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Gamma adjustment

 
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Corleone88



Joined: 09 Dec 2006
Posts: 396
Location: France


PostLink    Posted: Tue Oct 15, 2013 9:07 am    Post subject: Gamma adjustment Reply with quote


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Hello,

I have a BG808 + OPPO 103 + Lumagen XD + Darbee. After calibrating (Chromapure + Display 3 pro), I am happy with the greyscale and colours but not with the gamma (picture is too dark in low light) even if the theoritical results are ok : 2.22 almost everywhere in the greyscale. I tried to adjust the gamma factor on the XD (ouput->CMS->gamma factor), but if I lower it (0.85), I have to reduce the brightness of the Barco in order to get correct black with the black bars flashing pattern.
And I am not sure this is the right thing to do.
Basically, I have no idea on how to setup up the gamma correctly. I don't really know where to start and I don't know if there are patterns that I can use to set it up correctly. My only reference is the picture on my Pioneer Kuro which I think gives a great picture in low light but it is very subjective.
Thanks for your help
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Nashou66



Joined: 12 Jan 2007
Posts: 16167
Location: West Seneca NY


PostLink    Posted: Tue Oct 15, 2013 1:26 pm    Post subject: Reply with quote

Try the BT.1886 gamma in the latest Chromapure the curve gives a lower gamma for the low end and raises it for the high end.

http://www.chromapure.com/colorscience-gamma.asp


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CIR Engineering



Joined: 25 Aug 2008
Posts: 3868
Location: Chicago USA & Berlin Germany


PostLink    Posted: Tue Oct 15, 2013 2:23 pm    Post subject: Reply with quote

When you get the hang of things, you can use the internal test patterns in the Lumagen along with your software to adjust the grayscale and gamma manually. This will yield much better results.

The only test patterns you need are the Lumgen black bars contrast pattern and than the white and gray widows.

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
ChromaPure3 Pro Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Audyssey MultEQ Pro Audio Calibration System
Authorized Dealer for Lumagen & just about everything else Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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Corleone88



Joined: 09 Dec 2006
Posts: 396
Location: France


PostLink    Posted: Tue Oct 15, 2013 2:31 pm    Post subject: Reply with quote

CIR Engineering wrote:
When you get the hang of things, you can use the internal test patterns in the Lumagen along with your software to adjust the grayscale and gamma manually. This will yield much better results.

The only test patterns you need are the Lumgen black bars contrast pattern and than the white and gray widows.

craigr


I know this pattern. But what I don't know is how bright the black bars should be.
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Corleone88



Joined: 09 Dec 2006
Posts: 396
Location: France


PostLink    Posted: Tue Oct 15, 2013 2:32 pm    Post subject: Reply with quote

Nashou66 wrote:
Try the BT.1886 gamma in the latest Chromapure the curve gives a lower gamma for the low end and raises it for the high end.

http://www.chromapure.com/colorscience-gamma.asp

Ok thanks. I will read that carefully Smile
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CIR Engineering



Joined: 25 Aug 2008
Posts: 3868
Location: Chicago USA & Berlin Germany


PostLink    Posted: Tue Oct 15, 2013 2:37 pm    Post subject: Reply with quote

The bar in the very center of the screen in the middle of the stair steps is black. The steps to the left of the center bar are blacker than black getting darker in 1 IRE increments. The bars to the right in the steps are above black getting brighter by 1 IRE increments.

There are four wide bars, two on either side of the center step pattern. The dark bar is 2 IRE below black and the brighter bar is 2 IRE above black.

Most of the time on a CRT you will want to just barely be able to make out the thick blacker than black bars. They should not jump off the screen, but if you sit and stare at the pattern you should eventually be able to discern the blacker than black bars... or at least that's a good starting point.

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
ChromaPure3 Pro Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Audyssey MultEQ Pro Audio Calibration System
Authorized Dealer for Lumagen & just about everything else Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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Corleone88



Joined: 09 Dec 2006
Posts: 396
Location: France


PostLink    Posted: Thu Oct 17, 2013 7:50 am    Post subject: Reply with quote

CIR Engineering wrote:
The bar in the very center of the screen in the middle of the stair steps is black. The steps to the left of the center bar are blacker than black getting darker in 1 IRE increments. The bars to the right in the steps are above black getting brighter by 1 IRE increments.

There are four wide bars, two on either side of the center step pattern. The dark bar is 2 IRE below black and the brighter bar is 2 IRE above black.

Most of the time on a CRT you will want to just barely be able to make out the thick blacker than black bars. They should not jump off the screen, but if you sit and stare at the pattern you should eventually be able to discern the blacker than black bars... or at least that's a good starting point.

craigr


Thanks Craig. My English is not perfect Wink so by "make out the thick blacker than black bars", do you mean "barely see the thick blacker than black bars" ? But I don't understand how, by changing luma values around 5%, I can see a change on blacker than black bars.
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CIR Engineering



Joined: 25 Aug 2008
Posts: 3868
Location: Chicago USA & Berlin Germany


PostLink    Posted: Thu Oct 17, 2013 2:55 pm    Post subject: Reply with quote

Corleone88 wrote:
CIR Engineering wrote:
The bar in the very center of the screen in the middle of the stair steps is black. The steps to the left of the center bar are blacker than black getting darker in 1 IRE increments. The bars to the right in the steps are above black getting brighter by 1 IRE increments.

There are four wide bars, two on either side of the center step pattern. The dark bar is 2 IRE below black and the brighter bar is 2 IRE above black.

Most of the time on a CRT you will want to just barely be able to make out the thick blacker than black bars. They should not jump off the screen, but if you sit and stare at the pattern you should eventually be able to discern the blacker than black bars... or at least that's a good starting point.

craigr


Thanks Craig. My English is not perfect Wink so by "make out the thick blacker than black bars", do you mean "barely see the thick blacker than black bars" ? But I don't understand how, by changing luma values around 5%, I can see a change on blacker than black bars.

I am not suggesting that you change luma values around 5%. I am suggesting that you use the test pattern to set the black level on your projector. Make sure the Lumagen CMS is not in use when you set the black level on the projector. Then use the Lumagen after that.

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
ChromaPure3 Pro Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Audyssey MultEQ Pro Audio Calibration System
Authorized Dealer for Lumagen & just about everything else Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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Corleone88



Joined: 09 Dec 2006
Posts: 396
Location: France


PostLink    Posted: Mon Oct 21, 2013 12:22 pm    Post subject: Reply with quote

I calibrated my BG 808 this week-end and I am very happy with the picture now.
I followed Craig's advices to setup the black level with the brightness (=55). Then I adjusted the gamma and got a nice 2.2 gamma curve on 11 points. I added an extra point (12-point) on the 2 IRE and increased its value by 1.5 luma to get a nice picture in low light.
I watched Alien BR yesterday to check if everything looked fine. And it did, at least to my eyes Smile
Thanks for your help.
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Nashou66



Joined: 12 Jan 2007
Posts: 16167
Location: West Seneca NY


PostLink    Posted: Mon Oct 21, 2013 12:46 pm    Post subject: Reply with quote

Sweet!!! enjoy your theater!!

Nashou

_________________
Don't blame your underwear for your crooked ass~ unknown Greek philosopher


"Republicans believe every day is the Fourth of July, but the Democrats believe every day is April 15." --- President Reagan

One Smart Dog!!!

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CIR Engineering



Joined: 25 Aug 2008
Posts: 3868
Location: Chicago USA & Berlin Germany


PostLink    Posted: Mon Oct 21, 2013 1:46 pm    Post subject: Reply with quote

Corleone88 wrote:
I calibrated my BG 808 this week-end and I am very happy with the picture now.
I followed Craig's advices to setup the black level with the brightness (=55). Then I adjusted the gamma and got a nice 2.2 gamma curve on 11 points. I added an extra point (12-point) on the 2 IRE and increased its value by 1.5 luma to get a nice picture in low light.
I watched Alien BR yesterday to check if everything looked fine. And it did, at least to my eyes Smile
Thanks for your help.

Cool Cool

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
ChromaPure3 Pro Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Audyssey MultEQ Pro Audio Calibration System
Authorized Dealer for Lumagen & just about everything else Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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