Transparency, like sound or video quality, is subjective. It depends most on the listener's familiarity with digital artifacts, their awareness that artifacts may in fact be present, and to a lesser extent, the compression method,
bit rate used, input characteristics, and the listening or viewing conditions and equipment. Despite this, sometimes a general consensus is formed for what compression options
should provide transparent results for most people on most equipment. Due to the subjectivity and the changing nature of compression, recording, and playback technology, such opinions should be considered only as rough estimates rather than established fact. Judging transparency can be difficult, due to
observer bias, in which subjective like or dislike of a certain compression methodology emotionally influences their judgment. This bias is commonly referred to as
placebo, although this usage is slightly different from the medical use of the term. To scientifically prove that a compression method is
not transparent,
double-blind tests may be useful. The
ABX method of
hypothesis testing is normally used, with a
null hypothesis that the samples tested are the same and with an
alternative hypothesis that the samples are in fact different. There is no way to prove whether a certain lossy compression methodology
is transparent using hypothesis testing, since in hypothesis testing, a null hypothesis cannot be proven; it can either be rejected or fail to be rejected. Even when an ABX test or any other comparison fails, that does not prove that there is no difference; it can only be said that the difference could not be proven. All
lossless data compression methods are transparent, by nature.
In image compression Both the DSC in
DisplayPort and the default settings of
JPEG XL are regarded as
visually lossless. The losslessness is usually determined by a
flicker test: the display initially shows the compressed and the original side-by-side, switches them around for a tiny fraction of a second and then goes back to the original. This test is more sensitive than a side-by-side comparison ("visually almost lossless"), as the human eye is highly sensitive to temporal changes in light. There is also a
panning test that is purportedly more representative of sensitivity in the case of moving images than the
flicker test. == Difference from a lack of artifacts ==