ImageIO faster than GZIPStream at max speed

Question

I am looking for the fastest way to download an image from the GPU to a file, for later loading in the same application (so not necessarily PNG e.g.).

I noticed however that when I use a DeflaterStream directly, it is considerably slower than ImageIO with DeflaterStream ( so using ImageIO.write(deflaterstream) ).

Am I doing something wrong? Or is ImageIO just heavily optimized/better than fastest GZIP compression?

  glBindTexture(GL_TEXTURE_2D, textureId);

        int bpp = 4; // Assuming a 32-bit display with a byte each for red, green, blue, and alpha.
        ByteBuffer buffer = BufferUtils.createByteBuffer(SAVE_WIDTH * SAVE_HEIGHT * bpp);
        glGetTexImage(GL_TEXTURE_2D, 0, GL_RGBA8, GL_UNSIGNED_BYTE, buffer );

//        File file = new File("saves/s-" + layer + ".png"); // The file to save to.
        String format = "png"; // Example: "PNG" or "JPG"
//        BufferedImage image = new BufferedImage(SAVE_WIDTH, SAVE_HEIGHT, BufferedImage.TYPE_INT_ARGB);

        try {
            FileOutputStream bOut = new FileOutputStream("saves/p-"+ layer + ".gz");
            DeflaterOutputStream  gzipOut = new DeflaterOutputStream (bOut, new Deflater(Deflater.BEST_SPEED));
            //buffer.flip();
            System.out.println("Bytes remaining " + buffer.remaining());
            while (buffer.hasRemaining()) gzipOut.write(buffer.get());
            gzipOut.close();
            bOut.close();
        } catch (IOException ex) {
            Logger.getLogger(SaveStateManager.class.getName()).log(Level.SEVERE, null, ex);
        }

score 1 · Accepted Answer · answered Jan 09 '13 at 13:27

1

Conmpression is always expensive but you might be able to improve with

OutputStream bOut = new BufferedOutputStream(new FileOutputStream("saves/p-" + layer + ".gz"));
DeflaterOutputStream defOut = new DeflaterOutputStream(bOut, new Deflater(Deflater.BEST_SPEED));
//buffer.flip();
byte[] bytes = new byte[1024];
while (buffer.hasRemaining()) {
    int len = Math.min(buffer.remaining(), bytes.length);
    buffer.get(bytes, 0, len);
    defOut.write(bytes, 0, len);
}
defOut.close();

answered Jan 09 '13 at 13:27

Peter Lawrey

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Yes, I found out indeed getting more bytes in a batch increases my speed significantly. – RobotRock Jan 09 '13 at 13:43
You could try powers of 2 from 512 to find what appears to be optimial. – Peter Lawrey Jan 09 '13 at 13:44
Well, it's an image, so I figure I can just read WIDTH * HEIGHT * bitsperpixel. – RobotRock Jan 09 '13 at 13:56
Don't forget your L1 cache is ~32KB and using buffers about this size of larger can be slower. – Peter Lawrey Jan 09 '13 at 14:02

ImageIO faster than GZIPStream at max speed

1 Answers1