Various computer techniques are used to deal with the conversion of one aspect ratio pixel to another as well as the change in resolution and size. Some of these conversion techniques are superior to others and image artifacts can be introduced when size and aspect ratio changes are made if improper techniques are selected. For example, shrinking the resolution of a finely scanned image can accentuate the grain noise if one does not average together pixels that will be grouped together. This inappropriate technique is called re-sampling as opposed to the preferred technique of averaging, but it is often done because of it's speed. Similarly, when up-sampling an image because of the need for additional pixels in the output, many alternative techniques can be used.
Pixel replication is a simple and speedy operation.
It involves copying a pixel when an additional pixel is required. Unlike interpolation, a more complicated technique, replication can introduce jagged artifacts along edges in the resulting image. Care should be taken in selecting software that uses the proper techniques for changing the image size. For example, we could say, for a black and white image, that we have only 256 different shades of gray that we can paint onto any one tile. In this case we could express the dynamic range as having 256 levels or 8 bits.