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benareeno
Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada
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| Posted: Wed Dec 10, 2008 4:47 pm Post subject: BG808s and service level gamma adjustment? |
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I was looking through the menu's of this BG808s I recently aquired and noticed a gamma setting in one of the menus. Would this setting allow me to get proper gamma out of the projector without using a moome or equivalent box? Anyone ever work with it?
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Wed Dec 10, 2008 4:56 pm Post subject: Re: BG808s and service level gamma adjustment? |
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| benareeno wrote: | | I was looking through the menu's of this BG808s I recently aquired and noticed a gamma setting in one of the menus. Would this setting allow me to get proper gamma out of the projector without using a moome or equivalent box? Anyone ever work with it? |
No.
Kal, we need a gamma FAQ!!!!
I've written this dozens of times, so one more is not going to kill me!
First, read this article.
Whenever you see gamma adjustment with one value (like 2.2 or 2.35 or whatever). That is just adjusting the exponent of the curve. The higher the number the "taller" the peak. If you will notice, the curve is symmetrical.
Now, the gamma that Kim's does, that moome's does, that you can do and tweak even more in an HTPC or Lumagen VP is different. You can do just the exponent if you want, or more.
With any "black crushing" display--such as a CRT PJ--we want to reshape the curve so the it is asymmetrical. Basically, we want the bottom of the curve to be really steep--i.e. "come out of black faster". But, we want the rest of the curve (the upper 80% or more) to be pretty much like a "normal" gamma curve.
If you set your gamma high enought to pull it out of black fast enough with the exponent setting in the 808s (or any other device), what you will end up with is a very flat looking washed out picture. Hence the need for what I call "gamma curve reshaping".
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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perisoft
Joined: 29 Aug 2007
Posts: 2920
Location: Ithaca, NY
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| Posted: Thu Dec 11, 2008 12:03 am Post subject: |
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I've noticed exactly that with my 808s - gradations from 50IRE to 100IRE are far smaller per 10 IRE than from 0 to 50.
It would seem that if you could make the PJ do an *inverted* curve at the top, by screwing with the service level stuff, then you could add a normal gamma curve that would boost the (unaltered by the service adjustment) low end while returning the (altered by service level adjustment) high end to where it should be.
It'd be an unholy pain in the ass to do, though, even if possible.
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Gary M.
Guest
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| Posted: Thu Dec 11, 2008 12:06 am Post subject: |
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Kal tells about these controls in the dummies guide, they are for greyscale control
you can correct the lack of blue in the high-end (say to help when you don't defocus like me ) and correct in the middle range as well
read the guide
-Gary
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Person99
Joined: 09 Mar 2006
Posts: 4899
Location: Flower Mound, TX
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| Posted: Thu Dec 11, 2008 12:15 am Post subject: |
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| perisoft wrote: |
It would seem that if you could make the PJ do an *inverted* curve at the top, by screwing with the service level stuff |
Yeah, but you can't which is why we have the moome and Kim devices. 
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Dave
A train station is where the train stops. A bus station is where the bus stops. On my desk, I have a work station....
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kal
Forum Administrator
Joined: 06 Mar 2006
Posts: 18114
Location: Ottawa, Canada
TV/Projector: JVC DLA-NZ7
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| Posted: Thu Dec 11, 2008 1:37 am Post subject: |
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What everyone else said.
Simple rule: If a display has a gamma adjustment, it's usually not the gamma adjustment that we talk about here to come out of black faster (ie: have better shadow details).
I own a Barco with this gamma adjustment, it does nothing for gamma boosting, so I need to use an external tool (the RTC2200). As someone mentioned I get into this in my 'Greyscale and Colour Calibration for Dummies' guide:
Kal
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zGman
Joined: 22 May 2006
Posts: 599
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| Posted: Thu Dec 11, 2008 2:25 am Post subject: |
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Barco Gamma is helpful, but as noted, not the same as the add on units often discussed here.
Red and blue midlights are nice, usually set blue to zero, and red around 6 or 8 (red is backwards, more = less)
Blue slope and breakpoint are easy to see if you have a horizontal crossed 5 ire step pattern displayed,
but I have found more luck setting by eye than using a meter, you can see the blue sweep through the pattern.
Usually end up around 22 breakpoint and slope = max minus 2
You will still need a little blue defocus, and need to set up somewhere around 42 brightness,
and 72 contrast to get the curves to work out alright
G
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perisoft
Joined: 29 Aug 2007
Posts: 2920
Location: Ithaca, NY
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| Posted: Thu Dec 11, 2008 4:19 am Post subject: |
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| zGman wrote: |
You will still need a little blue defocus, and need to set up somewhere around 42 brightness,
and 72 contrast to get the curves to work out alright
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42 brightness would hose the black level completely with my BG808s. I usually run low to mid 30s - and the g2 is pretty much set correctly (within a gnat's ass). 72 contrast also seems quite high - I run 65, and while the brightness from 72 would be great, it starts blooming at 75 and it seems that 72 is pushing it pretty damned hard...
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zGman
Joined: 22 May 2006
Posts: 599
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| Posted: Thu Dec 11, 2008 4:35 pm Post subject: |
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Hi David,
The contrast and brightness control settings are only relative, the actual
output depends on the settings used for 'cut-off' and 'gain' for each color.
I use those settings when I do Barco grey scale, and they give me plenty
of range to work with in the 'cut-off' and 'gain' settings.
Also the gamma curve seems to track with contrast, and I have found that
blue "hump" gets worse if I set-up at a significantly lower contrast setting.
G
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