pi-frame-server/tests/dither.rs

// 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 sample_0_atkinson() -> Result<()> {
    compare_original(
        "sample_0.tiff",
        "sample_0_atkinson.tiff",
        &DitherMethod::Atkinson,
    )
}
#[test]
fn sample_1_atkinson() -> Result<()> {
    compare_original(
        "sample_1.tiff",
        "sample_1_atkinson.tiff",
        &DitherMethod::Atkinson,
    )
}

#[test]
fn sample_1_floydsteinberg() -> Result<()> {
    compare_original(
        "sample_1.tiff",
        "sample_1_floydsteinberg.tiff",
        &DitherMethod::FloydSteinberg,
    )
}