[HN Gopher] Film grain synthesis in AV1 (2019)
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Film grain synthesis in AV1 (2019)
Author : pantalaimon
Score : 31 points
Date : 2022-07-18 21:08 UTC (1 hours ago)
(HTM) web link (norkin.org)
(TXT) w3m dump (norkin.org)
| NonNefarious wrote:
| I had no idea AV1 or any other codec provided for this. Pretty
| interesting!
|
| What would undermine it is imperfect removal of real noise or
| grain from the source material: Then you'd have some remnants of
| the original grain, plus the synthesized grain... an incorrect
| result. It seems that this scheme requires perfectly clean input
| images.
|
| I hope this idea is taken further, and it becomes the norm among
| codecs or wrappers to provide room for an author-defined post-
| processing shader to be applied after decompression.
| asojfdowgh wrote:
| the synthesized noise only covers what is removed by the
| denoiser, so it all adds up to what the input is (assuming the
| left-in noise makes it through the encoder)
| adgjlsfhk1 wrote:
| It really doesn't. The whole reason this technique works is
| that our brain generally processes effects like noise and grain
| in terms of macro properties, and even if none of the pixels
| are anywhere like the right value, it will still look "right"
| as long as the noise distribution is closish.
| klodolph wrote:
| Various audio codecs have the same thing. They will synthesize
| background noise. The amount of background noise and the rough
| frequency spectrum are encoded in the stream.
|
| If you removed the noise, it would sound a bit weird. For
| telephone calls in particular, the background noise lets you
| know that the phone call is connected. If you filter it out,
| people think that the call was dropped.
| detaro wrote:
| In the phone case it's even called "comfort noise"
| babypuncher wrote:
| I'm not sure I like the idea of a film's photography
| potentially looking different based on the decoder used. I
| would much rather dedicate additional bits to preserving the
| noise that was present in the original film stock or added
| during post-production.
|
| Storage and bandwidth are only getting cheaper.
| rootw0rm wrote:
| Film grain synthesis? Oh man, I don't know how I feel about this
| one. Without viewing any comparisons, my first reaction is...why
| not just higher bitrate instead?
| Ameo wrote:
| Film grain is similar to noise which by definition compresses
| extremely poorly. By actually modeling the way the film grain
| is produced, they can avoid sending what is essentially random
| data over the wire while still preserving the visual effect of
| the film grain itself. That way, the bitrate can be spent to
| encode the actual video data at a higher quality.
| simbas wrote:
| you did a good job
| pornel wrote:
| This can be said about every lossy compression technique. Why
| do quantization that throws away details, and not send higher
| bitrate instead? Why do edge prediction that can smudge things,
| and not send higher bitrate instead? Why do inter-frame
| prediction which can cause wobbly motion and not send higher
| bitrate instead?
|
| The answer always is that the technique allows better use of
| bandwidth, so you can have a better image without increasing
| bandwidth. Or if you're able to increase the bandwidth, you can
| have _even better_ picture with the technique than without it
| (until the bandwidth is so high that you can send the video
| uncompressed, but that 's not happening anytime soon for video
| on the web).
| babypuncher wrote:
| Think of how much money Netflix saves by streaming movies to
| your TV at 5mbps instead of 10mbps. Serving a single user,
| the cost difference is negligible, but across 120 million
| users it probably saves them millions in bandwidth costs.
|
| I still buy blu-rays though so I am a firm believe in the
| "just throw more bits at it" solution.
| klodolph wrote:
| I like this quote from the article,
|
| > The correct answer to this question is that often the choice
| is not between the original film grain and the synthesized one.
| When video is transmitted over a channel with limited
| bandwidth, the choice is often between not having the film
| grain at all (or having the grain significantly distorted by
| compression) and having synthesized grain that looks
| subjectively similar to the original one.
|
| Film grain doesn't compress well. If you buy a 1080p Blu-ray
| disk, you can get a bit rate of something like 40 Mbit/s. Go
| watch 1080p video on Netflix, and you're going to get something
| closer to 5 Mbit/s. Yes, the codecs are different--yes, you can
| talk all you want about how everything is going to be fast when
| we all get 5G--but this is still the ground reality that most
| people are working with. The bit rate is more of a constraint
| you have to work within than a variable you can just tweak to
| get the results you want.
|
| By comparison, ProRes 422 has a target bit rate of 147 Mbit/s
| for 1920x1080@29.97.
| babypuncher wrote:
| Blu-Ray came out 16 years ago and streaming services still
| haven't really caught up in image quality. Physical media
| still has some life left in it.
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