alt Hacker NewsThis is very impressive, but “perceptually lossless” isn’t a thing and doesn’t make sense. It means “lossy”.
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I read “perceptually lossless” to be equivalent to “transparent”, a more common phrase used in the audio/video codec world. It’s the bitrate/quality at which some large fraction of human viewers can’t distinguish a losslessly-encoded sample and the lossy-encoded sample, for some large fraction of content (constants vary in research papers).
As an example, crf=18 in libx264 is considered “perceptually lossless” for most video content.
Can you propose a better term for the concept then? Perceiving something as lossless is a real world metric that has a proper use case. "Perceptually lossless" does not try to imply that it is not lossy.
why not? if you change one pixel by one pixel brightness unit it is perceptually the same.
for the record, I found liveportrait to be well within the uncanny valley. it looks great for ai generated avatars, but the difference is very perceptually noticeable on familiar faces. still it's great.
It means what it already says for itself, and does not need correcting into incorrectness.
"no perceived loss" is a perfectly internally consistent and sensible concept and is actually orthogonal to whether it's actually lossless or lossy.
For instance an actually lossless block of data could be perceptually lossy if displayed the wrong way.
In fact, even actual lossless data is always actually lossy, and only ever "perceptually lossless", and there is no such thing as actually lossless, because anything digital is always only a lossy approximation of anything analog. There is loss both at the ADC and at the DAC stage.
If you want to criticize a term for being nonsense misleading dishonest bullshit, then I guess "lossless" is that term, since it never existed and never can exist.
Why don't you think it's a thing? A trivial example is audio. A ton of audio speakers can produce frequencies people cannot hear. If you have an unprocessed audio recording from a high end microphone one of the first compressions things you can do is clip of imperceptible frequencies. A form of compression.
As there are several patents, published studies, IEEE papers and thousands of google results for the term, I think it's safe to say that many people do not agree with your interpretation of the term.
"As a rule, strong feelings about issues do not emerge from deep understanding." -Sloman and Fernbach
It is definitely a thing given a good perceptual metric. The metric even doesn't have to be very accurate if the distortion is highly bounded, like only altering the lowermost bit. It is unfortunate that most commonly used distortion metrics like PSNR are not really that, though.
Yeah, all lossy compression could be called "perceptually lossless" if the perception is bad enough...
Is this the real-time discussion all over again?
It may sound like marketing wank, but it does a appear to be an established term of art in academia as far back as 1997 [1]
It just means that a person can't readily distinguish between the compressed image and the uncompressed image. Usually because it takes some aspect(s) of the human visual system into account.
[1] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C22&q=per...