Segmenting fruits

My task is, to write a code in Matlab which one segments the fruits you can see on the picture below. So i should make 3 pictures, one where you can only see the orange, one with only grapefruit, and one with only lemon. Of course everything else should be black except the segmented object. I tried many methods but none of them worked for me. I guess i'm a bit newbie at image processing, so every helping hand would be great. Thank you. http://ift.tt/19whDjR