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Fast algorithm to invert an ARGB color value to ABGR?

Posted by: admin December 28, 2021 Leave a comment

Questions:

I’m using IntBuffer to manipulate pixels of a Bitmap, but the value in the buffer should be AABBGGRR, while the color constants are AARRGGBB. I know I can use Color.argb, Color.a, … to invert, but I think it’s not perfect.

I need to manipulate a very large number of pixels, so I need an algorithm that can perform this operator in short time. I think of this Bit Expression, but it’s not correct:

0xFFFFFFFF ^ pSourceColor

If there’s no better one, maybe I will use bit-shift operators (that performs Color.a, …) instead of calling the functions to reduce the time.

EDIT:

This is my current function to convert, though I think there shoul be a better algorithm (less operators) to perform it:

private int getBufferedColor(final int pSourceColor) {
    return
            ((pSourceColor >> 24) << 24) |          // Alpha
            ((pSourceColor >> 16) & 0xFF) |         // Red  -> Blue
            ((pSourceColor >> 8) & 0xFF) << 8 |     // Green
            ((pSourceColor) & 0xFF) << 16;          // Blue -> Red
}
Answers:

Since A and G are in place, you can probably do a little better by masking off the B and R and then adding them back. Haven’t tested it but ought to be 95% right:

private static final int EXCEPT_R_MASK = 0xFF00FFFF;
private static final int ONLY_R_MASK = ~EXCEPT_R_MASK;
private static final int EXCEPT_B_MASK = 0xFFFFFF00;
private static final int ONLY_B_MASK = ~EXCEPT_B_MASK;

private int getBufferedColor(final int pSourceColor) {
    int r = (pSourceColor & ONLY_R_MASK) >> 16;
    int b = pSourceColor & ONLY_B_MASK;
    return
      (pSourceColor & EXCEPT_R_MASK & EXCEPT_B_MASK) | (b << 16) | r;
}

###

In my opinion, the following function is fast enough to return the ABGR color while passing an ARGB color and vice-versa!

int argbToABGR(int argbColor) {
    int r = (argbColor >> 16) & 0xFF;
    int b = argbColor & 0xFF;
    return (argbColor & 0xFF00FF00) | (b << 16) | r;
}