2023-06-28 22:52:09 +00:00
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<!DOCTYPE html>
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<html>
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<head>
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<meta charset="utf-8">
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<title>Block video encoding test</title>
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<style type="text/css">
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.stretchy {
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width:267px;
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2023-07-03 03:58:19 +00:00
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height: 160px;
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2023-06-28 22:52:09 +00:00
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object-fit: fill;
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image-rendering: pixelated;
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}
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</style>
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</head>
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<body>
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<h1>Block video encoding test</h1>
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2023-07-03 12:49:52 +00:00
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<p>
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Test work for a video encoding using Atari 800-family GTIA grayscale mode on top of text cells.
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This allows a "block dictionary" of 128 2x8-pixel blocks on an 80x160 grayscale image,
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at cost of 1840 bytes per full frame or 800 bytes to reuse previous blocks.
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</p>
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<p>
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Currently just converts to grayscale and counts up unique blocks.
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Next step: decimate if > 128 unique blocks per image, and combine
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the most similar blocks in the output.
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</p>
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2023-06-28 22:52:09 +00:00
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<h2>Source video</h2>
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<div>
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<video id="source" src="llamigos.webm" class="stretchy" muted controls playsinline></video>
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</div>
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<h2>Work canvas</h2>
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<div>
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<canvas id="work" width="80" height="160" class="stretchy"></canvas>
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</div>
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<div>
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<span id="block-count">n/a</span> blocks per frame
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</div>
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<script type="text/javascript">
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let width = 80;
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let height = 160;
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let blockWidth = 2;
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let blockHeight = 8;
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let widthBlocks = width / blockWidth;
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let heightBlocks = height / blockHeight;
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function fromSRGB(val) {
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if (val <= 0.04045) {
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return val / 12.92;
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}
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return ((val + 0.055) / 1.055) ** 2.4;
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}
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function toSRGB(val) {
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if (val <= 0.0031308) {
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return val * 12.92;
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}
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return (val * 1.055) ** (1.0 / 2.4) - 0.055;
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}
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function luma(r, g, b) {
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return r * 0.299 + g * 0.586 + b * 0.114;
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}
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function update() {
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let ctx = work.getContext('2d');
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let pixels = new Uint8Array(width * height);
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// Extract the luma
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ctx.drawImage(source, 0, 0);
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let bits = ctx.getImageData(0, 0, width, height);
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let data = bits.data;
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for (let y = 0; y < height; y++) {
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for (let x = 0; x < width; x++) {
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let i = y * width + x;
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let r = fromSRGB(data[i * 4] / 255);
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let g = fromSRGB(data[i * 4 + 1] / 255);
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let b = fromSRGB(data[i * 4 + 2] / 255);
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let grayLinear = luma(r, g, b);
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let gray = toSRGB(grayLinear);
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let gray16 = Math.round(gray * 15);
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pixels[i] = gray16;
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}
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}
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2023-07-03 03:58:19 +00:00
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let blocks = [];
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let chars = new Uint16Array(widthBlocks * heightBlocks);
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for (let n = 0, y = 0; y < heightBlocks; y++) {
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for (let x = 0; x < widthBlocks; x++, n++) {
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let i = y * widthBlocks + x;
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blocks[i] = new Uint8Array(blockWidth * blockHeight);
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chars[n] = i;
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for (let yy = 0; yy < blockHeight; yy++) {
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for (let xx = 0; xx < blockWidth; xx++) {
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let ii = yy * blockWidth + xx;
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blocks[i][ii] = pixels[(y * blockHeight + yy) * width + (x * blockWidth + xx)];
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}
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}
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}
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}
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// Now we have 800 blocks for 80x160 image
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// But we can only use 128 + their mirror images
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//
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// First pass: sort.
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let zero = "0".charCodeAt(0);
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// Convert the 4bpp pixel indices into hex strings
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let blockMap = {};
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let keys = [];
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for (let i = 0; i < blocks.length; i++) {
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let key = blocks[i].map((n) => n.toString(16)).join('');
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console.log(key);
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if (!blockMap[key]) {
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blockMap[key] = blocks[i];
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keys.push(blockMap[key]);
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}
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}
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let span = document.querySelector('#block-count');
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span.textContent = `${keys.length}`;
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2023-06-28 22:52:09 +00:00
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2023-07-03 03:58:19 +00:00
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for (let y = 0; y < height; y++) {
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for (let x = 0; x < width; x++) {
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let i = y * width + x;
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let gray16 = pixels[i];
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let gray256 = Math.round(gray16 * 255 / 15);
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data[i * 4] = gray256;
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data[i * 4 + 1] = gray256;
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data[i * 4 + 2] = gray256;
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}
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}
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ctx.putImageData(bits, 0, 0);
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}
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let timer = null;
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source.addEventListener('playing', () => {
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if (!timer) {
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timer = setInterval(update, 1000 / 24);
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}
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update();
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});
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source.addEventListener('pause', () => {
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if (timer) {
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clearInterval(timer);
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timer = null;
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}
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});
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</script>
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</body>
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</html>
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