jxl-oxide: Fix CMYK to RGB conversion (#370)

* jxl-oxide: Fix CMYK to RGB conversion

* Update CHANGELOG.md

CHANGELOG.md

@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Fixed
 - `jxl-render`: Fix requested color encoding not applied in some cases (#369).
+- `jxl-oxide`: Fix CMYK to RGB conversion (#370).
 
 ## [0.9.1] - 2024-10-12
 

crates/jxl-color/src/convert.rs

@@ -12,6 +12,7 @@ mod tone_map;
 pub struct ColorEncodingWithProfile {
     encoding: ColourEncoding,
     icc_profile: Vec<u8>,
+    is_cmyk: bool,
 }
 
 impl std::fmt::Debug for ColorEncodingWithProfile {
@@ -22,6 +23,7 @@ impl std::fmt::Debug for ColorEncodingWithProfile {
                 "icc_profile",
                 &format_args!("({} byte(s))", self.icc_profile.len()),
             )
+            .field("is_cmyk", &self.is_cmyk)
             .finish()
     }
 }
@@ -32,6 +34,7 @@ impl ColorEncodingWithProfile {
         Self {
             encoding: ColourEncoding::Enum(encoding),
             icc_profile: Vec::new(),
+            is_cmyk: false,
         }
     }
 
@@ -47,6 +50,7 @@ impl ColorEncodingWithProfile {
                 Ok(Self {
                     encoding: ColourEncoding::IccProfile(raw.color_space()),
                     icc_profile: icc_profile.to_vec(),
+                    is_cmyk: raw.is_cmyk(),
                 })
             }
             Err(e) => Err(e),
@@ -73,6 +77,12 @@ impl ColorEncodingWithProfile {
             ColourEncoding::IccProfile(color_space) => *color_space == ColourSpace::Grey,
         }
     }
+
+    /// Returns whether the color encoding represents CMYK color space.
+    #[inline]
+    pub fn is_cmyk(&self) -> bool {
+        self.is_cmyk
+    }
 }
 
 impl ColorEncodingWithProfile {

crates/jxl-color/src/icc/parse.rs

@@ -215,6 +215,10 @@ impl IccProfile<'_> {
             ColourSpace::Unknown
         }
     }
+
+    pub(crate) fn is_cmyk(&self) -> bool {
+        &self.header.color_space == b"CMYK"
+    }
 }
 
 struct RawTag<'a> {

crates/jxl-oxide/src/fb.rs

@@ -211,19 +211,22 @@ impl<'r> ImageStream<'r> {
         }
 
         // Find black
-        for (ec_idx, (ec, (region, _))) in render
-            .extra_channels
-            .iter()
-            .zip(&regions_and_shifts[color_channels..])
-            .enumerate()
-        {
-            if ec.is_black() {
-                grids.push(&fb[color_channels + ec_idx]);
-                bit_depth.push(ec.bit_depth);
-                start_offset_xy.push((left - region.left, top - region.top));
-                break;
+        if render.is_cmyk {
+            for (ec_idx, (ec, (region, _))) in render
+                .extra_channels
+                .iter()
+                .zip(&regions_and_shifts[color_channels..])
+                .enumerate()
+            {
+                if ec.is_black() {
+                    grids.push(&fb[color_channels + ec_idx]);
+                    bit_depth.push(ec.bit_depth);
+                    start_offset_xy.push((left - region.left, top - region.top));
+                    break;
+                }
             }
         }
+
         // Find alpha
         for (ec_idx, (ec, (region, _))) in render
             .extra_channels

crates/jxl-oxide/src/lib.rs

@@ -599,28 +599,9 @@ impl JxlImage {
 
     /// Returns the pixel format of the rendered image.
     pub fn pixel_format(&self) -> PixelFormat {
-        use jxl_color::{ColourEncoding, ColourSpace};
-
         let encoding = self.ctx.requested_color_encoding();
-        let (is_grayscale, has_black) = match encoding.encoding() {
-            ColourEncoding::Enum(EnumColourEncoding {
-                colour_space: ColourSpace::Grey,
-                ..
-            }) => (true, false),
-            ColourEncoding::Enum(_) => (false, false),
-            ColourEncoding::IccProfile(_) => {
-                let profile = encoding.icc_profile();
-                if profile.len() < 0x14 {
-                    (false, false)
-                } else {
-                    match &profile[0x10..0x14] {
-                        [b'G', b'R', b'A', b'Y'] => (true, false),
-                        [b'C', b'M', b'Y', b'K'] => (false, true),
-                        _ => (false, false),
-                    }
-                }
-            }
-        };
+        let is_grayscale = encoding.is_grayscale();
+        let has_black = encoding.is_cmyk();
         let mut has_alpha = false;
         for ec_info in &self.image_header.metadata.ec_info {
             if ec_info.is_alpha() {
@@ -754,6 +735,7 @@ impl JxlImage {
         let frame_header = frame.header();
         let target_frame_region = image_region.translate(-frame_header.x0, -frame_header.y0);
 
+        let is_cmyk = self.ctx.requested_color_encoding().is_cmyk();
         let result = Render {
             keyframe_index,
             name: frame_header.name.clone(),
@@ -763,6 +745,7 @@ impl JxlImage {
             extra_channels: self.convert_ec_info(),
             target_frame_region,
             color_bit_depth: self.image_header.metadata.bit_depth,
+            is_cmyk,
             render_spot_color: self.render_spot_color,
         };
         Ok(result)
@@ -792,6 +775,7 @@ impl JxlImage {
         let frame_header = frame.header();
         let target_frame_region = image_region.translate(-frame_header.x0, -frame_header.y0);
 
+        let is_cmyk = self.ctx.requested_color_encoding().is_cmyk();
         let result = Render {
             keyframe_index: self.ctx.loaded_keyframes(),
             name,
@@ -801,6 +785,7 @@ impl JxlImage {
             extra_channels: self.convert_ec_info(),
             target_frame_region,
             color_bit_depth: self.image_header.metadata.bit_depth,
+            is_cmyk,
             render_spot_color: self.render_spot_color,
         };
         Ok(result)
@@ -928,6 +913,7 @@ pub struct Render {
     extra_channels: Vec<ExtraChannel>,
     target_frame_region: Region,
     color_bit_depth: BitDepth,
+    is_cmyk: bool,
     render_spot_color: bool,
 }