Invert bitmap colors

Question

I have the following problem. I have a charting program, and it\'s design is black, but the charts (that I get from the server as images) are light (it actually uses only 5 colo

Answer 1

OK seen that you're really only using 5 colors it's quite easy.

Regarding performances, I don't know about Android but I can tell you that in Java using setRGB is amazingly slower than getting back the data buffer and writing directly in the int[].

When I write "amazingly slower", to give you an idea, on OS X 10.4 the following code:

for ( int x = 0; x < width; x++ ) {
    for ( int y = 0; y < height; y++ ) {
        img.setRGB(x,y,0xFFFFFFFF);
    }
}

can be 100 times (!) slower than:

for ( int x = 0; x < width; x++ ) {
    for ( int y = 0; y < height; y++ ) {
        array[y*width+x] = 0xFFFFFFFF;
    }
}

You read correctly: one hundred time. Measured on a Core 2 Duo / Mac Mini / OS X 10.4.

(of course you need to first get access to the underlying int[] array but hopefully this shouldn't be difficult)

I cannot stress enough that the problem ain't the two for loops: in both cases it's the same unoptimized for loops. So it's really setRGB that is the issue here.

I don't know it works on Android, but you probably should get rid of setRGB if you want something that performs well.