Any pixel image needs to be enlarged equally on the X and Y axis, where the new height and width are factors of the original height and width. E.g. if you have a 16x16 image, you can enlarge it to 32x32, or 64x64 and have it not be distorted. By the same token if you enlarge a 16x16 image up to 24x24, there is no way to evenly distribute the pixels and you will get nixels/distortion.