confused about contrast ratios

Well a CRT screen is refreshed once every 1/25 second so any exposure
faster than this would in my opinion give a false value.

Dear oh dear. Even 1950's sets were refreshed interlaced at 1/50s

Recent modern CRT's refreshed the whole picture [from memory] at 100Hz,
changing bits that had been updated.



A standard CRT screen is refreshed with only half an interlaced picture in
1/50s therefore with a complete interlaced picture every 1/25s.
It is true some recent more expensive CRT TVs have a faster refresh rate but
they would be in the minority.
Fred

housetrained wrote:
What you see (in the specs) is NOT what you get. Compare the actual sets
with the specs and you will SEE what I mean. It's nearly all spin.

CRTs only have a contrast ratio of perhaps 500:1 and if you go to the
cinema the film will have a contrast ratio of no better than 1000:1

ANSI contrast ratio figures any higher than this are overkill, but
unfortunately LCD TV and projector manufacturers rarely quote ANSI
contrast - they make up their own definition of contrast which makes the
figure look high but unfortunately does not represent any actual real
life viewing situation and so is pretty meaningless.

CRTs only have a contrast ratio of perhaps 500:1 and if you go to the
cinema the film will have a contrast ratio of no better than 1000:1

ANSI contrast ratio figures any higher than this are overkill, but
unfortunately LCD TV and projector manufacturers rarely quote ANSI
contrast - they make up their own definition of contrast which makes the
figure look high but unfortunately does not represent any actual real
life viewing situation and so is pretty meaningless.


Ah, thanks for explaining that!

SteveT

"Robin Faichney" wrote in message
...
On Wed, 2 Jan 2008 21:21:34 -0000, "The Simpsons"
wrote:

"Peter Lynch" wrote in message
...
In an effort to get an idea of the C/R I was getting from my old TV,
I used my DSLR in AE mode. When pointed at the TV screen with the set
turned off (so all I was getting was ambient light from the room
reflected
off the screen) the camera told me I needed a 1/3 second exposure. Doing
the same measurement with a bright white image on screen, I got a meter
reading of 1/250. So my "contrast ratio" in real-life is about 80:1 and
I
find this quite acceptable.

So, on the basis that my little experiment is valid (please speak up if
you can see any obvious mistakes), is there any reason why I should pay
more for one screen with a higher C/R over a similar one with a lower
value
given that they would both be 10's or 100's of times more than I would
ever
see in real life?

Well a CRT screen is refreshed once every 1/25 second so any exposure
faster
than this would in my opinion give a false value.

He's just using the camera's meter, not taking a shot. What matters is
the period over which the metering takes place, and I've absolutely no
idea what that will be for a digital camera. Now I think about it, I'm
not sure an old-fashioned light meter would do the job properly
either. I've taken screen shots using a film camera, but not in a long
time, and I seem to remember using settings recommended in a magazine
or book.


Yes, you're right, he's not taking a shot! The metering however would be
continuous for the duration that the shutter was half pressed, theoretically
what the OP is doing should work.
I still reckon you can't beat using your own eyes in a decent showroom to
decide on what to buy. Just take your time deciding, in my case that was 3
months!
Fred

On Thu, 3 Jan 2008 19:11:10 -0000, "The Simpsons"
wrote:

I still reckon you can't beat using your own eyes in a decent showroom to
decide on what to buy.

Yes, but does anybody know of a decent showroom that will adjust all
it's displayed models such that they are optimized along the lines of my
post of about two days ago.

In the 'normal' showrooms nobody really knows what they're looking at,
which is fine for the average punter but for someone who is
knowledgeable enough to know what they're looking for it's a minefield.
--
Alan White
Mozilla Firefox and Forte Agent.
Twenty-eight miles NW of Glasgow, overlooking Lochs Long and Goil in Argyll, Scotland.
Webcam and weather:- http://windycroft.gt-britain.co.uk/weather

"Mike Henry" wrote in message
...
In , "The Simpsons"
wrote:
Well a CRT screen is refreshed once every 1/25 second so any exposure
faster than this would in my opinion give a false value.

Dear oh dear. Even 1950's sets were refreshed interlaced at 1/50s

Recent modern CRT's refreshed the whole picture [from memory] at 100Hz,
changing bits that had been updated.

A standard CRT screen is refreshed with only half an interlaced picture in
1/50s therefore with a complete interlaced picture every 1/25s.

No, that's only if it's a special mode called IIRC segmented frame (two
halves of a 25 frames-per-second picture). That gives you jerky 25 fps
motion, like the "film effect" that some producers are in love with.

Normal interlaced TV pictures, as stated, are nice and smooth at 50 fields
per second. In one 1/50th of a second the even lines are displayed, and in
the next the odd lines, and so on but each pair does is not making up two
"halves" of a jerky 25 frames/second picture. There are 50 different
movements per second that are recorded by the camera and displayed on the
screen. (It is this smooth motion that we've had for many years that the
cretins are trying to take away from us.)


See this link, look under DESCRIPTION
http://en.wikipedia.org/wiki/Interlace
UK PAL - the odd field (1/50s) + the even field(1/50s) = one complete
picture(1/25s).

Mike Henry wrote:

In , "Zimmy" wrote:
Personally, the problem I have with cheaper/older LCDs is too much contrast,
ie all the brightest shades get rounded to pure white and all the darkest
shades get rounded to pure black

Er, those two problems you describe are called "black crushing" and "white
crushing", not "too much contrast"(!) I think it's important to get the
terms correct since this is a technical group...

Is there any other effect of "too much contrast"?

--
Dave Farrance

In article , Mike Henry wrote:
Normal interlaced TV pictures, as stated, are nice and smooth at 50 fields
per second. In one 1/50th of a second the even lines are displayed, and in
the next the odd lines, and so on but each pair does is not making up two
"halves" of a jerky 25 frames/second picture. There are 50 different
movements per second that are recorded by the camera and displayed on the
screen. (It is this smooth motion that we've had for many years that the
cretins are trying to take away from us.)

pedant mode
Television lines are numbered in the order of transmission, not the order
they appear on screen, so it's actually lines Nos 1-312 and the first half
of line 313 that are displayed in one vertical scan, and then the second
half of line 313 followed by 314-625.

Some textbooks describe it as you have, but if you want to describe it in
terms of odd and even numbered lines, it would be better to say-

"In one 1/50th of a second the lines that would occupy even numbered
positions on the screen are displayed, and in the next the lines that would
occupy odd numbered positions on the screen, if it were the positions on the
screen that were numbered, which it isn't".
/pedant mode

I have seen both correct and incorrect descriptions in textbooks and
magazine articles, and it must confuse people who are new to it. For a
superficial understanding of how interlace works you could argue that line
numbers are not important, which is a fair point. However it becomes
important in the context of actual equipment that has to generate or read
signals on particular lines, because it is then vital that everybody agrees
upon which lines are which.

Rod.

Alan White schrieb:

In the 'normal' showrooms nobody really knows what they're looking at,
which is fine for the average punter but for someone who is
knowledgeable enough to know what they're looking for it's a minefield.

Really true, a possibility to judge on a good HD picture adjustment
would be receiption of Premiere HD´s special "HD perfekt" on Friday
night (21 hours GMT, unencrypted) from Astra 19 degr. east.
"High contrast pictures" are sometimes displayed with white peaks and
black peaks cut off, losing detail at both ends of the grey scale,
thanks to variations on HDMI video level standards (normal/extended),
not understood by set-top box designers...

best regards

Klaus

Dave Farrance schrieb:

Is there any other effect of "too much contrast"?


Please look at my answer some 10 lines above...

Klaus