The limit to brightness

Chatting to a neighbour recently he suggested to me that the modern telly as
he put it, was not good at bright and dark. I think hebasically meant that
bright was kind of dull and blacks were not black enough. I suggested more
contrast, but...
Not now being able to see, I would have thought this criticism of lcds was
now a thing of the past, but are we still in this stage, or has he just not
bought a good enough telly I wonder?

Bit daft I said asking me, I don't even have a screen on mine!

Brian

--
From the Sofa of Brian Gaff Reply address is active

Brian Gaff wrote:

I think hebasically meant
that bright was kind of dull and blacks were not black enough. I
suggested more contrast, but...

In terms of brightness, I would say my (expensive) Sony LCD TV is at
least the equal of any CRT TV I've owned.

Contrast is another issue, though. Cheap LCD TVs still seem to suffer
from glowing blacks, greatly reducing the apparent contrast ratio.

I spent a fortune to get a TV with zoned backlighting, so the black
bits of the picture really are completely dark.

Having said that, I don't think backlight bleed is much of a problem
these days unless you are unduly fussy (like me).

I think your neighbour has probably bought a cheap 'n' nasty TV (quite
possible); set it up wrongly (also quite possible); or is an extremely
fussy type (less likely).

--
SteveT

"Steve Thackery" wrote in message
...
Brian Gaff wrote:

I think hebasically meant that bright was kind of dull and blacks were
not black enough. I suggested more contrast, but...

In terms of brightness, I would say my (expensive) Sony LCD TV is at least
the equal of any CRT TV I've owned.

Contrast is another issue, though. Cheap LCD TVs still seem to suffer
from glowing blacks, greatly reducing the apparent contrast ratio.

I spent a fortune to get a TV with zoned backlighting, so the black bits
of the picture really are completely dark.

Having said that, I don't think backlight bleed is much of a problem these
days unless you are unduly fussy (like me).

I think your neighbour has probably bought a cheap 'n' nasty TV (quite
possible); set it up wrongly (also quite possible); or is an extremely
fussy type (less likely).

For me, the big problem with modern TVs (and this includes CRTs) is that
they cannot handle highlights well, and suffer horrendous crushing of
anything over a certain threshold. At best, when all three colours are
maxed-out, you just get featureless white. At worst, one of the colours
maxes-out and the other two still have usable detail, giving repulsive
magenta or cyan colour-casts. Overexposure on faces makes them even more
orange than a certain presenter of antiques programmes!

Comparing my 25-year-old 14" JVC telly against my 10-year-old Panasonic
(even when the latter was brand-new), the difference was fairly noticeable.
My fiancée's Samsung LCD TV is horrible, especially when playing through
HDMI from Blu-Ray discs or the Sky box, despite my surreptitiously tweaking
brightness, contrast and colour when she's not around to see if I can
improve things.

On Thu, 30 Aug 2012 19:19:14 +0100, Steve Thackery wrote:

Contrast is another issue, though. Cheap LCD TVs still seem to suffer
from glowing blacks, greatly reducing the apparent contrast ratio.

But the manufacturers tell you they've got a million to one contrast
ratio on their screens, so you must be wrong and it's your eyes that
are at fault.

Or they could just be making it up as they go along.

On 30/08/2012 19:19, Steve Thackery wrote:
I spent a fortune to get a TV with zoned backlighting, so the black bits
of the picture really are completely dark.

Hmm. I discussed this one with a salesman (yes, I know... but his
replay made sense). They've dropped this technology because although the
black bits in the middle of a dark area are great, the black bits next
to a bright bit aren't dark at all. Which means if you have a big black
bit next to a bright bit some of them aren't as black as others.

Wearing my engineer's hat it occurs to me that calibration must be a
nightmare too. As you've got one is this true?

Mind, I suspect my Sony has vignetting in the corners. But I hardly
ever notice, and when I do have trouble convincing myself it isn't a
shot effect or something...

Andy

Paul Ratcliffe writes:

On Thu, 30 Aug 2012 19:19:14 +0100, Steve Thackery wrote:

Contrast is another issue, though. Cheap LCD TVs still seem to suffer
from glowing blacks, greatly reducing the apparent contrast ratio.

But the manufacturers tell you they've got a million to one contrast
ratio on their screens, so you must be wrong and it's your eyes that
are at fault.

Or they could just be making it up as they go along.

Maybe that is the reason that the TV stations no longer broadcast the
testcard - so that people will not discover that it is impossible to
correctly adjust the set so that the greyscale bars correctly progress
from black to white with a contrast between each section. I wonder how
many people now take the trouble to adjust a new TV set - first with the
saturation right down (ie monochrome display) and iteratively adjust
brightness and contrast to get black black and white white with the
correct greyscale progression, and only what that is correct turn up the
saturation to make the colour bars and the skin tone look correct.

Mortimer wrote:

For me, the big problem with modern TVs (and this includes CRTs) is that
they cannot handle highlights well, and suffer horrendous crushing of
anything over a certain threshold. At best, when all three colours are
maxed-out, you just get featureless white.

Yep, good point, and there seem to be two potential causes. Firstly,
the screen itself may not have a linear response to brightness, such
that luminance values higher than a certain level tend to "crush".

But I think the more likely scenario is that the picture data itself
too often "tops out" at 256, 256, 256 RGB (so to speak - I don't know
the actual dynamic range of a TV picture).

If the latter is the case the screen itself is probably behaving
correctly and displaying "fully white" when it is told to, and the
problem is earlier in the chain.

I wonder whereabouts in the chain this "topping out" occurs. My
suspicion is at the broadcast end. But it is also possible that the
bit-depth of the video circuitry in the TV, or of the LCD screen
itself, is less than the bit-depth transmitted, in which case you'd get
that same visible problem.

We need someone in the industry to tell us which it is.

Of course, if the problem is at the broadcast end of the chain (as I
suspect) we would see exactly the same effect on a CRT TV. Perhaps the
problem isn't to do with LCD vs. CRTs, but really about analogue vs.
digital transmissions.

The fact that this "crushing" problem seems to occur only occasionally
makes me think it's due to crap cameras or broadcast equipment.

--
SteveT

Andy Champ wrote:

They've dropped this technology because although the black
bits in the middle of a dark area are great, the black bits next to a
bright bit aren't dark at all.

Correct, in theory. Zoned backlighting can only work "perfectly" when
there's a backlight LED for every pixel. None of the ones you can buy
are even close.

The nett effect is well known and called "blooming". It is only really
noticeable when you've got white writing on a black background.
Because the backlight has a coarser resolution than the display pixels,
you get a slight backlight glow surrounding the white letters.

It's important to emphasise that this is no worse than a normal
backlight bleed. In fact, another way to think of it is that, with a
non-zoned LCD screen, the "blooming" spreads right across the whole
screen.

The salesman's "big black bit next to a bright bit - some of them
aren't as black as others" is a non-problem in real life. I'm pretty
OCD about my TV picture and have studied it in indecent detail; there
are no visible artefacts like the salesman described, only the
white-text-on-a-black-background blooming effect. (I suppose in theory
you might be able to see blooming when looking at a starfield with a
black background, but I've never noticed it.)

So, zoned backlighting is not perfect - there is some blooming under
those particular conditions. But the question is - is it better than a
non-zoned backlight?

And for me, the answer is a definite and emphatic YES. Way, way
better. On my TV I only ever see blooming when looking at the
programme or film credits, whereas I can see normal backlight bleed in
every dark scene, and it drives me mad.

It's particularly annoying when it's streaky or patchy, which I'm
afraid it so often is. Three years ago I blew £1.5k on a Sony, and
there was a backlight streak at all four corners, pointing diagonally
inwards towards the centre of the screen. It drove me so mad I gave
the TV away after less than a year.

Just recently I looked at a very expensive Samsung 8000 series(they
still use edge lighting) in a darkened showroom and the backlight was
clearly visible - but, worst of all, was patchy like looking at clouds
in a night sky.

I did try dynamic backlighting (on that £1.5k Sony) - you know, where
the backlight is dimmed on dark scenes which would normally show
backlight bleed. But it's awful! You can see a dreadful "pumping"
effect whenever the picture make-up changes - it drove me mad.

I replaced the Sony with a similarly-priced Panasonic plasma, but the
refresh flicker (visible to me on all the plasmas I've seen) was just
too annoying to live with. That got sold as well.

In the end it cost me a stunning £3.5k to find a TV that I really
liked: a 55" LCD Sony with zoned backlighting. Not perfect (the
blooming is visible) but it is such a small defect, and in all other
respects it is so good, that I'm happy with it.

--
SteveT

In article , Steve Thackery
writes
Mortimer wrote:

For me, the big problem with modern TVs (and this includes CRTs) is that
they cannot handle highlights well, and suffer horrendous crushing of
anything over a certain threshold. At best, when all three colours are
maxed-out, you just get featureless white.

Yep, good point, and there seem to be two potential causes. Firstly,
the screen itself may not have a linear response to brightness, such
that luminance values higher than a certain level tend to "crush".

But I think the more likely scenario is that the picture data itself
too often "tops out" at 256, 256, 256 RGB (so to speak - I don't know
the actual dynamic range of a TV picture).

If the latter is the case the screen itself is probably behaving
correctly and displaying "fully white" when it is told to, and the
problem is earlier in the chain.

I wonder whereabouts in the chain this "topping out" occurs. My
suspicion is at the broadcast end. But it is also possible that the
bit-depth of the video circuitry in the TV, or of the LCD screen
itself, is less than the bit-depth transmitted, in which case you'd get
that same visible problem.

If it was at the broadcast end then all TV's, including CRTs, would
suffer from it at the same time, on the same images. They don't, so it
isn't at broadcast.

Its more likely to be related to how some panels handle the gamma
processing inherent in video. Gamma was necessary in the days of CRTs
due to their inherent non-linear response but is still beneficial today
as a means of data compression. If video was linearly encoded then most
of the precision in the highlights would simply be wasted, since you
need much more linear precision to see subtle shadow changes than you
need for highlights. Gamma attempts to even out the quantisation, so
approximately the same precision is used to quantify discernable
differences in shadows as highlights.

Still images use gamma as well. Most digital cameras digitise the video
signal off the sensor to 12-bit precision, some high end SLRs now do 14
or even 16-bit precision. However the jpg images they produce only need
8-bit precision for each primary colour. Jpg images are gamma encoded,
usually with the 2.2 gamma defined by the sRGB colorspace that has
become the defacto standard of the PC world (or the 1.8 gamma of Macs).

LCDs are, by comparison, fairly linear and the video signal, which is
already precompensated with a gamma response close to the inverse of the
phosphors of old CRTs (eg. 2.5 for PAL, 2.2 for NTSC) needs to be gamma
encoded within the set. How that is implemented and to what precision
can result in the "topping out" referred to.
--
Kennedy

Steve Thackery wrote:


It's particularly annoying when it's streaky or patchy, which I'm afraid
it so often is. Three years ago I blew £1.5k on a Sony, and there was a
backlight streak at all four corners, pointing diagonally inwards
towards the centre of the screen. It drove me so mad I gave the TV away
after less than a year.
Can I be your friend, just in case it ever happens again?

Bill