White Balance Issue - Page 2 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #11 of 24 Old 03-17-13, 08:31 PM Thread Starter
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Re: White Balance Issue

Yes KelvinS1965, I agree with you. The meter should work well. The grayscale and color look good on the screen after calibrate by adding LumagenMini Video Processor. Accept the dark scene look donít dark enough. The gamma at 1.97. Anything above 1.97, loss on black detail.
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post #12 of 24 Old 03-19-13, 05:16 PM
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Re: White Balance Issue

A gamma of less than 2 is pretty low, though I tweak my Mini3D at 5% and 1% so that the gamma drops to about 2.1/2.0 at this % but it is flat at 2.22 above 15% or so. If your room has light walls/ceiling then you may have to run this low anyway, but if it's a true 'bat cave' then you should be able to run higher, but only if your projector's on/off contrast can support a higher gamma.

Perhaps Michael would know better than I, but I believe that to run a gamma of 2.2 you need an on/off contrast of around 30,000:1 (maybe higher) which is above what your projector can do by some margin as I imagine it's native contrast is around the 5,000-6,000:1 level. It might be worth trying a BT1886 gamma setting as this takes into account the true on/off contrast of the display (but can be difficult to measure the on/off on very high contrast displays).
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post #13 of 24 Old 03-20-13, 11:38 AM
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Re: White Balance Issue

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KelvinS1965 wrote: View Post
Perhaps Michael would know better than I, but I believe that to run a gamma of 2.2 you need an on/off contrast of around 30,000:1 (maybe higher) which is above what your projector can do by some margin as I imagine it's native contrast is around the 5,000-6,000:1 level. It might be worth trying a BT1886 gamma setting as this takes into account the true on/off contrast of the display (but can be difficult to measure the on/off on very high contrast displays).
If i remember correctly only Kuro could measure 2.2 gamma in low scale (from 2-10 IRE) and with a luminosity peak at about 170 nits. Therefore, i would not expect any projector to achieve an accurate gamma (2.2 or 2.4) in low scale with 40 or 50 nits of light.
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post #14 of 24 Old 03-20-13, 05:42 PM
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Re: White Balance Issue

I'm not 100% sure if I understand what you mean Yiannis about 'in low scale'. I recently re did my greyscale and gamma on my X35 using a D3 (enhanced) and got a flat 2.2 gamma until I deliberately lowered the 10 and 5% points towards 2.1 (to help with shadow detail since my room isn't ideal yet).

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post #15 of 24 Old 03-21-13, 07:06 AM
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Re: White Balance Issue

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KelvinS1965 wrote: View Post
I'm not 100% sure if I understand what you mean Yiannis about 'in low scale'. I recently re did my greyscale and gamma on my X35 using a D3 (enhanced) and got a flat 2.2 gamma until I deliberately lowered the 10 and 5% points towards 2.1 (to help with shadow detail since my room isn't ideal yet).

Hello Kelvin!

By ''low scale'' i mean the information below 10 IRE. The type to figure out luminosity at various gamma points is the following:

IRE^GAMMA POINT X LUMINOSITY IN 100 IRE.

1 IRE = 0,01
2 ΙΡΕ = 0,02

and so on. For example:

Let's say that our peak white in 100% pattern is 50 nits and trying to spot a 2.2 gamma point below 10 IRE.

0,03^2.2x50= 0,02 nits.

So, in order to have a gamma point 2.2 at 3%, we need that our pj can achieve 0,02 nits. If not, our gamma point will be lighter.

0,02^2.2x50= 0,009 nits.

As you can see, the light does not be defined analogically in the various IRE but algorithmically, making very hard for most projectors to keep up the pace. Therefore, the majority of the units present the so called ''veil'' in low light scenes. Practically, in these kind of scenes our projectors output a lighter gamma point like 1.9-1.8 or lower.
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post #16 of 24 Old 03-21-13, 02:56 PM
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Re: White Balance Issue

Ah I get what you mean (should have read your earlier post more carefully ). One method I have used to adjust the very low end is to create an offset in Chromapure so that I can read directly from the projector. This gives more light to play with but even then I can only measure 10% and 5% in Chromapure since it doesn't measure below this. I can measure RGB in real time and put up a 1,2,3 or 4% pattern if I wish but I can only adjust my Lumagen to one of these points (parametric greyscale adjustment can be moved from 0.5 to 100.0 in 0.5 steps).

As you say though the light output is very low at these levels and most projectors will give a 'veil' in low light scenes, which is why I have a preference for JVC projectors: Even these aren't perfect though, but they are pretty good especially in a long throw, minimum iris set up like mine which maximises the available contrast. Until I build a dedicated room I won't even get the best out my X35 let alone something better, but some room improvements in the short term might help a bit...Id really like an X95 in a total black cave lined with black velvet, but that isn't happening anytime soon.

Anyway, enough rambling: I've found a good way to be happy with your display: Focus on some new speakers or subwoofer as I'm doing. I'm off to hear some 15 and 18" subs with 3000 watt amps on Sunday. They also have a custom inroom setup with 8 x 18" speakers and 12000 watts of amplification. Funny that they have an X35 in this (totally black room) and it looks like a totally different projector to mine because of the better room.
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post #17 of 24 Old 03-21-13, 05:53 PM
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Re: White Balance Issue

Quote:
KelvinS1965 wrote: View Post
Ah I get what you mean (should have read your earlier post more carefully ). One method I have used to adjust the very low end is to create an offset in Chromapure so that I can read directly from the projector. This gives more light to play with but even then I can only measure 10% and 5% in Chromapure since it doesn't measure below this. I can measure RGB in real time and put up a 1,2,3 or 4% pattern if I wish but I can only adjust my Lumagen to one of these points (parametric greyscale adjustment can be moved from 0.5 to 100.0 in 0.5 steps).
I see!!

To be honest, i don't like to measure anything off the lens, because to achieve an actual reading that has practical value i need to do so only in a ''bat cave'' (no reflections, no gamma shifting). If i cut off from the equation my actual room enviromental conditions (light brown ceiling, dark yellow wall) measuring directly off the lens, my adjustment would appear wrong in actual viewing.

What do you think?
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post #18 of 24 Old 03-22-13, 11:56 AM
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Re: White Balance Issue

Usually you would be correct regarding measuring off the lens not taking the screen/room into account. However, with Chromapure you can create an offset:

1. You take 100% (or 75%) white, red, green, blue, yellow, cyan & magenta measurements off the screen. This is the 'reference' meter.

2. You take the same readings directly from the lens and Chromapure creats an offset. This is the 'field' meter.

This means that you can take all the measurements directly from the lens using the 'field meter' so that you get more light to play with which helps the sensor especially at low % readings. The offset takes the room and screen effects into account.

I don't know if other calibration software can do this, but it's a useful feature. However my D3 Enhanced measures pretty well off the screen anyway.

Also, as my screen (and room) is pretty neutral I can just change a setting in Chromapure and measure directly from the projector lens without creating the offset and the results are very, very close compared to measuring off the screen. If you had an exotic screen or perhaps red walls then you would have to use the offset method.

That we are even discussing how hard measuring at low % is then at least it shows that projector's black levels are getting really good these days.
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post #19 of 24 Old 03-22-13, 06:24 PM
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Re: White Balance Issue

Thanks for the info Kelvin!
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post #20 of 24 Old 03-23-13, 02:20 PM
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Re: White Balance Issue

Quote:
mechman wrote: View Post
With CalMAN you can create a screen offset by reading the screen material itself with a spectro and entering that under the Environmental offsets area under the Advanced Workflow Options. I've never used this but I've been itching to try it out some time.
Can i itch you a bit more?? A guide how to do that would be nice!!
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