image-js/lib/compute/variance.js

Image processing and manipulation in JavaScript

/**
 * Compute the variance of each channel of an image.
 * @see {@link https://en.wikipedia.org/wiki/Variance}
 * @param image - Image to process.
 * @param options - Variance options.
 * @returns The variance of the channels of the image.
 */
export function variance(image, options) {
    const mean = image.mean(options);
    const sum = new Array(image.channels).fill(0);
    if (options) {
        for (const point of options.points) {
            for (let channel = 0; channel < image.channels; channel++) {
                sum[channel] +=
                    (image.getValue(point.column, point.row, channel) - mean[channel]) **
                        2;
            }
        }
    }
    else {
        for (let i = 0; i < image.size; i++) {
            for (let channel = 0; channel < image.channels; channel++) {
                sum[channel] +=
                    (image.getValueByIndex(i, channel) - mean[channel]) ** 2;
            }
        }
    }
    const nbValues = options
        ? options.points.length * image.channels
        : image.size * image.channels;
    return sum.map((channel) => channel / nbValues);
}
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