89 lines
2.7 KiB
JavaScript
89 lines
2.7 KiB
JavaScript
// Unsharp mask filter
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//
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// http://stackoverflow.com/a/23322820/1031804
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// USM(O) = O + (2 * (Amount / 100) * (O - GB))
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// GB - gaussian blur.
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//
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// Image is converted from RGB to HSV, unsharp mask is applied to the
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// brightness channel and then image is converted back to RGB.
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//
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'use strict';
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var glur_mono16 = require('glur/mono16');
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function hsv_v16(img, width, height) {
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var size = width * height;
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var out = new Uint16Array(size);
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var r, g, b, max;
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for (var i = 0; i < size; i++) {
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r = img[4 * i];
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g = img[4 * i + 1];
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b = img[4 * i + 2];
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max = (r >= g && r >= b) ? r : (g >= b && g >= r) ? g : b;
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out[i] = max << 8;
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}
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return out;
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}
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module.exports = function unsharp(img, width, height, amount, radius, threshold) {
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var v1, v2, vmul;
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var diff, iTimes4;
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if (amount === 0 || radius < 0.5) {
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return;
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}
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if (radius > 2.0) {
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radius = 2.0;
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}
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var brightness = hsv_v16(img, width, height);
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var blured = new Uint16Array(brightness); // copy, because blur modify src
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glur_mono16(blured, width, height, radius);
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var amountFp = (amount / 100 * 0x1000 + 0.5)|0;
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var thresholdFp = threshold << 8;
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var size = width * height;
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/* eslint-disable indent */
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for (var i = 0; i < size; i++) {
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v1 = brightness[i];
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diff = v1 - blured[i];
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if (Math.abs(diff) >= thresholdFp) {
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// add unsharp mask to the brightness channel
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v2 = v1 + ((amountFp * diff + 0x800) >> 12);
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// Both v1 and v2 are within [0.0 .. 255.0] (0000-FF00) range, never going into
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// [255.003 .. 255.996] (FF01-FFFF). This allows to round this value as (x+.5)|0
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// later without overflowing.
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v2 = v2 > 0xff00 ? 0xff00 : v2;
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v2 = v2 < 0x0000 ? 0x0000 : v2;
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// Avoid division by 0. V=0 means rgb(0,0,0), unsharp with unsharpAmount>0 cannot
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// change this value (because diff between colors gets inflated), so no need to verify correctness.
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v1 = v1 !== 0 ? v1 : 1;
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// Multiplying V in HSV model by a constant is equivalent to multiplying each component
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// in RGB by the same constant (same for HSL), see also:
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// https://beesbuzz.biz/code/16-hsv-color-transforms
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vmul = ((v2 << 12) / v1)|0;
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// Result will be in [0..255] range because:
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// - all numbers are positive
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// - r,g,b <= (v1/256)
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// - r,g,b,(v1/256),(v2/256) <= 255
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// So highest this number can get is X*255/X+0.5=255.5 which is < 256 and rounds down.
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iTimes4 = i * 4;
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img[iTimes4] = (img[iTimes4] * vmul + 0x800) >> 12; // R
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img[iTimes4 + 1] = (img[iTimes4 + 1] * vmul + 0x800) >> 12; // G
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img[iTimes4 + 2] = (img[iTimes4 + 2] * vmul + 0x800) >> 12; // B
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}
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}
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};
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