pi-frame-server/src/imageproc.rs

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Rust
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use image::RgbImage;
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use palette::{cast::FromComponents, IntoColor, Lab, Oklch, Srgb};
use palette::color_difference::{Ciede2000, EuclideanDistance};
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/// Palette used on the display; pixels can be one of these colors.
///
/// The RGB values are slightly adjusted to improve accuracy.
const DISPLAY_PALETTE: [Srgb; 7] = [
Srgb::new(0.047, 0.047, 0.055), // Black
Srgb::new(0.824, 0.824, 0.816), // White
Srgb::new(0.118, 0.376, 0.122), // Green
Srgb::new(0.114, 0.118, 0.667), // Blue
Srgb::new(0.549, 0.106, 0.114), // Red
Srgb::new(0.827, 0.788, 0.239), // Yellow
Srgb::new(0.757, 0.443, 0.165), // Orange
];
// fn octcolor_rgb(color: &OctColor) -> &Srgb<u8> {
// 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 {
Black,
White,
Green,
Blue,
Red,
Yellow,
Orange,
}
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impl From<DisplayColor> for Srgb {
fn from(value: DisplayColor) -> Self {
DISPLAY_PALETTE[value as usize]
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}
}
impl DisplayColor {
fn from_u8(value: u8) -> Self {
match value {
0 => Self::Black,
1 => Self::White,
2 => Self::Green,
3 => Self::Blue,
4 => Self::Red,
5 => Self::Yellow,
6 => Self::Orange,
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_ => panic!("unexpected DisplayColor {value}"),
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}
}
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fn into_byte(color1: Self, color2: Self) -> u8 {
let upper: u8 = color1.into();
let lower: u8 = color2.into();
upper << 4 | lower
}
}
impl From<DisplayColor> for u8 {
fn from(value: DisplayColor) -> Self {
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value as Self
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}
}
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/// Buffer to be sent to the ``EInk`` display.
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#[derive(Debug)]
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pub struct EInkBuffer(Vec<DisplayColor>);
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impl EInkBuffer {
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#[must_use]
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pub fn into_display_buffer(&self) -> Vec<u8> {
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let mut buf = Vec::with_capacity(self.0.len() / 2);
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for colors in self.0.chunks_exact(2) {
buf.push(DisplayColor::into_byte(colors[0], colors[1]));
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}
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buf
}
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#[must_use]
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pub fn new(width: usize, height: usize) -> Self {
let v = vec![DisplayColor::Black; width * height];
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Self(v)
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}
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// pub fn make_image(&self) -> RgbImage {
// RgbImage::from_fn(800, 480, |x, y| {
// let srgb = Srgb::from(self.0[y * 800 + x]);
// })
// }
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}
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// impl EInkBuffer {
// /// Converts the EInkBuffer into data that can be sent over the SPI API
// /// Bin-packs the two 4-bit colors into bytes.
// pub fn into_buffer(&self) -> Vec<u8> {
// vec![]
// }
//
// pub fn new(width: usize, height: usize) -> EInkBuffer {
// EInkBuffer {
// data: vec![DisplayColor::Black; width * height],
// width,
// height,
// }
// }
// pub fn set(&mut self, x: usize, y: usize, value: DisplayColor) {
// self.data[x + y * self.width] = value;
// }
// pub fn get(&self, x:usize, y:usize) -> DisplayColor {
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// self.data[x
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// }
// }
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pub trait Ditherer {
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fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer);
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}
// 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.
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#[must_use]
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pub fn nearest_neighbor(input_color: Lab) -> (DisplayColor, Lab) {
let (nearest, _, color_diff) = DISPLAY_PALETTE
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.iter()
.enumerate()
.map(|(idx, p_color)| {
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let c: Lab = (*p_color).into_color();
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(idx, input_color.difference(c), input_color - c)
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})
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.min_by(|(_, a, _), (_, b, _)| a.total_cmp(b))
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.expect("could not find a color");
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(DisplayColor::from_u8(nearest as u8), color_diff)
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}
pub struct NNDither();
impl Ditherer for NNDither {
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fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer) {
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assert!(img.width() == 800);
assert!(img.height() == 480);
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// sRGB view into the given image. zero copy!
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let srgb = <&[Srgb<u8>]>::from_components(&**img);
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for (idx, pixel) in srgb.iter().enumerate() {
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let (n, _) = nearest_neighbor(pixel.into_format().into_color());
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output.0[idx] = n;
}
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}
}
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pub struct FloydSteinbergDither();
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/// 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 {
(y * xsize + x) as usize
}
/// Compute the error-adjusted new lab value based on the error value of the currently scanned
/// pixel, plus 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();
Lab::from_components((
p_l + err_l * scalar,
p_a + err_a * scalar,
p_b + err_b * scalar,
))
}
struct DiffusionPoint {
xshift: i32,
yshift: i32,
scale: f32,
}
impl DiffusionPoint {
const fn new(xshift: i32, yshift: i32, scale: f32) -> Self {
Self {
xshift,
yshift,
scale,
}
}
}
const FLOYD_STEINBERG: [DiffusionPoint; 4] = [
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),
];
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const ATKINSON_DITHER: [DiffusionPoint; 6] = [
DiffusionPoint::new(1, 0, 1.0/8.0),
DiffusionPoint::new(2, 0, 1.0/8.0),
DiffusionPoint::new(-1, 1, 1.0/8.0),
DiffusionPoint::new(0, 1, 1.0/8.0),
DiffusionPoint::new(1, 1, 1.0/8.0),
DiffusionPoint::new(0, 2, 1.0/8.0),
];
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impl Ditherer for FloydSteinbergDither {
fn dither(&mut self, img: &RgbImage, output: &mut EInkBuffer) {
// create a copy of the image in Lab space, mutable.
let srgb = <&[Srgb<u8>]>::from_components(&**img);
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let (xsize, ysize) = img.dimensions();
let mut temp_img: Vec<Lab> = Vec::with_capacity((xsize * ysize) as usize);
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for pix in srgb {
temp_img.push(pix.into_format().into_color());
}
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// now we take our units.
for y in 0..ysize {
for x in 0..xsize {
let index = coord_to_idx(x, y, xsize);
let curr_pix = temp_img[index];
let (nearest, err) = nearest_neighbor(curr_pix);
// set the color in the output buffer.
output.0[index] = nearest;
// take the error, and propagate it.
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for point in ATKINSON_DITHER {
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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(
target_x,
target_y,
xsize,
);
if let Some(pix) = temp_img.get(target) {
temp_img[target] = get_error_adjusted(pix, &err, point.scale);
}
}
}
}
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}
}