Question

I have some really simple code that’s just not working:

int[] manualPixels = new int[width * height * 3];
for (int index = 0; index < manualPixels.length; index++) {
    if (index % 3 == 2) {
        manualPixels[index] = 255;
    }
}
BufferedImage pixelImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    
pixelImage.setRGB(0, 0, width, height, manualPixels, 0, width);

ImageIO.write(pixelImage, "jpeg", tempFile);

This should, as far as I can determine, output a red, green, or blue image, depending upon whether 0, 1, or 2 is used in the if statement in the for loop. The problem is that instead of that, I invariably get blue and black stripes, no matter which pixels I set. For instance:

I’m sure there must be some basic thing that I’m doing wrong here, I’m just not seeing what it is. Any ideas?

Answer 1

INT_RGB packs all the channels into the least significant three octets of an int. This means that you are setting every third pixel to blue, and the rest are left black. (This however doesn’t match with your image – did you change the code after generating it?)

Try this instead:

int[] manualPixels = new int[width * height];
for (int index = 0; index < manualPixels.length; index++) {
    switch (index % 3) {
        case 0: manualPixels[index] = 0xFF0000; break; // red
        case 1: manualPixels[index] = 0x00FF00; break; // green
        case 2: manualPixels[index] = 0x0000FF; break; // blue
    }
}