Add bad random dithering

Cargo.lock

@@ -457,6 +457,7 @@ dependencies = [
  "clap",
  "image",
  "palette",
+ "rand",
 ]
 
 [[package]]
@@ -631,6 +632,12 @@ dependencies = [
  "miniz_oxide",
 ]
 
+[[package]]
+name = "ppv-lite86"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b40af805b3121feab8a3c29f04d8ad262fa8e0561883e7653e024ae4479e6de"
+
 [[package]]
 name = "proc-macro2"
 version = "1.0.66"
@@ -664,6 +671,18 @@ version = "0.8.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "34af8d1a0e25924bc5b7c43c079c942339d8f0a8b57c39049bef581b46327404"
 dependencies = [
+ "libc",
+ "rand_chacha",
+ "rand_core",
+]
+
+[[package]]
+name = "rand_chacha"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6c10a63a0fa32252be49d21e7709d4d4baf8d231c2dbce1eaa8141b9b127d88"
+dependencies = [
+ "ppv-lite86",
  "rand_core",
 ]
 
@@ -672,6 +691,9 @@ name = "rand_core"
 version = "0.6.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ec0be4795e2f6a28069bec0b5ff3e2ac9bafc99e6a9a7dc3547996c5c816922c"
+dependencies = [
+ "getrandom",
+]
 
 [[package]]
 name = "rayon"

Cargo.toml

@@ -7,3 +7,4 @@ edition = "2021"
 clap = { version = "4.3.19", features = ["derive", "deprecated"] }
 image = "0.24.6"
 palette = "0.7.2"
+rand = { version = "0.8.5", features = ["small_rng"] }

src/dither.rs

@@ -12,6 +12,7 @@ use palette::{
     color_difference::{Ciede2000, EuclideanDistance, HyAb},
     Clamp, IntoColor, Lab, Srgb,
 };
+use rand::{rngs::SmallRng, Rng, SeedableRng};
 
 use crate::util;
 
@@ -122,7 +123,8 @@ pub struct AlgoThreshold;
 impl<C, D> Algorithm<C, D> for AlgoThreshold
 where
     Srgb: IntoColor<C>,
-    C: IntoColor<Srgb> + Copy,
+    C: Copy,
+    C: IntoColor<Srgb> ,
     D: Difference<C>,
 {
     fn run(mut image: RgbaImage, palette: Palette<C>) -> RgbaImage {
@@ -134,3 +136,40 @@ where
         image
     }
 }
+
+// TODO Fix probability calculation
+//
+// Choose probability for each color such that the expected value of a pixel is
+// its actual color (or as close as possible).
+//
+// We want to represent a pixel as a linear combination of palette colors with
+// factors in the range [0, 1] that sum up to 1. Then we can use those factors
+// as probabilities. This may not work for every palette.
+//
+// As a secondary optimization target, we might want to miminize the amount of
+// nonzero factors, if possible.
+pub struct AlgoRandom;
+
+impl<C, D> Algorithm<C, D> for AlgoRandom
+where
+    Srgb: IntoColor<C>,
+    C: AsMut<[f32; 3]>,
+    C: Copy,
+    C: IntoColor<Srgb>,
+    D: Difference<C>,
+{
+    fn run(mut image: RgbaImage, palette: Palette<C>) -> RgbaImage {
+        let mut rng = SmallRng::seed_from_u64(0);
+        let range_radius = 1.0;
+
+        for pixel in image.pixels_mut() {
+            let mut color: C = util::pixel_to_color(*pixel);
+            color.as_mut()[0] += rng.gen_range(-range_radius..=range_radius);
+            color.as_mut()[1] += rng.gen_range(-range_radius..=range_radius);
+            color.as_mut()[2] += rng.gen_range(-range_radius..=range_radius);
+            let color = palette.nearest::<D>(color);
+            util::update_pixel_with_color(pixel, color);
+        }
+        image
+    }
+}

src/main.rs

@@ -23,8 +23,8 @@ use image::{ImageFormat, RgbaImage};
 use mark::{
     bw,
     dither::{
-        AlgoThreshold, Algorithm, DiffCiede2000, DiffClamp, DiffEuclid, DiffHyAb, DiffManhattan,
-        DiffManhattanSquare, Difference, Palette,
+        AlgoRandom, AlgoThreshold, Algorithm, DiffCiede2000, DiffClamp, DiffEuclid, DiffHyAb,
+        DiffManhattan, DiffManhattanSquare, Difference, Palette,
     },
 };
 use palette::{color_difference::EuclideanDistance, Clamp, IntoColor, Lab, LinSrgb, Oklab, Srgb};
@@ -69,6 +69,7 @@ impl BwCmd {
 #[derive(Debug, Clone, Copy, clap::ValueEnum)]
 enum DitherAlgorithm {
     Threshold,
+    Random,
 }
 
 #[derive(Debug, Clone, Copy, clap::ValueEnum)]
@@ -158,6 +159,7 @@ impl DitherCmd {
     fn run_c<C>(self, image: RgbaImage) -> RgbaImage
     where
         Srgb: IntoColor<C>,
+        C: AsMut<[f32; 3]>,
         C: AsRef<[f32; 3]>,
         C: Clamp,
         C: Copy,
@@ -184,11 +186,15 @@ impl DitherCmd {
     fn run_cd<C, D>(self, image: RgbaImage) -> RgbaImage
     where
         Srgb: IntoColor<C>,
-        C: IntoColor<Srgb> + Clamp + Copy,
+        C: AsMut<[f32; 3]>,
+        C: Clamp,
+        C: Copy,
+        C: IntoColor<Srgb>,
         D: Difference<C>,
     {
         match self.algorithm {
             DitherAlgorithm::Threshold => self.run_acd::<AlgoThreshold, C, D>(image),
+            DitherAlgorithm::Random => self.run_acd::<AlgoRandom, C, D>(image),
         }
     }