how to make image transparent

I have an image like this

I want to make it transparent with a degree of transparency variable.

Answer 1

[Walter Roberson]

For example,

im = image(YourRGBImage);

for K = 0 : 20
  set(im, 'AlphaData', K/20);
  drawnow();
end

The form I used is for the case where you have the same transparency for the entire image. If you want to vary the transparency at different locations, then instead of setting the AlphaData to be a scalar, set it to be a double array with the same number of rows and columns as the image. Alpha of 0 is fully transparent and value of 1 is fully solid. (Do not use boolean for alpha data: MATLAB will complain about that.)

[kmla]

thank you for your answer but I'm working on a grey image. I use this code

   for c=1:0.1:3.9   
  for i =1:size(I1,1)
    for j=1:size(I1,2)
      S(i,j)=I1(i,j)*c;
    end
  end
figure, imshow(S)%
  end