ico-utils/dist/png-utils.js

A javascript library to create ICO file from PNG images and extract PNG images from ICO file.

import { joinBytesToNumber } from './helpers/bytesConverter.js';
const CHANNELS_PER_PIXEL = {
    0: 1,
    2: 3,
    3: 1,
    4: 2,
    6: 4,
};
export function parsePng(buffer) {
    const uint8 = new Uint8Array(buffer.slice(0, 33));
    if (!isPngSignatureValid(uint8.slice(0, 8))) {
        throw new Error('INVALID_PNG_IMAGE');
    }
    if (!isIhdrChunkValid(uint8.slice(8, 16))) {
        throw new Error('INVALID_PNG_IMAGE');
    }
    const width = joinBytesToNumber(Array.from(uint8.slice(16, 20).reverse()));
    const height = joinBytesToNumber(Array.from(uint8.slice(20, 24).reverse()));
    const bitsPerChannel = uint8[24];
    const colourType = uint8[25];
    const bitsPerPixel = bitsPerChannel * CHANNELS_PER_PIXEL[colourType];
    return { width, height, bpp: bitsPerPixel };
}
export function isPngSignatureValid(imageSignatureBytes) {
    const pngSignatureBytes = [0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a];
    return pngSignatureBytes.toString() === imageSignatureBytes.toString();
}
export function isIhdrChunkValid(chunkBeginBytes) {
    const ihdrChunkBeginBytes = [0x00, 0x00, 0x00, 0x0d, 0x49, 0x48, 0x44, 0x52];
    return ihdrChunkBeginBytes.toString() === chunkBeginBytes.toString();
}