How to replace a value in a matrix of pixels using matlab ?

I have a 225*225 image.I don't know how to replace a pixel value using indices value.please reply as soon as possible.

Thanks in advance.

[dhaarani chandrasekaran]

I have tried this code.But I am trying to replace values in a matrix based on some conditions without loop. please reply as soon as possible.

Answer 1

[mizuki]

If you want to replace the pixel (i,j)=(100,125) of the variable img with 0.2, use the following code:

i = 100;
j = 125;
img(i,j) = 0.2;