How to convert image from double to uint8 in matlab?

Question

I have an image I which is of type double. I want to convert the image from double to uint8. I have tried using both:

1. I=uint8(I)
2. I=im2uint8(I).

When I use the imshow(I) command, I get only a black image and nothing else. What am I doing wrong?

Answer 1

The im2uint8 function assumes that your double image is scaled to the range [0,1]. If your image has values larger than 1 or smaller than 0, these values will be clipped. See the following example:

im2uint8([-1 0 0.5 1 2])
ans =
    0    0  128  255  255

The solution is to scale the input image to [0,1] by subtracting the minimum value and dividing by the total range:

I = (I - min(I(:))) / (max(I(:)) - min(I(:)));
I = im2uint8(I);
imshow(I);