Why is video inverted for transmission?

[Richard Crowley]

"Randy Yates" wrote ...

Yes, that's the basic idea. That translates to our eyes not
having a high dynamic range, I think.

Our eyes have a *much greater* dynamic range than any film
or television medium. There is a constant effort get film and/or
television to even approach the dynamic range of normal eyesight.
Some people use special filters to visualize what a scene will
look like on film, etc.

OTOH, our eyes are also "auto color balancing". Not only do
we not have to consiously adjust between seeing indoors under
(for example) tungsten or fluorescent vs. outdoors under sun-
light, but we don't even consiously think about viewing interior
AND exterior (through a window or door) in the same "scene".
I think is our "auto color balance" function which neutralizes
the green cast.

 

[Richard Crowley]

"JosephKK" wrote ...

About the matching of the gamma curves, when i was young and had very
good eyes, and color TV was just becoming popular. There were still
plenty of broadcasts in monochrome and i could watch them on B&W sets
and color sets "side by side" on the showroom floors. There was
scant (if any, i sure did not notice) difference in the viewing
experience (at a reasonable distance from the screen). If there were
obvious/significant differences in the gamma correction they would
have showed up at that time. The changes to better match YUV were
rather minor tweaks, and the monochrome shows that i watch have no
observable color artefacts as a result of the change.

We still use many monochrome CRT monitors for TV
production. From camera viewfinders (either the tiny
1.5 inch field eyepiece ones, or the 5~7-inch studio
viewfinders) to the camera monitors in the control
room where the director is calling shots, etc.

 

[Allen]

Didn't his first sentence answer your question?

Only if he wanted it to. If he loves the "good old days" so much, that's
his choice. If his ancestors had followed the same line of thought he
would be living in a cave, and hunting and gathering for survival. I
won't be seeing any more posts from this clown. And thanks, Al, for your
response.
Allen

 

[Robert Peffers]

"JANA" wrote ...

And the latest computer screens (including laptops) are switching
back to the very shiny surface apparently because the "non-glare"
treatment also reduces the clarity of the image you are viewing
from the screen.


Some of that may have been from the thick glass envelope
over the front of the screen. Most glass looks slightly greenish
under conditions where you can see the glass itself vs. whatever
is on the other side.


Indeed, one of the many psychological effects that modern
technology depends on to interface with humans.

Not to mention the psychological fact that we humans, when watching TV,
expect the grass to be much greener that it is in real life. What we see as
a green lawn is, in face, quite brownish in fact.

 

[Don Bowey]

Only if he wanted it to. If he loves the "good old days" so much, that's
his choice. If his ancestors had followed the same line of thought he
would be living in a cave, and hunting and gathering for survival. I
won't be seeing any more posts from this clown. And thanks, Al, for your
response.
Allen

Well, birds of a feather....... Y'all disappointed with your lives, have
liver problems and who knows what else?

I expect that when someone complains about the state of electronics at some
period in history, that the response will be about electronics.

He's an ass and so are you.

 

[Nobody B.]

All this talk about blacks being on the bottom or the top is racist.

 

[Al in Dallas]

They are supposed to already be availible, but try to buy one.

The demand won't really start until people are forced to stop using
their analog tuners. At that point, people will have at least three
options: continue to use cable or satellite with a box that outputs
analog (these people incur no new costs), buy a digital TV, or buy a
digital tuner. The last option won't be considered unless it's less
expensive than switching to a non-OTA service and less expensive than
a digital TV. It looks like a great way to force people to stop using
antennas.

 

[Bob Myers]

About the matching of the gamma curves, when i was young and had very
good eyes, and color TV was just becoming popular. There were still
plenty of broadcasts in monochrome and i could watch them on B&W sets
and color sets "side by side" on the showroom floors. There was
scant (if any, i sure did not notice) difference in the viewing
experience (at a reasonable distance from the screen). If there were
obvious/significant differences in the gamma correction they would
have showed up at that time. The changes to better match YUV were
rather minor tweaks, and the monochrome shows that i watch have no
observable color artefacts as a result of the change.

Yes.

"Gamma" and so-called "gamma correction" are among the
most misunderstood topics in electronic displays, and have
been for about as long as CRTs have been in common use.
For this discussion, it should be sufficient to note that the
"gamma" characteristic of CRTs results inevitably from the
physics of the electron gun, and for any CRT will be fairly
close to a power-law curve where the exponent is close
to 2.5, give or take a bit. In TV practice, the inverse curve
which is required of the camera output, etc., is modified
slightly at the dark end, to take care of some real-world
factors and to help reduce the effects of noise at that end
of the curve as seen in the final CRT-displayed image. There
is no difference in the "gamma correction" used with
monochrome ("black and white") and color CRTs.

If you really want to get a great look at the basics of
"gamma", Charles Poynton's "FAQ" paper on the subject
is a good place to start:

http://www.poynton.com/GammaFAQ.html

Bob M.

 

[Joerg]

If you don't clamp the video, the brightness and contrast will change
as the overall scene changes. It sets the reference for the black level
in the video amplifier. if it drifts up, the screen gets brighter, and
if it drifts down, it gets darker.

Guys, it was a joke ...

Who cares about all that drift if the programming ain't worth watching
in the first place?

 

[Joerg]

Joerg [email protected] posted to
sci.electronics.design:




True, but a lot of the best stuff is B&W (notably much of Andy
Griffith, Bonanza, The Outer Limits, Masterpiece Theater, and so on).
Often a lot of the old good stuff is available on cable or satellite
that OTA stations cannot use because the audience is too small.

Yes, but then they make us pay around $50/month where $49 of those
Dollars are going towards junk I don't care for. Luckily there is the
VCR. Occasionally our video rental place in town has an old movie. Much
of that has never even been ported to DVD.

 

[Joerg]

They are supposed to already be availible, but try to buy one.

Exactly. Last time I asked at Walmart: "Huh? A what? No idea ..."

 

[Joerg]

The demand won't really start until people are forced to stop using
their analog tuners. At that point, people will have at least three
options: continue to use cable or satellite with a box that outputs
analog (these people incur no new costs), buy a digital TV, or buy a
digital tuner. The last option won't be considered unless it's less
expensive than switching to a non-OTA service and less expensive than
a digital TV. It looks like a great way to force people to stop using
antennas.

Or a great way to put a ding into advertising revenue because quite a
few well educated and thus rather affluent OTA diehards may discover the
obvious: You can already get some decent stuff over the Internet. For
example, if you want financial news you go to Bloomberg-TV on the web.

I can already see some pink slips at the stations.

 

[glen herrmannsfeldt]

Al in Dallas wrote:
(snip)

The demand won't really start until people are forced to stop using
their analog tuners. At that point, people will have at least three
options: continue to use cable or satellite with a box that outputs
analog (these people incur no new costs), buy a digital TV, or buy a
digital tuner. The last option won't be considered unless it's less
expensive than switching to a non-OTA service and less expensive than
a digital TV. It looks like a great way to force people to stop using
antennas.

As I understand it, the government is supposed to subsidize buying
the converters. That might keep them priced higher than they otherwise
would be, such that the actual cost is the same.

DVD recorders with ATSC tuners are now out, an presumably they
have video outputs for existing TVs. Maybe even RF outputs, maybe not.

-- glen

 

[glen herrmannsfeldt]

JosephKK wrote:

(snip)

About the matching of the gamma curves, when i was young and had very
good eyes, and color TV was just becoming popular. There were still
plenty of broadcasts in monochrome and i could watch them on B&W sets
and color sets "side by side" on the showroom floors. There was
scant (if any, i sure did not notice) difference in the viewing
experience (at a reasonable distance from the screen). If there were
obvious/significant differences in the gamma correction they would
have showed up at that time.

I suppose I was always surprised that gamma correction was noticed
in the first place, but I suppose it is.

I believe that NTSC did tests to show that it wouldn't be a
significant problem. Probably also expecting most people
to switch to color sets.

-- glen

 

[ChairmanOfTheBored]

They are supposed to already be availible, but try to buy one.

Totally available.

My first HDTV tuner will put out onto std 4:3 TVs no problem. Looks
far better than anything else that TV ever displayed too.

Try WalMart, and the USDigital HDTV tuner. Bigger brand names also
make them.

 

[ChairmanOfTheBored]

Al in Dallas [email protected] posted to sci.electronics.design:


They are already available, just google. Watch the price spike, and
then the sheeple bitch, and then the regulators step in. Time your
investments carefully.

You guys are dopes. There will be no spikes on a subject that has been
known about and previously covered for years.

Readily available. Sheesh!

 

[ChairmanOfTheBored]

Only if he wanted it to. If he loves the "good old days" so much, that's
his choice. If his ancestors had followed the same line of thought he
would be living in a cave, and hunting and gathering for survival. I
won't be seeing any more posts from this clown. And thanks, Al, for your
response.
Allen

I like my saber tooth adorned shaman's necklace!

At least we had a monolith to visit back then... :-]

 

[ChairmanOfTheBored]

Exactly. Last time I asked at Walmart: "Huh? A what? No idea ..."

There is a difference between asking someone that works at WalMart what
they carry, and actually knowing about it yourself.

http://www.walmart.com/catalog/product.do?product_id=5893822

http://www.walmart.com/catalog/product.do?product_id=4995009

Not everything is available AT the store either.

 

[ChairmanOfTheBored]

Exactly. Last time I asked at Walmart: "Huh? A what? No idea ..."

Try Ebay then dope.

http://cgi.ebay.com/Hisense-USDTV-D...ryZ61396QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[Ray Fischer]

Excellent web page about the structure of a video signal:
http://zone.ni.com/devzone/cda/tut/p/id/4750

It is indeed. Too bad it's going to be moot in 17 months when all the
broadcasters go over to digital only.