Definition: | unit for evaluating the subjective degradation of a picture under specified conditions of observation, derived from a reference image which has a medium rating using a given quality scale or impairment scale
NOTE 1 – Under certain conditions the imp units are summable, in the sense that the subjective degradation due to several non-correlated faults is the sum of the degradations due to each fault considered separately.
NOTE 2 – The method of use of imp units is described in CCIR Report 405.
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