Dithering

use dither.qweruse dither_image, dither_bits from dither      // Quillo 0.6: only these

image = { version = "0.25", default-features = false, features = ["png", "jpeg", "webp", "gif"] }base64 = "0.22"serde_json = { version = "1", features = ["preserve_order"] }

// A photo for a café's receipt printer (black dots only, 384 wide on 58 mm paper) and for a 7-colour e-ink sign.////   quillo run dither.qwe      then open http://localhost:8080/ditheruse "dither.qwer"let PHOTO = "dither_sample.png"route GET /dither {    {        receipt: dither_image(PHOTO, "data/dither/receipt.png", { method: "atkinson", width: 384, contrast: 1.2 })?,        eink: dither_image(PHOTO, "data/dither/eink.png", { palette: "eink-7" })?.width,        ordered: dither_image(PHOTO, "data/dither/bayer.png", { method: "bayer", palette: ["#000000", "#ff0000", "#ffffff"] })?.colors,        printer: slice(json.stringify(dither_bits(PHOTO, { width: 384 })?), 0, 80),        bad: dither_image(PHOTO, "data/dither/x.png", { method: "magic" }).error,    }}route GET /receipt.png {    dither_image(PHOTO, "data/dither/receipt.png", { method: "atkinson", width: 384, contrast: 1.2 })?    file("data/dither/receipt.png")}route GET /eink.png {    dither_image(PHOTO, "data/dither/eink.png", { palette: "eink-7" })?    file("data/dither/eink.png")}

//! Pictures dithered to a few colours: black and white for thermal receipt and label printers, the 3 and 7 colours of e-ink displays, or any palette; Floyd–Steinberg, Atkinson, Stucki, Bayer ordered and plain threshold; and 1-bit rows packed for printers.//! version: 1.0.0//!//! [dependencies]//! image = { version = "0.25", default-features = false, features = ["png", "jpeg", "webp", "gif"] }//! base64 = "0.22"//! serde_json = { version = "1", features = ["preserve_order"] }use base64::Engine;use image::imageops::FilterType;use image::{Rgb, RgbImage};use serde_json::{json, Value};fn hex(c: &str) -> Result<[f32; 3], String> {    let h = c.trim().trim_start_matches('#');    let v = u32::from_str_radix(h, 16).ok().filter(|_| h.len() == 6).ok_or_else(|| format!("`{}` is not a #rrggbb colour", c))?;    Ok([(v >> 16 & 255) as f32, (v >> 8 & 255) as f32, (v & 255) as f32])}fn palette(v: &Value) -> Result<Vec<[f32; 3]>, String> {    let named = |n: &str| -> Option<Vec<&'static str>> {        Some(match n {            "mono" | "" => vec!["#000000", "#ffffff"],            "eink-3" => vec!["#000000", "#ffffff", "#c81e1e"],            "eink-3-yellow" => vec!["#000000", "#ffffff", "#e6c800"],            "eink-7" => vec!["#000000", "#ffffff", "#00a000", "#0000c8", "#c80000", "#ffdc00", "#ff8000"],            "gray-4" => vec!["#000000", "#555555", "#aaaaaa", "#ffffff"],            "gameboy" => vec!["#0f380f", "#306230", "#8bac0f", "#9bbc0f"],            _ => return None,        })    };    match v {        Value::Null => Ok(vec![[0.0; 3], [255.0; 3]]),        Value::String(s) => named(s).ok_or_else(|| format!("`{}` is not a palette: mono, eink-3, eink-3-yellow, eink-7, gray-4, gameboy, or a list of colours", s))?.iter().map(|c| hex(c)).collect(),        Value::Array(a) if a.len() >= 2 && a.len() <= 256 => a.iter().map(|c| hex(c.as_str().unwrap_or(""))).collect(),        _ => Err("a palette is a name or a list of 2 to 256 #rrggbb colours".into()),    }}fn load(path: &str, width: i64) -> Result<RgbImage, String> {    let img = image::open(path).map_err(|e| format!("{}: {}", path, e))?;    let img = if width > 0 && width as u32 != img.width() {        let h = ((img.height() as f64 * width as f64 / img.width() as f64).round() as u32).max(1);        img.resize_exact(width as u32, h, FilterType::Lanczos3)    } else { img };    // Transparency on white, as on paper.    let rgba = img.to_rgba8();    let mut out = RgbImage::new(rgba.width(), rgba.height());    for (x, y, p) in rgba.enumerate_pixels() {        let a = p[3] as f32 / 255.0;        let m = |c: u8| (c as f32 * a + 255.0 * (1.0 - a)).round() as u8;        out.put_pixel(x, y, Rgb([m(p[0]), m(p[1]), m(p[2])]));    }    Ok(out)}fn nearest(c: [f32; 3], pal: &[[f32; 3]]) -> usize {    let mut best = (0, f32::MAX);    for (i, p) in pal.iter().enumerate() {        // Weighted by how the eye sees each channel.        let d = 0.30 * (c[0] - p[0]).powi(2) + 0.59 * (c[1] - p[1]).powi(2) + 0.11 * (c[2] - p[2]).powi(2);        if d < best.1 { best = (i, d) }    }    best.0}const BAYER: [[f32; 8]; 8] = [    [0., 32., 8., 40., 2., 34., 10., 42.], [48., 16., 56., 24., 50., 18., 58., 26.], [12., 44., 4., 36., 14., 46., 6., 38.], [60., 28., 52., 20., 62., 30., 54., 22.],    [3., 35., 11., 43., 1., 33., 9., 41.], [51., 19., 59., 27., 49., 17., 57., 25.], [15., 47., 7., 39., 13., 45., 5., 37.], [63., 31., 55., 23., 61., 29., 53., 21.],];// Each pixel's palette index.fn dither(img: &RgbImage, pal: &[[f32; 3]], method: &str, contrast: f32) -> Result<Vec<usize>, String> {    let (w, h) = (img.width() as usize, img.height() as usize);    let mut buf: Vec<[f32; 3]> = img.pixels().map(|p| {        let f = |c: u8| ((c as f32 - 128.0) * contrast + 128.0).clamp(0.0, 255.0);        [f(p[0]), f(p[1]), f(p[2])]    }).collect();    let kernel: &[(i32, i32, f32)] = match method {        "floyd-steinberg" | "" => &[(1, 0, 7.0 / 16.0), (-1, 1, 3.0 / 16.0), (0, 1, 5.0 / 16.0), (1, 1, 1.0 / 16.0)],        "atkinson" => &[(1, 0, 0.125), (2, 0, 0.125), (-1, 1, 0.125), (0, 1, 0.125), (1, 1, 0.125), (0, 2, 0.125)],        "stucki" => &[(1, 0, 8.0 / 42.0), (2, 0, 4.0 / 42.0), (-2, 1, 2.0 / 42.0), (-1, 1, 4.0 / 42.0), (0, 1, 8.0 / 42.0), (1, 1, 4.0 / 42.0), (2, 1, 2.0 / 42.0), (-2, 2, 1.0 / 42.0), (-1, 2, 2.0 / 42.0), (0, 2, 4.0 / 42.0), (1, 2, 2.0 / 42.0), (2, 2, 1.0 / 42.0)],        "bayer" | "threshold" => &[],        m => return Err(format!("`{}` is not a method: floyd-steinberg, atkinson, stucki, bayer or threshold", m)),    };    let spread = 255.0 / (pal.len() as f32 - 1.0).max(1.0);    let mut out = vec![0usize; w * h];    for y in 0..h {        for x in 0..w {            let i = y * w + x;            let mut c = buf[i];            if method == "bayer" {                let t = (BAYER[y % 8][x % 8] + 0.5) / 64.0 - 0.5;                c = [c[0] + t * spread, c[1] + t * spread, c[2] + t * spread];            }            let k = nearest(c, pal);            out[i] = k;            if !kernel.is_empty() {                let e = [c[0] - pal[k][0], c[1] - pal[k][1], c[2] - pal[k][2]];                for &(dx, dy, f) in kernel {                    let (nx, ny) = (x as i32 + dx, y as i32 + dy);                    if nx >= 0 && (nx as usize) < w && (ny as usize) < h {                        let j = ny as usize * w + nx as usize;                        for ch in 0..3 { buf[j][ch] += e[ch] * f }                    }                }            }        }    }    Ok(out)}fn opts(o: &Value) -> (String, i64, f32) {    let method = o.get("method").and_then(|m| m.as_str()).unwrap_or("floyd-steinberg").to_lowercase();    let width = o.get("width").and_then(|w| w.as_i64()).unwrap_or(0);    let contrast = o.get("contrast").and_then(|c| c.as_f64()).unwrap_or(1.0) as f32;    (method, width, contrast)}/// A picture dithered and saved as a PNG at `out_path` (folders made): `options` are `method` (`"floyd-steinberg"`, `"atkinson"`, `"stucki"`, `"bayer"`, `"threshold"`), `palette` (`"mono"`, `"eink-3"`, `"eink-7"`, `"gray-4"`, `"gameboy"`, or a list of `#rrggbb`), `width` to resize to first (384 dots for 58 mm paper, 576 for 80 mm), `contrast` (1.0; more for photos on receipts)./// `{ path, width, height, colors }`, `colors` the pixels of each palette colour.pub fn dither_image(path: &str, out_path: &str, options: serde_json::Value) -> Result<Value, String> {    let (method, width, contrast) = opts(&options);    let pal = palette(options.get("palette").unwrap_or(&Value::Null))?;    let img = load(path, width)?;    let idx = dither(&img, &pal, &method, contrast)?;    let mut out = RgbImage::new(img.width(), img.height());    let mut counts = vec![0u64; pal.len()];    for (i, p) in out.pixels_mut().enumerate() {        let c = pal[idx[i]];        counts[idx[i]] += 1;        *p = Rgb([c[0] as u8, c[1] as u8, c[2] as u8]);    }    if let Some(d) = std::path::Path::new(out_path).parent().filter(|d| !d.as_os_str().is_empty()) { std::fs::create_dir_all(d).map_err(|e| e.to_string())?; }    out.save_with_format(out_path, image::ImageFormat::Png).map_err(|e| format!("{}: {}", out_path, e))?;    Ok(json!({ "path": out_path, "width": out.width(), "height": out.height(), "colors": counts }))}/// A picture as 1-bit rows for a printer or an e-ink panel: `{ width, height, bytes_per_row, base64 }`, 8 dots a byte, the leftmost the highest bit, 1 for black, rows padded to whole bytes, as ESC/POS `GS v 0`, ZPL `^GF` and TSPL `BITMAP` take them. `options` as for `dither_image` (no palette: black and white).pub fn dither_bits(path: &str, options: serde_json::Value) -> Result<Value, String> {    let (method, width, contrast) = opts(&options);    let img = load(path, width)?;    let pal = vec![[0.0f32; 3], [255.0; 3]];    let idx = dither(&img, &pal, &method, contrast)?;    let (w, h) = (img.width() as usize, img.height() as usize);    let bpr = (w + 7) / 8;    let mut bytes = vec![0u8; bpr * h];    for y in 0..h {        for x in 0..w {            if idx[y * w + x] == 0 { bytes[y * bpr + x / 8] |= 0x80 >> (x % 8) }        }    }    let black = bytes.iter().map(|b| b.count_ones() as u64).sum::<u64>();    Ok(json!({ "width": w, "height": h, "bytes_per_row": bpr, "black_dots": black, "base64": base64::engine::general_purpose::STANDARD.encode(&bytes) }))}