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dotCooCoo
6f9f9dfa95
Automatic counted flat art's colors with a median cut that never splits a box narrower than 24 levels, so evenly spaced levels about 17 apart (gray) or 13 apart (sepia) shared boxes: 16 clean gray levels traced in 14 colors and 16 sepia levels in 9. When flat art's pixels fall in 2 to 16 histogram bins, each holding at least the share a color needs to be counted, and every two bins lie at least 12 levels apart on some channel, Automatic now takes one color per bin. If mixed-color merging then finds two of those colors mixed through each other (dithering, or a thin region beside a close level), the picture is counted by median cut as before, with rare colors added. Anti-aliased art whose levels lie more than 20 apart is counted level by level too, because its blended edge pixels are left out of the count. Noisy pictures, anti-aliased art whose levels lie 20 or fewer apart and pictures of 17 levels or more are counted as before, and continuous-tone classification is unchanged.
415 lines
21 KiB
Rust
415 lines
21 KiB
Rust
//! Colour reduction and noise removal. Colours are compared in Oklab, where equal distances look
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//! equally different.
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use crate::{Mode, Palette, Raster, TraceParams, parallel_map};
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mod cut_edge;
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mod denoise;
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mod palette;
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mod rare;
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use cut_edge::{choosing_pixels, compact, settled, settled_wide, settles_wide};
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pub(crate) use cut_edge::{continuous_tone, settle_cut_edges};
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pub use denoise::denoise;
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pub(crate) use denoise::denoise_keeping;
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pub use palette::FULL_TONE_MAX;
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use palette::{Bin, HistKey, TracedAs, Used, color_palette, flat_count, flat_palette, kmeans_1d, labs, nearest_1d, nearest_lab, nearest_library};
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#[cfg(test)]
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pub(crate) use rare::kept_rare;
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use rare::{rare_colours, refine_around};
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/// Label of a transparent (untraced) pixel.
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pub const TRANSPARENT: u16 = u16::MAX;
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/// A palette-indexed image.
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#[derive(Clone, Debug, PartialEq)]
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pub struct Quantized {
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/// One palette index per pixel (row-major), or [`TRANSPARENT`].
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pub labels: Vec<u16>,
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pub palette: Vec<[u8; 3]>,
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}
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/// A pixel's gray (Rec. 601 luma): what Grayscale traces it as.
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pub(crate) fn luma(p: [u8; 4]) -> u8 {
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((p[0] as u32 * 299 + p[1] as u32 * 587 + p[2] as u32 * 114 + 500) / 1000) as u8
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}
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/// Reduce `img` to a palette according to `params.mode`. A raster whose bytes are not
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/// `width * height * 4` (its fields are public) has no pixels to reduce: no labels, no palette.
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pub fn quantize(img: &Raster, params: &TraceParams) -> Quantized {
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let want = (img.width as usize).checked_mul(img.height as usize).and_then(|n| n.checked_mul(4));
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if want != Some(img.rgba.len()) {
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return Quantized { labels: vec![], palette: vec![] };
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}
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quantize_keeping(img, params).0
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}
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/// [`quantize`], and the palette colours that are rare but kept on purpose (see [`rare_colours`]):
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/// noise removal must not erase their regions.
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pub(crate) fn quantize_keeping(img: &Raster, params: &TraceParams) -> (Quantized, Vec<[u8; 3]>) {
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let px = img.rgba.as_chunks::<4>().0.iter().map(|c| [c[0], c[1], c[2], c[3]]);
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match params.mode {
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Mode::BlackAndWhite => {
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let t = params.threshold;
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let labels = px
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.map(|p| {
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if p[3] < 128 {
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TRANSPARENT
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} else if luma(p) < t {
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1
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} else {
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0
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}
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})
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.collect();
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(Quantized { labels, palette: vec![[255, 255, 255], [0, 0, 0]] }, vec![])
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}
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Mode::Grayscale => {
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// The pixels that choose the grays: the opaque ones, except the semi-transparent ones
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// along the cut edge (see `choosing_pixels`).
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let choose = choosing_pixels(img, true);
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let own = own_colours(img);
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let own_choosing = own_colours_among(img, &choose);
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let histogram = |only_own: bool| {
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let mut hist = [0u64; 256];
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for ((p, &f), &c) in img.rgba.as_chunks::<4>().0.iter().zip(&own_choosing).zip(&choose) {
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if p[3] >= 128 && c && (f || !only_own) {
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hist[luma([p[0], p[1], p[2], p[3]]) as usize] += 1;
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}
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}
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hist
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};
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let (every, calm) = (histogram(false), histogram(true));
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let hist = if palette_from_own(calm.iter().sum::<u64>() as f64, every.iter().sum::<u64>() as f64) { calm } else { every };
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let levels = kmeans_1d(&hist, params.colors.clamp(2, 256) as usize);
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let mut lut = [0u16; 256];
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for (v, slot) in lut.iter_mut().enumerate() {
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*slot = nearest_1d(&levels, v as f64) as u16;
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}
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let labels = px.map(|p| if p[3] < 128 { TRANSPARENT } else { lut[luma(p) as usize] }).collect();
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let palette = levels.iter().map(|&l| {
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let g = l.round().clamp(0.0, 255.0) as u8;
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[g, g, g]
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});
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let q = merge_mixed(compact(labels, palette.collect()), img.width as usize, img.height as usize, &[]);
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(if settles_wide(params) { settled_wide(q, img, &own, true) } else { settled(q, img, &own) }, vec![])
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}
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// Logo mode traces without quantising; asked directly, it quantises like Color.
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Mode::Color | Mode::Logo => {
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// 15-bit colour histogram with per-bin sums (exact bin means), fitted to the image's
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// range per channel so that close tones (a dark, low-contrast photo) stay apart.
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let hk = HistKey::new(img);
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let pixels = img.rgba.as_chunks::<4>().0;
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// The pixels that choose the colors: the opaque ones, except the semi-transparent ones
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// along the cut edge (see `choosing_pixels`).
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let choose = choosing_pixels(img, false);
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let own = own_colours(img);
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let own_choosing = own_colours_among(img, &choose);
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let (mut all, mut every, mut calm) = (vec![Bin::default(); 1 << 15], vec![Bin::default(); 1 << 15], vec![Bin::default(); 1 << 15]);
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for ((p, &f), &c) in pixels.iter().zip(&own_choosing).zip(&choose) {
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if p[3] >= 128 {
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let k = hk.key(p[0], p[1], p[2]);
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all[k].add(p);
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if c {
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every[k].add(p);
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if f {
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calm[k].add(p);
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}
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}
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}
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}
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let used =
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|bins: &[Bin]| -> Vec<Used> { bins.iter().enumerate().filter(|(_, b)| b.n > 0).map(|(i, b)| (i, b.mean(), b.n as f64)).collect() };
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let (all, every, calm) = (used(&all), used(&every), used(&calm));
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let count = |u: &[Used]| u.iter().map(|b| b.2).sum::<f64>();
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let from = if palette_from_own(count(&calm), count(&every)) { &calm } else { &every };
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// Automatic on flat art: colours too rare for its count, but distinct and drawn as
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// regions of their own, are added (see `rare_colours`).
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let detail = (params.color_detail / 100.0).clamp(0.0, 1.0);
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let flat = if params.palette == Palette::Automatic { flat_count(from, detail) } else { None };
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let flat_auto = flat.is_some();
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let mut rare: Vec<[u8; 3]> = vec![];
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// The picture in the colors `params` asks for, or in one color per clean level when
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// `levels` is given; fewer come back when it has fewer, or when noise made several of
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// one (see `merge_mixed`). Also whether `merge_mixed` merged any.
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let mut reduce = |levels: Option<usize>| {
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rare.clear();
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let mut centers = match levels {
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Some(n) => flat_palette(from, n),
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None => color_palette(from, params),
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};
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// The anti-aliasing beside a rare color along the cut edge, with the indexes of
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// that color and of the color on the other side of it (see `rare_colours`).
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let mut traced_as: Vec<TracedAs> = vec![];
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if flat_auto {
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let (found, blends) = rare_colours(img, &own_choosing, &choose, &hk, ¢ers);
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if !found.is_empty() {
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let common = centers.len();
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traced_as = blends;
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centers.extend(found);
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centers = refine_around(from, centers, common);
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rare = centers.iter().skip(common).map(|c| c.map(|v| v.round().clamp(0.0, 255.0) as u8)).collect();
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}
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}
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let mut lut = vec![0u16; 1 << 15];
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let center_labs = labs(¢ers.iter().copied().chain(traced_as.iter().map(|t| t.0)).collect::<Vec<_>>());
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let library = params.palette == Palette::DocumentLibrary && !params.swatches.is_empty();
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let nearest = if library { nearest_library } else { nearest_lab };
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// Every opaque pixel takes a color, the cut edge's too. A bin takes the color
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// nearest to the mean of the pixels in it that choose the colors, and a bin with
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// none of them the color nearest to the mean of all its pixels. A bin nearest to
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// the anti-aliasing beside a rare color takes that rare color when it is at least
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// halfway from the color on the other side to it, and that color otherwise.
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for (i, c, _) in all.iter().chain(&every) {
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let n = nearest(¢er_labs, oklab(*c));
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lut[*i] = n.checked_sub(centers.len()).and_then(|t| traced_as.get(t)).map_or(n, |&(_, rare, other)| {
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let (Some(r), Some(o)) = (centers.get(rare), centers.get(other)) else { return rare };
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let d2: f64 = (0..3).map(|q| (r[q] - o[q]).powi(2)).sum();
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let t = if d2 > 0.0 { (0..3).map(|q| (c[q] - o[q]) * (r[q] - o[q])).sum::<f64>() / d2 } else { 1.0 };
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if t >= 0.5 { rare } else { other }
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}) as u16;
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}
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let labels =
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img.rgba.as_chunks::<4>().0.iter().map(|p| if p[3] < 128 { TRANSPARENT } else { lut[hk.key(p[0], p[1], p[2])] }).collect();
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let palette = centers.iter().map(|c| [c[0].round() as u8, c[1].round() as u8, c[2].round() as u8]).collect();
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let q = compact(labels, palette);
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// A swatch library's colours are used as they are.
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if library {
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return (q, false);
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}
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let before = q.palette.len();
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let q = merge_mixed(q, img.width as usize, img.height as usize, &rare);
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let merged = q.palette.len() < before;
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(q, merged)
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};
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// Clean levels (see `flat_count`) each take a color unless `merge_mixed` finds two of
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// them mixed (dithering, or a thin region of a level beside a close one): such a
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// picture takes the colors median cut counts, with rare colors added.
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let q = match flat {
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Some((_, Some(levels))) => match reduce(Some(levels)) {
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(q, false) => q,
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(_, true) => reduce(None).0,
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},
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_ => reduce(None).0,
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};
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let q = if settles_wide(params) { settled_wide(q, img, &own, false) } else { settled(q, img, &own) };
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rare.retain(|c| q.palette.contains(c));
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(q, rare)
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}
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}
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}
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/// The opaque pixels whose colour is the picture's own, not a blend: a pixel is a blend when it
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/// lies between the two pixels on opposite sides of it (left and right, above and below, or
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/// across a diagonal) that differ by more than 20 levels, which is what anti-aliasing and blur
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/// leave along an edge. A line one pixel wide is no blend (the pixels on its two sides are alike),
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/// nor is noise.
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fn own_colours(img: &Raster) -> Vec<bool> {
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let opaque: Vec<bool> = img.rgba.as_chunks::<4>().0.iter().map(|p| p[3] >= 128).collect();
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own_colours_among(img, &opaque)
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}
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/// [`own_colours`] among the pixels that `among` marks: the others are neither own colours nor
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/// the neighbours a pixel is a blend of.
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fn own_colours_among(img: &Raster, among: &[bool]) -> Vec<bool> {
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own_colours_among_by(img, among, PIXELS_PER_SHARE)
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}
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/// [`own_colours_among`], with the rows worked on in bands of about `per_share` pixels (see [`over_rows`]).
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fn own_colours_among_by(img: &Raster, among: &[bool], per_share: usize) -> Vec<bool> {
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let (w, h) = (img.width as isize, img.height as isize);
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let px = img.rgba.as_chunks::<4>().0;
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let at = |x: isize, y: isize| {
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let i = (x >= 0 && y >= 0 && x < w && y < h).then_some((y * w + x) as usize)?;
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let p = px.get(i).filter(|_| among.get(i).copied().unwrap_or(false))?;
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Some([f64::from(p[0]), f64::from(p[1]), f64::from(p[2])])
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};
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over_rows(img.width as usize, img.height as usize, per_share, |rows| {
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let mut out = Vec::with_capacity(rows.len() * img.width as usize);
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for y in rows.start as isize..rows.end as isize {
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for x in 0..w {
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let Some(p) = at(x, y) else {
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out.push(false);
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continue;
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};
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let blend = [(1, 0), (0, 1), (1, 1), (1, -1)].into_iter().any(|(dx, dy)| {
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let (Some(a), Some(b)) = (at(x - dx, y - dy), at(x + dx, y + dy)) else { return false };
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let d = [0, 1, 2].map(|k| b[k] - a[k]);
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let len2: f64 = d.iter().map(|v| v * v).sum();
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if len2 <= 400.0 {
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return false;
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}
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let t = (0..3).map(|k| (p[k] - a[k]) * d[k]).sum::<f64>() / len2;
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let off2: f64 = (0..3).map(|k| (p[k] - a[k] - t * d[k]).powi(2)).sum();
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t > 0.06 && t < 0.94 && off2 < len2 / 16.0
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});
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out.push(!blend);
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}
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}
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out
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})
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}
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/// About how many pixels one thread works through at a time in the passes over every pixel that
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/// [`over_rows`] spreads over the available cores. A picture of fewer pixels is worked through on
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/// one thread.
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const PIXELS_PER_SHARE: usize = 1 << 16;
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/// `f` of each band of rows of a picture `w` pixels wide and `h` rows high, each band about
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/// `per_share` pixels (at least one row), spread over the available cores (one thread on the web),
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/// and the results joined in row order. Each band's result depends only on its rows, so the
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/// joined result is the same however many threads there are. A picture with no pixels gives no
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/// result.
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fn over_rows<R: Send>(w: usize, h: usize, per_share: usize, f: impl Fn(std::ops::Range<usize>) -> Vec<R> + Sync) -> Vec<R> {
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if w == 0 || h == 0 {
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return Vec::new();
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}
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let rows = (per_share / w.max(1)).max(1);
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let bands: Vec<std::ops::Range<usize>> = (0..h).step_by(rows).map(|y| y..(y + rows).min(h)).collect();
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if bands.len() <= 1 {
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return bands.into_iter().flat_map(&f).collect();
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}
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parallel_map(&bands, |rows| f(rows.clone())).into_iter().flatten().collect()
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}
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/// Whether the palette is made from the picture's own colours alone (`own` of `all` opaque
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/// pixels), so that the blends along edges take none of its colours. A picture with next to none
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/// is all soft edges: there every pixel counts.
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fn palette_from_own(own: f64, all: f64) -> bool {
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own >= 0.05 * all && own >= 16.0
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}
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/// sRGB (0–255) to Oklab × 100 (Björn Ottosson, "A perceptual color space for image processing",
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/// 2020): equal distances look equally different, and 2 or 3 is about the least one sees.
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fn oklab(c: [f64; 3]) -> [f64; 3] {
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let lin = c.map(|v| {
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let v = (v / 255.0).clamp(0.0, 1.0);
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if v <= 0.04045 { v / 12.92 } else { ((v + 0.055) / 1.055).powf(2.4) }
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});
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let l = (0.412_221_470_8 * lin[0] + 0.536_332_536_3 * lin[1] + 0.051_445_992_9 * lin[2]).cbrt();
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let m = (0.211_903_498_2 * lin[0] + 0.680_699_545_1 * lin[1] + 0.107_396_956_6 * lin[2]).cbrt();
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let s = (0.088_302_461_9 * lin[0] + 0.281_718_837_6 * lin[1] + 0.629_978_700_5 * lin[2]).cbrt();
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[
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100.0 * (0.210_454_255_3 * l + 0.793_617_785 * m - 0.004_072_046_8 * s),
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100.0 * (1.977_998_495_1 * l - 2.428_592_205 * m + 0.450_593_709_9 * s),
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100.0 * (0.025_904_037_1 * l + 0.782_771_766_2 * m - 0.808_675_766 * s),
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]
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}
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/// [`oklab`] of an sRGB colour, for the tests.
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#[cfg(test)]
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pub(crate) fn tests_oklab(c: [u8; 3]) -> [f64; 3] {
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oklab(c.map(f64::from))
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}
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/// `q` with the colours that noise made of one colour merged, largest mix first.
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///
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/// Asked for more colours than a picture has, k-means splits a flat colour along its noise, and
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/// the two halves would trace as specks of one all over the other. Such halves are close (under 30
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/// levels apart: noise is about as strong in a dark colour as in a light one, so the distance is
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/// taken in RGB) and thoroughly mixed: the pixels of the lesser one have, on average, more than
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/// half a neighbour of the other each; or they are closer still (under 12 levels) and mixed in
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/// patches (compression blocks). The bands of a gradient are close too, but each keeps to itself
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/// and they stay apart. The colours in `keep` merge with none.
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fn merge_mixed(q: Quantized, w: usize, h: usize, keep: &[[u8; 3]]) -> Quantized {
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let k = q.palette.len();
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// A rare colour kept on purpose (see `rare_colours`) is distinct by choice: it merges with none.
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let kept: Vec<bool> = q.palette.iter().map(|c| keep.contains(c)).collect();
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if k < 2 || q.labels.len() != w * h {
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return q;
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}
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// How many pixels each colour has, and how many neighbouring pairs each pair of colours.
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let mut count = vec![0.0f64; k];
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let mut touch = vec![0.0f64; k * k];
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let label = |i: usize| q.labels.get(i).map(|&l| l as usize).filter(|&l| l < k);
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for i in 0..w * h {
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let Some(a) = label(i) else { continue };
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count[a] += 1.0;
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for j in [(i % w + 1 < w).then_some(i + 1), (i + w < w * h).then_some(i + w)].into_iter().flatten() {
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if let Some(b) = label(j).filter(|&b| b != a) {
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touch[a * k + b] += 1.0;
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touch[b * k + a] += 1.0;
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}
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}
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}
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let mut color: Vec<[f64; 3]> = q.palette.iter().map(|c| c.map(f64::from)).collect();
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// Which colour each has merged into (itself when none).
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let mut into: Vec<usize> = (0..k).collect();
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loop {
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let mut best: Option<(f64, usize, usize)> = None;
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for a in 0..k {
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for b in a + 1..k {
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if into[a] != a || into[b] != b || count[a] <= 0.0 || count[b] <= 0.0 || kept[a] || kept[b] {
|
||
continue;
|
||
}
|
||
let mixed = touch[a * k + b] / count[a].min(count[b]);
|
||
let apart = (0..3).map(|c| (color[a][c] - color[b][c]).powi(2)).sum::<f64>().sqrt();
|
||
if (mixed > 0.5 && apart < 30.0 || mixed > 0.15 && apart < 12.0) && best.is_none_or(|x| mixed > x.0) {
|
||
best = Some((mixed, a, b));
|
||
}
|
||
}
|
||
}
|
||
let Some((_, a, b)) = best else { break };
|
||
color[a] = [0, 1, 2].map(|c| (color[a][c] * count[a] + color[b][c] * count[b]) / (count[a] + count[b]));
|
||
count[a] += count[b];
|
||
count[b] = 0.0;
|
||
into[b] = a;
|
||
for c in 0..k {
|
||
if c != a && c != b {
|
||
touch[a * k + c] += touch[b * k + c];
|
||
touch[c * k + a] = touch[a * k + c];
|
||
}
|
||
}
|
||
}
|
||
if into.iter().enumerate().all(|(i, &t)| i == t) {
|
||
return q;
|
||
}
|
||
// A colour may have merged into one that merged again: follow each to where it ended up.
|
||
for i in 0..k {
|
||
let mut to = into[i];
|
||
while into[to] != to {
|
||
to = into[to];
|
||
}
|
||
into[i] = to;
|
||
}
|
||
let labels = q.labels.iter().map(|&l| into.get(l as usize).map_or(l, |&t| t as u16)).collect();
|
||
compact(labels, color.iter().map(|c| [c[0].round() as u8, c[1].round() as u8, c[2].round() as u8]).collect())
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::*;
|
||
|
||
#[test]
|
||
fn blend_pixels_are_found_the_same_however_the_picture_is_shared_out() {
|
||
// Slanted stripes of red and blue, blended over three pixels at each edge, with a little
|
||
// noise and a band of half-transparent pixels along the bottom. Odd sizes, so that the last
|
||
// band of rows is short.
|
||
let (w, h) = (173u32, 97u32);
|
||
let (red, blue) = ([200.0, 30.0, 40.0], [20.0, 60.0, 180.0]);
|
||
let img = Raster::from_fn(w, h, |x, y| {
|
||
let s = (x + y / 2) % 24;
|
||
let t = f64::from(s.saturating_sub(9).min(3)) / 3.0 - f64::from(s.saturating_sub(21).min(3)) / 3.0;
|
||
let noise = f64::from((x * 7 + y * 13) % 5) - 2.0;
|
||
let c = [0, 1, 2].map(|k| (red[k] + t * (blue[k] - red[k]) + noise).clamp(0.0, 255.0) as u8);
|
||
[c[0], c[1], c[2], if y + 2 >= h { 160 } else { 255 }]
|
||
});
|
||
let all = w as usize * h as usize;
|
||
let opaque: Vec<bool> = img.rgba.as_chunks::<4>().0.iter().map(|p| p[3] >= 128).collect();
|
||
// One row per share, a few rows per share, and the whole picture as one.
|
||
let own: Vec<Vec<bool>> = [1, 3 * w as usize + 5, all].iter().map(|&s| own_colours_among_by(&img, &opaque, s)).collect();
|
||
assert_eq!(own[0].len(), all);
|
||
assert!(own[0].iter().any(|&o| !o), "the edges have blend pixels");
|
||
assert!(own.iter().all(|o| *o == own[0]));
|
||
}
|
||
|
||
#[test]
|
||
fn a_picture_with_no_pixels_is_not_shared_out() {
|
||
// No band for each of the rows of a picture with no columns, however many rows it has.
|
||
assert!(over_rows(0, usize::MAX, PIXELS_PER_SHARE, |_| vec![0u8]).is_empty());
|
||
assert!(over_rows(5, 0, PIXELS_PER_SHARE, |_| vec![0u8]).is_empty());
|
||
let img = Raster::new(0, u32::MAX, vec![]).unwrap();
|
||
assert!(own_colours_among(&img, &[]).is_empty());
|
||
}
|
||
}
|