make lab conversion parallel; use hyab

Cargo.lock

@@ -1463,6 +1463,7 @@ dependencies = [
  "mime",
  "minijinja",
  "palette",
+ "rayon",
  "rusqlite",
  "serde",
  "strum",

Cargo.toml

@@ -16,6 +16,7 @@ linux-embedded-hal = { version = "0.4.0"}
 mime = "0.3.17"
 minijinja = "2.1.0"
 palette = "0.7.6"
+rayon = "1.10.0"
 rusqlite = { version = "0.32.1", features = ["bundled"] }
 serde = { version = "1.0.204", features = ["derive"] }
 strum = { version = "0.26.3", features = ["derive"] }

src/dither.rs

@@ -6,6 +6,7 @@ use tracing::instrument;
 use image::Rgb as imgRgb;
 use palette::color_difference::{Ciede2000, HyAb};
 use palette::{cast::FromComponents, IntoColor, Lab, Srgb};
+use rayon::prelude::*;
 
 #[derive(
     strum::EnumString, strum::Display, Serialize, Deserialize, PartialEq, Eq, Debug, Clone,
@@ -94,7 +95,7 @@ fn nearest_neighbor(input_color: Lab, palette: &[Lab]) -> (u8, Lab) {
         .map(|(idx, p_color)| {
             (
                 idx,
-                input_color.difference(*p_color), // this is CIEDIE2000 based and highly accurate.
+                input_color.hybrid_distance(*p_color), // this is CIEDIE2000 based and highly accurate.
                 input_color - *p_color,
             )
         })
@@ -214,11 +215,9 @@ impl<'a> Ditherer for ErrorDiffusion<'a> {
         // first, a view into the rgb components
         let srgb = <&[Srgb<u8>]>::from_components(&**img);
         let (xsize, ysize) = img.dimensions();
-        // our destination buffer.
-        let mut temp_img: Vec<Lab> = Vec::with_capacity((xsize * ysize) as usize);
-        for pix in srgb {
-            temp_img.push(pix.into_format().into_color());
-        }
+        // our temporary buffer. we push the error here.
+        let mut temp_img: Vec<Lab> = srgb.par_iter().map(|p| p.into_format().into_color()).collect();
+
         let lab_palette: Vec<Lab> = output.palette.iter().map(|c| Lab::from_color(*c)).collect();
 
         // TODO: rework this to make more sense.