Question

I have two BufferedImage objects, src and dest. Both are grayscale, src is 1bpc (B&W basically), and dest could really be any sort of color space/bpc/etc.

I need to be able to draw some color onto dest using src as a bitmask. Basically, if the pixel in src is black, then dest should be changed to the draw color. But if the pixel in src is white, the dest should be left alone.

If it matters, I am also applying an affine transform during the draw operation.

Graphics2D g = dest.createGraphics();
// do something here???
g.drawImage(src, transform, null);
g.dispose();

In a pure B&W world this would involve a simple | of the pixel values together – but it seems like there’s probably a correct way to do this using image operations.

Gut instinct says that this is a matter of setting the Composite and some sort of alpha – but I’m at a total loss as to what values to use. I have very little experience with the more advanced aspects of graphics 2d – any pointers would be greatly appreciated.

Answer 1

I think that I’ve come up with an effective solution using this article

This is certainly efficient, although I’m not sure if follows best practices or not:

BufferedImage dest; // input
BufferedImage src; // input

...

byte[] r = new byte[]{(byte)0,(byte)255}; // 255=black, we could set it to some other gray component as desired
byte[] g = new byte[]{(byte)0,(byte)255};
byte[] b = new byte[]{(byte)0,(byte)255};
byte[] a = new byte[]{(byte)255,(byte)0};
IndexColorModel bitmaskColorModel = new IndexColorModel(1, 2, r, g, b, a);

BufferedImage masked = new BufferedImage(bitmaskColorModel, src.getRaster(), false, null);

Graphics2D g = dest.createGraphics();
g.drawImage(masked, transform, null);
g.dispose();