The pixel resolution is determined and fixed by the size of the image matrix. If you increase the image size using imresize() it will give you more pixels but don't be deceived that this gives you more resolution physically in the real world. You can increase the number of pixels all you want and it won't give you more real resolution. In other words, if an image is blurry, scaling up the number of pixels by a thousand in each dimension will not now suddenly let you resolve points a thousand times closer together. It will still be a blurry image, just bigger.