how to divide an image into 2x2 blocks and then work on each block seperately pixel by pixel?

in each block , I want to check that if a single pixel is colored (if r ,g and b components of that pixel come to be equal then its a grayscale otherwise that will be colored ) then the rest of the three pixels should get the value of that pixel and if 2 pixels are colored then their average should be given to all the 4 pixels.

[Walter Roberson]

Duplicate with less information is at http://www.mathworks.com/matlabcentral/answers/11894-how-to-traverse-an-image-in-2x2-block-wise-wayand-then-check-suitable-conditions

Answer 1

[Sean de Wolski]

alleq = all(bsxfun(@eq,I(:,:,1),I(:,:,2:3)),3);  %find equal planes
blkproc(alleq,[2 2],@(x)any(x(:))) %traverse em'

Answer 2

[lola]

   I = imread('tire.tif');
   f = @(x) uint8(round(mean2(x)*ones(size(x))));
   I2 = blkproc(I,[2 2],f);
   imshow(I)
   figure, imshow(I2);
if you need any other rgb images you need to convert it first to gray(rgb2gray)