How do I create an RGB image mask using a 2-D logical matrix?

I am trying to create an image mask using a logical 2-D matrix as the mask. The 3-D image matrix and the 2-D mask matrix are the same dimensions. Wherever the logical mask is true, I want to keep the image as is. Where the mask is false, I want to change the intensity of the image. How do I go about doing this?

Here is my attempt so far:

[ maskedImage ] = maskImage( input_image, mask_image )

red = input_image(:, :, 1);
green = input_image(:, :, 2);
blue = input_image(:, :, 3);

if mask == 1
   input_image(:, :, 1) = red;
   input_image(:, :, 2) = green;
   input_image(:, :, 3) = blue;
else
   input_image(:, :, 1) = red .* 0.3;
   input_image(:, :, 2) = green .* 0.3;
   input_image(:, :, 3) = blue .* 0.3;
end

maskedImage = input_image;

end

I know that my indexing is incorrect, because I want to change the values in the image matrix where the values in the mask matrix are false, but I don't know how. I apologize if this has been asked, but I could not find an answer regarding a transparent mask.

Answer 1

[Stephen23]

Try this instead:

function imgDat = maskImage(imgDat, maskIdx)

maskIdx = repmat(maskIdx,[1,1,3]);
imgDat(~maskIdx) = imgDat(~maskIdx) * 0.3;

[iceburg]

Thanks! That worked like a charm!

[Stephen23]

Glad to help. You can also Accept answers that solve your question... this is always appreciated :)