Explain further. Do you want to crop? Are your extracted values from a rectangular or irregularly shaped region? How did you extract them? What are you going to do with this new matrix? Do you have the Image Processing Toolbox?
Where did you upload your image? http://www.mathworks.com/matlabcentral/answers/7924-where-can-i-upload-images-and-files-for-use-on-matlab-answers
Have you seen my Image Segmentation Tutorial: http://www.mathworks.com/matlabcentral/fileexchange/?term=authorid%3A31862
This would be a good thing to read before you post: http://www.mathworks.com/matlabcentral/answers/6200-tutorial-how-to-ask-a-question-on-answers-and-get-a-fast-answer