How can I substitute values in a matrix if they equal a certain value?

I have two matrices X1 and X2 (both have dimensions 512x512) I would like to write code to create a new matrix that has the element values from X1 in, unless the element equals 255- in which case I would like to use the element from the same coordinate from X2 instead.

I hope this makes sense! Thanks for your help :)

Answer 1

[Mischa Kim]

Claire, you could use something like

 X3 = X1;
 X3(X1==255) = X2(X1==255);

[Claire]

Thanks :)

Answer 2

[lvn]

I hope this is what you mean:

newmatrix=X1;
newmatrix(X1==255)=X2(X1==255);

[Claire]

Thanks :)