Change a single pixel value in a Grayscale JPEG image

I have a grayscale jpeg image X. I want to change its pixel value. For example change pixel at (14,20) to 1,How can I do it. I tried the following but it doesn't WORK:

Xc=X; %Xc is image with a pixel value changed from X[X is original image]
X(14,20); %What is the value at 14,20

Xc(14,20)=1 %Change Pixel value at 14,20 to 1

When i view its values in Variable Editor,I don't get value changed at (14,20) in Xc image.

What are the Errors or suggestion?

Answer 1

[Thomas]

Are you sure you are checking Xc in the variable editor, you might be checking X (original image). the above does work..

I have tried

X=imread('1.jpg')   % My image was color so was MxNxP
Xc=X(:,:,1)         % crateda  grayscale image MxN
Xc(14,20)     % here my output was ans=129
Xc(14,20)=1   % changed the value of (14,20) to 1
Xc(14,20)      % here my output was ans=1

If I change a block of values in Xc to 1 and do the imshow(Xc) - gives me a black box..

[LOKESH]

Thanks I made mistake while reading axes..