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Most popular edge color first

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Andrew 2023-06-01 14:09:38 +12:00 committed by Josh Holmer
parent 402d04c3c9
commit 27d6fe5eb3
1 changed files with 26 additions and 6 deletions
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32
src/reduction/palette.rs
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@ -78,11 +78,14 @@ pub fn sorted_palette(png: &PngImage) -> Option<PngImage> {
return None;
}
let palette = match &png.ihdr.color_type {
ColorType::Indexed { palette } => palette,
ColorType::Indexed { palette } if palette.len() > 1 => palette,
_ => return None,
};
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);
// Sort the palette
enumerated.sort_by(|a, b| {
@ -99,6 +102,7 @@ pub fn sorted_palette(png: &PngImage) -> Option<PngImage> {
};
color_val(a.1).cmp(&color_val(b.1))
});
enumerated.insert(0, first);
// Extract the new palette and determine if anything changed
let (old_map, palette): (Vec<_>, Vec<RGBA8>) = enumerated.into_iter().unzip();
@ -130,6 +134,7 @@ pub fn sorted_palette_battiato(png: &PngImage) -> Option<PngImage> {
return None;
}
let palette = match &png.ihdr.color_type {
// Images with only two colors will remain unchanged from previous luma sort
ColorType::Indexed { palette } if palette.len() > 2 => palette,
_ => return None,
};
@ -137,11 +142,16 @@ pub fn sorted_palette_battiato(png: &PngImage) -> Option<PngImage> {
let matrix = co_occurrence_matrix(palette.len(), png);
let edges = weighted_edges(&matrix);
let mut old_map = battiato_tsp(palette.len(), edges);
// Keep the same first element
// This is safe to do if the palette is full since the delta filters are wrapping operations
if palette.len() == 256 {
let first = old_map.iter().position(|&i| i == 0).unwrap();
old_map.rotate_left(first);
// 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_idx = old_map.iter().position(|&i| i == keep_first).unwrap();
// If the index is past halfway, reverse the order so as to minimize the change
if first_idx >= old_map.len() / 2 {
old_map.reverse();
old_map.rotate_right(first_idx + 1);
} else {
old_map.rotate_left(first_idx);
}
// Check if anything changed
@ -169,6 +179,16 @@ pub fn sorted_palette_battiato(png: &PngImage) -> 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 {
let mut counts = vec![0; num_colors];
for line in png.scan_lines(false) {
counts[line.data[0] as usize] += 1;
counts[line.data[line.data.len() - 1] as usize] += 1;
}
counts.iter().enumerate().max_by_key(|(_, &v)| v).unwrap().0
}
// Calculate co-occurences matrix
fn co_occurrence_matrix(num_colors: usize, png: &PngImage) -> Vec<Vec<usize>> {
let mut matrix = vec![vec![0; num_colors]; num_colors];