how to change the pixel value of an image

i have an image and i need to change the pixel value of that image in any co-ordinate.

Answer 1

[Jeff E]

Assuming a grayscale image:

>> img = uint8([10 30 50 ; 3 4 10])

img =

   10   30   50
    3    4   10

>> img(2,2) = 0

img =

   10   30   50
    3    0   10

>>