Dynamic TV pictures

Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast dynamic
range on the picture. The example he gave was of a spotlight momentarily
dazzling the camera also dazzled the viewer on a good quality transmission,
but he claims, no lcd seems to do more than give a kind of flat medium
bright effect on such content, as if there is a clamp fitted to stop this.
Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.
Brian

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

On Sat, 2 Nov 2013 09:52:01 -0000, "Brian Gaff"
wrote:

Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast dynamic
range on the picture. The example he gave was of a spotlight momentarily
dazzling the camera also dazzled the viewer on a good quality transmission,
but he claims, no lcd seems to do more than give a kind of flat medium
bright effect on such content, as if there is a clamp fitted to stop this.
Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.
Brian

The only problem I notice is at the dark end of the range. The
contrast is too low to see details. The bright end seems much the same
as it was with analog TV.

Steve

--
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"Stephen Wolstenholme" wrote in message
...
On Sat, 2 Nov 2013 09:52:01 -0000, "Brian Gaff"
wrote:

Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast
dynamic
range on the picture. The example he gave was of a spotlight momentarily
dazzling the camera also dazzled the viewer on a good quality
transmission,
but he claims, no lcd seems to do more than give a kind of flat medium
bright effect on such content, as if there is a clamp fitted to stop this.
Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.
Brian

The only problem I notice is at the dark end of the range. The
contrast is too low to see details. The bright end seems much the same
as it was with analog TV.

In my experience, non-CRT TVs seem to handle over-exposed highlights much
worse than CRTs did: there's more tendency to display featureless areas of
strong cyan, magenta or yellow/orange, presumably where one of the three
colours has reached absolute maximum and the other two are just short of
this so yielding non-white highlights.

Interestingly the effect seems to be more noticeable when playing from a
Blu-Ray disc than from DVD or from live (Freeview or satellite) broadcasts.

The absence of flicker is very welcome: when I see a CRT TV nowadays I'm
very conscious of the flicker, which I never used to be when I watched one
all the time.

Black response can be poor, though it's more banding and JPEG random
blockiness than lack of true black, which suggests that maybe I've got the
brightness slightly too high. One good thing about non-CRT screens is that
the screen is much darker in the unilluminated areas - there's less
reflection of ambient light.

On 02/11/13 09:52, Brian Gaff wrote:
Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast dynamic
range on the picture. The example he gave was of a spotlight momentarily

If carefully set up, an analogue TV, with a CRT display, is capable of
going to near perfect black. In practice, they would either be set up so
that maximum black was still slightly lit, or they would be set up so
that they went black whilst the image was still grey. (Any emissive
display can go to black, which was the big advantage of plasma displays.)

dazzling the camera also dazzled the viewer on a good quality transmission,

That's not possible as the transmitted signal only had a limited range
between peak white and black level, and, except for night time scenes,
one would expect the full range to be used.

but he claims, no lcd seems to do more than give a kind of flat medium
bright effect on such content, as if there is a clamp fitted to stop this.

Dynamic range on LCDs is limited by the inability to to make the LCD
cell completely opaque, i.e. it limits how black blacks can be and
doesn't affect the white end limit. There are also issues to do with
quantisation errors in the digital signal. Although the signal can
represent pure black, the next level up is not infinitesimally lighter.

Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.

Digital signals have a maximum possible whiteness, just like real world
analogue ones. Also, one would generally want to use the full dynamic
range of the LCD cells for all normal pictures, to minimise the
consequences of poor contrast ratio due to blacks being grey.

Note that the ability of real world analogue receivers to provide a high
contrast ratio was affected by the quality of the DC restoration. Black
and white sets generally had none, so low contrast night scenes would
come out mid-grey, rather than almost black.

Also, if I remember correctly, UHF analogue signals were actually
transmitted with maximum white being zero modulation, so it was
impossible to transmit a whiter than white colour, even if you
temporarily exceeded the maximum transmitter power.

(I believe one of the advantage of LED backlights is that they can be
automatically turned down in night scenes, allowing the full range of
the panel to continue to be used.)

Brian Gaff wrote:

Now this was a conversation with a sighted person about a week ago.
He pointed out that many TVs like Sony in the analogue days had a
vast dynamic range on the picture

Brian, no disrespect to your friend, but I think this is nonsense.
There's no way was any CRT bright enough to genuinely dazzle anyone.
Yes, there's a subjective tendency to THINK you're being dazzled - I
once caught myself narrowing my eyes when the camera panned up to the
sun - but that's just a biological reaction, not real dazzle.

Has anyone got the dynamic range figures for a typical (or good ) CRT?
They are surprisingly poor.


--
SteveT

NY wrote:

The absence of flicker is very welcome: when I see a CRT TV nowadays
I'm very conscious of the flicker, which I never used to be when I
watched one all the time.

Yes, me too! Also, I had to sell my very expensive Panny plasma for
exactly the same reason - I can detect flicker on them (Panny even had
the balls to plaster a "400Hz" sticker all over it, but that wasn't a
true refresh rate at all.

--
SteveT

"Brian Gaff" wrote in message
...
Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast
dynamic range on the picture. The example he gave was of a spotlight
momentarily dazzling the camera also dazzled the viewer on a good quality
transmission, but he claims, no lcd seems to do more than give a kind of
flat medium bright effect on such content, as if there is a clamp fitted
to stop this.
Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.
Brian

Another factor with CRTs is poor EHT regulation which was a feature of many
TV CRTs, though not computer monitor CRTs. This could contribute to the
dazzle effect you describe as the maximum brightness can be instantaneously
higher than normal on a shot change from dark to light.

Stephen Wolstenholme wrote:

The only problem I notice is at the dark end of the range. The
contrast is too low to see details. The bright end seems much the same
as it was with analog TV.

Adjust the gamma?

Bill

Steve Thackery wrote:
Brian Gaff wrote:

Now this was a conversation with a sighted person about a week ago.
He pointed out that many TVs like Sony in the analogue days had a
vast dynamic range on the picture

Brian, no disrespect to your friend, but I think this is nonsense.
There's no way was any CRT bright enough to genuinely dazzle anyone.
Yes, there's a subjective tendency to THINK you're being dazzled - I
once caught myself narrowing my eyes when the camera panned up to the
sun - but that's just a biological reaction, not real dazzle.

Yes, I've done that. And I think I've been dazzled by a CRT screen. My
old analyser had a good bright screen and if I turned it on after a
period of working by dim light (in a loft or whatever) it would seem a
bit dazzley.

I wonder if the extreme brightness of the horizontal line during frame
collapse could be obtained from the whole screen, were it driven so to do?

Bill

Regardless of anything else, the maximum amount of light a TV screen
is physically capable of emitting will be the brightness of the light
source behind the LCD panel, usually a fluorescent lamp or LEDs. The
total power consumption of my TV measures about 75W, and though I'm
not sure what proportion ends up as light, even if all did, that
amount spread over a large screen couldn't show an object looking as
bright as a 75W lightbulb. It's probably a typical value for any flat
screen except a plasma, and you only have to put your hand above a
plasma screen to realise what it's doing with most of the energy it's
consuming.

It's easier to give an estimate for a shadowmask CRT, because I have
some of those Mullard data books that specify the maximum beam current
around 1mA, and the final anode voltage 25kV, so I'm sure you can work
out the maximum display power yourself. Then you have to remember that
once again this is spread over the entire screen, so any bright object
that doesn't fill the screen will only dissipate a portion of it, and
a lot of it will have been stopped by a metal sieve anyway.

All of this suggests that the capability of *any* TV set to dazzle
someone is nothing like that of any typical thing like a lamp or a
reflection of the Sun that would be dazzling in real life. At best, a
picture can only ever be regarded as a scaled down representation of
something, rather than an attempt at an absolute replica.

Rod.

On Sat, 2 Nov 2013 09:52:01 -0000, "Brian Gaff"
wrote:

Now this was a conversation with a sighted person about a week ago. He
pointed out that many TVs like Sony in the analogue days had a vast dynamic
range on the picture. The example he gave was of a spotlight momentarily
dazzling the camera also dazzled the viewer on a good quality transmission,
but he claims, no lcd seems to do more than give a kind of flat medium
bright effect on such content, as if there is a clamp fitted to stop this.
Is he right? I'd have thought that as long as the backlight was bright
enough this effect should still be good.