add regression test, sample images, reference dithers

src/api.rs

@@ -1,5 +1,5 @@
 use crate::display::EInkPanel;
-use crate::dither::{DitherMethod, DitherPalette, DitheredImage};
+use crate::dither::{DitherMethod, Palette, DitheredImage};
 use axum::async_trait;
 use axum::extract::{FromRequest, Multipart, State};
 use axum::http::{header, StatusCode};
@@ -96,7 +96,7 @@ pub fn router() -> Router<Context> {
 struct ImageRequest {
     image: Box<RgbImage>,
     dither_method: DitherMethod,
-    palette: DitherPalette,
+    palette: Palette,
 }
 
 #[async_trait]
@@ -124,7 +124,7 @@ where
                 Some("palette") => {
                     let data = field.bytes().await?;
                     let val = str::from_utf8(&data)?;
-                    palette = Some(DitherPalette::from_str(val)?);
+                    palette = Some(Palette::from_str(val)?);
                 }
                 Some("dither_method") => {
                     let data = field.bytes().await?;
@@ -140,7 +140,7 @@ where
                 Ok(Self {
                     image: i,
                     dither_method: dither_method.unwrap_or(DitherMethod::NearestNeighbor),
-                    palette: palette.unwrap_or(DitherPalette::Default),
+                    palette: palette.unwrap_or(Palette::Default),
                 })
             },
         )

src/dither.rs

@@ -31,12 +31,12 @@ const SIMPLE_PALETTE: [Srgb; 7] = [
 ];
 
 #[derive(strum::EnumString, Serialize, Deserialize, PartialEq, Eq, Debug)]
-pub enum DitherPalette {
+pub enum Palette {
     Default,
     Simple,
 }
 
-impl DitherPalette {
+impl Palette {
     #[must_use]
     pub const fn value(&self) -> &[Srgb] {
         match self {
@@ -46,7 +46,9 @@ impl DitherPalette {
     }
 }
 
-#[derive(strum::EnumString, Serialize, Deserialize, PartialEq, Eq, Debug)]
+#[derive(
+    strum::EnumString, strum::Display, Serialize, Deserialize, PartialEq, Eq, Debug, Clone,
+)]
 pub enum DitherMethod {
     NearestNeighbor,
     FloydSteinberg,
@@ -59,11 +61,11 @@ impl DitherMethod {
     #[must_use]
     pub fn get_ditherer(&self) -> Box<dyn Ditherer> {
         match self {
-            Self::NearestNeighbor => Box::new(NNDither {}),
-            Self::Atkinson => Box::new(ErrorDiffusionDither::new(ATKINSON_DITHER_POINTS)),
-            Self::FloydSteinberg => Box::new(ErrorDiffusionDither::new(FLOYD_STEINBERG_POINTS)),
-            Self::Stuki => Box::new(ErrorDiffusionDither::new(STUKI_DITHER_POINTS)),
-            Self::Sierra => Box::new(ErrorDiffusionDither::new(SIERRA_DITHER_POINTS)),
+            Self::NearestNeighbor => Box::new(NearestNeighbor {}),
+            Self::Atkinson => Box::new(ErrorDiffusion::new(ATKINSON_DITHER_POINTS)),
+            Self::FloydSteinberg => Box::new(ErrorDiffusion::new(FLOYD_STEINBERG_POINTS)),
+            Self::Stuki => Box::new(ErrorDiffusion::new(STUKI_DITHER_POINTS)),
+            Self::Sierra => Box::new(ErrorDiffusion::new(SIERRA_DITHER_POINTS)),
         }
     }
 }
@@ -144,12 +146,10 @@ fn nearest_neighbor(input_color: Lab, palette: &[Srgb]) -> (u8, Lab) {
     (nearest as u8, color_diff)
 }
 
-pub struct NNDither();
+pub struct NearestNeighbor();
 
-impl Ditherer for NNDither {
+impl Ditherer for NearestNeighbor {
     fn dither(&mut self, img: &RgbImage, output: &mut DitheredImage) {
-        assert!(img.width() == 800);
-        assert!(img.height() == 480);
 
         // sRGB view into the given image. zero copy!
         let srgb = <&[Srgb<u8>]>::from_components(&**img);
@@ -246,16 +246,16 @@ static STUKI_DITHER_POINTS: &[DiffusionPoint] = &[
 pub type DiffusionMatrix<'a> = &'a [DiffusionPoint];
 
 #[derive(Debug)]
-pub struct ErrorDiffusionDither<'a>(&'a [DiffusionPoint]);
+pub struct ErrorDiffusion<'a>(&'a [DiffusionPoint]);
 
-impl<'a> ErrorDiffusionDither<'a> {
+impl<'a> ErrorDiffusion<'a> {
     #[must_use]
     pub const fn new(dm: DiffusionMatrix<'a>) -> Self {
         Self(dm)
     }
 }
 
-impl<'a> Ditherer for ErrorDiffusionDither<'a> {
+impl<'a> Ditherer for ErrorDiffusion<'a> {
     #[instrument]
     fn dither(&mut self, img: &RgbImage, output: &mut DitheredImage) {
         // create a copy of the image in Lab space, mutable.
@@ -275,7 +275,10 @@ impl<'a> Ditherer for ErrorDiffusionDither<'a> {
                 let curr_pix = temp_img[index];
                 let (nearest, err) = nearest_neighbor(curr_pix, &output.palette);
                 // set the color in the output buffer.
-                *output.buf.get_mut(index).unwrap() = nearest;
+                *output
+                    .buf
+                    .get_mut(index)
+                    .expect("always in bounds of image") = nearest;
                 // take the error, and propagate it.
                 for point in self.0 {
                     // bounds checking.

src/lib.rs

@@ -0,0 +1 @@
+pub mod dither;

src/main.rs

@@ -1,11 +1,13 @@
 pub mod api;
 pub mod display;
-pub mod errors;
 pub mod dither;
+pub mod errors;
+
+use std::path::PathBuf;
 
 use crate::display::{EInkPanel, FakeEInk, Wrapper};
-use crate::dither::{DitherMethod, DitheredImage};
-use clap::{Parser, Subcommand};
+use crate::dither::{DitherMethod, DitheredImage, Palette};
+use clap::{Args, Parser, Subcommand};
 use image::RgbImage;
 use tracing::{error, info};
 
@@ -19,6 +21,8 @@ struct Cli {
 
 #[derive(Debug, Subcommand)]
 enum Command {
+    /// Convert an image into a dithered form.
+    Convert(ConvertArgs),
     /// Load a single image
     Show,
     /// Display a test pattern
@@ -27,13 +31,37 @@ enum Command {
     Serve,
 }
 
+#[derive(Args, Debug)]
+struct ConvertArgs {
+    #[arg(short, long, default_value_t = DitherMethod::NearestNeighbor)]
+    dither_method: DitherMethod,
+    input_file: PathBuf,
+    output_file: PathBuf,
+}
+
 #[tokio::main]
 async fn main() -> anyhow::Result<()> {
     tracing_subscriber::fmt::init();
     let cli = Cli::parse();
     println!("CLI {cli:?}");
 
-    if matches!(cli.command, Command::Show) {
+    match cli.command {
+        Command::Convert(a) => {
+            let input = image::ImageReader::open(a.input_file)?
+                .decode()?
+                .into_rgb8();
+            let mut method = a.dither_method.get_ditherer();
+
+            let mut result = DitheredImage::new(
+                input.width(),
+                input.height(),
+                Palette::Default.value().to_vec(),
+            );
+            method.dither(&input, &mut result);
+
+            result.into_rgbimage().save(a.output_file)?;
+        }
+        Command::Show => {
             let img: RgbImage = image::ImageReader::open("image.png")?.decode()?.into();
             error!("HI");
             let mut display = FakeEInk {};
@@ -44,13 +72,12 @@ async fn main() -> anyhow::Result<()> {
             dither.dither(&img, &mut eink_buf);
             display.display(&eink_buf)?;
         }
-    if matches!(cli.command, Command::Test) {
+        Command::Test => {
             let mut display = Wrapper::new()?;
 
             display.test()?;
         }
-
-    if matches!(cli.command, Command::Serve) {
+        Command::Serve => {
             let display = FakeEInk {};
 
             let ctx = api::Context::new(Box::new(display));
@@ -60,6 +87,7 @@ async fn main() -> anyhow::Result<()> {
             info!("Listening on 0.0.0.0:3000");
             axum::serve(listener, app).await?;
         }
+    }
 
     Ok(())
 }

tests/dither.rs

@@ -0,0 +1,56 @@
+// Regression tests for dithering methods. This file ensures that changes made to how the
+// algorithms are implemented does not affect the actual algorithm. This is done with
+// 'known-good' sample images (see `samples/`). If changes to the algorithms are made,
+// these tests will fail, and that is to be expected. In that case the reference images
+// will need to be updated as well.
+
+use anyhow::Result;
+use image::{ImageReader, RgbImage};
+use pi_frame_server::dither::{DitherMethod, DitheredImage, Palette};
+
+fn compare_original(sample_file: &str, reference_file: &str, method: &DitherMethod) -> Result<()> {
+    let image: RgbImage = ImageReader::open(format!("samples/{sample_file}"))?
+        .decode()?
+        .into_rgb8();
+
+    // process
+    let mut method = method.get_ditherer();
+
+    let mut result = DitheredImage::new(
+        image.width(),
+        image.height(),
+        Palette::Default.value().to_vec(),
+    );
+
+    method.dither(&image, &mut result);
+
+    let expected = ImageReader::open(format!("tests/known_samples/{reference_file}"))?
+        .decode()?
+        .into_rgb8()
+        .into_raw();
+
+    let output = result.into_rgbimage().into_raw();
+
+    assert_eq!(output, expected);
+
+    Ok(())
+}
+#[test]
+fn test_sample_images() -> Result<()> {
+    compare_original(
+        "sample_0.tiff",
+        "sample_0_atkinson.tiff",
+        &DitherMethod::Atkinson,
+    )?;
+    compare_original(
+        "sample_1.tiff",
+        "sample_1_atkinson.tiff",
+        &DitherMethod::Atkinson,
+    )?;
+    compare_original(
+        "sample_1.tiff",
+        "sample_1_floydsteinberg.tiff",
+        &DitherMethod::FloydSteinberg,
+    )?;
+    Ok(())
+}