node.js swf extraction definebitslossless2 incorrect pixels

I made an library to extract images and binary (

) data from an SWF File.


But for tag ( images with alpha), I have a problem: some pixels aren't at their right place, but the others are OK.

Here's my current code (written in ) using Jimp library for image manipulation (I also tried , same thing)

private async DefineBitsLossless2(buff: SWFBuffer, tag: any, tagHeader: any, Callback: Function) {

        var id     = buff.readUIntLE(16);

        var format = buff.readUInt8();

        var width  = buff.readUIntLE(16);

        var height = buff.readUIntLE(16);



        var data   = buff.buffer.slice(buff.pointer, (buff.pointer + tagHeader.length) - 7);

                     buff.addPointer(tagHeader.length - 7);



        if(format != 5) {

            throw new Error(`Unsupported DefineBitsLossless2 image format. Only format 5 is supported, got format ${format}`);

        }



        var GZBuffer = this.concatSWFHeader(zlib.unzipSync(data), data);

        var image    = await new Jimp(width, height);

        var position = 0;



        for(var y = 0; y < height; y++) {

            for(var x = 0; x < width; x++) {

                var alpha = GZBuffer.readUInt8(position++);

                var red   = GZBuffer.readUInt8(position++);

                var green = GZBuffer.readUInt8(position++);

                var blue  = GZBuffer.readUInt8(position++);



                image.setPixelColor(Jimp.rgbaToInt(red, green, blue, alpha), x, y);

            }

        }



        image.getBuffer(Jimp.MIME_PNG, function(err, buffer) {

            tag.id     = id;

            tag.format = format;

            tag.width  = width;

            tag.height = height;

            tag.data   = buffer;

            Callback(null);

        });

    } 







private concatSWFHeader(buff: Buffer, swf: Buffer) {

    return Buffer.concat([swf.slice(0, 8), buff]);

}

Here's the result of this SWF that I used for test pruposes:

Using my library:



Using FFDec (Free Flash Decompiler in Java)



I followed this Adobe guide to make my library (see the page for tag)

What's wrong with my code?