Re: Will F1 be on BBC HD?
- From: Dan <no.spam.here.invalid>
- Date: Mon, 02 Mar 2009 13:38:23 +0000
"Bigbird" <bigbird.usenetNOSPAM@xxxxxxxxx> wrote:
Your analogy with the chess board is wrong because the analogue
source does not ever fit to the digital screen.
Is my CRT a digital screen?
In some ways, yes. It has distinct vertical stripes of
red/green/blue across the screen, and the quality and detail of the
image displayed will depend on how well the resolution of the
striping copes with the intended resolution of the broadcast image.
CRTs are configured with sometimes surprisingly large amounts of
overscan in order to get the optimum match of broadcast resolution
to screen resolution and thus the sharpest image.
Why do so many standard TV pictures look so much better on my old CRT
that on so many HD TVs. You seem to be trying say they don't, but this
is where my eyes versus your insistence otherwise clearly diverge.
In a CRT, the ray of electrons being fired at the screen is in
continuous motion. It doesn't light pixels precisely, it scans
across them. This combined with the difference between striping
resolution and broadcast resolution causes a blurring or smoothing
effect - broadcast pixels being 'smeared' across multiple stripes.
If the scanning direction isn't exactly 90 degress to the stripes
(can easily happen if the TV has taken a few knocks or was never set
up properly), this can cause further blurring.
Also, the flatter the CRT screen, the harder it is to create a
uniform resolution as the speed of the scanning beam has to be
modulated as it crosses the screen, to compensate for varying
distance the beam has to cross. Display a perfect grid on a CRT and
it's very rare to see perfect squares across the whole display.
The end result of this is an an effect akin to anti-aliasing -
details get blurred together and smoothed out. This not only reduces
the intended image detail but on a digitally compressed source, it
also reduces visibility of compression artifacts. Blocking effects
and 'mosquito noise' (noise effects around sharp contrast boundarys)
are smoothed away.
On a digitally compressed source, SD often looks dreadful on an LCD
because the LCD shows all the detail - including all the compression
artifacts in their pin-sharp ugly glory. Image 'enhancement' systems
in the TV often make the problem worse, processing the unwanted
artifacts to create even more artifacts and 'sharpening' the image
to produce ugly ringing effects, and creating 'vibrant' colours that
bleed into each other unpleasantly.
Cheap LCD panels don't always have a native resolution that the
image can be conveniently scaled to, causing further unpleasant
scaling artifacts. In addition, LCDs are often bigger than the CRT
they replace too - which exaggerates the effect as the artifacts are
visibly bigger.
You can see similar effects comparing TV video displayed on a CRT TV
and on a similar size CRT computer monitor. The dot pitch
(effectively pixel resolution) of the computer monitor is so much
higher, it shows up all the flaws in the TV image, and often looks
'worse' as a result.
Use a high quality source - such as a DVD encoded with a high data
rate (6-8 megabits/second, say), or a high quality pure analogue
source, and then you should notice the LCD providing a much more
detailed image than a similar size CRT.
Now when you plug a HD image into your LCD you immediately notice a
massive improvement. Not only is the higher resolution putting
vastly more detail into the image, but also the apparent size of
MPEG compression artifacts is much smaller. Also, since HD is being
marketed based on image quality, the current HD broadcasts are not
nearly as over-compressed as SD services tend to be. (Certainly in
the UK, anyway.)
The first time I plugged a true HD source into my LCD tv, I was
shocked by how good it looked. I expected an improvement, but
nowhere near as big an improvement as I actually got.
By way of example if I watched the GP2 on my brothers 50" HD TV it
would only look good at it's native resolution i.e 576p I assume, but
then the AR would be slightly off IIRC. Upscaling it looked crap, even
if I sat further back. More pixels do not, alone, equal better picture
without a source to match. This is the chessboard analogy.
The quality of upscaling is often very dependent on the thing doing
the upscaling. I get a much better image having my DVD player
upscale to 1080p than I do if I let the TV do the upscaling.
Dan
.
- References:
- Re: Will F1 be on BBC HD?
- From: Phil Newnham
- Re: Will F1 be on BBC HD?
- From: Bigbird
- Re: Will F1 be on BBC HD?
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