I just recently started out with Image processing and taken up a course related to it in Grad school. But I already have a project to do without too much information about the subject, however I've made some steady progress. I am trying to segment the pills from their respective backgrounds. For images with contrasting backgrounds, I've been able to segment the pills using Otsu's method. With regards to images with similar backgrounds, Otsu's method doesn't quite work. I've been reading quite a few papers with regards to segmenting, but most of the papers that I've read use a manual thresholding value depending upon the kind of image. Is it possible to detect the correct thresholding value and automatically threshold an image and use techniques such as seed-growing or clustering to segment the image ?

The color space I've been using is Lab*, so I'd appreciate it if you could recommend the appropriate color space that I should be using too.

The images in question:

original 1

result 1

original 2

result 2

original 3

result 3