apply_texture_adjustments(step, sharp);
+    const size_t               row       = size_t(step.height / 2) * size_t(step.width);
+    const size_t               mid       = size_t(step.width / 2);
+    CHECK(sharpened.pixels[row + mid - 1] < 100); // undershoot on the dark side of the step
+    CHECK(sharpened.pixels[row + mid] > 150);     // overshoot on the light side
+}
+
+TEST_CASE("a grayscale image stays grayscale and its hue slider does nothing", "[TextureDisplacement]")
+{
+    const DecodedHeightTexture src = make_gray_ramp();
+    REQUIRE_FALSE(src.has_color());
+
+    TextureAdjustments hue;
+    hue.hue_deg = 120.f;
+    const DecodedHeightTexture out = apply_texture_adjustments(src, hue);
+    // Not promoted to RGB: a grey image has no colour to offer the layer's colour feature, and storing it
+    // as RGB would triple the PNG for a row of identical greys.
+    CHECK_FALSE(out.has_color());
+    CHECK(out.rgb.empty());
+    CHECK(out.pixels == src.pixels);
+}
+
+TEST_CASE("a colour image's height stays the luminance of its adjusted colour", "[TextureDisplacement]")
+{
+    // The invariant that keeps the relief and the colour from drifting apart: whatever the adjustment did
+    // to the channels, the height is recomputed from the channels that came out.
+    const DecodedHeightTexture src = make_rgb_flat(200, 60, 30);
+    REQUIRE(src.has_color());
+
+    TextureAdjustments adj;
+    adj.brightness = 0.2f;
+    adj.contrast   = 0.3f;
+    adj.hue_deg    = 75.f;
+    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
+    REQUIRE(out.has_color());
+
+    for (size_t i = 0; i < out.pixels.size(); ++i) {
+        const long expect = std::lround(0.299 * out.rgb[i * 3] + 0.587 * out.rgb[i * 3 + 1] +
+                                        0.114 * out.rgb[i * 3 + 2]);
+        REQUIRE(long(out.pixels[i]) == expect);
+    }
+    // The hue turn actually moved the colour, so the check above is not passing on an unchanged image.
+    CHECK(out.rgb != src.rgb);
+}
+
+TEST_CASE("a full turn of the hue leaves a colour where it started", "[TextureDisplacement]")
+{
+    const DecodedHeightTexture src = make_rgb_flat(200, 60, 30);
+    TextureAdjustments         adj;
+    adj.hue_deg                    = 360.f;
+    const DecodedHeightTexture out = apply_texture_adjustments(src, adj);
+    REQUIRE(out.has_color());
+    // Rounding through 8-bit channels, so a level or two of slack rather than exact equality.
+    for (size_t i = 0; i < out.rgb.size(); ++i)
+        REQUIRE(std::abs(int(out.rgb[i]) - int(src.rgb[i])) <= 2);
+}
+
+TEST_CASE("the adjustment blur radius ramps from zero and stays under its cost cap", "[TextureDisplacement]")
+{
+    CHECK_THAT(adjustment_blur_radius(0.f, 512, 512), Catch::Matchers::WithinAbs(0.f, 1e-6f));
+    // 5% of the short side, as the Smoothing slider uses.
+    CHECK_THAT(adjustment_blur_radius(1.f, 512, 512), Catch::Matchers::WithinAbs(25.6f, 1e-3f));
+    CHECK_THAT(adjustment_blur_radius(0.5f, 512, 512), Catch::Matchers::WithinAbs(12.8f, 1e-3f));
+    // Capped, so a large image at the top of the slider cannot cost without bound.
+    CHECK_THAT(adjustment_blur_radius(1.f, 8192, 8192), Catch::Matchers::WithinAbs(48.f, 1e-3f));
+    // Sized off the short side, not the long one.
+    CHECK_THAT(adjustment_blur_radius(1.f, 4096, 200), Catch::Matchers::WithinAbs(10.f, 1e-3f));
+}
+
+TEST_CASE("downscaling a height texture averages the texels it drops and never upscales",
+          "[TextureDisplacement]")
+{
+    // Averaging, not decimation: a one-texel checkerboard halved must come out uniformly mid-grey. Picking
+    // one texel per block would instead come out all black or all white - detail the adjustment never
+    // produced, shown in the preview.
+    const DecodedHeightTexture small = downscale_height_texture(make_gray_checkerboard(16, 16), 8);
+    CHECK(small.width == 8);
+    CHECK(small.height == 8);
+    CHECK(std::all_of(small.pixels.begin(), small.pixels.end(), [](uint8_t v) { return v == 127; }));
+
+    // Already within the limit: handed back as it is.
+    const DecodedHeightTexture ramp = make_gray_ramp(64, 4);
+    const DecodedHeightTexture same = downscale_height_texture(ramp, 256);
+    CHECK(same.width == ramp.width);
+    CHECK(same.height == ramp.height);
+    CHECK(same.pixels == ramp.pixels);
+
+    // Aspect preserved, and a colour source keeps its colour.
+    const DecodedHeightTexture wide = downscale_height_texture(make_rgb_flat(200, 60, 30, 400, 100), 100);
+    CHECK(wide.width == 100);
+    CHECK(wide.height == 25);
+    CHECK(wide.has_color());
+}
+
+TEST_CASE("a layer's live image adjustment reaches its decode", "[TextureDisplacement]")
+{
+    // This is what makes the image-adjustment panel's sliders move the relief: decode_height_texture()
+    // applies the layer's preview_adjust, so everything downstream of the decode - the displacement, the
+    // colour, the thumbnails, the bake - sees the adjusted image without being told about the panel.
+    TextureDisplacementLayer layer;
+    layer.image_data = make_checkerboard_png(32, 32);
+
+    const DecodedHeightTexture raw = decode_height_texture(layer);
+    REQUIRE_FALSE(raw.empty());
+
+    // An untouched panel, and a closed one, cost nothing and change nothing.
+    layer.preview_adjust = TextureAdjustments{};
+    CHECK(decode_height_texture(layer).pixels == raw.pixels);
+
+    layer.preview_adjust.brightness = 0.5f;
+    const DecodedHeightTexture bright = decode_height_texture(layer);
+    CHECK(bright.pixels != raw.pixels);
+    CHECK(bright.pixels == apply_texture_adjustments(raw, layer.preview_adjust).pixels);
+
+    // Back to identity gives the stored image back, so closing the panel really does revert the layer.
+    layer.preview_adjust = TextureAdjustments{};
+    CHECK(decode_height_texture(layer).pixels == raw.pixels);
+}
+
+TEST_CASE("changing a live adjustment is not served the previous one from cache", "[TextureDisplacement]")
+{
+    // The decode caches by the image_data pointer, which does not change while a slider moves - so the
+    // adjustment has to be part of the key or every slider move past the first would redraw the same
+    // pixels. Same for the smoothed copy, which is computed on top of the adjusted one.
+    TextureDisplacementLayer layer;
+    layer.image_data = make_checkerboard_png(32, 32);
+    const DecodedHeightTexture raw = decode_height_texture(layer);
+    REQUIRE_FALSE(raw.empty());
+
+    layer.preview_adjust.brightness = 0.5f;
+    const std::vector<uint8_t> bright = decode_height_texture(layer).pixels;
+    layer.preview_adjust.brightness   = -0.5f;
+    const std::vector<uint8_t> dark   = decode_height_texture(layer).pixels;
+    CHECK(bright != dark);
+    CHECK(dark == apply_texture_adjustments(raw, layer.preview_adjust).pixels);
+
+    // The same question again with smoothing on, which is cached separately and keyed by both.
+    layer.smoothing                 = 0.5f;
+    layer.preview_adjust.brightness = 0.5f;
+    const std::vector<uint8_t> smooth_bright = decode_height_texture(layer).pixels;
+    layer.preview_adjust.brightness          = -0.5f;
+    const std::vector<uint8_t> smooth_dark   = decode_height_texture(layer).pixels;
+    CHECK(smooth_bright != smooth_dark);
+}