png-to-rgba/src/index.ts

import { PNG } from 'pngjs';

export type RGBAarrType = [number, number, number, number][][];

function PNGToRGBAArray(data: Buffer) {
    const png = PNG.sync.read(data);
    const width = png.width;
    const height = png.height;
    const pixels = png.data;
    const rgba: RGBAarrType = [];
    for (let i = 0; i < height; i++) {
        rgba[i] = [];
        for (let j = 0; j < width; j++) {
            const index = (i * width + j) * 4;
            rgba[i][j] = [pixels[index], pixels[index + 1], pixels[index + 2], pixels[index + 3]];
        }
    }
    return {
        rgba,
        width,
        height,
        png
    };
}

function RGBAArrayToPNG(arr: RGBAarrType, opt: import('pngjs').PNGOptions = {}) {
    const png = new PNG({
        colorType: 6,
        inputHasAlpha: true,
        ...opt,
        width: arr[0].length,
        height: arr.length,
    });
    for (let i = 0; i < arr.length; i++) {
        for (let j = 0; j < arr[i].length; j++) {
            const index = (i * arr[i].length + j) * 4;
            png.data[index] = arr[i][j][0];
            png.data[index + 1] = arr[i][j][1];
            png.data[index + 2] = arr[i][j][2];
            png.data[index + 3] = arr[i][j][3];
        }
    }
    return PNG.sync.write(png);
}

export default {
    PNGToRGBAArray,
    RGBAArrayToPNG
}