Not showing foreground in smooth transitions - matlab

Question

I would like to achieve image blending with smooth transitions using alpha blending using and smoothed mask. I used Gaussian filter for the mask and now I'm trying to combine the other two images. I'm using the smoothed mask as a weight.
x_i and y_i .... color information for pixel i
alpha_i ... value of the mask in pixel i
formula: z_i = alpha_i*x_i + (1 - alpha_i)*y_i
My attempt:
mask = imread('mask.png');
foreground = imread('fg.jpg');
background = imread('bg.jpg');
[r,c,~]=size(mask);
A = zeros(size(foreground),'like', foreground);
fspe = fspecial('gaussian', 100);
smoothMask = imfilter(double(mask), fspe, 'same');
for i=1:r
for j=1:c
for d=1:3
alpha = mask(i,j,d);
A(i,j,d) = alpha*foreground(i,j,d)+(1-alpha)*background(i,j,d);
end
end
end
imshow(A);
In the end I get the background but the foreground is white. Please help.

Answer 1

Your A is of type double and in range [0..255]. When imshowing images of type double the expected scale is [0..1] this is why all pixels are shown saturated.
Fix:
imshow(A,[])
Or
imshow(A/255)
A word about vectorization: In Matlab it is quite redundant to explicitly loop through all rows columns and channels just to multiply and sum images (3D arrays). It can be easily done
A = mask.*foreground + (1-mask).*background;
Isn't it lovely?
Note the difference between * operator and .* operator - it's the difference between matrix multiplication and element-wise multiplication.