Pure integer arithmetic

src/codecs/tiff.rs

@@ -553,26 +553,30 @@ fn ycbcr_to_rgb8(ycbcr: &[[u8; 3]], lr: f32, lg: f32, lb: f32, out: &mut [[u8; 3
 }
 
 fn cmyk_to_rgb(cmyk: &[u8; 4]) -> [u8; 3] {
-    let c = f32::from(cmyk[0]);
-    let m = f32::from(cmyk[1]);
-    let y = f32::from(cmyk[2]);
-    let kf = 1. - f32::from(cmyk[3]) / 255.;
+    let c = cmyk[0] as u32;
+    let m = cmyk[1] as u32;
+    let y = cmyk[2] as u32;
+    let k = cmyk[3] as u32;
+
+    let k_inv = 255 - k;
     [
-        ((255. - c) * kf) as u8,
-        ((255. - m) * kf) as u8,
-        ((255. - y) * kf) as u8,
+        (((255 - c) * k_inv) / 255) as u8,
+        (((255 - m) * k_inv) / 255) as u8,
+        (((255 - y) * k_inv) / 255) as u8,
     ]
 }
 
 fn cmyk_to_rgb16(cmyk: &[u16; 4]) -> [u16; 3] {
-    let c = f32::from(cmyk[0]);
-    let m = f32::from(cmyk[1]);
-    let y = f32::from(cmyk[2]);
-    let kf = 1. - f32::from(cmyk[3]) / 65535.;
+    let c = cmyk[0] as u64;
+    let m = cmyk[1] as u64;
+    let y = cmyk[2] as u64;
+    let k = cmyk[3] as u64;
+
+    let k_inv = 65535 - k;
     [
-        ((65535. - c) * kf) as u16,
-        ((65535. - m) * kf) as u16,
-        ((65535. - y) * kf) as u16,
+        (((65535 - c) * k_inv) / 65535) as u16,
+        (((65535 - m) * k_inv) / 65535) as u16,
+        (((65535 - y) * k_inv) / 65535) as u16,
     ]
 }
 

tests/conversions.rs

@@ -103,3 +103,37 @@ fn test_decode_8bit_ycbcr_lzw_invalid_coefficients() {
     let result = TiffDecoder::new(std::io::Cursor::new(data));
     assert!(result.is_err());
 }
+
+#[cfg(feature = "tiff")]
+#[test]
+fn test_decode_8bit_cmyk() -> Result<(), image::ImageError> {
+    let img_path = PathBuf::from("tests/images/tiff/testsuite/cmyk_u8_edge_case.tif");
+    let data = fs::read(img_path).expect("Test image missing");
+
+    let tiff_decoder = TiffDecoder::new(std::io::Cursor::new(data))?;
+
+    assert_eq!(tiff_decoder.color_type(), image::ColorType::Rgb8);
+
+    let mut buffer = vec![0u8; tiff_decoder.total_bytes() as usize];
+    tiff_decoder.read_image(&mut buffer)?;
+    assert_eq!(buffer, vec![190, 190, 190]);
+
+    Ok(())
+}
+
+#[cfg(feature = "tiff")]
+#[test]
+fn test_decode_8bit_cmyk_truncation() -> Result<(), image::ImageError> {
+    let img_path = PathBuf::from("tests/images/tiff/testsuite/cmyk_u8_trunc_case.tif");
+    let data = fs::read(img_path).expect("Test image missing");
+
+    let tiff_decoder = TiffDecoder::new(std::io::Cursor::new(data))?;
+
+    assert_eq!(tiff_decoder.color_type(), image::ColorType::Rgb8);
+
+    let mut buffer = vec![0u8; tiff_decoder.total_bytes() as usize];
+    tiff_decoder.read_image(&mut buffer)?;
+    assert_eq!(buffer, vec![126, 126, 126]);
+
+    Ok(())
+}