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AV1@Scale: Film Grain Synthesis, The Awakening

(netflixtechblog.com)
252 points CharlesW | 7 comments | 03 Jul 25 16:34 UTC | HN request time: 1.091s | source | bottom
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fidotron ◴[03 Jul 25 17:02 UTC] No.44457084[source]▶
There are definite philosophical questions over the merits of adding noise, but the problem with their example here is their denoising process appears to excessively blur everything, so both it and the synthesized grain image look noticeably less sharp than the source. The grain itself also looks too much like basic noise, and not really grain like.
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1. dperfect ◴[03 Jul 25 17:45 UTC] No.44457483[source]▶
> both it and the synthesized grain image look noticeably less sharp than the source

That's true, but at a given bitrate (until you get to very high bitrates), the compressed original will usually look worse and less sharp because so many bits are spent trying to encode the original grain. As a result, that original grain tends to get "smeared" over larger areas, making it look muddy. You lose sharpness in areas of the actual scene because it's trying (and often failing) to encode sharp grains.

Film Grain Synthesis makes sense for streaming where bandwidth is limited, but I'll agree that in the examples, the synthesized grain doesn't look very grain-like. And, depending on the amount and method of denoising, it can definitely blur details from the scene.

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2. bee_rider ◴[03 Jul 25 18:27 UTC] No.44457879[source]▶
It seems like a shame that they didn’t include a screenshot of the original (with natural grain), after suffering from low-bitrate streaming. Aka the actual baseline.

I can see why they want to compare against the actual local copy of the video with the natural grain. But that’s the perfect copy that they can’t actually hope to match.

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3. joemi ◴[03 Jul 25 18:36 UTC] No.44457965[source]▶
> It seems like a shame that they didn’t include a screenshot of the original (with natural grain), after suffering from low-bitrate streaming.

Isn't that the image captioned "Regular AV1 (without FGS) @ 8274 kbps"?

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4. Zee2 ◴[03 Jul 25 18:42 UTC] No.44458017[source]▶
They did.
5. bee_rider ◴[03 Jul 25 18:51 UTC] No.44458092{3}[source]▶
I think I misread the figures.

But still, they have:

> A source video frame from They Cloned Tyrone

> Regular AV1 (without FGS) @ 8274 kbps

> AV1 with FGS @ 2804 kbps

Just to emphasize the problem, would it be nice to see:

Regular AV1 (without FGS) @ 2804 kbps

It should look really bad, right? Which would emphasize their results.

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6. zerocrates ◴[03 Jul 25 18:54 UTC] No.44458114{3}[source]▶
I think the distinction here is, they provide the "regular" stream, and the FGS stream noting that it's much smaller yet looks similar. What they don't have is a lower-bandwidth "regular" one, what 2000-or-so kbps looks like without FGS.
7. joemi ◴[03 Jul 25 20:33 UTC] No.44458934{4}[source]▶
But why do they need to emphasize it even more than the examples they gave? The "AV1 with FGS @ 2804 kbps" already looks as good or better than the "AV1 (without FGS) @ 8274 kbps", so it'll definitely look better than AV1 without FGS at an even lower bandwidth.