image-js/lib/utils/setBlendedPixel.js

Image processing and manipulation in JavaScript

import { Image } from '../Image.js';
import { getDefaultColor } from './getDefaultColor.js';
import { assert } from './validators/assert.js';
/**
 * Blend the given pixel with the pixel at the specified location in the image.
 * @param image - The image with which to blend.
 * @param column - Column of the target pixel.
 * @param row - Row of the target pixel.
 * @param color - Color with which to blend the image pixel. Default: `Opaque black`.
 */
export function setBlendedPixel(image, column, row, color) {
    color = color ?? getDefaultColor(image);
    if (!image.alpha) {
        image.setPixel(column, row, color);
    }
    else {
        assert(image instanceof Image);
        const sourceAlpha = color.at(-1);
        if (sourceAlpha === image.maxValue) {
            image.setPixel(column, row, color);
            return;
        }
        const targetAlpha = image.getValue(column, row, image.channels - 1);
        const newAlpha = sourceAlpha + targetAlpha * (1 - sourceAlpha / image.maxValue);
        image.setValue(column, row, image.channels - 1, newAlpha);
        for (let component = 0; component < image.components; component++) {
            const sourceComponent = color[component];
            const targetComponent = image.getValue(column, row, component);
            const newComponent = (sourceComponent * sourceAlpha +
                targetComponent * targetAlpha * (1 - sourceAlpha / image.maxValue)) /
                newAlpha;
            image.setValue(column, row, component, newComponent);
        }
    }
}
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