madVR - high quality video renderer (GPU assisted)

[Warez]

Originally Posted by huhn

@Warez
check your levels maybe they are over exposed and the fine gradian is cut out.

May i ask where can i find these things?
What levels? brightness?

[Sunspark]

Out of curiosity, does anyone here downscale 4K to HD in order to get the full chroma that comes with it, instead of upscaling chroma at HD using one of the scaling algorithms?

This video is interesting to contemplate https://youtu.be/kIf9h2Gkm_U

According to that video, if the source is 4K one would get free 4:4:4 chroma in addition to the luma when downscaling to HD.

Where MadVR is concerned you can downscale using DXVA2 in the GPU, or you can do it in software with the pixel shaders such as cubic.

I wonder how noticeable the difference is, upscaling chroma vs downscaling from 4K?

I took a quick look, the HUD says it is still upscaling the chroma.

[ryrynz]

Originally Posted by Sunspark

I wonder how noticeable the difference is, upscaling chroma vs downscaling from 4K?

Not much different which is why they do it. Noticeable on certain test patterns and situations only.

[huhn]

Originally Posted by Warez

May i ask where can i find these things?
What levels? brightness?

depends on the TV.
level setting doesn't have to be identical between 2 display modes like SDR and HDR.
they have al kinds of names.

Originally Posted by Sunspark

Out of curiosity, does anyone here downscale 4K to HD in order to get the full chroma that comes with it, instead of upscaling chroma at HD using one of the scaling algorithms?

This video is interesting to contemplate https://youtu.be/kIf9h2Gkm_U

According to that video, if the source is 4K one would get free 4:4:4 chroma in addition to the luma when downscaling to HD.

Where MadVR is concerned you can downscale using DXVA2 in the GPU, or you can do it in software with the pixel shaders such as cubic.

I wonder how noticeable the difference is, upscaling chroma vs downscaling from 4K?

I took a quick look, the HUD says it is still upscaling the chroma.

not really true well known and wrong at the same time.

you can not downscale the 4K luma to FHD and match the chroma channel that easily it still needs a X shift that's a scaling operation chanaging every chroma pixel.
DXVA2 and what ever browser do as downscaling is so terrible the luma channel will get massive damage.

you unchecked scale chroma separately from luma if it saves performance so it is still scaling chroma first else it wouldn't.

assuming a lossless encode and the same scaling algorithm downscaling 4K to 1080 instead of getting a 1080 source would always be better to bad they don't do that.

[flossy_cake]

Chroma subsampling is another annoying problem that we're saddled with for generations. It's a terrible thing that is baked into every video, just like interlacing used to be baked into every video and creates problems. Of course under ideal conditions it shouldn't be noticeable, but I sold a Panasonic OLED because its chroma upscaling was broken and looked bad even at 3.5m viewing distance - I could see the chroma jaggies at 3.5m, not pixel peeping. I've encountered many older TV shows with wrong chroma position baked into the source. I can fix this with Avisynth script but it's a pain and changes from season to season, or episode to episode. Even one of my local TV stations has wrong chroma position. Many TV channels using wrong colourimetry as well.

Unless you get the chroma position exactly correct then it may not be "true 1080p" supersampled from 4k. It's kind of interesting how we can spot chroma position errors with our eyes, but very difficult to come up with an algorithm to detect it in the source. From algorithm's perspective, there is no way to know if that chroma is supposed to be hanging over the edge, or if it's bad position. But when we look at it we can tell it's not supposed to be like that.