supprt multiple dithering matrix options

src/imageproc.rs

@@ -1,7 +1,7 @@
 use image::RgbImage;
 
-use palette::{cast::FromComponents, IntoColor, Lab, Oklch, Srgb};
 use palette::color_difference::{Ciede2000, EuclideanDistance};
+use palette::{cast::FromComponents, IntoColor, Lab, Oklch, Srgb};
 
 /// Palette used on the display; pixels can be one of these colors.
 ///
@@ -16,18 +16,7 @@ const DISPLAY_PALETTE: [Srgb; 7] = [
     Srgb::new(0.757, 0.443, 0.165), // Orange
 ];
 
-// fn octcolor_rgb(color: &OctColor) -> &Srgb<u8> {
+// TODO: support different color palettes.
-//     match color {
-//         OctColor::Black => &DISPLAY_PALETTE[0],
-//         OctColor::White => &DISPLAY_PALETTE[1],
-//         OctColor::Green => &DISPLAY_PALETTE[2],
-//         OctColor::Blue => &DISPLAY_PALETTE[3],
-//         OctColor::Red => &DISPLAY_PALETTE[4],
-//         OctColor::Yellow => &DISPLAY_PALETTE[5],
-//         OctColor::Orange => &DISPLAY_PALETTE[6],
-//         OctColor::HiZ => &DISPLAY_PALETTE[1],
-//     }
-// }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum DisplayColor {
@@ -121,17 +110,9 @@ impl EInkBuffer {
 // }
 
 pub trait Ditherer {
-    fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer);
+    fn dither(&self, img: &RgbImage, output: &mut EInkBuffer);
 }
 
-// fn color_distance(c1: LinSrgb, c2: LinSrgb) -> f32 {
-//     let r2 = (c2.red - c1.red).powf(2.0);
-//     let g2 = (c2.green - c1.green).powf(2.0);
-//     let b2 = (c2.blue - c1.blue).powf(2.0);
-//
-//     (r2 + g2 + b2).sqrt()
-// }
-
 /// Find the closest approximate palette color to the given sRGB value.
 /// This uses euclidian distance in linear space.
 #[must_use]
@@ -151,7 +132,7 @@ pub fn nearest_neighbor(input_color: Lab) -> (DisplayColor, Lab) {
 pub struct NNDither();
 
 impl Ditherer for NNDither {
-    fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer) {
+    fn dither(&self, img: &RgbImage, output: &mut EInkBuffer) {
         assert!(img.width() == 800);
         assert!(img.height() == 480);
 
@@ -165,8 +146,6 @@ impl Ditherer for NNDither {
     }
 }
 
-pub struct FloydSteinbergDither();
-
 /// Compute the vector index for a given image by using the size of rows. Assumes that images
 /// are indexed in row-major order.
 const fn coord_to_idx(x: u32, y: u32, xsize: u32) -> usize {
@@ -174,7 +153,7 @@ const fn coord_to_idx(x: u32, y: u32, xsize: u32) -> usize {
 }
 
 /// Compute the error-adjusted new lab value based on the error value of the currently scanned
-/// pixel, plus a scalar factor.
+/// pixel multiplied by a scalar factor.
 fn get_error_adjusted(orig: &Lab, err: &Lab, scalar: f32) -> Lab {
     let (p_l, p_a, p_b) = orig.into_components();
     let (err_l, err_a, err_b) = err.into_components();
@@ -185,6 +164,9 @@ fn get_error_adjusted(orig: &Lab, err: &Lab, scalar: f32) -> Lab {
     ))
 }
 
+
+/// ``DiffusionPoint`` is part of the diffusion matrix, represented by a shift in x and y and an error
+/// scaling factor.
 struct DiffusionPoint {
     xshift: i32,
     yshift: i32,
@@ -192,6 +174,7 @@ struct DiffusionPoint {
 }
 
 impl DiffusionPoint {
+    /// Creates a new ``DiffusionPoint``
     const fn new(xshift: i32, yshift: i32, scale: f32) -> Self {
         Self {
             xshift,
@@ -201,13 +184,14 @@ impl DiffusionPoint {
     }
 }
 
-const FLOYD_STEINBERG: [DiffusionPoint; 4] = [
+static FLOYD_STEINBERG_POINTS: &[DiffusionPoint] = &[
     DiffusionPoint::new(1, 0, 7.0 / 16.0),
     DiffusionPoint::new(-1, 1, 3.0 / 16.0),
     DiffusionPoint::new(0, 1, 5.0 / 16.0),
     DiffusionPoint::new(1, 1, 1.0 / 16.0),
 ];
-const ATKINSON_DITHER: [DiffusionPoint; 6] = [
+
+static ATKINSON_DITHER_POINTS: &[DiffusionPoint] = &[
     DiffusionPoint::new(1, 0, 1.0 / 8.0),
     DiffusionPoint::new(2, 0, 1.0 / 8.0),
     DiffusionPoint::new(-1, 1, 1.0 / 8.0),
@@ -216,8 +200,62 @@ const ATKINSON_DITHER: [DiffusionPoint; 6] = [
     DiffusionPoint::new(0, 2, 1.0 / 8.0),
 ];
 
-impl Ditherer for FloydSteinbergDither {
+static SIERRA_DITHER_POINTS: &[DiffusionPoint] = &[
-    fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer) {
+    DiffusionPoint::new(1, 0, 5.0 / 32.0),
+    DiffusionPoint::new(2, 0, 3.0 / 32.0),
+    DiffusionPoint::new(-2, 1, 2.0 / 32.0),
+    DiffusionPoint::new(-1, 1, 4.0 / 32.0),
+    DiffusionPoint::new(0, 1, 5.0 / 32.0),
+    DiffusionPoint::new(1, 1, 4.0 / 32.0),
+    DiffusionPoint::new(2, 1, 2.0 / 32.0),
+    DiffusionPoint::new(-1, 2, 2.0 / 32.0),
+    DiffusionPoint::new(0, 2, 3.0 / 32.0),
+    DiffusionPoint::new(1, 2, 2.0 / 32.0),
+];
+
+static STUKI_DITHER_POINTS: &[DiffusionPoint] = &[
+    DiffusionPoint::new(1, 0, 8.0 / 42.0),
+    DiffusionPoint::new(2, 0, 4.0 / 42.0),
+    DiffusionPoint::new(-2, 1, 2.0 / 42.0),
+    DiffusionPoint::new(-1, 1, 4.0 / 42.0),
+    DiffusionPoint::new(0, 1, 8.0 / 42.0),
+    DiffusionPoint::new(1, 1, 4.0 / 42.0),
+    DiffusionPoint::new(2, 1, 2.0 / 42.0),
+    DiffusionPoint::new(-2, 2, 1.0 / 42.0),
+    DiffusionPoint::new(-1, 2, 2.0 / 42.0),
+    DiffusionPoint::new(0, 2, 4.0 / 42.0),
+    DiffusionPoint::new(1, 2, 2.0 / 42.0),
+    DiffusionPoint::new(1, 2, 1.0 / 42.0),
+];
+
+pub enum DiffusionMatrix {
+    FloydSteinberg,
+    Atkinson,
+    Sierra,
+    Stuki,
+}
+
+impl DiffusionMatrix {
+    fn value(&self) -> &'static [DiffusionPoint] {
+        match *self {
+            Self::FloydSteinberg => FLOYD_STEINBERG_POINTS,
+            Self::Atkinson => ATKINSON_DITHER_POINTS,
+            Self::Sierra => SIERRA_DITHER_POINTS,
+            Self::Stuki => STUKI_DITHER_POINTS,
+        }
+    }
+}
+
+pub struct ErrorDiffusionDither(DiffusionMatrix);
+impl ErrorDiffusionDither {
+    #[must_use]
+    pub const fn new(dm: DiffusionMatrix) -> Self {
+        Self(dm)
+    }
+}
+
+impl Ditherer for ErrorDiffusionDither {
+    fn dither(&self, img: &RgbImage, output: &mut EInkBuffer) {
         // create a copy of the image in Lab space, mutable.
         let srgb = <&[Srgb<u8>]>::from_components(&**img);
         let (xsize, ysize) = img.dimensions();
@@ -235,18 +273,14 @@ impl Ditherer for FloydSteinbergDither {
                 // set the color in the output buffer.
                 output.0[index] = nearest;
                 // take the error, and propagate it.
-                for point in ATKINSON_DITHER {
+                for point in self.0.value() {
                     let Some(target_x) = x.checked_add_signed(point.xshift) else {
                         continue;
                     };
                     let Some(target_y) = y.checked_add_signed(point.yshift) else {
                         continue;
                     };
-                    let target = coord_to_idx(
+                    let target = coord_to_idx(target_x, target_y, xsize);
-                        target_x,
-                        target_y,
-                        xsize,
-                    );
                     if let Some(pix) = temp_img.get(target) {
                         temp_img[target] = get_error_adjusted(pix, &err, point.scale);
                     }

src/main.rs

@@ -3,7 +3,7 @@ pub mod display;
 pub mod imageproc;
 
 use crate::display::Wrapper;
-use crate::imageproc::{Ditherer, EInkBuffer, FloydSteinbergDither, NNDither};
+use crate::imageproc::{DiffusionMatrix, EInkBuffer, ErrorDiffusionDither, Ditherer};
 use clap::{Parser, Subcommand};
 use image::RgbImage;
 
@@ -36,7 +36,7 @@ fn main() -> anyhow::Result<()> {
         let mut display = Wrapper::new()?;
 
         let mut eink_buf = EInkBuffer::new(800, 480);
-        let mut dither = FloydSteinbergDither{};
+        let dither = ErrorDiffusionDither::new(DiffusionMatrix::Atkinson);
 
         dither.dither(&img, &mut eink_buf);
         let raw_buf = eink_buf.into_display_buffer();
@@ -52,7 +52,7 @@ fn main() -> anyhow::Result<()> {
     if matches!(cli.command, Command::Convert) {
         let img: RgbImage = image::io::Reader::open("myimage.png")?.decode()?.into();
         let mut eink_buf = EInkBuffer::new(800, 480);
-        let mut dither = FloydSteinbergDither{};
+        let dither = ErrorDiffusionDither::new(DiffusionMatrix::Atkinson);
 
         dither.dither(&img, &mut eink_buf);
         let raw_buf = eink_buf.into_display_buffer();