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Old 23rd November 2019, 17:30   #7217  |  Link
Ajvar
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Join Date: Jul 2014
Posts: 115
Quote:
Originally Posted by benwaggoner View Post
Grain is essentially uncompressible random noise. It's random spatially and temporally, includes chroma, and is typically very high frequency. So it can use the vast majority of bits encoding a frame, is sensitive to QP differences between I, P, B, and b frames, and is otherwise a worst-case nightmare.

While encoding 4K content might take only 2x the bitrate as 1080p, doing grain is much more linear. 80 Mbps 4K is only twice that of Blu-ray 1080p. There are cases of grain that is quite literally impossible to encode without perceptible artifacts. Heck, just encoding a flat gray slide with JUST grain on it can be very challenging.

And that grain, even in lossless, can be quite distracting to a viewer. There's certainly way more fine detail grain on the Blade Runner Blu-ray than Ridley Scott ever saw when he was working on it, due to perf screens, dimmer projectors, etcetera.
I remember years ago when x265 was at stage of v1.6 - 1.7 people complained about default denoising of HEVC. I remember a grey wall all in terrible grain and HEVC encode then made grain disappear like it never existed and without any artificial look. People complained at x265 encoder exactly for this. Just saying.
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