There are other problems that occur when converting from one file format to another. One of the most vexing comes up when converting to a destination format that supports fewer colors than are contained in the original image.
Also, the number of colors in an image may not be a problem, but the specific colors contained in the original image may be. For example, consider the conversion of a 256-color image from one format to another. Both formats support images with up to 256 different colors in the bitmap, so the number of colors is not a problem. What is a problem, however, is that the source format chooses the colors that can go in the palette from a field of 16 million (24-bit palette), while the target format can store colors only from a range of 65,535 (16-bit palette). It is quite likely that the source image will contain colors not defined in the palette of the target image. The application doing the conversion will have to rely on some color aliasing scheme, which usually fails to provide satisfactory results.