• New Patreon Tier and Early Access Content available. If you would like to support AVForums, we now have a new Patreon Tier which gives you access to selected news, reviews and articles before they are available to the public. Read more.

Sky HD box output of SD channels.. 1080i or 720i ?

FL350

Standard Member
Hi all,

Sky HD is 1080i output, but what happens when you are watching an standard definition (SD) channel... what is the output then? Is is downscaled to 720i ?

Reason I ask is i recently upgraded to Sky HD, but at the same time got a Samsung 1080p 50" plasma (PS50B530S) thinking at the time that the progressive would be better for HD! This is now being returned due to colour saturation, but my wife also noticed a distinct deterioration of quality of picture in normal SD channels such as BBC...and that was through a HDMI cable, though slightly better through a regular SCART, but still alot worse that with the old Sky+ box.

I'm now wondering whether to replace the TV with a 1080i or 1080p, and wondering which will handle the SD channels the best... my wife tends to spend 90% of her time watching SD...

Incidentally I would be replacing it with either the LG 50PS3000 (1080p) or perhaps the LG 50PQ6000 (1080i) or the Samsung PS50B451B (1080i)

Any advice gratefully received!

Thanks...
 
Last edited:

Broadz

Distinguished Member
It depends what you have the HDMI output set to. If set to 1080i, it will upscale all SD transmissions to 1080i. If set to 720p, it will upscale all SD transmissions (and downscale all HD transmissions) to 720p. If set to 576p, it will upscale all SD transmissions (and downscale all HD transmissions) to 576p. If left at Automatic, HD will be played at 1080i, SD at 576p.

You can of course still watch SD transmissions via scart, in which case it will still be at 576i.

Outputting at anything other than 1080i will then force your TV to upscale the picture back to 1080i/1080p before displaying it to you.
 
Last edited:

FL350

Standard Member
Ok thanks for that... so watching SD channels on a 1080i or 1080p... if the output from the Sky box is set to 1080i there should be absolutely no difference in picture quality between 'i or p' because the TV either accepts the 1080i signal as it is or adjusts it to fit in the case of a 1080p set? Am I correct...?

So the question of whether to buy 1080i or 1080p is really not relevant... it depends solely on the output of the Sky box...?
 

funkyspider

Prominent Member
Taking an SD broadcast and stretching it to fill a 50" screen will always look like a degraded quality image at a close viewing distance. Plasma are generally better than LCD for SD as the picture has a 'softer' appearance. People are often disapointed when they replace a smaller screen for a large one.

I don't think it will have much bearing what you set sky to output, something will have to upscale the image to fill the pixels on the screen.

What is your viewing distance ?
 

Broadz

Distinguished Member
You would only go for 1080p if you watch a lot of Blu Ray - as no broadcast television (Sky, Freesat, Virgin) has any higher definition than 1080i.
 

StevieBuck

Prominent Member
'HD Ready' TVs support 720p and 1080i. 'Full HD' TVs support 720p, 1080i and 1080p. In regards to the TVs you've mentioned, I'm not really sure why you'd want to go for one that just supports 1080i over one that does both 1080i & 1080p?
 

FL350

Standard Member
Thanks guys...

Well firstly my viewing distance ranges from 3m (10') to 4 or 5m (15')... (L shape seating...) ...and incidentally my old TV was a 50" Plasma so I'm not changing screen sizes...

On the issue of why i would go for a 1080i as opposed to 1080p I think thats perhaps where my understanding is lacking...

From reading the forums, the suggestion was (or my intrepretation was...!) that 1080i is better for SD channel quality, and on that basis, considering my wife watches 90% SD, I'd get much less ear-ache if I optimised there, and not for HD!

However from what you all say, there should be absolutely no difference between i and p since the picture quality is dependant on the Sky box output... so the issue of SD quality perhaps lies with this Samsung TV that I am returning... at least I hope!
 
Last edited:

PE06MCG

Established Member
Your TV can only show a 'p' picture so will change the received 'i' signal to 'p' anyway but this will be displayed as either 1080p or about 720p dependent on your TV's settings or capabilities.

SD via HDMI from a SKY STB starts with 'p' as its output but if you think it is better you can change this 576p to 720p or 1080i.
If you want your TV to receive 576i and let the TV do all the processing, you must use the scart connection.
 

FL350

Standard Member
I thought Sky output is only 'i' not 'p' ? So are you saying that the output is 'p' for the lower resolutions, but 'i' for 1080 output?

When you say 'your TV' are you referring to the Samsung specifically as a 1080p set?

If the TV is 'i' surely it will only show an interlaced picture at 1080... if it is progressive it will show (feed) the whole screen all the time... on this basis do progressive TV's receiving a SD output scaled up to 1080 suffer poorer quality because they are trying to fill the whole screen progressively as opposed to only half at a time through interlacing? ...does this make sense?!
 
Last edited:

PE06MCG

Established Member
I thought Sky output is only 'i' not 'p' ? So are you saying that the output is 'p' for the lower resolutions, but 'i' for 1080 output?

When you say 'your TV' are you referring to the Samsung specifically as a 1080p set?

If the TV is 'i' surely it will only show an interlaced picture at 1080... if it is progressive it will show (feed) the whole screen all the time... on this basis do progressive TV's receiving a SD output scaled up to 1080 suffer poorer quality because they are trying to fill the whole screen progressively as opposed to only half at a time through interlacing? ...does this make sense?!

Via HDMI SD is 576p only (ie your TV is not allowed to do a better job of making the full frame).

The TV contains circuitry that changes 'i' to 'p'.

Effectively every 50th of a second half a frame containing odd lines ('i') is transmitted then a 50th of a second later mixed with the other half a frame containing even lines to produce the full ('p') frame your TV can display.
The deinterlacing algorithm's used by your TV are much more complex than this but hopefully you get the idea.

LCD's and plasma's cannot display 'i' signals unlike the CRT's which rely on it.
 

FL350

Standard Member
DJ Dave... why? From Silver Fox all TV's (plasma) display in 'p' by converting the 'i' signal... so why would 'i' be better? ...or is this just down to your experience?

So is the difference just down to the screen resolution then? ...the higher the resolution of 'p' does not handle the poor SD signal as well as the lower resolution 'i' screen hence you get pixalation etc...?
 
Last edited:

zofinger

Established Member
After reading here how to change the HDMI output on Sky HD i have set mine from 1080i to automatic.

Therefore when I switch to BBC1 for example my TV states it's 576p input and when i go to an HD channel it changes to 1080i input. Having looked at 1080i input on SD channels and now 576p input i definitely prefer to latter (as the picture appears slightly less 'soft' to my eyes).

Thanks for the post - I never new that function existed! (btw - only had sky HD for 2 days).:facepalm:
 
F

Fatwaz

Guest
DJ Dave... why? From Silver Fox all TV's (plasma) display in 'p' by converting the 'i' signal... so why would 'i' be better? ...or is this just down to your experience?

So is the difference just down to the screen resolution then? ...the higher the resolution of 'p' does not handle the poor SD signal as well as the lower resolution 'i' screen hence you get pixalation etc...?

by setting the box to ouput at 1080i you are just letting the signal from sky go from box to tv and any scaling and interlacing is done by the tv.when you select 720p the sky box is downscaling and deinterlacing and most peoples tv's will be better than the sky box at this so 1080i is normally the best option.
 

choddo2006

Distinguished Member
DJ Dave... why? From Silver Fox all TV's (plasma) display in 'p' by converting the 'i' signal... so why would 'i' be better? ...or is this just down to your experience?

So is the difference just down to the screen resolution then? ...the higher the resolution of 'p' does not handle the poor SD signal as well as the lower resolution 'i' screen hence you get pixalation etc...?

Before you buy a new TV, get them to show you (in a proper shop, not Currys) what SD from Sky looks like and see if you like it. Do Panny make a 50" X10 any more? A lot of people think that SD over HDMI looks worse - I think it just looks more like it really is. Worth trying SCART.


All this talk of "1080i" TVs..... there's no such thing. I assume you mean HDReady which originally had to support 720p and 1080i inputs but didn't have 1080p support and also didn't have 1920x1080 panels.

Even HDReady screens can take 1080p signals now (but still don't have 1920x1080 panels)

A typical HDReady 50" plasma is 1366x768. Doesn't mean it's automatically going to be any better at SD though, it's all in the processing, not the pixel count.
 

technowizard

Established Member
So is the difference just down to the screen resolution then? ...the higher the resolution of 'p' does not handle the poor SD signal as well as the lower resolution 'i' screen hence you get pixalation etc...?

The Sky+HD box does not output at 1080p, it only uses 1080i, 720p or 576p via HDMI. Since all HD content is 1080i, there would be no point in offering 1080p. I assume that the reason why the lower resolutions are progressive is because some older TVs or even monitors will be compatible with progressive via HDMI but not interlaced via HDMI. It does not have 720i as such a video format is not accepted nor does it exist. It has been moaned about many a time why sky won't output 576i via HDMI but it is probably for compatibility reasons, my samsung TV, for example, will not display 576i via HDMI, so it was probably done to minimise issues for the consumer.
As mentioned earlier no screen can be interlaced as LCD and Plasma are unable to deliver interlaced signal without de-interlacing first.
If an interlaced 1080i signal is de-interlaced correctly, and most tvs will, there would be almost no difference between 1080i and 1080p as they are the same resolution.

Hope this helps.
 

PE06MCG

Established Member
Off subject I know but the reason 576i was not provided by Sky I believe was because it was omitted from the minimum requirements set by the HDMI standards.

This then allowed them to produce only the 576p via HDMI (ie the STB does the processing).

I think most of us with HD sets that already deinterlace (by necessity) the 1080i signal feel our Displays would also do a better job with the 576i if given the choice.

I am not suggesting they have deliberately made the SD appear to be a lot worse than it could be compared to HD but it is most certainly the way it happens.
 
Last edited by a moderator:

FL350

Standard Member
Thanks guys! There is certainly a whole world of information out there that us 'layman' TV watchers really know nothing about!

Technowizard you say: If an interlaced 1080i signal is de-interlaced correctly, and most tvs will, there would be almost no difference between 1080i and 1080p as they are the same resolution.

Ok but screen resolutions currently differ from HD Ready TV's to HD TV's with relative (screen) resolutions of 1366x768 and 1920x1080 respectively... On the basis of an HD output from the Sky box, I understand what you say above that there will be no difference...

What happens though when the Sky box takes say BBC 1, upscales it to 1080i and it is received by the TV... does the screen resolution not then play a part, by perhaps softening the image over 1366x768 as opposed to 1920x1080? Or are we back to the TV's processor's ability to interpret and display the image...?
 
Last edited:

PE06MCG

Established Member
The process is as follows:
The STB takes the SD output that it has already deinterlaced from 576i to 576p reinterlaces it again, upscales it to 1080i then with all those processing defects it has introduced it asks your TV if it wouldn't mind converting it to 1080p or for HD Ready 720p so that you can see it on your Display.
 

FL350

Standard Member
...so how well the TV converts it to 1080p or 720p really depends on the quality of the processor... and thats where you get the 'good' SD pictures as opposed to the 'average'...?
 

choddo2006

Distinguished Member
...so how well the TV converts it to 1080p or 720p really depends on the quality of the processor... and thats where you get the 'good' SD pictures as opposed to the 'average'...?

Yes, and the quality of the Sky box' deinterlacing (if you're using 576p for SD) and scaling (if you're using 1080i for SD)

It's possible to put a box like the DVDO Edge in front of the TV. It will take a 576p signal, convert it back to 576i, deinterlace it again properly and then scale it up to whatever the TV wants so that the TV doesn't have to do anything (if it's a 1080p screen. most HDReady screens will still apply a final bit of scaling as you can't send them their native res)

And then if you want to get VERY picky you can chain a Lumagen video processor after that, as they are better at scaling than the DVDO box :)

At that point, the expenditure becomes a bottleneck.
 

FL350

Standard Member
This has been very enlightening... many thanks to you all for taking the time to post...

Last question... anyone care to name the manufacturers that produce the better processors... or are they generally standard 'off the shelf' components, in particular price brackets?!
 

mksuperhoop

Established Member
This has been very enlightening... many thanks to you all for taking the time to post...

Last question... anyone care to name the manufacturers that produce the better processors... or are they generally standard 'off the shelf' components, in particular price brackets?!
just read all of above and think i understand it :rolleyes:
i know a lot of 'what's best' is down to personal preference but,
could someone just confirm the best setting for sky+ hd output from a technical point, that will let the full hd plasma do as much, if not all the work?
if there is one :confused:
 

choddo2006

Distinguished Member
just read all of above and think i understand it :rolleyes:
i know a lot of 'what's best' is down to personal preference but,
could someone just confirm the best setting for sky+ hd output from a technical point, that will let the full hd plasma do as much, if not all the work?
if there is one :confused:

Auto generally but to be honest, 1080i might be either just as good or even better on some setups and then you don't have the second of syncing when going between SD and HD.
 

Jack_is_Back

Established Member
Auto generally but to be honest, 1080i might be either just as good or even better on some setups and then you don't have the second of syncing when going between SD and HD.
The blank screen delay is quite a pain when switching channels (especially for my channel-hopping missus). I leave my box set to 1080i, fortunately there seems to be no degradation in PQ.

Surely anyone with Sky HD should only consider a 1920 x 1080 res to avoid any further scaling?

I also wonder how many folk don't have there FullHD sets configured to show 'full pixel' or '1:1 pixel mapping'? Both my Sony and Panasonic TVs were set to overscan by default.
 

The latest video from AVForums

Is 8K TV dead? Philips OLED+907, Pioneer LX505 AVR plus B&W 700 S3 Reviews & Visit + AV/HiFi News
Subscribe to our YouTube channel

Full fat HDMI teeshirts

Support AVForums with Patreon

Top Bottom