Any one tell me why we write this 0xff000000 in filters?

Question

Here is my code for GrayScale filter want to know about this

class GrayScale extends RGBImageFilter {
  @Override
    public int filterRGB(int x, int y, int rgb) {
    int a = rgb & 0xff000000;
    int r = (rgb >> 16) & 0xff;
    int g = (rgb >> 8) & 0xff;
    int b = rgb & 0xff;
    rgb = (r * 77 + g * 151 + b * 28) >> 8; 
    return a | (rgb << 16) | (rgb << 8) | rgb;
    }
}

`rgb & 0xff000000` means that you apply a mask to your rgb color to get the alpha value of it. — Alexis C., Dec 07 '13 at 14:49

score 14 · Accepted Answer · answered Dec 07 '13 at 14:50

The format of your input is 0xAARRGGBB where AA is the alpha (transparency), RR is the red, GG is the green, and BB is the blue component. This is hexadecimal, so the values range from 00 to FF (255).

Your question is about the extraction of the alpha value. This line:

int a = rgb & 0xFF000000

If you consider a value like 0xFFFFFFFF (white), AND will return whatever bits are set in both the original colour and the mask; so you'll get a value of 0xFF, or 255 (correctly).

Thanks this line was confusing me too much now I got it. – user3066663 Dec 07 '13 at 14:56 — user3066663, Dec 07 '13 at 14:56

score 1 · Answer 2 · answered Dec 07 '13 at 14:49

1

The

int a = rgb & 0xff000000;
...
return a | ...;

simply preserves the top 8 bits of rgb (which contain the alpha component).

answered Dec 07 '13 at 14:49

NPE

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score 0 · Answer 3 · edited May 23 '17 at 11:53

0

Beside Ashes999 and NPE answers, if you want to know how it's treated internally in java, check out this post

edited May 23 '17 at 11:53

Community

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answered Dec 07 '13 at 14:53

devBinnooh

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Any one tell me why we write this 0xff000000 in filters?

3 Answers3