MATLAB: How to create a mask on an image and have the background white

imageImage Processing Toolboxmaskwhite background

Hi, I create a mask into an image and I did this:
i=roipoly(f1,p1,p2);
mask=repmat(i,[1,1,3]);
f1(~mask)=1;
imshow(f1)
and it work very well but my problem is that I want to have the background white instead of black. How can I create a mask into an image, leaving a region of interest as it is (image) and all the rest as color white?
I appreciate some suggestions. Martha

Best Answer

If f1 is a uint8 RGB image, you can set
f1(~mask) = 255;
See attached masking demo, attached below this image it creates:
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