Assertions should be used as a debugging feature only. You may use them for sanity checks that test for conditions that should always be TRUE and that indicate some programming errors if not or to check for the presence of certain features like extension functions or certain system limits and features.

Beginning with PHP 4.3, bits and channels are present for other image types, too. However, the presence of these values can be a bit confusing. As an example, GIF always uses 3 channels per pixel, but the number of bits per pixel cannot be calculated for an animated GIF with a global color table.