[majormajor]

> So long as the synthesized noise doesn't have an obvious temporal pattern, comparing stills should be fine.

The problem is that the initial noise-removal and compression passes still removed detail (that is more visible in motion than in stills) that you aren't adding back.

If you do noise-removal well you don't have to lose detail over time.

But it's much harder to do streaming-level video compression on a noisy source without losing that detail.

The grain they're adding somewhat distracts from the compression blurriness but doesn't bring back the detail.

[Thorrez]

>The grain they're adding somewhat distracts from the compression blurriness but doesn't bring back the detail.

Instead of wasting bits trying to compress noise, they can remove noise first, then compress, then add noise back. So now there aren't wasted bits compressing noise, and those bits can be used to compress detail instead of noise. So if you compare FGS compression vs non-FGS compression at the same bitrate, the FGS compression did add some detail back.

[strogonoff]

I imagined that at some point someone would come up with the idea “let’s remove more noise to compress things better and then add it back on the client”. Turns out, it is Netflix (I mean, who else wins so much from saving bandwidth).

Personally I rejected the idea after thinking about it for a couple of minutes, and I’m not yet sure I was wrong.

The challenge with noise is that it is actually cannot be perfectly automatically distinguished and removed from what could be finer details and textures even in a still photo, not to mention high-resolution footage. If removing noise was as simple as that, digital photography would be completely different. If you have removed noise, you can’t just add back missing detail later—if you could, you would not have removed it in the first place (alas, no algorithm is good enough, and even human eye can be faulty).

[Thorrez]

I'm not saying that the final result is as good as the original.

I'm saying that the final result is better than standard compression at the same bitrate.

[strogonoff]

That might be true; however, if this takes hold I would be surprised if they choose to keep producing and shipping the tasty grain high fidelity footage.

Considering that NR is generally among the very first steps in development pipeline (as that’s where it is the most effective), and the rest of dynamic range wrangling and colour grading comes on top of it, they might consider it a “waste” to 1) process two times (once with this new extreme NR, once with minimal NR that leaves the original grain), 2) keep around both copies, and especially (the costliest step) to 3) ship that delicious analog noise over Internet to people who want quality.

I mean, how far do we go? It’ll take even less bandwidth to just ship prompts to a client that generates the entire thing on the fly. Imagine the compression ratios…

[Thorrez]

That argument could be made to reject any form of lossy compression.

Lossy compression enables many use cases that would otherwise be impossible. Is it annoying that streaming companies drive the bitrate overly low? Yes. However, we shouldn't blame the existence of lossy compression algorithms for that. Without lossy compression, streaming wouldn't be feasible in the first place.