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Don't use most popular edge colour if tied (#673)

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If multiple edge colours were tied for most popular, the one chosen
would depend on the current palette order, which could cause it to
change if run a second time.

This further improves determinism for #649. There is still one more
issue I've found affecting the images there which I'll try to address in
another PR.
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andrews05 2025-02-03 06:15:55 +13:00 committed by GitHub
parent 8f298be7fb
commit e6f84264e5
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1 changed files with 13 additions and 7 deletions
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20
src/reduction/palette.rs
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@ -87,7 +87,7 @@ pub fn sorted_palette(png: &PngImage) -> Option<PngImage> {
let mut enumerated: Vec<_> = palette.iter().enumerate().collect();
// Put the most popular edge color first, which can help slightly if the filter bytes are 0
let keep_first = most_popular_edge_color(palette.len(), png);
let first = enumerated.remove(keep_first);
let first = keep_first.map(|f| enumerated.remove(f));
// Sort the palette
enumerated.sort_by(|a, b| {
@ -104,7 +104,9 @@ pub fn sorted_palette(png: &PngImage) -> Option<PngImage> {
};
color_val(a.1).cmp(&color_val(b.1))
});
enumerated.insert(0, first);
if let Some(first) = first {
enumerated.insert(0, first);
}
// Extract the new palette and determine if anything changed
let (remapping, palette): (Vec<_>, Vec<RGBA8>) = enumerated.into_iter().unzip();
@ -204,7 +206,7 @@ fn apply_palette_reorder(png: &PngImage, remapping: &[usize]) -> Option<PngImage
}
// Find the most popular color on the image edges (the pixels neighboring the filter bytes)
fn most_popular_edge_color(num_colors: usize, png: &PngImage) -> usize {
fn most_popular_edge_color(num_colors: usize, png: &PngImage) -> Option<usize> {
let mut counts = [0u32; 256];
for line in png.scan_lines(false) {
if let &[first, .., last] = line.data {
@ -212,14 +214,18 @@ fn most_popular_edge_color(num_colors: usize, png: &PngImage) -> usize {
counts[last as usize] += 1;
}
}
counts
let max = counts
.iter()
.copied()
.take(num_colors)
.enumerate()
.max_by_key(|&(_, v)| v)
.unwrap_or_default()
.0
.unwrap();
// Ensure there's a clear winner - return None if multiple colors are tied
let max_equal = counts.iter().filter(|&v| v == max.1).count();
if max_equal > 1 {
return None;
}
Some(max.0)
}
// Find the most popular color in the image, along with its count