why does `imfill` fill the whole image?

Hi! I converted my image from HSV to bw, and then use `bwareaopen` to eliminate some background noise. After that I still find some 'holes' in the white disks that I need. So I was thinking to use 'imfill' to eliminate the holes. However, after 'infill', I either get a white image showing nothing (this happens when I didn't save the image out and directly called 'imfill' after `bwareaopen`) or the same image as after bwareaopen`. I don't understand why. Could somebody help me out? Thank you!

my codes:

bwIm2=bwareaopen(bwIm,10)
bw=imfill(bwIm2,'holes')

Answer 1

[Akira Agata]

You should delete light area connected to image border before applying imfill. By using imclearborder function before applying imfill, you can obtain the target image, like:

bwTmp = imclearborder(bwIm);
bw = imfill(bwTmp,'holes');

[Ziming Zhong]

Thank you!!!