Convert image to byte array quickly

Question

I am converting an image object into a byte array like this:

private byte[] getImageBytes() throws IOException {
    byte[] bytes;
    try (ByteArrayOutputStream baos = new ByteArrayOutputStream()) {
        ImageIO.write(copyImage(image), "png", baos);
        baos.flush();
        bytes = baos.toByteArray();
    }
    return bytes;
}

private BufferedImage copyImage(Image img) {
    BufferedImage copyOfImage = new BufferedImage(getSize().width, getSize().height, BufferedImage.TYPE_INT_RGB);
    Graphics g = copyOfImage.createGraphics();
    g.drawImage(img, 0, 0, getWidth(), getHeight(), null);
    return copyOfImage;
}

The problem is, that it takes more than 300ms to convert a 90KB image. If the image's size is around 1.2MB then the conversion takes only moderately longer (around 450ms). I have measured the time of the copyImage-method. It only takes around 1ms. The problem seems to be the ImageIO.write method.

Do you know of any way to speed this up?

Answer 1

In getImageBytes() you are compressing the image to PNG which can take time. The fastest ImageIO.write call you can achieve is

ImageIO.write(copyImage(image), "bmp", baos);

where there is no compression. Still, ImageIO contains reference implementations of image formats which are not designed for speed.