MATLAB: How to multiply binary image and rgb image in matlab

image processing

I have a binary image which is the segmented form of another color image . As you know , a binary image is 2-d but an rgb image is 3-d , how want to multiply them together ? i tried this code but an error is generated: function skinCrop(bwSkin,colorSkin)

for i = 1:size(colorImage,1)
    for j = 1:size(colorImage,2)
        if bwImage(i,j) == 0
            colorImage(i,j,:) = 0;
        end
    end
end
imshow(colorImage);
end

and here there is the error:

Index exceeds matrix dimensions.

Best Answer

There are several ways to do what you want, though bsxfun() is the method I usually use (though it's more cryptic than the .* straightforward method). I first learned that from Sean DeWolski of the Mathworks. However, if bwImage is not the same integer type as colorImage, you will have to modify it.

% Mask the image using bsxfun() function
maskedRgbImage = bsxfun(@times, colorImage, cast(bwImage, 'like', colorImage));

If they're already both the same data type, then having cast in there won't hurt so I always put it in there regardless.

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MATLAB: Creation of a mask on RGB image

Instead of multiplying pixels in the mask by a constant value, you can mulitply all pixels by an "image" of the saturation multiplier.

So rather than the scalar "1.6", which could as well have been a element-by-element multiplication, your original strategy could have been executed as

[M,N] = size(Imm)
satFactorMat = 1.6*ones(M,N);
satFactorMat(binaryImage) = 1.6;
saturationImage = saturationImage .* satFactorMat;

So now hopefully it is clear you don't really need the mask concept for the operation of altering the image itself, you just might use it to define the satFactorMat "topography", which looks like a mesa.Now you can just smooth it out using something like a smoothing function; you can use imgaussfilt

satFactorMat = imgaussfilt(satFactorMat,6);

You may need to convert everything to doubles first before doing the imgaussfilt and elementwise multiplication, and then convert back to uint8.

Also, note that multiplying is dangerous because you may end up with values outside valid range (>255). So it would be safe to exponentiate (but then you have to normalize your pixel values onto (0,1) first.

hsvImage = double(hsvImage)/255;
% ... everythign in between
% except instead of multiply by satFactorMat, you can do something like
satPowerMat = ones(M,N);
satPowerMat(binaryImage) = 0.3;
satPowerMat = imgaussfilt(satPowerMat,6);
saturationImage = saturationImage .* satPowerMat;
% Recombine
hsvImage = cat(3, hueImage, saturationImage, valueImage);
hsvImage = uint8(hsvImage*255);

MATLAB: How can we map binary image on original RGB image

Try this:

% Mask the image.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));

where mask is your binary image.

Best Answer

Related Solutions

MATLAB: Creation of a mask on RGB image

MATLAB: How can we map binary image on original RGB image

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