Algorithm for converting RGB image to Grayscale in detail

Simple steps to convert RGB image to Grayscale

Answer 1

[Walter Roberson]

http://www.johndcook.com/blog/2009/08/24/algorithms-convert-color-grayscale/

http://en.wikipedia.org/wiki/Grayscale#Converting_color_to_grayscale

Note: the formula in that Wikipedia section is for the sRGB color space. rgb2gray() uses a different formula, based upon the assumption that the values are in a linear colorspace instead of in sRGB.

Answer 2

[Image Analyst]

One way:

grayImage = rgb2gray(rgbImage);

Another way is to take one color channel:

grayImage = rgbImage(:, :, 2); % Take green channel.

Some useful formulas are here:

http://www.easyrgb.com/index.php?X=MATH

[Rawan hamdi]

This is my code and i get an error which says Index exceeds matrix dimensions.

Error in ==> graysc at 14 gray(i,j) = 0.29 * rgb(:,:,1) + 0.59 * rgb(:,:,2) + 0.11 * rgb(:,:,3);

%%code

function [gray] = graysc(input)

rgb = double(imread(input));

[h,w,k] = size(rgb);

gray = zeros(h,w,k);

    for i = 1 : h

        for j =1 : w

          % Assume you have an RGB image of class double, or create a random one

    gray(i,j) = 0.29 * rgb(:,:,1) + 0.59 * rgb(:,:,2) + 0.11 * rgb(:,:,3);

         end
    end

imshow(gray);

end

[Image Analyst]

What is the value of k? It should be 3. Then, don't use k when you allocate space for gray with zeros(). Just do

gray = zeros(h, w);