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Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 15:28
by cosmoxl
I've made lanczos3 as default scaler and I guess it's working.
However, when 720p50/60 videos are played and 720p50/60 is output the scaler used is nearest neighbor.
I understand that no luma scaling is having to be done as the resolutions match, but there's always chroma upscaling isn't there?
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 16:34
by davilla
cosmoxl wrote: 05 May 2018, 15:28
I've made lanczos3 as default scaler and I guess it's working.
However, when 720p50/60 videos are played and 720p50/60 is output the scaler used is nearest neighbor.
When display matches video, there is no scaling, yes ? It would be a 1:1 pixel match.
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 16:43
by koying
cosmoxl wrote: 05 May 2018, 15:28
I understand that no luma scaling is having to be done as the resolutions match, but there's always chroma upscaling isn't there?
Upscalers are applied on the RGB tranformation of the YUV frames.
Interpolating chroma doesn't make sense, as 1 chroma pixel applies to 4 luma pixels per definition (for yuv420).
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:03
by cosmoxl
davilla wrote: 05 May 2018, 16:34
cosmoxl wrote: 05 May 2018, 15:28
I've made lanczos3 as default scaler and I guess it's working.
However, when 720p50/60 videos are played and 720p50/60 is output the scaler used is nearest neighbor.
When display matches video, there is no scaling, yes ? It would be a 1:1 pixel match.
Davilla, you really need to read everything I write. I explained why I was still concerned about the scaler in the next sentence.
Chroma is always upscaled to the luma size, then further scalers are used if needed. So, there's still need for hi quality scalers as far as I understand.
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:05
by cosmoxl
koying wrote: 05 May 2018, 16:43
cosmoxl wrote: 05 May 2018, 15:28
I understand that no luma scaling is having to be done as the resolutions match, but there's always chroma upscaling isn't there?
Upscalers are applied on the RGB tranformation of the YUV frames.
Interpolating chroma doesn't make sense, as 1 chroma pixel applies to 4 luma pixels per definition (for yuv420).
Then why does madvr make such a fuss over chroma upscaling?
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:09
by wesk05
If you don't interpolate, how do you get to 4:4:4 or 4:2:2 from 4:2:0. Chroma upsampling is required for all output modes except 4K 50/60Hz 4:2:0 (Even for this I'm not sure whether it is perfectly 1:1).
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:11
by cosmoxl
wesk05 wrote: 05 May 2018, 17:09
If you don't interpolate, how do you get to 4:4:4 or 4:2:2 from 4:2:0. Chroma upsampling is required for all output modes except 4K 50/60Hz 4:2:0 (Even for this I'm not sure whether it is perfectly 1:1).
exactly
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:16
by wesk05
I haven't seen any BT.2020 to BT.709 gamut mapping code in Kodi. Even the HDR tonemapping code seems to be flawed. It seems to be assuming that the source gamma correction is 2.4 for PQ transfer.
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:42
by koying
wesk05 wrote: 05 May 2018, 17:09
If you don't interpolate, how do you get to 4:4:4 or 4:2:2 from 4:2:0. Chroma upsampling is required for all output modes except 4K 50/60Hz 4:2:0 (Even for this I'm not sure whether it is perfectly 1:1).
Maybe we don't understand each other.
Per definition (for 4:2:0, still), 1 chroma applies to 4 luma. You don't "upscale" the chroma, you just apply the same chroma to 4 pixels. If you interpolate those chroma pixels, you are breaking the YUV definition.
We are still talking about the 720p image on a 720p resolution, from cosmoxl example, ofc.
Re: Testing MrMC 3.7.0
Posted: 05 May 2018, 17:47
by cosmoxl
koying wrote: 05 May 2018, 17:42
wesk05 wrote: 05 May 2018, 17:09
If you don't interpolate, how do you get to 4:4:4 or 4:2:2 from 4:2:0. Chroma upsampling is required for all output modes except 4K 50/60Hz 4:2:0 (Even for this I'm not sure whether it is perfectly 1:1).
Maybe we don't understand each other.
Per definition (for 4:2:0, still), 1 chroma applies to 4 luma. You don't "upscale" the chroma, you just apply the same chroma to 4 pixels. If you interpolate those chroma pixels, you are breaking the YUV definition.
We are still talking about the 720p image on a 720p resolution, from cosmoxl example, ofc.
Even in my example of 720p output as 720p the quarter size chroma layer still has to be upscaled to the luma reslution of the video. If nearest neighbor is used for that, that's bad.