87 lines
2.1 KiB
JavaScript
87 lines
2.1 KiB
JavaScript
import { isNodePattern } from '@jimp/utils';
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/**
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* Get an image's histogram
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* @return {object} An object with an array of color occurrence counts for each channel (r,g,b)
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*/
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function histogram() {
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const histogram = {
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r: new Array(256).fill(0),
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g: new Array(256).fill(0),
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b: new Array(256).fill(0)
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};
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this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function(
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x,
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y,
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index
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) {
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histogram.r[this.bitmap.data[index + 0]]++;
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histogram.g[this.bitmap.data[index + 1]]++;
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histogram.b[this.bitmap.data[index + 2]]++;
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});
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return histogram;
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}
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/**
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* Normalize values
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* @param {integer} value Pixel channel value.
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* @param {integer} min Minimum value for channel
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* @param {integer} max Maximum value for channel
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* @return {integer} normalized values
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*/
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const normalize = function(value, min, max) {
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return ((value - min) * 255) / (max - min);
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};
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const getBounds = function(histogramChannel) {
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return [
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histogramChannel.findIndex(value => value > 0),
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255 -
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histogramChannel
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.slice()
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.reverse()
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.findIndex(value => value > 0)
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];
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};
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/**
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* Normalizes the image
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* @param {function(Error, Jimp)} cb (optional) a callback for when complete
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* @returns {Jimp} this for chaining of methods
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*/
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export default () => ({
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normalize(cb) {
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const h = histogram.call(this);
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// store bounds (minimum and maximum values)
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const bounds = {
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r: getBounds(h.r),
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g: getBounds(h.g),
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b: getBounds(h.b)
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};
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// apply value transformations
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this.scanQuiet(0, 0, this.bitmap.width, this.bitmap.height, function(
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x,
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y,
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idx
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) {
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const r = this.bitmap.data[idx + 0];
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const g = this.bitmap.data[idx + 1];
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const b = this.bitmap.data[idx + 2];
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this.bitmap.data[idx + 0] = normalize(r, bounds.r[0], bounds.r[1]);
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this.bitmap.data[idx + 1] = normalize(g, bounds.g[0], bounds.g[1]);
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this.bitmap.data[idx + 2] = normalize(b, bounds.b[0], bounds.b[1]);
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});
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if (isNodePattern(cb)) {
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cb.call(this, null, this);
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}
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return this;
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}
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});
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