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Significance Of JVC RS2's New Gamma Controls - More "Image Pop?"

post #1 of 12
9/19/07 at 7:30am
Thread Starter 
One criticism of the JVC and the LCOS/SXRD technology in general is that it
lags behind DLP in terms of generating ANSI contrast. Most DLPs can produce a more contrasty, "punchy" image in mid to brighter scenes.

I know that fooling around with the gamma controls of a display can alter the
impression of "punch" in an image, to some degree. In his widescreen review of the JVC RS1 projector, Greg Rogers wrote:

"This is the first lamp-based projector that has a native full-field contrast ratio high enough to nearly emulate a CRT projector, so I was surprised that a CRT-like gamma curve of 2.4 or 2.5 wasn't included. I believe that would have increased the image depth in moderately bright to bright movies."

Now, one of the features boasted by JVC of the new RS1 is greater control over the gamma: "The OSD menu offers RGB adjustment at several points along the gamma curve"

AnandTech.com showed pictures they took of that onscreen menu:

http://www.anandtech.com/printarticle.aspx?i=3089

And you can see options in the menu for gamma points of 1.8 up to 2.6 (including, of course, the 2.4 and 2.5 desired by Greg Rogers).

So, does this not mean that one can use the gamma to have settings in which
some degree of more image depth or punch can be rendered in the brighter scenes in which LCOS usually falls short?

I'm certainly not implying fooling with the gamma can bring it into parity with
DLP technology ANSI. I'm just wondering what significance the new gamma
controls have in this issue.

As a side question, I'd like to know about the ANSI contrast of LCD projectors. In general, how does LCD projection ANSI compare with DLP and LCOS?

Thanks,
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post #2 of 12
9/19/07 at 7:52am
A good ANSI for LCD technology seems to be around 250:1. I say that the big difference can not be explained by good dlps 500:1+ ANSI. It is the higher pixel to pixel contrast that is the big difference. I am pretty sure this is the case but we always get hang up on the ANSI.
There is much to learn in the contrast thread by Mark Petterson that put a lot of effort in finding optimal test patterns.

I long for when 4-panel technology comes to home theater. NHK in collaboration with JVC achieved 1000000:1 in sequential contrast. Three panels for chroma and luminance and one panel for the luminance of the combined RGB. This would provide great ANSI contrast.
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post #3 of 12
9/19/07 at 9:21am
Quote:
Originally Posted by R Harkness View Post

So, does this not mean that one can use the gamma to have settings in which

The new adjustable gamma feature won't affect ANSI contrast and give the RS-1 a punchier more DLP like image but what it will do is allow a person to dial in a gamma curve that looks better. I and others have experimented with different gamma curves using a combination of gamma settings from an outboard VP and the RS-1 gamma settings. A higher gamma makes the image look "richer" and with more depth. The one thing I didn't like though is that higher gamma seemed to crush blacks too much. With an adjustable gamma such as this a person can use the base gamma curve that they want and then tweak different ranges to suit their tastes (including the all important one at the very bottom of the luminance range).

Btw, also mentioned in the anandtech article is the implication that JVC will allow RGB greyscale adjustments in different IRE ranges rather than shifting the whole curve up or down as the RS-1 does now. If true this should be a big boon to calibrators.

Quote:
Originally Posted by Ohlson View Post

There is much to learn in the contrast thread by Mark Petterson that put a lot of effort in finding optimal test patterns

Mattias, thanks for the plug on the contrast thread and giving my distant cousin "Mark Petterson" some limelight for a change
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post #4 of 12
9/19/07 at 10:43am

I will leave my mistake in print.

Mark P , playing it safe
How do you like the fact that JVC are in on 4-panel efforts?
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post #5 of 12
9/19/07 at 10:54am
Thread Starter 
Thanks men. I'll be interested to see how the different gamma adjustments look to my eye as well.

Interesting about LCD contrast. I'd thought ANSI wasn't an LCD strong suit, but recently I saw the Panasonic 1000 and the JVC HD1 playing the same material in the same room and the Panasonic seemed to have the punchier ANSI contrast, so that got me wondering. However, it was a completely uncontrolled demo under bad conditions so it can't count for much.
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post #6 of 12
9/19/07 at 11:11am
Quote:
Originally Posted by Ohlson View Post


I will leave my mistake in print.

Mark P , playing it safe
How do you like the fact that JVC are in on 4-panel efforts?

Sounds like an interesting development. How does 4-panel improve ANSI contrast?
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post #7 of 12
9/19/07 at 11:48am
Well the modulation effort is applied in a serial way and the effect is that the dynamic range is multplied minus optical inefficiencies.

1 RGB panels creates the ANSI pattern
2 The Y controlling panel "blocks" light in the dark squares.
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post #8 of 12
9/19/07 at 12:42pm
Selection of gamma is always a tradeoff between depth/richness of blacks on the one hand and shadow detail on the other. For example, here is a comparison of output using different gamma curves.


As you can see, the most profound difference occurs at the low end.

A 2.5 gamma produces half the output at 10% stim as does a standard 2.2 gamma. The higher you go the less pronounced the difference becomes. This is why higher gammas will yield higher contrast ratios, but will also seem to crush the blacks.
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post #9 of 12
9/19/07 at 12:49pm
Thread Starter 
Yeah, even playing with the "brightness" control of my plasma, which alters the gamma and raises/lowers black level, the effects can be fascinating. When I'm viewing a moderately bright image - say a daylight interior close up of an actor's face - lowering the brightness produces a pronounced depth to the image. The actor's face starts to take on a more sculptural dimensionality. Unfortunately, the trade off becomes too evident in darker scenes with the crushed blacks. I always wondered if there was
a sort of "EQ" version of gamma in which I could dial it in the "mid range" to get that depth in the mid tones, without dialing down the deeper black levels into crushing.
The RS2 gave me a bit of hope for that, but it appears it doesn't really work that way.
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post #10 of 12
9/19/07 at 1:35pm
Quote:
Originally Posted by Ohlson View Post

Well the modulation effort is applied in a serial way and the effect is that the dynamic range is multplied minus optical inefficiencies.

1 RGB panels creates the ANSI pattern
2 The Y controlling panel "blocks" light in the dark squares.

Interesting. Improving both ANSI and on/off could really be a boon for LCOS.

Quote:
Originally Posted by TomHuffman View Post

Selection of gamma is always a tradeoff between depth/richness of blacks on the one hand and shadow detail on the other. For example, here is a comparison of output using different gamma curves.

This is very true for a fixed gamma. The thing I like about the JVC approach is that the gamma curve can be adjusted along the IRE/%stim range so a person can have a higher gamma for most of the range but a lower (brighter) gamma at the bottom. I don't know if the JVC gamma adjustment will allow fine enouogh increments at the bottom to really dial it in but it's better than the fixed gamma settings we have now
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post #11 of 12
1/2/08 at 12:29pm
I would like complete control of the gamma but we are limited to how much we can change it because the people that do the transfer from film to dvd must assume a certain gamma and unless you want to screw up the color rendition, your pretty much stuck with that gamma.

let me illustrate say you have a color in one scene that mixes 25 percent blue with 25 percent red and 50 percent green to get a particular color with a particular color saturation. Now you increase the gamma Ie. you increase the slope of the gray scale transfer function on a log graph of the ire vs luminance output.

Now instead of getting the previous color mix you get instead 15 percent blue, 15 percent red and 50 percent green. You can't change gamma without effecting both the hue and the saturation.

Aren't you kinda stuck with the gamma you have been given?
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post #12 of 12
1/3/08 at 1:02pm
"You can't change gamma without effecting both the hue and the saturation."

Gamma is IRE output vs. video level input, so if it's the same for all colors there should be no effect on hue/saturation.
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