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Sky+HD Box HDMI Output Settings - some thoughts


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Old 14-04-2010, 23:31
crunchie
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I've changed the output of my Sky+HD HDMI output from 1080i to Automatic - this means that the TV does the upscaling and not the Sky+HD Box. Personally I think the SD pictures are a tad sharper like this. Does anyone else have a preference? I find that, on my Panasonic G20 plasma, leaving the Sky+HD Box on 1080i for everything resulted in 4:3 pictures have small black bars on the left, right and bottom of the picture. Setting the Box to Automatic removes these bars with 4:3 pictures which now completely fill the 4:3 area.

The only disadvantage with this Automatic Sky+HD Box setting is that it takes a little longer for the TV picture to show up when watching SD, then HD, then SD channels. Also, there's a brief flash of onscreen "snow" before the TV changes it's resolution from 576p to 1080i (or the other way round). Is this Sky+HD Box setting likely to damage my TV at all?

One more thing - does a 1080p TV upscale regular SD 576p channels to 1080i or 1080p? And do they upscale Sky HD's 1080i picture to 1080p or leave it at 1080i?

Many thanks!
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Old 15-04-2010, 01:15
robot1000
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It's been discussed before

http://www.digitalspy.co.uk/forums/s...d.php?t=835898
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Old 15-04-2010, 01:33
Dave-H
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Indeed it has, but just for the record, all flat panel TVs are inherently progressive, so you could say that you're seeing 1080p. The box outputs 1080i in HD, and 576p in SD (when on auto) so the TV is just de-interlacing the former and just scaling the latter.
I assume you have a "full HD" 1080 panel, and it sounds as if you have exact pixel mapping enabled (overscan off).
This is probably why you were sometimes seeing narrow pictures when watching SD channels in 1080i mode. A lot of SD programmes, especially old ones, do not fill the frame properly. This shouldn't happen with HD programmes as the specification is much tighter.
You probably have overscan on when in SD so it hides the problem in automatic mode.
My Panasonic TV does black out when switching between SD and HD, but it's pretty quick re-synchronising. I've seldom seen any bursts of shash, although the Sony TV in my workroom, which is fed from the same source, does quite often show a burst of shash.
I doubt very much if it's doing any harm.
I always use automatic mode as the SD picture is then slightly sharper to my eyes, and I want the aspect ratio switching to work automatically.
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Old 15-04-2010, 10:07
Nigel Goodwin
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One more thing - does a 1080p TV upscale regular SD 576p channels to 1080i or 1080p? And do they upscale Sky HD's 1080i picture to 1080p or leave it at 1080i?
Neither - 1080i, 1080P, 720P, 576i are broadcast standards (although 720P isn't used in the UK). LCD and Plasma screens aren't interlaced or progresssive, they work in an entirely different way - so the TV's scaler scales it to fit the SCREEN, it doesn't make it i or P, which would be pointless.

BTW, you can't upscale 1080i to 1080P anyway, they are boith the exact same resolution.
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Old 15-04-2010, 10:39
SilverFox2
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Neither - 1080i, 1080P, 720P, 576i are broadcast standards (although 720P isn't used in the UK). LCD and Plasma screens aren't interlaced or progresssive, they work in an entirely different way - so the TV's scaler scales it to fit the SCREEN, it doesn't make it i or P, which would be pointless.

BTW, you can't upscale 1080i to 1080P anyway, they are boith the exact same resolution.
Correct as usual.

Plasma and LCD displays can also only show RGB colourspace so they have to convert whatever colourspace they receive to RGB.

My Amstrad HD STB already outputs RGB but other makes of Sky HD STB output colourspace differently including 4:2:2.

Could this have any effect on the PQ variation this subject usually brings ?
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Old 15-04-2010, 13:20
Dave-H
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LCD and Plasma screens aren't interlaced or progresssive, they work in an entirely different way -
Yes, of course they don't "scan" in the traditional way at all. I was over-simplifying there!


My Amstrad HD STB already outputs RGB but other makes of Sky HD STB output colourspace differently including 4:2:2.
Interesting, I don't remember this being mentioned before. Are you saying that the signal that Amstrad boxes put out (via HDMI presumably) is different to other boxes?
If so I'm surprised because Sky have always kept such tight control over the specifications of their boxes, and even if they have decided to change the spec. I would then expect the Samsung boxes to be the same.
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Old 15-04-2010, 14:11
bobcar
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BTW, you can't upscale 1080i to 1080P anyway, they are boith the exact same resolution.
This has been discussed before but even though they have the same number of pixels in the signal unless the 1080i is just a 1080p source mapped directly and the TV recognises this and treats it accordingly they are not the same resolution after processing.

Depending on how the TV de-interlaces and whether the original source was progressive or interlaced they may end up with quite different resolutions in practice. With plain bob de-interlacing you get 520 lines with blending something in between, other methods similarly vary.

Again it's been mentioned before but often 720p will give far better results than 1080i including better vertical resolution for fast moving images.
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Old 15-04-2010, 14:14
anniebrion
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Invisi-bump
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Old 15-04-2010, 14:54
crunchie
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....often 720p will give far better results than 1080i including better vertical resolution for fast moving images.
I have a 1080p TV, so, for the best resolution, should I set Sky and the DVD Recorder/Player to output 1080i or 720p?
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Old 15-04-2010, 15:26
SilverFox2
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Yes, of course they don't "scan" in the traditional way at all. I was over-simplifying there!



Interesting, I don't remember this being mentioned before. Are you saying that the signal that Amstrad boxes put out (via HDMI presumably) is different to other boxes?
If so I'm surprised because Sky have always kept such tight control over the specifications of their boxes, and even if they have decided to change the spec. I would then expect the Samsung boxes to be the same.
I have personally not tested output from any other Sky HD STB than Amstrad but this thread link on another forum may allow you decide if my comments are correct.

http://www.avforums.com/forums/video...l#post11436358

Posts #220 to #225 refer.
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Old 15-04-2010, 15:58
bobcar
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I have a 1080p TV, so, for the best resolution, should I set Sky and the DVD Recorder/Player to output 1080i or 720p?
Usually it would be best to set Sky to either automatic or 1080i though try them all to see what gives the best picture (only Automatic will give auto aspect ratio switching). Sky etc transmits HD in 1080i so there is usually no point in setting the box to 1080i unless your TV is really crap at deinterlacing.

Similarly with the DVD try them all. I have my DVD set to 576p (as DVDs of films are naturally progressive and the DVD player has an easier job recognising this) and my Blu-ray set to 1080p because it upscales better than my TV.
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Old 15-04-2010, 16:21
Dave-H
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I have personally not tested output from any other Sky HD STB than Amstrad but this thread link on another forum may allow you decide if my comments are correct.

http://www.avforums.com/forums/video...l#post11436358

Posts #220 to #225 refer.
Thanks, very interesting.
Elements of this thread in there too -
http://www.digitalspy.co.uk/forums/s....php?t=1243515
Looks like a very big can of worms possibly opening up!
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