Fix/truncated palette

src/reduction/palette.rs

@@ -14,9 +14,8 @@ pub fn reduced_palette(png: &PngImage, optimize_alpha: bool) -> Option<PngImage>
  if png.ihdr.bit_depth != BitDepth::Eight {
  return None;
  }
- let palette = match &png.ihdr.color_type {
- ColorType::Indexed { palette } if palette.len() > 1 => palette,
- _ => return None,
+ let ColorType::Indexed { palette } = &png.ihdr.color_type else {
+ return None;
  };
 
  let mut used = [false; 256];
@@ -43,8 +42,9 @@ pub fn reduced_palette(png: &PngImage, optimize_alpha: bool) -> Option<PngImage>
  let data = if did_change {
  // Reassign data bytes to new indices
  png.data.iter().map(|b| byte_map[*b as usize]).collect()
- } else if condensed.len() < palette.len() {
- // Data is unchanged but palette will be truncated
+ } else if condensed.len() != palette.len() {
+ // Data is unchanged but palette is different size
+ // Note the new palette could potentially be larger if the original had a missing entry
  png.data.clone()
  } else {
  // Nothing has changed

tests/reduction.rs

@@ -1049,6 +1049,43 @@ fn palette_should_be_reduced_with_both() {
  remove_file(output).ok();
 }
 
+#[test]
+fn palette_should_be_reduced_with_missing() {
+ let input = PathBuf::from("tests/files/palette_should_be_reduced_with_missing.png");
+ let (output, opts) = get_opts(&input);
+
+ let png = PngData::new(&input, &opts).unwrap();
+
+ assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
+ assert_eq!(png.raw.ihdr.bit_depth, BitDepth::Eight);
+ if let ColorType::Indexed { palette } = &png.raw.ihdr.color_type {
+ assert_eq!(palette.len(), 2);
+ }
+
+ match oxipng::optimize(&InFile::Path(input), &output, &opts) {
+ Ok(_) => (),
+ Err(x) => panic!("{}", x),
+ };
+ let output = output.path().unwrap();
+ assert!(output.exists());
+
+ let png = match PngData::new(output, &opts) {
+ Ok(x) => x,
+ Err(x) => {
+ remove_file(output).ok();
+ panic!("{}", x)
+ }
+ };
+
+ assert_eq!(png.raw.ihdr.color_type.png_header_code(), INDEXED);
+ assert_eq!(png.raw.ihdr.bit_depth, BitDepth::Two);
+ if let ColorType::Indexed { palette } = &png.raw.ihdr.color_type {
+ assert_eq!(palette.len(), 3);
+ }
+
+ remove_file(output).ok();
+}
+
 #[test]
 fn rgba_16_reduce_alpha() {
  test_it_converts(