Image classification using KNN

Hello, I have my bajor paper deadline soon and I have to clasify some Chest X-Rays using KNN. I calculated the histogram for each lung and made an excel with the results. My teacher wants me to extract one image from the date base and compare it's histogram with the other ones to determine the diagonst but I really cannot manage to do this. Can anyone help me please?

[Image Analyst]

I've never heard of a "diagonst". What is it? In the meantime, I've attached a KNN demo. Also check out imhist() and knnsearch().