Dark scenes are very poor, they look very speckly and it looks like the HD cameras dont cope too well with dim light.

Only in some circumstances, i have seen plenty of very dark scenes in HD and not a bit of grain in sight.

Depents on how good the cameraman is with his settings.

Maybe they were caught with a film camera and then converted to HD.

Films are generally fine but I cant remember a home grown show not having terrible dark scenes.

It depends on the codec as much as anything. MPEG4 is hard to beat. I don't know what each respective channel uses but as someone who encodes HD material at home, I can say I've yet to find anything that comes close to MPEG 4 in the quality stakes.

Here's a comparison pic I made a while ago:

4,500kbs on the left. 3,700kbs on the right.

Both un-enhanced screen captures from the same video encoded using MPEG4 at the different rates.

I find it hard to spot any difference.

http://img216.imageshack.us/img216/8...iontestsw2.jpg

How this compares to the rates used by HD broadcasts I don't know but I suspect they're possibly lower (megabits vs megabytes etc).

Personally, I always 5,000KBS for my own recordings for quality. However, I'd doubt transmission can come close to that bit rate.

HD works best in very bright light. The sharpness drops off in medium light and you often get grain in low light.

That said, there's a lot of difference in quality between programming. The BBC over Christmas used a scene from a nature programme of a polar bear cub sliding down a glacier as an advert for HD. The picture quality was terrible in my opinion, really soft and a bad advert for HD.

Contrast this with the Natural World "Mountains of the Monsoon" which has the best HD footage I've ever seen over broadcast, blu ray standard in many places.

All I can say is the BBC need to get the cameras used in the Natural World M of the M standardised throughout the organisation along with the lenses and bit rates because its simply sublime.

BBC is typically 16Mb/s, ITV around 12Mb/s from memory. Considerably lower than what you are using.

I may be wrong but as I understand it bit rate only affects quality in handling moving quickly moving objects. A still image can be transmitted using a very low bitrate without any loss of quality at all. Hence the use of Variable Bit Rate (VBR) which requires a double pass of the source material to identify where the larger differences exist between frames and increase the bit rate for these and reduce it for very small changes in frame content. This results in smaller files and lower average bit rates without loss of quality at the cost of increasing encoding times.

This is absolutely correct.

It also explains why people who do not habitually watch content with a lot of fast movement (i.e. sport and 'action' films/drama) find far less to complain about on channels with low bitrates which some people find almost unwatchable.

Sorry but that is nonsense, I can easily tell the difference from a 22" from 12' away!

I didn't say you couldn't tell the difference between a 22" and a 32" which you obviously can, and from a great deal further away than 12'.

What I was saying was that you cannot tell the difference in resolution between SD and HD. This is a function of the physics of optics and the construction of the human eye. The tables and charts are calculated for normal human vision but I doubt that anyone has vision so good that could resolve resolution differences to much greater extent. Of course, this is not to say that there aren't other aspects of HD that won't make a difference that you can percieve to tell the two apart.

Technically there is no difference in resolution between SD and HD, resolution is expressed as picture elements/linear measurement eg pixels/inch. In fact a SD picture displayed on a 720 x 576 pixel monitor has the same resolution as a 1920 x 1080 HD picture on a 60" monitor with 1920 x 1080 pixels. The HD picture does have a greater resolving power (it can reproduce finer detail when displayed at the same phsyical size as a SD source).
It might seem to be a little pedantic but as any one used to manipulate high res digital images in software will tell you, misuse and basic misunderstanding of this creates all sorts of confusion.
If you read my earlier post, it explains that a SD image and a HD image on the same matrix display has the same resolution, but of course the HD source has a higher resolving power
Last edited by grahamlthompson : 27-01-2009 at 14:11

Well, I hate to say it but I do feel you are being pedantic just for the sake of it. I absolutely disagree that those of us who work in this area refer to the resolution of the display surface as 'the resolution'. It's normal to use the term 'resolution' to as a shorthand for 'effective resolution', a parameter derived by more or less complex equations from the source material and the display (or recording) surface.

But this is a red herring. It has nothing whatever to do with whether or not the human eye can determine the difference in effective resolution at a particular distance which is well established and shown by tables and charts such as the one here.

Read the paragraph starting

Pixel resolution
The term resolution is often used as a pixel count in digital imaging, even though American, Japanese, and international standards specify that it should not be so used, at least in the digital camera field

and ending

None of these pixel resolutions are true resolutions, but they are widely referred to as such; they serve as upper bounds on image resolution.

at

http://www.nationmaster.com/encyclop..._various_media

I have absolutely no disagreement with that (which seems to back up what I said). I merely question what on earth it has to do with the topic at hand which is the resolving power of the human eye and its ability to differentiate different effective resolutions at different didtances.

I didn't mean I couldn't tell the difference between a 32 and a 22" from 12', I meant I can easily tell the difference between an HD and an SD programme on a 22" monitor from 12'. While what you are saying may be partly true, I think you are ignoring the quality loss from upscaling, and the fact that HD simply has a higher bitrate.

The more pixels you have the sharper an image becomes because the lines which make up all of the detail and outlines in the image are much better defined.

You have to remember a picture is made up of circles (yes these are called pixels but its easy to forget they are round).

The smaller the circles are, the straighter the line actually appears as the boundary is more delineated as less of the curve of each pixel intrudes into the neighbouring area. Or to put it another way, you need to remember lines are actually made up of a collection of adjacent circles.

Even if the eye cannot see individual pixels therefore, increasing the pixel count can nevertheless sharpen an images appearance up because the colours of different areas don't merge as much at the boundaries. The larger the pixels the more space there is between pixels where the different coloured pixels interact.

The number of pixels has to become very high before no difference at all can be detected.

With a smaller monitor of a certain resolution, the pixels on the monitor are made smaller because they have to cram the same number of pixels into a smaller viewable area.

This can in theory make the difference harder to see. However, I still think you can see the difference. If I stand a 14" portable tv displaying SD next to my 42" plasma displaying HD, the HD looks better even on the same picture. So despite the smaller pixels, the difference is still viewable.

There's also another aspect to HD picture quality. It captures colours much better - they're far more saturated so even if you can't see the increase in sharpness, (which I'd dispute), you can see the increase in saturation and contrast.

According to their advertising, at least one of the US satellite channels is in 1080p. (And no, I don't remember which one!)

I did say that my observations were soley concerned with resolution. There are indeed other factors to take into account.

Whether one disputes the figures for human perception or not they are well established and based on properly conducted scientific research.

All this heated debate of pixels and resolutions!

I remember being fascinated as a kid looking close up with a magnifying glass at a printed picture in a newspaper and being able to see it is as only made up of lots of little printed dots. Yet if you read the paper at arms length it looked like a real photograph.

It's not really much different today... It's now just electronic pixels instead of printed dots.... the further away you get, the less you see the dots/pixels, SD or HD.... and I dont need to watch the TV thru' a magnifying glass....... yet!

I remember when TV's were so small that they literally had a device (a large magnifying glass to put in front of the screen) to give your 12" monochrome all the magnificence of a 14". You could also get colour with a coloured filter provided the sky was blue and the grass green

Here's one for the doubters

http://www.thevalvepage.com/tv/misc/..._Magnifier.htm

Forum title: HD - IS IT WORTH IT?

Worth what exactly? It's worth having - picture quality is excellent. Worth 80 quid? Perhaps. Worth 300 quid for a recordable box? I'd say so. Its a matter of opinion. Is it worth 'it' to you?

Glen.

I know someone who had a colour filter where the top was blue, central area pink and bottom was green. You could just about count the 405 lines too, sigh.

I always remember Gordon Honeycombe looking a bit off colour.

Well my friend did, i would never have such rubbish.

I was given a set like that (long since u/s) as a teenager.

I think the screen was around 9" and the magnifier was a plastic affair that was actually filled with some liquid.


Edit: I've just looked at the URL and see it mentions the plastic casing and liquid filling.

Sadly I never saw the set with the CRT operational.

Not unless you have a Big telly and actually stand over it to watch.

I have a FoxSat-HDR connected to a 5 year old 32" plasma (Hitachi 32PD5200). This screen has a native resolution of 854x1024 pixels and supports 720p and 1080i sources. I sit approximately 3.5m (11'6") from the screen and I definately can tell the difference between HD and upscalled SD images.

The HD image is more vibrant, has a lot more detail and has noticebly better contrast. However, the thing that I notice most about HD transmissions is actually the 5.1 Dolby Digital surround sound.

I recorded a lot of 'Later with Jools Holland' over the Christmas period and it all sounds great - even the stuff I don't like!