private int[] populateARGB() {
        // populate array with a blend of color components
        final int[] argb = new int[256 * 256];
        for (int i = 0; i < 256; i++) {
            for (int j = 0; j < 256; j++) {
                final int red = i;
                final int green = 255 - i;
                final int blue = j;
                argb[i * 256 + j] = ((0xff00 | red) << 8 | green) << 8 | blue;
            }
        }

        // also draw a black and white strip down main diagonal
        for (int i = 0; i < 256; i++) {
            argb[i * 256 + i] = 0xff000000;
            if (i < 255) {
                argb[i * 256 + i + 1] = 0xffffffff;
            }
        }
        return argb;
    }
Populate an integer pixel array for a 256-by-256 image with varied colors across the image area and a white and black line down the main diagonal.

@return a valid array of integers.
src/test/java/org/apache/commons/imaging/formats/png/PngWritePredictorTest.java