From 3302928cb7b4e608e74eddba19241bccbfd0ecc3 Mon Sep 17 00:00:00 2001
From: saji <saji@saji.dev>
Date: Wed, 31 Jul 2024 00:09:44 -0500
Subject: [PATCH] optimize palette L*A*B* conversion, revert HyAb

HyAb makes the image look worse for higher contrast images.
We can look into adding quality control knobs in the future.
---
 src/dither.rs | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/src/dither.rs b/src/dither.rs
index d4a17b6..d192cc3 100644
--- a/src/dither.rs
+++ b/src/dither.rs
@@ -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