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matmenmatmen
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update only the covered part of the gain map when drawing
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‎CHANGELOG.md‎

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# Changelog
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## 3.20.1
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### Performance
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- Drawing on an image with a gain map (an HDR photo) is much faster: `drawBox()` and `drawCircle()` only recompute the part of the map they cover, instead of the whole map for every call. 400 scanlines over a 1820x1820 Ultra HDR photo take 0.3 s instead of 5.8 s, with the same result.
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## 3.20.0
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### New

‎src/util/gain.ts‎

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@@ -12,14 +12,17 @@ export const encodeSRGB = (v: number): number => 255 * (v <= 0.0031308 ? 12.92 *
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// the luma weights (BT.709, linear) a single channel map's ratio uses
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const LUMA = [0.2126, 0.7152, 0.0722];
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// per channel: the log2 gain of a stored value
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const gainTables = (map: GainMap): Float32Array[] => [0, 1, 2].map(c => {
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const min = map.gainMapMin[c], max = map.gainMapMax[c], gamma = map.gamma[c];
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return new Float32Array(256).map((_, v) => min + (max - min) * (v / 255) ** (1 / gamma));
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});
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/** The map's log2 gains, 3 per pixel */
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export function decodeGains(map: GainMap): Float32Array {
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const { bitmap } = map.image;
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const gains = new Float32Array(bitmap.length / 4 * 3);
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const tables = [0, 1, 2].map(c => {
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const min = map.gainMapMin[c], max = map.gainMapMax[c], gamma = map.gamma[c];
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return new Float32Array(256).map((_, v) => min + (max - min) * (v / 255) ** (1 / gamma));
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});
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const tables = gainTables(map);
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for (let i = 0, g = 0; i < bitmap.length; i += 4, g += 3) {
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gains[g] = tables[0][bitmap[i]];
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gains[g + 1] = tables[1][bitmap[i + 1]];
@@ -101,18 +104,24 @@ export function redraw(image: Image, map: GainMap, left: number, top: number, ri
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if (right <= left || bottom <= top) return;
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const mapWidth = map.width, mapHeight = map.height;
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const sx = mapWidth / width, sy = mapHeight / height;
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const gains = decodeGains(map);
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const oS = map.offsetSDR, oH = map.offsetHDR;
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const lo = Math.min(0, ...map.gainMapMin), hi = Math.max(0, ...map.gainMapMax, extraMax);
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const S = [0, 0, 0], H = [0, 0, 0], sumS = [0, 0, 0], sumH = [0, 0, 0];
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const i0 = Math.max(0, Math.floor(left * sx)), i1 = Math.min(mapWidth, Math.ceil(right * sx));
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const j0 = Math.max(0, Math.floor(top * sy)), j1 = Math.min(mapHeight, Math.ceil(bottom * sy));
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if (i1 <= i0 || j1 <= j0) return;
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// only the map pixels the drawing covers are read and recomputed (a small box on a large image shouldn't cost the
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// whole map)
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const tables = gainTables(map), stored = map.image.bitmap;
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const regionWidth = i1 - i0;
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const next = new Float32Array(regionWidth * (j1 - j0) * 3);
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for (let j = j0; j < j1; j++) {
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const y0 = Math.max(0, Math.floor(j / sy)), y1 = Math.min(height, Math.max(y0 + 1, Math.floor((j + 1) / sy)));
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for (let i = i0; i < i1; i++) {
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const x0 = Math.max(0, Math.floor(i / sx)), x1 = Math.min(width, Math.max(x0 + 1, Math.floor((i + 1) / sx)));
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const g = 3 * (j * mapWidth + i);
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const boost = [2 ** gains[g], 2 ** gains[g + 1], 2 ** gains[g + 2]];
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const m = 4 * (j * mapWidth + i), g = 3 * ((j - j0) * regionWidth + (i - i0));
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const boost = [2 ** tables[0][stored[m]], 2 ** tables[1][stored[m + 1]], 2 ** tables[2][stored[m + 2]]];
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sumS.fill(0);
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sumH.fill(0);
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for (let y = y0; y < y1; y++)
@@ -132,10 +141,35 @@ export function redraw(image: Image, map: GainMap, left: number, top: number, ri
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s += LUMA[c] * (sumS[c] / n + oS[c]);
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h += LUMA[c] * (sumH[c] / n + oH[c]);
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}
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gains[g] = gains[g + 1] = gains[g + 2] = ratio(h, s, lo, hi);
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} else for (let c = 0; c < 3; c++) gains[g + c] = ratio(sumH[c] / n + oH[c], sumS[c] / n + oS[c], lo, hi);
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next[g] = next[g + 1] = next[g + 2] = ratio(h, s, lo, hi);
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} else for (let c = 0; c < 3; c++) next[g + c] = ratio(sumH[c] / n + oH[c], sumS[c] / n + oS[c], lo, hi);
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}
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}
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// when the new gains are in the map's range (usual: drawing seldom brightens beyond the highlights), only those
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// pixels are stored and the others stay as they are
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const { gainMapMin: min, gainMapMax: max, gamma } = map;
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let fits = !single || (min[0] === min[1] && min[1] === min[2] && max[0] === max[1] && max[1] === max[2] && gamma[0] === gamma[1] && gamma[1] === gamma[2]);
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for (let g = 0; fits && g < next.length; g += 3)
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for (let c = 0; c < 3; c++) if (!(next[g + c] >= min[c] && next[g + c] <= max[c])) fits = false;
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if (fits) {
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for (let j = j0; j < j1; j++)
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for (let i = i0, g = 3 * (j - j0) * regionWidth, m = 4 * (j * mapWidth + i0); i < i1; i++, g += 3, m += 4)
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for (let c = 0; c < 3; c++) {
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const t = max[c] > min[c] ? (next[g + c] - min[c]) / (max[c] - min[c]) : 0;
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stored[m + c] = 255 * Math.min(1, Math.max(0, t)) ** gamma[c];
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}
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return;
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}
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// otherwise the range grows, and every stored value is recomputed for it
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const gains = decodeGains(map);
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for (let j = j0; j < j1; j++)
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for (let i = i0, g = 3 * (j - j0) * regionWidth, m = 3 * (j * mapWidth + i0); i < i1; i++, g += 3, m += 3) {
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gains[m] = next[g];
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gains[m + 1] = next[g + 1];
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gains[m + 2] = next[g + 2];
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}
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encodeGains(map, gains, mapWidth, mapHeight, single);
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}
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‎tests/gain-redraw.js‎

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const fs = require('fs').promises;
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const {Image} = require('..');
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const panic = message => {
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console.error(message);
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process.exit(1);
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};
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// the map's log2 gain at a map pixel (red channel)
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const gain = (map, x, y) => map.gainMapMin[0] + (map.gainMapMax[0] - map.gainMapMin[0]) * (map.image.bitmap[4 * (y * map.width + x)] / 255) ** (1 / map.gamma[0]);
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const mapBytes = image => Buffer.from(image.gainMap.image.bitmap);
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(async () => {
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const file = await fs.readFile('./tests/gainmap/single-channel.jpg');
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// drawing in a small area only changes the map where it was drawn: the rest of the map keeps its stored values,
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// and the range stays
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{
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const image = await Image.decode(file), before = mapBytes(image), range = [image.gainMap.gainMapMin.slice(), image.gainMap.gainMapMax.slice()];
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const map = image.gainMap, sx = map.width / image.width, sy = map.height / image.height;
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const box = {x: 100, y: 80, width: 60, height: 40};
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image.drawBox(box.x, box.y, box.width, box.height, 0x000000ff);
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if (JSON.stringify([map.gainMapMin, map.gainMapMax]) !== JSON.stringify(range)) panic('drawBox: the range of the map changed');
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const after = mapBytes(image);
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let changed = 0;
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for (let y = 0; y < map.height; y++) for (let x = 0; x < map.width; x++) {
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const i = 4 * (y * map.width + x), inside = x >= Math.floor(box.x * sx) && x < Math.ceil((box.x + box.width) * sx) && y >= Math.floor(box.y * sy) && y < Math.ceil((box.y + box.height) * sy);
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const differs = before[i] !== after[i] || before[i + 1] !== after[i + 1] || before[i + 2] !== after[i + 2];
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if (differs && !inside) panic(`drawBox: the map changed outside the box at ${x},${y}`);
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if (differs) changed++;
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}
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if (changed === 0) panic('drawBox: black over highlights should change the map');
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// black has no highlight: no boost where it covers the map pixel completely
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const cx = Math.floor((box.x + box.width / 2) * sx), cy = Math.floor((box.y + box.height / 2) * sy);
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if (Math.abs(gain(map, cx, cy)) > 0.02) panic(`drawBox: the gain under black is ${gain(map, cx, cy)}`);
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}
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// many thin boxes: the same map as drawing them one by one on a copy without a shortcut (the order doesn't matter)
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{
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const a = await Image.decode(file), b = await Image.decode(file);
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for (let y = 0; y < a.height; y += 8) a.drawBox(0, y, a.width, 1, 0x00000055);
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for (let y = a.height - (a.height % 8 || 8); y >= 0; y -= 8) b.drawBox(0, y, b.width, 1, 0x00000055);
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let worst = 0;
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for (let y = 0; y < a.gainMap.height; y += 7) for (let x = 0; x < a.gainMap.width; x += 7) worst = Math.max(worst, Math.abs(gain(a.gainMap, x, y) - gain(b.gainMap, x, y)));
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if (worst > 0.05) panic(`drawBox: scanlines in a different order give different maps (${worst})`);
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if (mapBytes(a).equals(mapBytes(await Image.decode(file)))) panic('drawBox: scanlines should change the map');
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}
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// a drawing brighter than the map's range grows it, and the pixels the drawing didn't touch keep their gain
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{
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const image = await Image.decode(file), map = image.gainMap;
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const before = Array.from({length: 20}, (_, i) => gain(map, i * 7 % map.width, i * 11 % map.height));
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const max = map.gainMapMax[0];
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// an HDR source with a stronger map, composited over a part of the image
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const source = new Image(80, 80).fill(0xffffffff);
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source.gainMap = (await Image.decode(file)).gainMap.clone();
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source.gainMap.gainMapMax = [max + 2, max + 2, max + 2];
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source.gainMap.image.fill(0xffffffff);
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image.composite(source, 10, 10);
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if (!(map.gainMapMax[0] > max)) panic(`composite: the range should have grown beyond ${max}, it is ${map.gainMapMax[0]}`);
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for (let i = 0; i < 20; i++) {
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const x = i * 7 % map.width, y = i * 11 % map.height;
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// (not where the source went: the map pixels of the image's 10 to 90)
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if (x <= Math.ceil(90 * map.width / image.width) && y <= Math.ceil(90 * map.height / image.height)) continue;
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const now = gain(map, x, y);
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if (Math.abs(now - before[i]) > 0.03) panic(`composite: the gain at ${x},${y} changed from ${before[i]} to ${now} with the range`);
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}
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}
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})().catch(error => panic(error.stack || String(error)));

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