The Digital Fact Book - Quantel

DDynamic Rounding ®Dynamic Rounding is a mathematical technique devised by Quantel for truncating the wordlength of pixels to a specified number of bits. Rather than simply ignoring the lower bits,it uses their information to control, via a randomizer, the dither of the LSB of the truncatedresult. This effectively removes the artifacts, such as banding, that could otherwise be visible.Dynamic Rounding is non-cumulative on any number of passes and produces statisticallycorrect results. Earlier attempts at a solution have involved increasing the number of bits,making the size of LSBs smaller but not removing the inherent problem.Some form of limiting the number of bits is required as there are many instances in digitalsystems where a number, representing a pixel value, uses more bits than the systemnormally accommodates. For example, a nominally 12-bit system might have a problemhandling a 24-bit word. This has to be rectified in a way that will keep as much informationas possible and not cause noticeable defects – even after many processes. A commonexample is image processing which generally involves multiplying the pixel values of twoimages, as in digital mixing. Assuming the equipment is nominally 12-bit, the mixing producesa 24-bit result from two original 12-bit numbers. At some point this has to be truncated,or rounded, back to 12-bits either to fit within the structure of the equipment or to beaccepted by external interfaces. Simply dropping the lower bits can result in unwantedvisible artifacts especially when handling pure, noise-free, computer generated pictures.16 bits to 8 bits16 8 Higher order8Lower orderCarry in8APseudo-random binarysequence generatorA > B8BDynamic Rounding is licensable from Quantel and is used in a growing number of digitalproducts both from Quantel and other manufacturers.See also: Digital mixing, LSB78