wip: add new EInk image impl

src/imageproc.rs

@@ -1,4 +1,5 @@
-use image::RgbImage;
+use image::{GenericImageView, GrayImage, ImageBuffer, Luma, RgbImage};
+use palette::FromColor;
 use tracing::instrument;
 
 use image::Rgb as imgRgb;
@@ -18,7 +19,10 @@ const DISPLAY_PALETTE: [Srgb; 7] = [
     Srgb::new(0.757, 0.443, 0.165), // Orange
 ];
 
-// TODO: support different color palettes.
+pub enum Error {
+    DitherError,
+    PaletteIndexError(usize),
+}
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum DisplayColor {
@@ -70,8 +74,44 @@ pub struct EInkImage {
     height: u32,
 }
 
+pub struct TestEInkImage {
+    buf: ImageBuffer<Luma<u8>, Vec<u8>>,
+    palette: Vec<Srgb>,
+}
+impl TestEInkImage {
+    pub fn into_display_buffer(&self) -> Vec<u8> {
+        let mut buf = Vec::with_capacity(self.buf.len() / 2);
+        for pix in self.buf.chunks_exact(2) {
+            buf.push(pix[0] << 4 | pix[1]);
+        }
+        buf
+    }
+
+    pub fn into_rgbimage(&self) -> RgbImage {
+        RgbImage::from_fn(self.buf.width(), self.buf.height(), |x, y| {
+            let idx = self.buf.get_pixel(x, y).0[0];
+            let disp_color = self.palette.get(idx as usize).unwrap();
+            let arr: [u8; 3] = disp_color.into_format().into();
+            imgRgb(arr)
+        })
+    }
+
+    /// Constructs a new EInk Image based on the given color palette for
+    /// color indexing.
+    #[must_use]
+    pub fn new(palette: Vec<Srgb>) -> Self {
+        Self {
+            buf: GrayImage::new(800, 480),
+            palette,
+        }
+    }
+}
+// TODO: Evaluate using Imagebuffer<Luma<u8>, Vec<u8>> instead.
+// This is what the imageops index_map function does.
+// advantages are we get all the 2d array helping functions for free.
 impl EInkImage {
     #[must_use]
+
     pub fn into_display_buffer(&self) -> Vec<u8> {
         let mut buf = Vec::with_capacity(self.data.len() / 2);
 
@@ -108,8 +148,9 @@ impl EInkImage {
 }
 
 pub trait Ditherer {
-    fn dither(&self, img: &RgbImage, output: &mut EInkImage);
+    fn dither(&mut self, img: &RgbImage, output: &mut EInkImage);
 }
+pub type DitherFunc = dyn Fn(&RgbImage, &mut TestEInkImage) -> Result<(), Error>;
 
 /// Find the closest approximate palette color to the given sRGB value.
 /// This uses euclidian distance in linear space.
@@ -123,14 +164,27 @@ pub fn nearest_neighbor(input_color: Lab) -> (DisplayColor, Lab) {
             (idx, input_color.difference(c), input_color - c)
         })
         .min_by(|(_, a, _), (_, b, _)| a.total_cmp(b))
-        .expect("could not find a color");
+        .expect("Should always find a color");
+    (DisplayColor::from_u8(nearest as u8), color_diff)
+}
+
+fn nearest_neighbor2(input_color: Lab, palette:&[Srgb]) -> (DisplayColor, Lab) {
+    let (nearest, _, color_diff) = palette
+        .iter()
+        .enumerate()
+        .map(|(idx, p_color)| {
+            let c: Lab = Lab::from_color(*p_color);
+            (idx, input_color.difference(c), input_color - c)
+        })
+        .min_by(|(_, a, _), (_, b, _)| a.total_cmp(b))
+        .expect("Should always find a color");
     (DisplayColor::from_u8(nearest as u8), color_diff)
 }
 
 pub struct NNDither();
 
 impl Ditherer for NNDither {
-    fn dither(&self, img: &RgbImage, output: &mut EInkImage) {
+    fn dither(&mut self, img: &RgbImage, output: &mut EInkImage) {
         assert!(img.width() == 800);
         assert!(img.height() == 480);
 
@@ -152,13 +206,13 @@ 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 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();
+fn compute_error_adjusted_color(orig: &Lab, err: &Lab, weight: f32) -> Lab {
+    let (orig_l, orig_a, orig_b) = orig.into_components();
     let (err_l, err_a, err_b) = err.into_components();
     Lab::from_components((
-        p_l + err_l * scalar,
-        p_a + err_a * scalar,
-        p_b + err_b * scalar,
+        err_l.mul_add(weight, orig_l), // scalar * err_l + p_l
+        err_a.mul_add(weight, orig_a),
+        err_b.mul_add(weight, orig_b),
     ))
 }
 
@@ -255,10 +309,12 @@ impl ErrorDiffusionDither {
 
 impl Ditherer for ErrorDiffusionDither {
     #[instrument]
-    fn dither(&self, img: &RgbImage, output: &mut EInkImage) {
+    fn dither(&mut self, img: &RgbImage, output: &mut EInkImage) {
         // create a copy of the image in Lab space, mutable.
+        // 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());
@@ -282,7 +338,7 @@ impl Ditherer for ErrorDiffusionDither {
                     };
                     let target = coord_to_idx(target_x, target_y, xsize);
                     if let Some(pix) = temp_img.get(target) {
-                        temp_img[target] = get_error_adjusted(pix, &err, point.scale);
+                        temp_img[target] = compute_error_adjusted_color(pix, &err, point.scale);
                     }
                 }
             }