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optimize palette L*A*B* conversion, revert HyAb

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HyAb makes the image look worse for higher contrast images.
We can look into adding quality control knobs in the future.
This commit is contained in:
saji 2024-07-31 00:09:44 -05:00
parent 25ac7d584b
commit 3302928cb7
1 changed files with 8 additions and 7 deletions
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15
src/dither.rs
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@ -4,7 +4,7 @@ use serde::{Deserialize, Serialize};
use tracing::instrument;
use image::Rgb as imgRgb;
use palette::color_difference::Ciede2000;
use palette::color_difference::{Ciede2000, HyAb};
use palette::{cast::FromComponents, IntoColor, Lab, Srgb};
/// Palette used on the display; pixels can be one of these colors.
@ -133,13 +133,12 @@ pub trait Ditherer {
/// Find the closest approximate palette color to the given sRGB value.
/// This uses euclidian distance in linear space.
fn nearest_neighbor(input_color: Lab, palette: &[Srgb]) -> (u8, Lab) {
fn nearest_neighbor(input_color: Lab, palette: &[Lab]) -> (u8, Lab) {
let (nearest, _, color_diff) = palette
.iter()
.enumerate()
.map(|(idx, p_color)| {
let c: Lab = Lab::from_color(*p_color);
(idx, input_color.difference(c), input_color - c)
(idx, input_color.difference(*p_color), input_color - *p_color)
})
.min_by(|(_, a, _), (_, b, _)| a.total_cmp(b))
.expect("Should always find a color");
@ -150,12 +149,13 @@ pub struct NearestNeighbor();
impl Ditherer for NearestNeighbor {
fn dither(&mut self, img: &RgbImage, output: &mut DitheredImage) {
// sRGB view into the given image. zero copy!
let srgb = <&[Srgb<u8>]>::from_components(&**img);
let lab_palette: Vec<Lab> = output.palette.iter().map(|c| Lab::from_color(*c)).collect();
for (idx, pix) in output.buf.iter_mut().enumerate() {
let (n, _) = nearest_neighbor(srgb[idx].into_format().into_color(), &output.palette);
let (n, _) = nearest_neighbor(srgb[idx].into_format().into_color(), &lab_palette);
*pix = n;
}
}
@ -267,13 +267,14 @@ impl<'a> Ditherer for ErrorDiffusion<'a> {
for pix in srgb {
temp_img.push(pix.into_format().into_color());
}
let lab_palette: Vec<Lab> = output.palette.iter().map(|c| Lab::from_color(*c)).collect();
// TODO: rework this to make more sense.
for y in 0..ysize {
for x in 0..xsize {
let index = coord_to_idx(x, y, xsize);
let curr_pix = temp_img[index];
let (nearest, err) = nearest_neighbor(curr_pix, &output.palette);
let (nearest, err) = nearest_neighbor(curr_pix, &lab_palette);
// set the color in the output buffer.
*output
.buf