Converting an image pixel from color ARGB to grayscale ARGB manually

Question

So I've got a project to convert an image to black and white manually by altering the argb values with an algorithm. I've tried averaging the RGB values and I come out with an almost completely grayscale image but there's still hints of color in it. Anyone have any algorithm examples to convert a pixel in aRGB to greyscale manually?

This is what I've been doing so far:

            //Apply the filter
            reds = ((reds+greens+blues)/3);
            greens = ((reds+greens+blues)/3);
            blues = ((reds+greens+blues)/3);

Worth noting that due to the biology of the human eye, red, green, and blue should not be evenly weighted when an image is converted to grayscale. — Jonathan Grynspan, Feb 24 '13 at 20:22

harold · Answer 1 · 2013-02-24T15:05:33.403

4

It looks like you're changing the inputs of the Right Hand Side while expecting its value to remain constant. Why not use this?

reds = (reds + greens + blues) / 3;
greens = reds;
blues = reds;

edited Feb 24 '13 at 15:05

answered Feb 24 '13 at 15:00

harold

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@user1088595 don't feel bad, I just mixed up left and right :) – harold Feb 24 '13 at 15:05
I think it would be a good idea to mark this answer as correct. – Juan Lopes Feb 24 '13 at 16:32

score 3 · Answer 2 · answered Feb 24 '13 at 20:20

I've always been under the impression that, due to our eyes' differing sensitivities to red, green and blue wavelengths, grayscale should be computed using:

(int) (0.299 * red + 0.587 * green + 0.114 * blue)

Years ago, this used to be easy information to find, but now I can't find too many sources for it. Wikipedia's entry on grayscale is one.

Converting an image pixel from color ARGB to grayscale ARGB manually

2 Answers2