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

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

Answer 1

[Image Analyst]

If f1 is a uint8 RGB image, you can set

f1(~mask) = 255;

See attached masking demo, attached below this image it creates:

[Martha]

Thank you very much! It works very well, and thanks as well for the masking demo.

[Me Fernz]

Hello what if the image that will be used is an RGB image? I have tried the code but it does not apply. please help! thank you!

[Image Analyst]

Use bsxfun()

[Me Fernz]

Thank you!!

[Image Analyst]

% Mask the image using bsxfun() function to multiply the mask by each channel individually.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));