colon cleanse

How does a comercial colon cleanse differ from what we do in preparing for a colonoscopy? I've got pictures of my colon and it looked pretty darn clean a couple months ago, LOL... I am on a very healthy diet (fruits, veggies, yogurt,whole grains & seeds plus a probiotic and vitamins)and have very regular bowel movements but I had an abdominal x-ray last week and the Doc reading it said it looked like I was constipated. He was surprised to hear I have a very regular schedule for pooping (once in morning, afternoon and sometimes at night). He suggested a laxative but I go fine without it. I was wondering if maybe I'm not processing everything. Any suggestions?