388 lines
12 KiB
TypeScript
388 lines
12 KiB
TypeScript
// Code copied and slightly modified from https://github.com/evanw/thumbhash
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/**
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* Encodes an RGBA image to a ThumbHash. RGB should not be premultiplied by A.
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*
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* @param w The width of the input image. Must be ≤100px.
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* @param h The height of the input image. Must be ≤100px.
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* @param rgba The pixels in the input image, row-by-row. Must have w*h*4 elements.
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* @returns The ThumbHash as a Uint8Array.
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*/
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export function rgbaToThumbHash(w: number, h: number, rgba: Uint8Array) {
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// Encoding an image larger than 100x100 is slow with no benefit
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if (w > 100 || h > 100) throw new Error(`${w}x${h} doesn't fit in 100x100`);
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const { PI, round, max, cos, abs } = Math;
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// Determine the average color
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let avg_r = 0,
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avg_g = 0,
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avg_b = 0,
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avg_a = 0;
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for (let i = 0, j = 0; i < w * h; i++, j += 4) {
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const alpha = rgba[j + 3] / 255;
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avg_r += (alpha / 255) * rgba[j];
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avg_g += (alpha / 255) * rgba[j + 1];
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avg_b += (alpha / 255) * rgba[j + 2];
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avg_a += alpha;
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}
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if (avg_a) {
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avg_r /= avg_a;
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avg_g /= avg_a;
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avg_b /= avg_a;
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}
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const hasAlpha = avg_a < w * h;
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const l_limit = hasAlpha ? 5 : 7; // Use fewer luminance bits if there's alpha
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const lx = max(1, round((l_limit * w) / max(w, h)));
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const ly = max(1, round((l_limit * h) / max(w, h)));
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const l: number[] = []; // luminance
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const p: number[] = []; // yellow - blue
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const q: number[] = []; // red - green
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const a: number[] = []; // alpha
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// Convert the image from RGBA to LPQA (composite atop the average color)
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for (let i = 0, j = 0; i < w * h; i++, j += 4) {
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const alpha = rgba[j + 3] / 255;
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const r = avg_r * (1 - alpha) + (alpha / 255) * rgba[j];
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const g = avg_g * (1 - alpha) + (alpha / 255) * rgba[j + 1];
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const b = avg_b * (1 - alpha) + (alpha / 255) * rgba[j + 2];
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l[i] = (r + g + b) / 3;
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p[i] = (r + g) / 2 - b;
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q[i] = r - g;
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a[i] = alpha;
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}
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// Encode using the DCT into DC (constant) and normalized AC (varying) terms
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const encodeChannel = (channel: number[], nx: number, ny: number) => {
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let dc = 0;
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const ac: number[] = [];
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let scale = 0;
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const fx: number[] = [];
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for (let cy = 0; cy < ny; cy++) {
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for (let cx = 0; cx * ny < nx * (ny - cy); cx++) {
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let f = 0;
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for (let x = 0; x < w; x++) fx[x] = cos((PI / w) * cx * (x + 0.5));
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for (let y = 0; y < h; y++)
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for (let x = 0, fy = cos((PI / h) * cy * (y + 0.5)); x < w; x++)
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f += channel[x + y * w] * fx[x] * fy;
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f /= w * h;
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if (cx || cy) {
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ac.push(f);
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scale = max(scale, abs(f));
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} else {
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dc = f;
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}
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}
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}
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if (scale) for (let i = 0; i < ac.length; i++) ac[i] = 0.5 + (0.5 / scale) * ac[i];
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return [dc, ac, scale];
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};
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const [l_dc, l_ac, l_scale] = encodeChannel(l, max(3, lx), max(3, ly));
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const [p_dc, p_ac, p_scale] = encodeChannel(p, 3, 3);
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const [q_dc, q_ac, q_scale] = encodeChannel(q, 3, 3);
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const [a_dc, a_ac, a_scale] = hasAlpha ? encodeChannel(a, 5, 5) : [];
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// Write the constants
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const isLandscape = w > h;
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const header24 =
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round(63 * (l_dc as number)) |
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(round(31.5 + 31.5 * (p_dc as number)) << 6) |
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(round(31.5 + 31.5 * (q_dc as number)) << 12) |
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(round(31 * (l_scale as number)) << 18) |
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((hasAlpha ? 1 : 0) << 23);
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const header16 =
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(isLandscape ? ly : lx) |
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(round(63 * (p_scale as number)) << 3) |
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(round(63 * (q_scale as number)) << 9) |
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((isLandscape ? 1 : 0) << 15);
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const hash = [
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header24 & 255,
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(header24 >> 8) & 255,
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header24 >> 16,
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header16 & 255,
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header16 >> 8,
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];
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const ac_start = hasAlpha ? 6 : 5;
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let ac_index = 0;
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if (hasAlpha) hash.push(round(15 * (a_dc as number)) | (round(15 * (a_scale as number)) << 4));
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// Write the varying factors
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for (const ac of hasAlpha ? [l_ac, p_ac, q_ac, a_ac] : [l_ac, p_ac, q_ac])
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for (const f of ac as number[])
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hash[ac_start + (ac_index >> 1)] |= round(15 * f) << ((ac_index++ & 1) << 2);
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return new Uint8Array(hash);
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}
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/**
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* Decodes a ThumbHash to an RGBA image. RGB is not be premultiplied by A.
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*
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* @param hash The bytes of the ThumbHash.
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* @returns The width, height, and pixels of the rendered placeholder image.
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*/
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export function thumbHashToRGBA(hash: Uint8Array) {
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const { PI, min, max, cos, round } = Math;
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// Read the constants
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const header24 = hash[0] | (hash[1] << 8) | (hash[2] << 16);
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const header16 = hash[3] | (hash[4] << 8);
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const l_dc = (header24 & 63) / 63;
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const p_dc = ((header24 >> 6) & 63) / 31.5 - 1;
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const q_dc = ((header24 >> 12) & 63) / 31.5 - 1;
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const l_scale = ((header24 >> 18) & 31) / 31;
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const hasAlpha = header24 >> 23;
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const p_scale = ((header16 >> 3) & 63) / 63;
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const q_scale = ((header16 >> 9) & 63) / 63;
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const isLandscape = header16 >> 15;
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const lx = max(3, isLandscape ? (hasAlpha ? 5 : 7) : header16 & 7);
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const ly = max(3, isLandscape ? header16 & 7 : hasAlpha ? 5 : 7);
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const a_dc = hasAlpha ? (hash[5] & 15) / 15 : 1;
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const a_scale = (hash[5] >> 4) / 15;
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// Read the varying factors (boost saturation by 1.25x to compensate for quantization)
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const ac_start = hasAlpha ? 6 : 5;
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let ac_index = 0;
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const decodeChannel = (nx: number, ny: number, scale: number) => {
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const ac: number[] = [];
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for (let cy = 0; cy < ny; cy++)
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for (let cx = cy ? 0 : 1; cx * ny < nx * (ny - cy); cx++)
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ac.push(
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(((hash[ac_start + (ac_index >> 1)] >> ((ac_index++ & 1) << 2)) & 15) / 7.5 - 1) * scale
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);
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return ac;
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};
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const l_ac = decodeChannel(lx, ly, l_scale);
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const p_ac = decodeChannel(3, 3, p_scale * 1.25);
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const q_ac = decodeChannel(3, 3, q_scale * 1.25);
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const a_ac = hasAlpha ? decodeChannel(5, 5, a_scale) : null;
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// Decode using the DCT into RGB
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const ratio = thumbHashToApproximateAspectRatio(hash);
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const w = round(ratio > 1 ? 32 : 32 * ratio);
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const h = round(ratio > 1 ? 32 / ratio : 32);
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const rgba = new Uint8Array(w * h * 4),
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fx: number[] = [],
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fy: number[] = [];
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for (let y = 0, i = 0; y < h; y++) {
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for (let x = 0; x < w; x++, i += 4) {
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let l = l_dc,
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p = p_dc,
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q = q_dc,
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a = a_dc;
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// Precompute the coefficients
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for (let cx = 0, n = max(lx, hasAlpha ? 5 : 3); cx < n; cx++)
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fx[cx] = cos((PI / w) * (x + 0.5) * cx);
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for (let cy = 0, n = max(ly, hasAlpha ? 5 : 3); cy < n; cy++)
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fy[cy] = cos((PI / h) * (y + 0.5) * cy);
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// Decode L
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for (let cy = 0, j = 0; cy < ly; cy++)
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for (let cx = cy ? 0 : 1, fy2 = fy[cy] * 2; cx * ly < lx * (ly - cy); cx++, j++)
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l += l_ac[j] * fx[cx] * fy2;
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// Decode P and Q
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for (let cy = 0, j = 0; cy < 3; cy++) {
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for (let cx = cy ? 0 : 1, fy2 = fy[cy] * 2; cx < 3 - cy; cx++, j++) {
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const f = fx[cx] * fy2;
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p += p_ac[j] * f;
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q += q_ac[j] * f;
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}
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}
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// Decode A
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if (hasAlpha)
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for (let cy = 0, j = 0; cy < 5; cy++)
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for (let cx = cy ? 0 : 1, fy2 = fy[cy] * 2; cx < 5 - cy; cx++, j++)
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a += a_ac![j] * fx[cx] * fy2;
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// Convert to RGB
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const b = l - (2 / 3) * p;
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const r = (3 * l - b + q) / 2;
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const g = r - q;
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rgba[i] = max(0, 255 * min(1, r));
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rgba[i + 1] = max(0, 255 * min(1, g));
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rgba[i + 2] = max(0, 255 * min(1, b));
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rgba[i + 3] = max(0, 255 * min(1, a));
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}
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}
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return { w, h, rgba };
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}
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/**
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* Extracts the average color from a ThumbHash. RGB is not be premultiplied by A.
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*
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* @param hash The bytes of the ThumbHash.
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* @returns The RGBA values for the average color. Each value ranges from 0 to 1.
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*/
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export function thumbHashToAverageRGBA(hash: Uint8Array) {
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const { min, max } = Math;
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const header = hash[0] | (hash[1] << 8) | (hash[2] << 16);
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const l = (header & 63) / 63;
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const p = ((header >> 6) & 63) / 31.5 - 1;
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const q = ((header >> 12) & 63) / 31.5 - 1;
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const hasAlpha = header >> 23;
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const a = hasAlpha ? (hash[5] & 15) / 15 : 1;
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const b = l - (2 / 3) * p;
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const r = (3 * l - b + q) / 2;
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const g = r - q;
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return {
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r: max(0, min(1, r)),
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g: max(0, min(1, g)),
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b: max(0, min(1, b)),
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a,
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};
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}
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/**
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* Extracts the approximate aspect ratio of the original image.
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*
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* @param hash The bytes of the ThumbHash.
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* @returns The approximate aspect ratio (i.e. width / height).
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*/
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export function thumbHashToApproximateAspectRatio(hash: Uint8Array) {
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const header = hash[3];
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const hasAlpha = hash[2] & 0x80;
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const isLandscape = hash[4] & 0x80;
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const lx = isLandscape ? (hasAlpha ? 5 : 7) : header & 7;
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const ly = isLandscape ? header & 7 : hasAlpha ? 5 : 7;
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return lx / ly;
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}
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/**
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* Encodes an RGBA image to a PNG data URL. RGB should not be premultiplied by
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* A. This is optimized for speed and simplicity and does not optimize for size
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* at all. This doesn't do any compression (all values are stored uncompressed).
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*
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* @param w The width of the input image. Must be ≤100px.
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* @param h The height of the input image. Must be ≤100px.
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* @param rgba The pixels in the input image, row-by-row. Must have w*h*4 elements.
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* @returns A data URL containing a PNG for the input image.
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*/
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export function rgbaToDataURL(w: number, h: number, rgba: Uint8Array) {
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const row = w * 4 + 1;
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const idat = 6 + h * (5 + row);
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const bytes = [
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137,
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80,
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78,
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71,
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13,
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10,
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26,
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10,
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0,
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0,
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0,
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13,
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73,
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72,
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68,
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82,
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0,
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0,
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w >> 8,
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w & 255,
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0,
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0,
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h >> 8,
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h & 255,
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8,
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6,
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0,
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0,
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0,
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0,
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0,
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0,
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0,
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idat >>> 24,
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(idat >> 16) & 255,
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(idat >> 8) & 255,
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idat & 255,
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73,
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68,
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65,
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84,
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120,
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1,
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];
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const table = [
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0, 498536548, 997073096, 651767980, 1994146192, 1802195444, 1303535960, 1342533948, -306674912,
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-267414716, -690576408, -882789492, -1687895376, -2032938284, -1609899400, -1111625188,
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];
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let a = 1,
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b = 0;
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for (let y = 0, i = 0, end = row - 1; y < h; y++, end += row - 1) {
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bytes.push(y + 1 < h ? 0 : 1, row & 255, row >> 8, ~row & 255, (row >> 8) ^ 255, 0);
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for (b = (b + a) % 65521; i < end; i++) {
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const u = rgba[i] & 255;
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bytes.push(u);
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a = (a + u) % 65521;
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b = (b + a) % 65521;
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}
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}
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bytes.push(
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b >> 8,
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b & 255,
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a >> 8,
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a & 255,
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0,
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0,
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0,
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0,
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0,
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0,
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0,
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0,
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73,
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69,
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78,
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68,
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174,
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66,
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96,
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130
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);
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for (let [start, end] of [
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[12, 29],
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[37, 41 + idat],
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]) {
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let c = ~0;
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for (let i = start; i < end; i++) {
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c ^= bytes[i];
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c = (c >>> 4) ^ table[c & 15];
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c = (c >>> 4) ^ table[c & 15];
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}
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c = ~c;
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bytes[end++] = c >>> 24;
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bytes[end++] = (c >> 16) & 255;
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bytes[end++] = (c >> 8) & 255;
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bytes[end++] = c & 255;
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}
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return 'data:image/png;base64,' + btoa(String.fromCharCode(...bytes));
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}
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/**
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* Decodes a ThumbHash to a PNG data URL. This is a convenience function that
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* just calls "thumbHashToRGBA" followed by "rgbaToDataURL".
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*
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* @param hash The bytes of the ThumbHash.
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* @returns A data URL containing a PNG for the rendered ThumbHash.
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*/
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export function thumbHashToDataURL(hash: Uint8Array): string {
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const image = thumbHashToRGBA(hash);
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return rgbaToDataURL(image.w, image.h, image.rgba);
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}
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/**
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* Convenience function added to the original thumbhash code, allows generating a thumbhash image directly from
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* thumbhash string.
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* @param thumbhash string from which thumbhashDataURL should be generated
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* @returns A data URL containing a PNG for the rendered ThumbHash
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*/
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export function thumbHashStringToDataURL(thumbhash: string): string {
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const hash = Uint8Array.from(atob(thumbhash), (c) => c.charCodeAt(0));
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return thumbHashToDataURL(hash);
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}
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