image-js/lib/filters/increaseContrast.js

Image processing and manipulation in JavaScript

import { ImageColorModel } from '../utils/constants/colorModels.js';
import checkProcessable from '../utils/validators/checkProcessable.js';
/**
 * Increase the contrast of an image by spanning each channel on the range [0, image.maxValue].
 * This algorithm is based on the level algorithm.
 * @param image - The image to enhance.
 * @param options - Increase contrast options.
 * @returns The enhanced image.
 */
export function increaseContrast(image, options = {}) {
    const { uniform = false } = options;
    checkProcessable(image, {
        bitDepth: [8, 16],
    });
    const minMax = image.minMax();
    let min = minMax.min;
    let max = minMax.max;
    if (uniform) {
        let maxDiffIndex = -1;
        let previousDiff = -1;
        for (let i = 0; i < minMax.max.length; i++) {
            const difference = minMax.max[i] - minMax.min[i];
            if (difference > previousDiff) {
                maxDiffIndex = i;
                previousDiff = difference;
            }
        }
        min = minMax.min[maxDiffIndex];
        max = minMax.max[maxDiffIndex];
    }
    let channels = new Array(image.components)
        .fill(0)
        .map((value, index) => index);
    if (image.colorModel === ImageColorModel.GREYA) {
        channels = [0];
    }
    else if (image.colorModel === ImageColorModel.RGBA) {
        channels = [0, 1, 2];
    }
    return image.level({
        inputMin: min,
        inputMax: max,
        outputMin: 0,
        outputMax: image.maxValue,
        channels,
        ...options,
    });
}
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