Merge #679

crates/color/src/cms/icc.rs

@@ -1,7 +1,7 @@
 //! ICC profiles through `moxcms` (pure Rust): built-in RGB spaces and user-supplied `.icc` files,
 //! and the profiles exports embed ([`encode_builtin`]), written in code from the CMS.
 
-use std::sync::{Arc, OnceLock};
+use std::sync::{Arc, Mutex, OnceLock};
 
 use moxcms::{
     ColorProfile, DataColorSpace, Layout, LocalizableString, LutMultidimensionalType, LutStore, LutWarehouse, Matrix3d, ProfileClass, ProfileText,
@@ -27,6 +27,9 @@ fn intent_index(i: Intent) -> usize {
 
 type Xf = Option<Arc<TransformF32Executor>>;
 
+/// A direct transform's cache key: destination name, intent index, black-point compensation.
+type DirectKey = (String, usize, bool);
+
 /// A parsed ICC profile plus lazily-built transforms to/from sRGB.
 pub struct IccProfile {
     pub name: String,
@@ -37,6 +40,21 @@ pub struct IccProfile {
     srgb: ColorProfile,
     to_srgb: [OnceLock<Xf>; 4],
     from_srgb: [OnceLock<Xf>; 4],
+    /// Direct transforms into other RGB profiles ([`Self::to_rgb_of`]), by destination, intent
+    /// and black-point compensation.
+    direct: Mutex<Vec<(DirectKey, Option<Arc<Direct>>)>>,
+}
+
+/// A transform from one profile into an RGB profile without passing through sRGB: into the
+/// destination's primaries with linear tone curves, where black-point compensation is a linear
+/// remap, then onto its own curves.
+struct Direct {
+    to_linear: Arc<TransformF32Executor>,
+    /// Linear → the destination's curves; `None` when the destination isn't a matrix profile
+    /// (the first transform goes straight into it, without compensation).
+    to_dest: Option<Arc<TransformF32Executor>>,
+    /// The source black's luminance in the linear destination (0: no compensation).
+    black: f32,
 }
 
 impl std::fmt::Debug for IccProfile {
@@ -72,6 +90,7 @@ impl IccProfile {
             srgb: ColorProfile::new_srgb(),
             to_srgb: Default::default(),
             from_srgb: Default::default(),
+            direct: Mutex::new(Vec::new()),
         })
     }
 
@@ -135,6 +154,72 @@ impl IccProfile {
         Some(dst.into_iter().map(|x| x.clamp(0.0, 1.0)).collect())
     }
 
+    /// Device values (RGB / CMYK / Gray, 0..1) → `dest`'s RGB, converted directly with `intent`:
+    /// not through sRGB, so colours outside sRGB keep their place in a wider space. With `bpc`
+    /// (and an intent other than absolute), this profile's black maps onto the destination's
+    /// black (black-point compensation, the darkest ink the profile prints becoming RGB 0 rather
+    /// than a dark grey). `None` when `dest` isn't RGB or no transform can be built.
+    pub fn to_rgb_of(&self, dest: &IccProfile, v: &[f32], intent: Intent, bpc: bool) -> Option<[f32; 3]> {
+        let t = self.direct_xf(dest, intent, bpc && intent != Intent::AbsoluteColorimetric)?;
+        let mut src = v.to_vec();
+        src.resize(self.channels(), 0.0);
+        let mut lin = [0.0f32; 3];
+        t.to_linear.transform(&src, &mut lin).ok()?;
+        let Some(to_dest) = &t.to_dest else { return Some(lin.map(|x| x.clamp(0.0, 1.0))) };
+        if t.black > 0.0 {
+            lin = lin.map(|x| (x - t.black) / (1.0 - t.black));
+        }
+        let lin = lin.map(|x| x.clamp(0.0, 1.0));
+        let mut out = [0.0f32; 3];
+        to_dest.transform(&lin, &mut out).ok()?;
+        Some(out.map(|x| x.clamp(0.0, 1.0)))
+    }
+
+    fn direct_xf(&self, dest: &IccProfile, intent: Intent, bpc: bool) -> Option<Arc<Direct>> {
+        if dest.kind != ProfileKind::Rgb {
+            return None;
+        }
+        let key = (dest.name.clone(), intent_index(intent), bpc);
+        let mut cache = self.direct.lock().unwrap_or_else(|e| e.into_inner());
+        if let Some((_, t)) = cache.iter().find(|(k, _)| *k == key) {
+            return t.clone();
+        }
+        let t = self.build_direct(dest, intent, bpc).map(Arc::new);
+        cache.push((key, t.clone()));
+        t
+    }
+
+    fn build_direct(&self, dest: &IccProfile, intent: Intent, bpc: bool) -> Option<Direct> {
+        let d = &dest.profile;
+        let matrix = d.red_trc.is_some() && d.green_trc.is_some() && d.blue_trc.is_some();
+        if !matrix {
+            let xf = self.profile.create_transform_f32(self.layout(), d, Layout::Rgb, Self::opts(intent)).ok()?;
+            return Some(Direct { to_linear: xf, to_dest: None, black: 0.0 });
+        }
+        let mut linear = d.clone();
+        for trc in [&mut linear.red_trc, &mut linear.green_trc, &mut linear.blue_trc] {
+            *trc = Some(ToneReprCurve::Parametric(vec![1.0]));
+        }
+        // A coding-independent code point names the transfer curve outright (moxcms's sRGB has
+        // one) and would override the linear curves.
+        linear.cicp = None;
+        let to_linear = self.profile.create_transform_f32(self.layout(), &linear, Layout::Rgb, Self::opts(intent)).ok()?;
+        let to_dest = linear.create_transform_f32(Layout::Rgb, d, Layout::Rgb, Self::opts(Intent::RelativeColorimetric)).ok()?;
+        // The source black: the darkest colour the profile reproduces, found as lcms does for an
+        // output profile (black sent into the profile and read back), made neutral.
+        let black = if bpc && self.kind == ProfileKind::Cmyk {
+            let inks = self.from_srgb([0.0; 3], Intent::RelativeColorimetric)?;
+            let mut lin = [0.0f32; 3];
+            to_linear.transform(&inks, &mut lin).ok()?;
+            let y = |c: &moxcms::Xyzd| c.y as f32;
+            let lum = lin[0] * y(&d.red_colorant) + lin[1] * y(&d.green_colorant) + lin[2] * y(&d.blue_colorant);
+            lum.clamp(0.0, 0.5)
+        } else {
+            0.0
+        };
+        Some(Direct { to_linear, to_dest: Some(to_dest), black })
+    }
+
     /// Whether transforms can be built for this profile (checked at registration).
     pub fn usable(&self) -> bool {
         self.to_xf(Intent::RelativeColorimetric).is_some() && self.inverse_xf(Intent::RelativeColorimetric).is_some()

crates/color/src/cms/mod.rs

@@ -356,10 +356,37 @@ impl Cms {
         }
     }
 
-    /// CMYK in the working space → display sRGB (`absolute` simulates the paper colour).
+    /// CMYK in the working space → display sRGB (`absolute` simulates the paper colour). An ICC
+    /// CMYK profile converts as [`Self::cmyk_to_rgb`] does into sRGB (with the settings'
+    /// black-point compensation), so what shows is what an RGB export writes.
     pub fn cmyk_to_srgb(&self, cmyk: [f32; 4], absolute: bool) -> [f32; 3] {
+        if let (false, CmykSpace::Icc(p)) = (absolute, &self.cmyk)
+            && let Some(srgb) = builtin_rgb_cache(SRGB)
+            && let Some(v) = p.to_rgb_of(&srgb, &cmyk.map(|v| v.clamp(0.0, 1.0)), Intent::RelativeColorimetric, self.settings.bpc)
+        {
+            return v;
+        }
         Self::cmyk_to_srgb_in(&self.cmyk, cmyk, absolute)
     }
+    /// 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
+    /// RGB space holds (Wide Gamut RGB keeps CMYK cyan that sRGB can't show), and with the
+    /// settings' black-point compensation. The built-in CMYK spaces go through sRGB as before
+    /// (Generic CMYK compensates in its own model).
+    pub fn cmyk_to_rgb(&self, cmyk: [f32; 4], intent: Intent) -> [f32; 3] {
+        let cmyk = cmyk.map(|v| v.clamp(0.0, 1.0));
+        let src = match &self.cmyk {
+            CmykSpace::Icc(p) => Some(p.clone()),
+            CmykSpace::Generic(_) | CmykSpace::Device => None,
+        };
+        let dest = match &self.rgb {
+            RgbSpace::Icc(p) => Some(p.clone()),
+            RgbSpace::Srgb => builtin_rgb_cache(SRGB),
+        };
+        src.zip(dest)
+            .and_then(|(s, d)| s.to_rgb_of(&d, &cmyk, intent, self.settings.bpc))
+            .unwrap_or_else(|| self.srgb_to_rgb(self.cmyk_to_srgb(cmyk, false)))
+    }
     /// Display sRGB → working CMYK with `intent`.
     pub fn srgb_to_cmyk(&self, srgb: [f32; 3], intent: Intent) -> [f32; 4] {
         Self::srgb_to_cmyk_in(&self.cmyk, srgb, intent, self.settings.bpc)
@@ -424,6 +451,10 @@ impl Cms {
                 let [c, m, y, k] = self.to_cmyk(c, intent);
                 Color::Cmyk { c, m, y, k }
             }
+            (Color::Cmyk { c, m, y, k }, Model::Rgb) => {
+                let [r, g, b] = self.cmyk_to_rgb([*c, *m, *y, *k], intent);
+                Color::Rgb { r, g, b }
+            }
             (_, Model::Rgb) => {
                 let [r, g, b] = self.srgb_to_rgb(self.display_rgb(c));
                 Color::Rgb { r, g, b }

crates/color/src/cms/tests_icc.rs

@@ -60,3 +60,54 @@ fn a_loaded_profile_is_embedded_as_loaded() {
     register_icc(&bytes, Some("Embedded As Loaded RGB".into())).unwrap();
     assert_eq!(&*icc_bytes("Embedded As Loaded RGB").unwrap(), &bytes[..]);
 }
+
+/// Settings with an ICC CMYK profile (Generic CMYK's, loaded as a file is) and Wide Gamut RGB.
+fn icc_cmyk(bpc: bool) -> Cms {
+    let name = register_icc(&icc_bytes(GENERIC_CMYK).unwrap(), Some("Test ICC CMYK".into())).unwrap().name;
+    Cms::new(&ColorSettings { rgb: WIDE_GAMUT_RGB.into(), cmyk: name, bpc, ..ColorSettings::default() }).unwrap()
+}
+
+#[test]
+fn icc_cmyk_converts_into_a_wide_rgb_space_directly_without_clipping_to_srgb() {
+    let wide = icc_cmyk(true);
+    let cyan = [1.0, 0.0, 0.0, 0.0];
+    let direct = wide.cmyk_to_rgb(cyan, Intent::RelativeColorimetric);
+    // Through sRGB, cyan clips to sRGB's gamut first: in the wider space that reads as a red
+    // channel well above zero.
+    let hub = wide.srgb_to_rgb(wide.cmyk_to_srgb(cyan, false));
+    assert!(direct[0] + 0.15 < hub[0], "direct {direct:?}, through sRGB {hub:?}");
+    // Same colour either way where sRGB holds it: a mid grey and paper white.
+    for inks in [[0.0, 0.0, 0.0, 0.5], [0.0; 4]] {
+        let (d, h) = (wide.cmyk_to_rgb(inks, Intent::RelativeColorimetric), wide.srgb_to_rgb(wide.cmyk_to_srgb(inks, false)));
+        assert!(d.iter().zip(h).all(|(a, b)| (a - b).abs() < 0.02), "{inks:?}: direct {d:?}, through sRGB {h:?}");
+    }
+    // Cms::convert takes the direct route for CMYK.
+    let Color::Rgb { r, .. } = wide.convert(&Color::Cmyk { c: 1.0, m: 0.0, y: 0.0, k: 0.0 }, Model::Rgb, Intent::RelativeColorimetric) else {
+        panic!("RGB")
+    };
+    assert!((r - direct[0]).abs() < 1e-6);
+}
+
+#[test]
+fn black_point_compensation_maps_the_darkest_ink_to_rgb_black() {
+    let rich = [0.75, 0.68, 0.67, 0.9];
+    let (on, off) = (icc_cmyk(true).cmyk_to_rgb(rich, Intent::RelativeColorimetric), icc_cmyk(false).cmyk_to_rgb(rich, Intent::RelativeColorimetric));
+    // Without compensation the profile's black is a dark grey; with it, rich black goes most of
+    // the way to RGB black (not all: it isn't quite the darkest ink the profile prints).
+    assert!(off.iter().all(|v| *v > 0.1), "without: {off:?}");
+    assert!(on.iter().zip(off).all(|(a, b)| *a < 0.08 && *a < b * 0.5), "with: {on:?}, without: {off:?}");
+    // The screen shows what an sRGB conversion writes, compensated alike.
+    let srgb = |bpc| {
+        let c = icc_cmyk(bpc);
+        Cms::new(&ColorSettings { rgb: SRGB.into(), ..c.settings().clone() }).unwrap()
+    };
+    for bpc in [true, false] {
+        let c = srgb(bpc);
+        assert_eq!(c.cmyk_to_srgb(rich, false), c.cmyk_to_rgb(rich, Intent::RelativeColorimetric), "bpc {bpc}");
+    }
+    // White is untouched, and absolute colorimetric never compensates.
+    let white = icc_cmyk(true).cmyk_to_rgb([0.0; 4], Intent::RelativeColorimetric);
+    assert!(white.iter().all(|v| *v > 0.99), "{white:?}");
+    let abs = |bpc| icc_cmyk(bpc).cmyk_to_rgb(rich, Intent::AbsoluteColorimetric);
+    assert_eq!(abs(true), abs(false));
+}

crates/pdf/src/output.rs

@@ -375,6 +375,11 @@ impl Dest {
                 };
                 Color::Cmyk { c, m, y, k }
             }
+            // CMYK straight into the destination RGB (the destination shares the source's CMYK).
+            (_, Color::Cmyk { c, m, y, k }) => {
+                let [r, g, b] = self.cms.cmyk_to_rgb([*c, *m, *y, *k], intent);
+                Color::Rgb { r, g, b }
+            }
             _ => {
                 let [r, g, b] = self.cms.srgb_to_rgb(source.display_rgb(c));
                 Color::Rgb { r, g, b }