Dither is an intentionally applied form of noise used to randomize quantization error, preventing large-scale patterns such as color banding in images. Dither is routinely used in processing of both digital audio and digital video data, and is often one of the last stages of audio production to compact disc.
Hepatic porphyria. Hepatic porphyrias is a form of porphyria in which the enzyme deficiency occurs in the liver. Examples include (in order of synthesis pathway): Acute intermittent porphyria. Porphyria cutanea tarda and Hepatoerythropoietic porphyria.
This enzyme is down-regulated by heme. The four acute hepatic porphyrias are due to different enzyme deficiencies (Table 1). The most common of these is acute intermittent porphyria (AIP), but the others can produce the same neurovisceral symptoms. The enzyme deficiency limits the capacity of the liver to increase heme synthesis.