bwdist is computing image complement

I have a binary image and used bwdist on the image and the resulting image was the exact compliment of the original image. I thought that bwdist would return a grayscale image based (obviously) on the distance transform. The original image is essentially an asymmetric blob of white surrounded by black, so I expected bwdist to return the same shape but with blurred borders (I need the distance transform data so just blurring the edges is not an option). Am I just expecting something that this function does not do?

Answer 1

[Sean de Wolski]

It is probably not just the complement as you suspect. You're probably viewing it on the range [0 1] so values greater than or equal (all false values in the original) appear to be true. What is returned if you enter:

range(D(:)); %D is the output of bwdist

try viewing a slice of it over the whole range, i.e.:

imshow(D,[]);

or

imtool(D); %play with adjust contrast button.

[Christopher]

Ok I get it. I didn't realize bwdist returned unscaled values. Thanks