15 replies to this topic

[lpnp]

I would like to know the processing involved for different input and output resolutions and scanning methods, something like http://forums.openpl...de-interlacing/

 

From the other thread, I know that 576i50 to 1080i50 conversion involves 576i50 -> 576p50 -> 1080p50 -> 1080i50, but if the final output is 1080p50, does it skip the last conversion or add another 1080i50 -> 1080p50 conversion?

 

If both STB and TV can support 1080p50 and 1080i50, which is the better output format for 576i50 input, 1080p50 or 1080i50? Is it the fewer processing steps involved the better (assuming TV and STB have the same SoC)?

 

Is it possible to use the following examples to explain the process? And how can I tell what 1080p frame rates my STB can support? My TV claims to support 1080p50.

 

576i50 -> 1080p50

576p50 -> 1080p50

576p50 -> 1080i50

 

Can the following generic conversions be summarized as sequences of processing steps?

[res1]p[fps1] -> [res2]p[fps2]
[res1]i[fps1] -> [res2]p[fps2]
[res1]p[fps1] -> [res2]i[fps2]
[res1]i[fps1] -> [res2]i[fps2]

 

res = resolution, fps = frames per second

[Erik Slagter]

If you have the STB do the scaling and deinterlacing, it will only use one step, never more. I think you're confused about the bob-weave-deinterlacer, which I described functionally in discrete steps. You should not interpret that as several steps in the actual process, it won't degrade the picture quality (further).

 

Whether your STB supports 1080p50, see the comparison chart: http://openpli.org/wiki/comparison. All STB's support 1080p, but the older ones do support only 1080p25 and that is definitely NOT what you want.

 

I would really advise to use the 1080p50 output mode if your STB has it (see A/V settings). It will make sure both 1080i50 and 720p50 are sent to your television without degradation.

[Rob van der Does]

I would really advise to use the 1080p50 output mode if your STB has it (see A/V settings). It will make sure both 1080i50 and 720p50 are sent to your television without degradation.

But if it's a 4k-TV the TV will do one more upscaling. In that case one would better use 'autoresolution' to prevent the box from any upscaling at all, so there will be only one (by the TV)?

[lpnp]

Hi Erik,


Thanks for the reply.


My STB is Zgemma Star H2 which seems to support 1080p50. How does a STB convert 576i50 to 1080p50, although it's done in a single step, does it do more or less work than 576i50 -> 1080i50? Do LCD TVs always convert signals to progressive eventually? Is it better to use 1080p50 instead of 1080i50 in this case?


What's the best plugin that can make output frame rate match that of the input? I heard that setting A/V refresh rate to multi wasn't enough, so I'm currently using autoresolution.

[lpnp]

Hi Rob,

I tried to output the original resolution using autoresolution, but the STB OSD became blurry, is there something I can do to fix this?

[Rob van der Does]

LOL, my experience as well. My main reason not to use AR in the end

[lpnp]

Rob, I think we've been through the same trouble.

I initially wanted to output the original resolution to let the TV handle the upscaling. The blurry OSD made me change my mind, but I also need to think about the double upscaling problem if I change to a non-1080 TV (e.g. 4K TV).

So as a compromise, I want to let the STB do the upscaling to avoid the blurry OSD problem, but I also want to make sure the STB is doing as little processing as possible to avoid quality degradation when the signal is upscaled again by the TV. That's where the 1080p vs 1080i for 576i50 input question comes from.

[Erik Slagter]

IMHO the best approach is always to output the highest resolution/lacing possible. That means that if you have an UHD tv, set the output to 1080p50. That means the TV only has to duplicate each pixel in both directions. No real scaling necessary, nor deinterlacing. Quality is 100% the same as if watched on a 1920x1080 sze panel TV.

[lpnp]

What if the STB is connected to a monitor whose resolution is not an exact multiple of 1920x1080 (but with the same aspect ratio)? Is progressive or interlaced scan better in this case?

[Erik Slagter]

It's always best to deinterlace first before any scaling. Well, at least if the deinterlacing is lossless (like it is with bob&weave). For scaling interlaced material there are dedicated algorithms, which may or may not work that well.

 

I guess you'd best try it yourself.

[lpnp]

Thanks, I'll try. But in theory, does 576i -> 1080i do more or less work than 576i -> 1080p?

[Erik Slagter]

At some point there will be deinterlacing needed. Your LCD or plasma or OLED panel does not have an electron beam and a phosphor that dies out. So you can choose to do the deinterlacing at the source or do it at the sink. Scaling of non-interlaced content is easier, so, again, I'd recommend to do it at the source. Unless the deinterlacing is lossy (i.e. deinterlacing from i50 to p25), then don't do it.

 

576 will look **** one way or another, I wouldn't spent too much effort on it.

[lpnp]

Thanks. I guess there's no way to fix blurry OSD displayed in non-native resolution (e.g. 720x576)?

[Rob van der Does]

IMHO the best approach is always to output the highest resolution/lacing possible. That means that if you have an UHD tv, set the output to 1080p50. That means the TV only has to duplicate each pixel in both directions. No real scaling necessary, nor deinterlacing. Quality is 100% the same as if watched on a 1920x1080 sze panel TV.

That's not how it works. If that was the case the TV would have 'blocks' of 2x2 pixels, and I can assure you that's not the case: they would be clearly visible from a short range.
So the TV also scales up, using an interpolation algorithm.

[Erik Slagter]

It doesn't matter. Scaling in this case is lossless, so not worth trying to ommit.

[Erik Slagter]

Thanks. I guess there's no way to fix blurry OSD displayed in non-native resolution (e.g. 720x576)?

I think you can work that out yourself  Hint: the output is 720, so the OSD is resolution: ...