Transparency (data compression): Difference between revisions

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In [[data compression]] and [[psychoacoustics]], '''transparency''' is the result of [[lossy data compression]] accurate enough that the compressed result is [[perception|perceptually]] indistinguishable from the uncompressed input, i.e. '''perceptually lossless'''. In other words, transparent compression has no perceptible [[compression artifact]]s.

A '''transparency threshold''' is a given value at which transparency is reached. It is commonly used to describe compressed data bitrates. For example, the transparency threshold for MP3 to [[linear PCM]] audio is said to be between 175 and 245&nbsp;kbit/s, at [[44.1 kHz|44.1&nbsp;kHz]], when encoded as [[Variable_bitrate|VBR]] MP3 (corresponding to the -V3 and -V0 settings of the highly popular [[LAME]] MP3 encoder).<ref name="LAME Recommended Encoder Settings">{{citation

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== Difference from a lack of artifacts ==

A perceptually lossless compression is always free of [[compression artifacts]], but the inverse is not true: it is possible for a compressor to produce a signal that appears natural-looking imagebut with altered contents. Such a confusion is widely present in the field of [[radiology]] (specifically for the study of [[diagnostically acceptable irreversible compression]]), where ''visually lossless'' is taken to mean anywhere from artifact-free<ref>{{cite journal |author=European Society of Radiology |title=Usability of irreversible image compression in radiological imaging. A position paper by the European Society of Radiology (ESR) |journal=Insights into Imaging |date=April 2011 |volume=2 |issue=2 |pages=103–115 |doi=10.1007/s13244-011-0071-x |doi-access=free |pmid=22347940 |pmc=3259360}}</ref> to being indistinguishable on a side-to-side view,<ref>{{cite journal |last1=Kim |first1=Kil Joong |last2=Kim |first2=Bohyoung |last3=Lee |first3=Kyoung Ho |last4=Mantiuk |first4=Rafal |last5=Richter |first5=Thomas |last6=Kang |first6=Heung Sik |title=Use of Image Features in Predicting Visually Lossless Thresholds of JPEG2000 Compressed Body CT Images: Initial Trial |journal=Radiology |date=September 2013 |volume=268 |issue=3 |pages=710–718 |doi=10.1148/radiol.13122015|doi-access=free }}</ref> neither being as stringent as the ''flicker'' test.

==See also==