meta.js

    function unpackImage(buf) {
        const bytes = new Uint8Array(buf);

        const byteCount = new Uint32Array(buf.slice(8, 12))[0];
        const width = bytes[12] | (bytes[13] << 8);
        const height = bytes[14] | (bytes[15] << 8);
        const format = bytes[16];
        const paletteEntryCount = bytes[17];

        if(format != 2) // palette
            return null;

        const canvas = document.createElement("canvas");
        canvas.width = width;
        canvas.height = height;
        const ctx = canvas.getContext("2d");
        const imageData = ctx.createImageData(width, height);

        const palette = bytes.slice(18, 18 + paletteEntryCount * 4);

        if(bytes[6] == 0x50 && bytes[7] == 0x4B) { // "PK"
            const bitDepth = Math.ceil(Math.log2(paletteEntryCount));
            let outOff = 0;
            let offset = 18 + paletteEntryCount * 4;

            let col = 0, bit = 0;
            for(; offset < byteCount; offset++) {
                for(let b = 0; b < 8; b++) {
                    col <<= 1;
                    col |= (bytes[offset] >> (7 - b)) & 1;

                    if(++bit == bitDepth) {
                        imageData.data[outOff++] = palette[col * 4 + 0];
                        imageData.data[outOff++] = palette[col * 4 + 1];
                        imageData.data[outOff++] = palette[col * 4 + 2];
                        imageData.data[outOff++] = palette[col * 4 + 3];
                        bit = 0; col = 0;
                    }
                }
            }
        } else if(bytes[6] == 0x52 && bytes[7] == 0x4C) { // "RL"
        const bitDepth = Math.ceil(Math.log2(paletteEntryCount));
            let outOff = 0;
            let offset = 18 + paletteEntryCount * 4;

            let col = 0, bit = 0, count = 0;
            let parseState = 0;
            for(; offset < byteCount; offset++) {
                for(let b = 0; b < 8; b++) {
                    switch(parseState) {
                        case 0: // flag
                            if(bytes[offset] & (0x80 >> b))
                                parseState = 1;
                            else
                                parseState = 2;
                            break;

                        case 1: // repeat count
                            count <<= 1;
                            count |= (bytes[offset] >> (7 - b)) & 1;

                            if(++bit == 8) {
                                parseState = 2;
                                bit = 0;
                            }
                            break;

                        case 2: // value
                            col <<= 1;
                            col |= (bytes[offset] >> (7 - b)) & 1;

                            if(++bit == bitDepth) {
                                for(let c = 0; c <= count; c++) {
                                    imageData.data[outOff++] = palette[col * 4 + 0];
                                    imageData.data[outOff++] = palette[col * 4 + 1];
                                    imageData.data[outOff++] = palette[col * 4 + 2];
                                    imageData.data[outOff++] = palette[col * 4 + 3];
                                }
                                bit = 0; col = 0; count = 0; parseState = 0;
                            }
                            break;
                    }
                }
            }
        // else RW
        } else
            return null;

        ctx.putImageData(imageData, 0, 0);

        return canvas.toDataURL();
    }