Merge pull request #2503 from vangel76/fix/2493-generic-cmyk-black-roundtrip

Color: Generic CMYK black round-trips through hex (#2493)

crates/color/src/cms/generic.rs

@@ -171,9 +171,25 @@ impl GenericCmyk {
         xyz_to_lab(self.to_xyz(cmyk))
     }
 
-    /// Display sRGB: media-relative (paper shows as white) or absolute (simulate paper colour).
-    pub fn to_srgb(&self, cmyk: [f32; 4], absolute: bool) -> [f32; 3] {
-        xyz_to_srgb(if absolute { self.to_xyz(cmyk) } else { self.to_xyz_rel(cmyk) })
+    /// Display XYZ: media-relative (paper shows as white) or absolute (simulate paper colour).
+    /// With `bpc` (media-relative only) the press black displays as black, undoing the
+    /// compensation [`Self::gamut_map`] applies on the way in, so sRGB black separated to the
+    /// darkest rich black shows as black again.
+    pub fn display_xyz(&self, cmyk: [f32; 4], absolute: bool, bpc: bool) -> [f32; 3] {
+        if absolute {
+            return self.to_xyz(cmyk);
+        }
+        let x = self.to_xyz_rel(cmyk);
+        if !bpc {
+            return x;
+        }
+        let bp = self.black_rel;
+        [0, 1, 2].map(|i| ((x[i] - bp[i]) / (1.0 - bp[i] / D50[i])).max(0.0))
+    }
+
+    /// Display sRGB, see [`Self::display_xyz`].
+    pub fn to_srgb(&self, cmyk: [f32; 4], absolute: bool, bpc: bool) -> [f32; 3] {
+        xyz_to_srgb(self.display_xyz(cmyk, absolute, bpc))
     }
 
     /// Lab of the darkest printable black (media-relative).
@@ -425,11 +441,12 @@ impl GenericCmyk {
         self.from_lab(srgb_to_lab(rgb), intent, bpc)
     }
 
-    /// ΔE2000 between an sRGB colour and its best (relative colorimetric) reproduction.
-    pub fn gamut_error(&self, src: Lab) -> f32 {
-        let target = self.gamut_map(src, Intent::RelativeColorimetric, false);
+    /// ΔE2000 between a colour and its best (relative colorimetric) reproduction as it displays
+    /// (with `bpc`, the press black showing as black).
+    pub fn gamut_error(&self, src: Lab, bpc: bool) -> f32 {
+        let target = self.gamut_map(src, Intent::RelativeColorimetric, bpc);
         let cmyk = self.separate(target);
-        delta_e2000(self.to_lab_rel(cmyk), target)
+        delta_e2000(xyz_to_lab(self.display_xyz(cmyk, false, bpc)), src)
     }
 }
 

crates/color/src/cms/mod.rs

@@ -346,10 +346,10 @@ impl Cms {
         }
     }
 
-    fn cmyk_to_srgb_in(space: &CmykSpace, cmyk: [f32; 4], absolute: bool) -> [f32; 3] {
+    fn cmyk_to_srgb_in(space: &CmykSpace, cmyk: [f32; 4], absolute: bool, bpc: bool) -> [f32; 3] {
         let cmyk = cmyk.map(|v| v.clamp(0.0, 1.0));
         match space {
-            CmykSpace::Generic(g) => g.to_srgb(cmyk, absolute),
+            CmykSpace::Generic(g) => g.to_srgb(cmyk, absolute, bpc),
             CmykSpace::Device => naive_cmyk_to_rgb(cmyk),
             CmykSpace::Icc(p) => {
                 let i = if absolute { Intent::AbsoluteColorimetric } else { Intent::RelativeColorimetric };
@@ -376,7 +376,7 @@ impl Cms {
         {
             return v;
         }
-        Self::cmyk_to_srgb_in(&self.cmyk, cmyk, absolute)
+        Self::cmyk_to_srgb_in(&self.cmyk, cmyk, absolute, self.settings.bpc)
     }
     /// CMYK in the working space → working RGB with `intent`. An ICC CMYK profile converts
     /// directly into the RGB profile: not through display sRGB, which would clip colours a wider
@@ -408,6 +408,15 @@ impl Cms {
             _ => lab::srgb_to_lab(self.cmyk_to_srgb(cmyk, false)),
         }
     }
+    /// Lab of working-space CMYK as it displays: [`Self::cmyk_to_lab`] plus, for the built-in
+    /// Generic CMYK, the black-point compensation of [`Self::cmyk_to_srgb`] (its press black shows
+    /// as black). Unclipped, for interpolating tables.
+    pub fn cmyk_display_lab(&self, cmyk: [f32; 4]) -> Lab {
+        match &self.cmyk {
+            CmykSpace::Generic(g) => lab::xyz_to_lab(g.display_xyz(cmyk.map(|v| v.clamp(0.0, 1.0)), false, self.settings.bpc)),
+            _ => self.cmyk_to_lab(cmyk),
+        }
+    }
     /// Lab → working CMYK with `intent`.
     pub fn lab_to_cmyk(&self, l: Lab, intent: Intent) -> [f32; 4] {
         match &self.cmyk {
@@ -429,7 +438,7 @@ impl Cms {
     /// CIE Lab (D50) of any colour.
     pub fn lab(&self, c: &Color) -> Lab {
         match *c {
-            Color::Cmyk { c, m, y, k } => self.cmyk_to_lab([c, m, y, k]),
+            Color::Cmyk { c, m, y, k } => self.cmyk_display_lab([c, m, y, k]),
             Color::Lab { l, a, b } => Lab::new(l, a, b),
             _ => lab::srgb_to_lab(self.display_rgb(c)),
         }
@@ -490,7 +499,7 @@ impl Cms {
             Color::Rgb { .. } | Color::Lab { .. } => {
                 let src = self.lab(c);
                 match &self.cmyk {
-                    CmykSpace::Generic(g) => g.gamut_error(src),
+                    CmykSpace::Generic(g) => g.gamut_error(src, self.settings.bpc),
                     CmykSpace::Device => 0.0,
                     CmykSpace::Icc(_) => {
                         let back = self.cmyk_to_srgb(self.to_cmyk(c, Intent::RelativeColorimetric), false);
@@ -523,7 +532,7 @@ impl Cms {
             ProofTarget::Cmyk(name) => match cmyk_space(name) {
                 Ok(sp) => {
                     let cmyk = Self::srgb_to_cmyk_in(&sp, srgb, proof.intent, self.settings.bpc);
-                    Self::cmyk_to_srgb_in(&sp, cmyk, proof.simulate_paper)
+                    Self::cmyk_to_srgb_in(&sp, cmyk, proof.simulate_paper, self.settings.bpc)
                 }
                 Err(_) => srgb,
             },
@@ -534,7 +543,7 @@ impl Cms {
     pub fn proof_cmyk_to_srgb(&self, cmyk: [f32; 4], proof: &ProofSetup) -> [f32; 3] {
         match &proof.target {
             ProofTarget::Cmyk(name) => match cmyk_space(name) {
-                Ok(sp) => Self::cmyk_to_srgb_in(&sp, cmyk, proof.simulate_paper),
+                Ok(sp) => Self::cmyk_to_srgb_in(&sp, cmyk, proof.simulate_paper, self.settings.bpc),
                 Err(_) => self.cmyk_to_srgb(cmyk, proof.simulate_paper),
             },
             _ => self.cmyk_to_srgb(cmyk, proof.simulate_paper),

crates/color/src/cms/tests.rs

@@ -245,6 +245,20 @@ fn loads_system_cmyk_icc() {
     assert_eq!(c.cmyk_to_srgb([0.0; 4], false).map(|v| (v * 255.0).round() as u8), [255, 255, 255]);
 }
 
+/// With black-point compensation, sRGB black separates to the press's darkest black and that black
+/// displays as black again (hex 000000 -> C67 M67 Y67 K100 -> 000000, not a dark grey).
+#[test]
+fn generic_cmyk_black_round_trips_with_bpc() {
+    let c = cms();
+    let cmyk = c.srgb_to_cmyk([0.0; 3], Intent::RelativeColorimetric);
+    let back = c.cmyk_to_srgb(cmyk, false).map(|v| (v * 255.0).round() as u8);
+    assert_eq!(back, [0, 0, 0], "{cmyk:?}");
+    // The paper still shows as white, and without compensation the press black stays a dark grey.
+    assert_eq!(c.cmyk_to_srgb([0.0; 4], false), [1.0, 1.0, 1.0]);
+    let raw = cms_no_bpc().cmyk_to_srgb(cmyk, false);
+    assert!(raw.iter().all(|v| *v > 0.05), "{raw:?}");
+}
+
 #[test]
 fn lab_colours_round_trip_through_the_cms() {
     let c = cms_no_bpc();

crates/color/src/cms/tests_icc.rs

@@ -22,7 +22,8 @@ fn cmyk_profiles_convert_like_the_cms() {
         assert_eq!(parse(&bytes).color_space, moxcms::DataColorSpace::Cmyk);
         let p = IccProfile::from_bytes(None, &bytes).unwrap();
         assert_eq!((p.name.as_str(), p.kind), (name, ProfileKind::Cmyk));
-        let cms = Cms::new(&ColorSettings { cmyk: name.into(), ..Default::default() }).unwrap();
+        // The encoded profile converts without black-point compensation, so compare without it.
+        let cms = Cms::new(&ColorSettings { cmyk: name.into(), bpc: false, ..Default::default() }).unwrap();
         for cmyk in [[0.0; 4], [1.0, 0.0, 0.0, 0.0], [0.2, 0.7, 0.1, 0.3], [0.0, 0.0, 0.0, 1.0], [0.5, 0.5, 0.5, 0.0]] {
             let want = cms.cmyk_to_srgb(cmyk, false);
             let got = p.to_srgb(&cmyk, Intent::RelativeColorimetric).unwrap();

crates/pdf/src/tests_cmykimages.rs

@@ -340,7 +340,7 @@ fn the_output_settings_convert_cmyk_images_and_compression_recompresses_them_in_
     assert_ne!(converted, flat(ink, 16));
     let source = cms::active();
     let dest = cms::Cms::new(&cms::ColorSettings { cmyk: DEVICE_CMYK.into(), ..source.settings().clone() }).unwrap();
-    let want = dest.lab_to_cmyk(source.cmyk_to_lab(ink.map(|v| v as f32 / 255.0)), source.settings().intent).map(|v| (v * 255.0).round() as u8);
+    let want = dest.lab_to_cmyk(source.cmyk_display_lab(ink.map(|v| v as f32 / 255.0)), source.settings().intent).map(|v| (v * 255.0).round() as u8);
     assert!(close(&converted[..4], &want, 3), "{converted:?} vs {want:?}");
     // To RGB: the colour shown on screen.
     let (w, blob, _) = first(json!({"output": {"conversion": "destination", "destination": SRGB}}));

crates/render/src/ink.rs

@@ -153,7 +153,7 @@ pub(crate) struct InkLut(CmykLut);
 impl InkLut {
     fn build(cms: &Cms) -> Self {
         Self(CmykLut::build(|inks| {
-            let [x, y, z] = lab::lab_to_xyz(cms.cmyk_to_lab(inks));
+            let [x, y, z] = lab::lab_to_xyz(cms.cmyk_display_lab(inks));
             [x, y, z, 0.0]
         }))
     }

crates/render/src/tests_memory.rs

@@ -1535,7 +1535,8 @@ fn proof_previews_draw_changes_as_a_new_renderer_does() {
     // A square in spot color `Lab Spot`, defined in Lab in a color group, on its own plate.
     let lab_doc = || {
         let mut d = proof_doc();
-        let lab = Color::lab(50.0, 60.0, 40.0);
+        // Outside the press gamut, so its CMYK alternate looks different from the Lab colour.
+        let lab = Color::lab(50.0, 90.0, 70.0);
         let swatch = vectorcraft_color::Swatch { name: "Lab Spot".into(), paint: Paint::solid(lab), global: true, spot: true };
         d.swatch_groups.push(vectorcraft_color::SwatchGroup { name: "Lab".into(), swatches: vec![swatch] });
         let fill = Paint::Solid { color: lab, swatch: Some("Lab Spot".into()), tint: 1.0 };

docs/target-app-parity.md

@@ -570,7 +570,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
 - **Advanced art:** live Blends (steps/distance/smooth colour, editable spine, anchor-targeted Blend tool, faithful interpolation, knockout), Envelope Distort (warp/mesh/top object, Reset, full Envelope Options, mesh handles, Edit Contents; type, images, symbols, gradients, patterns and appearance distorted everywhere), Liquify tools with options and pen pressure, Puppet Warp with rotating pins, Perspective Grid with presets, movable planes and projected type (choosing a perspective tool shows the grid; Hide Grid hides it with the tool still chosen), Gradient Mesh, Shape Builder (stroke-only open paths and lines cut the regions they cross and enclose regions of their own, and regions they bound merge without seams where the lines cross at rounded coordinates (#893); filled open paths count as closed; erase mode while Alt/Option is held: a minus pointer, red highlights of what will go, a click or drag deletes the regions touched, the pieces of open lines and the edges (outline pieces between the points where paths meet, opening their paths there) it passes over, one undo step, `shapeBuilder.merge {erase}` and `shapeBuilder.regions` edges over MCP), Live Paint (every path an edge, open lines included), Image Trace (12 presets, colour layers traced in parallel; a trace past two million anchor points is refused with advice rather than running out of memory, an image over 64 megapixels is traced scaled down to that size (aspect kept, paths at the image's own size) and one over 192 megapixels is refused, and a selection too large to outline shows its bounds (#525); Object › Image Trace › Make and Make and Expand trace at once with the Default preset, #543; with an image selected the Control bar and the Properties panel show Image Trace, whose arrow traces with any preset, Mask (`object.maskImage`: a clipping path on the image's outline, selected so its handles crop), Crop Image (a crop box on the image, starting on its part over the artboard, dragged by its handles or inside it, the outside dimmed, with X/Y/W/H, Apply and Cancel in the Control bar, Enter and Escape, #734; `object.cropImage {rect}` for agents, `{trim: true}` cuts an image to its pixels that aren't fully transparent, pixel for pixel) and Embed or Unembed in place of Fill and Stroke; with an Image Trace object selected, its Preset (choosing another traces again), View, the Image Trace panel and Expand, plus Release in Properties; the five View modes (Tracing Result, with Outlines, Outlines, Outlines with Source Image, Source Image) redraw a trace on screen without tracing again, are saved with it and `imageTrace.setView` sets them, while exports and Expand keep the result; the panel's Advanced section is a header that stays open or closed as it was left (part of #641); Color mode's Palette: Limited, Full Tone (as many colours as the tones need, Less … More), Automatic (flat art with its own colours, else Full Tone; a heuristic) and Document Library (the most used colours of the document's swatches or a swatch library, filled with the swatch colours as they are), part of #641; Advanced › Create: Fills and/or Strokes, where lines up to the Stroke width trace as stroked centre lines (distance transform, thinning, a skeleton graph with spurs pruned, curve fitting; one width per line; without Fills, wider areas become stroked outlines), part of #641), pattern swatches with pattern editing mode, live Repeat (radial/grid/mirror). Object › Expand turns radial, grid and mirror repeats into groups of their instances (#1765, #1756).
 - **Paint and appearance (M3):**
   - **Swatches:** names follow the colour model and are unique; Swatch Options (process/spot, Global, Gray/RGB/HSB/CMYK/Web, live preview); editing a global or spot swatch recolours every linked fill, stroke and text run in one undo step; multi-select and delete with confirmation; New Swatch and New Color Group dialogs (a group from the selected artwork's colours); swatches in colour groups convert, separate and count like any other. The Swatches panel selects ranges and whole groups, has a find field, and drags swatches to reorder, regroup or paint art; Add Used Colors, Select All Unused, Merge, Ungroup and Sort by Kind; a CMYK document keeps applied colours in CMYK. Swatch libraries: nine generated colour libraries and five gradient libraries in a library panel, saved as `.vcswatches`, `.gpl`, swatch exchange (`.ase`) or CSS, and loaded from `.vcswatches`, `.gpl` and `.ase` files (`.ase` both ways: RGB, CMYK, Lab and Gray; global, spot and process; groups) and from color books (`.acb`, read only: the RGB, CMYK or Lab colors of a book such as a Pantone book a user owns, named with its prefix and suffix, spot unless it says process, #831); `swatch.library.copyToUser` copies a loaded library into the User Defined folder without replacing a file, and a file with the same extension and bytes as a User Defined library opens as that library. Tints of global and spot colours ("Name 40%") stay linked and separate as a percentage of their plate. Spot colours can be defined in Lab (Spot Colors options). A built-in [Registration] swatch prints on every plate.
-  - **Colour:** a Color Picker (colour field, H/S/B/R/G/B channel slider, HSB/RGB/Lab/CMYK fields, hex, web-only snapping, out-of-gamut correction); the Color panel shows a selected colour in its own model and, with nothing selected, the new-art defaults in the mode picked last, which it keeps between sessions; Alt-click paints the other proxy; proxies look through groups and show "?" for mixed paint; Invert, Complement, Apply Last Color (`,`) and Apply Last Gradient (`.`) keep the colour model; every paint command feeds the recent colours. The Color Guide has 21 harmony rules, Steps and Variation options and Limit to Library. Adjust Color Balance (its Global mode shifts tints) and Saturate preview live; Edit Colors and Recolor also reach meshes, images and patterns. Recolor Artwork has colour reduction, five recolour methods, presets, Limit to Library, a colour-wheel Edit tab and Edit Color Group; a local Color Themes panel saves five-colour themes. Fill/Stroke chips open swatch and mixer popovers (the Properties panel has the Control bar's Fill and Stroke chips, Stroke link and weight spinner, with nothing selected too), panels have Illustrator's Window menu keys (Align Shift+F7, Transform Shift+F8, Pathfinder Cmd+Shift+F9, Layers F7, Character Cmd+T…; every panel can be given one in Edit › Keyboard Shortcuts), and Eyedropper Options pick up and apply chosen attributes (Alt and Shift+Alt, image pixels). An ICC CMYK profile converts straight into the RGB working space (not through sRGB, so a wider space such as Wide Gamut RGB keeps colours sRGB can't hold) with the colour settings' black-point compensation, on the canvas and in RGB exports alike. Fills and strokes can overprint (Attributes panel, Overprint Black options), and CMYK documents blend in inks on screen, in PDF and when flattening. Document Color Mode converts the art, symbols, pattern tiles and swatches through the colour settings: Gray stays Gray, RGB greys separate into four-colour greys and a rich black as Illustrator does, or go on the black plate only with `grays: "black"` (also for `document.open {colorMode}`).
+  - **Colour:** a Color Picker (colour field, H/S/B/R/G/B channel slider, HSB/RGB/Lab/CMYK fields, hex, web-only snapping, out-of-gamut correction); the Color panel shows a selected colour in its own model and, with nothing selected, the new-art defaults in the mode picked last, which it keeps between sessions; Alt-click paints the other proxy; proxies look through groups and show "?" for mixed paint; Invert, Complement, Apply Last Color (`,`) and Apply Last Gradient (`.`) keep the colour model; every paint command feeds the recent colours. The Color Guide has 21 harmony rules, Steps and Variation options and Limit to Library. Adjust Color Balance (its Global mode shifts tints) and Saturate preview live; Edit Colors and Recolor also reach meshes, images and patterns. Recolor Artwork has colour reduction, five recolour methods, presets, Limit to Library, a colour-wheel Edit tab and Edit Color Group; a local Color Themes panel saves five-colour themes. Fill/Stroke chips open swatch and mixer popovers (the Properties panel has the Control bar's Fill and Stroke chips, Stroke link and weight spinner, with nothing selected too), panels have Illustrator's Window menu keys (Align Shift+F7, Transform Shift+F8, Pathfinder Cmd+Shift+F9, Layers F7, Character Cmd+T…; every panel can be given one in Edit › Keyboard Shortcuts), and Eyedropper Options pick up and apply chosen attributes (Alt and Shift+Alt, image pixels). An ICC CMYK profile converts straight into the RGB working space (not through sRGB, so a wider space such as Wide Gamut RGB keeps colours sRGB can't hold) with the colour settings' black-point compensation, on the canvas and in RGB exports alike (the built-in Generic CMYK compensates both ways, so RGB black separated to a rich black displays as black again). Fills and strokes can overprint (Attributes panel, Overprint Black options), and CMYK documents blend in inks on screen, in PDF and when flattening. Document Color Mode converts the art, symbols, pattern tiles and swatches through the colour settings: Gray stays Gray, RGB greys separate into four-colour greys and a rich black as Illustrator does, or go on the black plate only with `grays: "black"` (also for `document.open {colorMode}`).
     View › Proof Setup › Color blindness – Tritanopia-type turns Proof Colors on and proofs the canvas with the tritanopia simulation of Brettel, Viénot and Mollon (1997). The Separations Preview panel's Proof Setup list offers the same target (`view.proofSetup {target: "tritanopia"}`). Grays keep their value.
   - **Eyedropper sources (#1251):** ordinary and Shift clicks, Shift+Alt appearance append, raster pixels and gradient-stop sampling can read visible locked/template art and sources outside isolation. Sampling leaves the source and selection intact; Alt reverse still uses editable hits, and hidden art stays excluded. Engine/tool/hit regressions cover the editing boundary, color models and one-step Undo/Redo. The general object/image workflow is described in [public HelpX](https://helpx.adobe.com/illustrator/using/tool-techniques/eyedropper-tool.html); the lock/isolation expectations come from the user report and these regressions, without a new full-parity measurement.
   - **Sample Color from Screen:** an eyedropper button in the Color Picker and `ui.sampleScreenColor` (which can be given a key in Keyboard Shortcuts) pick a color anywhere on the screen with the system's sampler: `NSColorSampler` on macOS, the EyeDropper API in browsers that have it. The color becomes the fill or the stroke as one undo step, or the Color Picker's color, converted from display sRGB into the working RGB space. Windows, Linux and other browsers have no sampler yet; the button is gray there.