How to convert pixels to gray scale?

Question

Ok, I am using Processing which allows me to access pixels of any image as int[]. What I now want to do is to convert the image to gray-scale. Each pixel has a structure as shown below:

...........PIXEL............
[red | green | blue | alpha]
<-8--><--8---><--8--><--8-->

Now, what transformations do I need to apply to individual RGB values to make the image gray-scale ??
What I mean is, how much do I add / subtract to make the image gray-scale ?

Update

I found a few methods here: http://www.johndcook.com/blog/2009/08/24/algorithms-convert-color-grayscale/

Geeky Guy · Accepted Answer · 2013-06-14T21:29:38.800

12

For each pixel, the value for the red, green and blue channels should be their averages. Like this:

int red = pixel.R;
int green = pixel.G;
int blue = pixel.B;

pixel.R = pixel.G = pixel.B = (red + green + blue) / 3;

Since in your case the pixel colors seem to be stored in an array rather than in properties, your code could end up looking like:

int red = pixel[0];
int green = pixel[1];
int blue = pixel[2];

pixel[0] = pixel[1] = pixel[2] = (red + green + blue) / 3;

The general idea is that when you have a gray scale image, each pixel's color measures only the intensity of light at that point - and the way we perceive that is the average of the intensity for each color channel.

edited Jun 14 '13 at 21:29

answered Jun 14 '13 at 21:21

Geeky Guy

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I also found a few more methods: http://www.johndcook.com/blog/2009/08/24/algorithms-convert-color-grayscale/ – An SO User Jun 14 '13 at 21:21
one up to your comment because of the luminosity method described there. I never thought about weighting the values like that. – Geeky Guy Jun 14 '13 at 21:25
I want to get more into image processing.. Where do I begin ?? – An SO User Jun 14 '13 at 21:25
@LittleChild I think [Programmers](http://programmers.stackexchange.com) is a good place to ask that. As for me, I learned a little on college, but never went into much depth on it. Now I wanna make videogames and I want to get more into it as well. – Geeky Guy Jun 14 '13 at 21:28

score 2 · Answer 2 · edited Jun 14 '13 at 21:36

2

The following code loads an image and cycle through its pixels, changing the saturation to zero and keeping the same hue and brightness values.

PImage img;

void setup () {
    colorMode(HSB, 100);
    img = loadImage ("img.png");
    size(img.width,img.height);
    color sat = color (0,0,0);

    img.loadPixels();

    for (int i = 0; i < width * height; i++) {
        img.pixels[i]=color (hue(img.pixels[i]), sat, brightness(img.pixels[i]));
    }

    img.updatePixels();
    image(img,0,0);
}

edited Jun 14 '13 at 21:36

Geeky Guy

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answered Jun 14 '13 at 21:33

user2468700

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No, He is using `Processing` which is a dialect of Java – An SO User Jun 14 '13 at 21:39

How to convert pixels to gray scale?

Update

2 Answers2

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