create a sparse BufferedImage in java

Question

I have to create an image with very large resolution, but the image is relatively "sparse", only some areas in the image need to draw.

For example with following code

/* this take 5GB memory */

    final BufferedImage img = new BufferedImage( 36000, 36000, BufferedImage.TYPE_INT_ARGB);

/* draw something */

    Graphics g = img.getGraphics();
    g.drawImage(....);

/* output as PNG */

    final File out = new File("out.png"); 
    ImageIO.write(img, "png", out); 

The PNG image on the end I created is ONLY about 200~300 MB.

The question is how can I avoid creating a 5GB BufferedImage at the beginning? I do need an image with large dimension, but with very sparse color information.

Is there any Stream for BufferedImage so that it will not take so much memory?

Answer 1

Is there a reason for not using a lazy-initialized Map or similar structure full of smaller BufferedImages?

Edit: That's a pretty specialized data structure. If you want to draw across images, tile them in a some reasonable fashion and apply a corresponding AffineTransform to each one. Then you can just iterate over the Collection and draw to each one and null it out or Flyweight it if it's blank right afterward. I don't know of non-painful way to combine them all into a PNG inside Java though.

Answer 2

You example uses TYPE_INT_ARGB as the image type which is 4 bytes per pixel. If the image has a limited number of colours you might be able to use a different image type with fewer bytes per pixel.

This could reduce the number of bytes per pixel but the best case scenario is 1 byte per pixel which will still use over 1 GB.

Otherwise you could attempt to divide the rendering into multiple images and merge them together separatly.