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Shadow details restored - Thank you Crescendo !!
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beun



Joined: 28 Jun 2006
Posts: 676



PostLink    Posted: Sun Feb 10, 2008 6:57 am    Post subject: Reply with quote


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Aubrey,

What the plot shows is how the brightnes changes from the start of the line to the end of the line. If all the lines are the same than this would show a picture that is black on the left side (the low voltage at the beginning of the line) and changes linearly to peak white on the right (the high voltage at the end of the line) like this:



What the gamma curve does is to accelerate the change from black to white in the darker portions of the picture only. Tse's curves are 5 divisions wide and 7 high, while mine happen to be 7 divisions wide and 5 high. If I do a horizontal and vertical non-linear stretch on my picture in order to get the aspect ratio's of tse's and my curve the same they are a bit more easily comparable.



and as you can see not all that different. The RTC2200 curve shown is the maximum amount of gamma that can be applied, so you can dial in your transfer curve anywhere in between the straight line (no gamma and linear response) and the curved line above it (maximum gamma).


Kim

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ESL-0.5 Full Range Electrostatic Loudspeakers | RTC2200 Component to VGA Converter with Gamma Boost
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paw



Joined: 08 Mar 2006
Posts: 1176
Location: Arvada, CO


PostLink    Posted: Mon Feb 11, 2008 3:53 am    Post subject: Reply with quote

Thanks Kim. Just what I was looking for. I never thought of modifying the picture make them compatible. Great idea.
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tony359



Joined: 04 Aug 2006
Posts: 378



PostLink    Posted: Mon Mar 24, 2008 12:58 am    Post subject: Reply with quote

Hi

I use an HTPC and I boosted gamma since a while. Now, waiting for HD projector, I'm going to buy a PS3 and see HD movie at 1080i with my 1271.

Tonight I saw Underworld and despite the black level was a bit higher to compesate, the dark scenes are too dark. So I think I'm going to buy this magig box but my question is: why we should need a gamma booster on CRT? Is there a reason? If the CRT and the source were correct we should not need any boost. Perhaps the CRT gamma is different from the one that come out from the RGB?

Ciao
Antonio
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kal
Forum Administrator


Joined: 06 Mar 2006
Posts: 15385
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Mon Mar 24, 2008 1:24 pm    Post subject: Reply with quote

Hi Antonio - The problem is that the response curve on CRTs isn't correct as compared to a lot of other display technologies. CRT requires boosting in the lower end for shadow details to become apparent again.

Kal

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tony359



Joined: 04 Aug 2006
Posts: 378



PostLink    Posted: Mon Mar 24, 2008 1:48 pm    Post subject: Reply with quote

Thanks Kal.

But I miss something: if I connect a DVD player to the CRT, should I need the gamma boost? How these CRT were projected? TO work with what? In other words: is there any devices that compensate for the CRT gamma?

Ciao
Antonio
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kal
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Joined: 06 Mar 2006
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TV/Projector: JVC DLA-RS56


PostLink    Posted: Mon Mar 24, 2008 1:51 pm    Post subject: Reply with quote

The only device that compensate for gamma are HTPCs, some of the higher end scalers, and boxes like the RTC2200. I don't know of any source devices that provide a gamma boost.

So yes, if you connect an upscaling DVD player directly to a CRT projector, you most likely won't have a gamma boost. I don't know of any DVD players that provide gamma adjustment.

Kal

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tony359



Joined: 04 Aug 2006
Posts: 378



PostLink    Posted: Mon Mar 24, 2008 2:01 pm    Post subject: Reply with quote

I'm puzzled.

Do you mean that all CRT projectors does not work properly without a gamma boost? I thought it was a fault of my personal 1271...

What about in the past where no gamma boost was available?

Ciao
Antonio
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kal
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PostLink    Posted: Mon Mar 24, 2008 2:08 pm    Post subject: Reply with quote

It's not that they don't WORK correctly. It's that they can all use some degree of gamma boost in the low end. Some models more than others. Nobody NEEDS a gamma boost for the unit to work right, but I don't know anyone that hasn't used it once they've seen what I does.

Kal

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tony359



Joined: 04 Aug 2006
Posts: 378



PostLink    Posted: Mon Mar 24, 2008 2:14 pm    Post subject: Reply with quote

What I mean is: if I measure with a Spyder (for example) the gamma response of a CRT wiyhout any boost, is the measured gamma correct or not? Is this gamma boost something we install to satisfy our eyes or is something we install to restore correct gamma response?

In this last case, seems odd to me that CRT projectors were made with a gamma response that cannot be corrected by any player device...

Ciao
A
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kal
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PostLink    Posted: Mon Mar 24, 2008 2:20 pm    Post subject: Reply with quote

tony359 wrote:
What I mean is: if I measure with a Spyder (for example) the gamma response of a CRT wiyhout any boost, is the measured gamma correct or not?

If you measure with a Spyder2 or the HCFR sensor, the response will not be correct. Gamma will be too low in the bottom end.

tony359 wrote:
Is this gamma boost something we install to satisfy our eyes or is something we install to restore correct gamma response?

Both.

tony359 wrote:
In this last case, seems odd to me that CRT projectors were made with a gamma response that cannot be corrected by any player device...

The source device has no idea what the display device will be. Why would they put all the extra effort of putting gamma curve adjustment tools in the source devices when 99% of people won't care and many displays won't need it?

Kal

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Curt Palme
CRT Tech


Joined: 08 Mar 2006
Posts: 23477
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Mon Mar 24, 2008 2:27 pm    Post subject: Reply with quote

tony359 wrote:


In this last case, seems odd to me that CRT projectors were made with a gamma response that cannot be corrected by any player device...

Ciao
A


Well, let's put it another way. Why are there no digitals out that can do perfect blacks without unplugging them? Mr. Green

Each display technology has it's flaws, the gamma is one of the CRT ones that has now been overcome.
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tony359



Joined: 04 Aug 2006
Posts: 378



PostLink    Posted: Mon Mar 24, 2008 2:27 pm    Post subject: Reply with quote

Ok, clear.

But I'm still puzzled on why CRT manufacturer design the set without a gamma boost since, if I correctly understand, there is no CRT that can display gamma correctly from any source! Smile

However you answered to my question: the need for gamma boosting is needed to restore correct gamma.

Curt
I posted after you posted!
Sure, but that is a technology flaw, not curable in any ways (unplugging them is a solution!).
But if CRT has not linear gamma, why Sony, Barco etc... did not project them with some gamma booster inside the units?

Ciao
A
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Farhan



Joined: 23 May 2008
Posts: 10



PostLink    Posted: Mon Nov 17, 2008 6:58 am    Post subject: Reply with quote

Hmmm my CRT RPTV's service menu has a item called Gamma. It seems to act like a brightness control but also affects contrast. I left it in the default position of 2 since I have no way of measuring it to match it to 2.2 or 2.5 whatever its supposed to be.
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