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