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Editorial Comments on the ChromaPure Guide

 
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dcchan2



Joined: 20 Mar 2015
Posts: 3
Location: Mississauga, ON


PostLink    Posted: Fri Mar 20, 2015 7:39 pm    Post subject: Editorial Comments on the ChromaPure Guide Reply with quote


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Thanks for the excellent guide on ChromaPure Calibration; I found it extremely useful.

However, I do have some editorial comments on the guide. I was going to send the comments via PM, but being a new member, was unable to do that.

Here are the comments:
Typo
1.2.6
Just below the "window test pattern", the text says
"For display types that are not plasma or CRT, always use full field test patterns. A window (should be full field) test pattern fills the entire screen like this

White balance adjustments
It appears that the adjustments made in Step 2.4.4 (80% white balance) will totally overwrite those made in Step 2.2.2.13 (100% white balance), essentially rendering that adjustment redundant (except for situations where that step was used to adjust luminance rather than 100% white balance)


2.4.6. It would appear that the "TIP" regarding 10-point system should be moved up to 2.4.4, as that step would also have been performed differently with a 10-point system.
Also, for a 10-point system, when will the white balance for the other steps (10%, 30-70%, 90%) be performed?


2.5, TIP. "Below that the gamma should get progressively higher,..." Shouldn't that be lower? (2.1 at 10%, vs 2.3 from 40-90%)
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kal
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Joined: 06 Mar 2006
Posts: 15821
Location: Ottawa, Canada

TV/Projector: JVC DLA-RS56


PostLink    Posted: Sat Mar 21, 2015 1:21 pm    Post subject: Reply with quote

Thanks for the commentary! It's really appreciated.

I've fixed the typo in 1.2.6 (window vs full field) - that was definitely a mistake.

For the last item (the 2.5 gamma tip) I've changed the wording somewhat:

Quote:
TIP: What Gamma Curve Do I Aim For? The gamma curve that the vast majority of users should aim for will measure about 2.3 from 40%-90% video. Below 40-90% video the amount of gamma correction should progressively increase, producing a gamma of about 2.1 at 10%. (The lower the gamma correction value, the more gamma correction that is applied). This gamma curve will produce excellent results for both high-contrast projectors in dark home theaters and flat panel displays in well-lit living rooms.

It wasn't explained that as the gamma correction value (the number) gets lower, there's more gamma correction applied. So when someone says "increase gamma" they actually mean lower the value. It's a common / confusing subject. Hopefully the wording changes I made make this clearer.

For the other ones I'm going to have to think about them a bit (I don't have time at the moment), and review with Tom of ChromaPure as well. I'll get back to you.

Cheers,

Kal

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TomHuffman



Joined: 01 Jun 2010
Posts: 71
Location: Springfield, MO


PostLink    Posted: Sat Mar 21, 2015 8:49 pm    Post subject: Re: Editorial Comments on the ChromaPure Guide Reply with quote

dcchan2 wrote:
White balance adjustments
It appears that the adjustments made in Step 2.4.4 (80% white balance) will totally overwrite those made in Step 2.2.2.13 (100% white balance), essentially rendering that adjustment redundant (except for situations where that step was used to adjust luminance rather than 100% white balance)


2.4.6. It would appear that the "TIP" regarding 10-point system should be moved up to 2.4.4, as that step would also have been performed differently with a 10-point system.
Also, for a 10-point system, when will the white balance for the other steps (10%, 30-70%, 90%) be performed?

1. That's fine. The purpose of the white balance adjustment when setting contrast is only to verify that the display is capable of getting good white balance out to 100% white. If it is not you may wish to dial contrast back a little. Getting a precise adjustment at 80% is more important than the 100% reading in case they conflict.

2. Not necessarily. For example, on the Samsungs, it is good practice to use the 2-point first, which gives you 90% of what you need, and then just use the 10-point for minor touch-up. 10-point includes all the points you mention. Use at each level only if needed. If you have already done a 2-point, it probably won't be needed except at a couple of points.

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dcchan2



Joined: 20 Mar 2015
Posts: 3
Location: Mississauga, ON


PostLink    Posted: Fri Apr 03, 2015 12:59 am    Post subject: Re: Editorial Comments on the ChromaPure Guide Reply with quote

TomHuffman wrote:

2. Not necessarily. For example, on the Samsungs, it is good practice to use the 2-point first, which gives you 90% of what you need, and then just use the 10-point for minor touch-up. 10-point includes all the points you mention. Use at each level only if needed. If you have already done a 2-point, it probably won't be needed except at a couple of points.


Thanks for the clarification. However, IMHO, the TIP may easily be misinterpreted, in which case it would produce worse results than a 2-point adjustment.

Section 2.4 describes in detail how to set up an endless loop between the 80% and the 20% test patterns, and adjust the RGB HighEnd and RGB LowEnd controls to get the most neutral colours (at 80% and 20%).

The TIP at the end of 2.4.6 says "Some displays will offer the ability to adjust grayscale at 10 points, instead of simply the standard RGB HighEnd and RGB LowEnd. If you have such a display, then use the 10-point system." My initial interpretation of this was to use the display's 10-point control to get the most neutral colours for the 80% and 20% test pattern - and that would have been wrong! The 10-point control should only be used with 10-point test patterns, but I suspect most new users (the intended readers of the Dummies' Guide) would not be aware of that.
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kal
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PostLink    Posted: Fri Apr 03, 2015 2:16 pm    Post subject: Reply with quote

I updated the tip to be clearer:

Quote:
TIP: Some displays will offer the ability to adjust grayscale at 10 points, instead of simply the standard RGB HighEnd and RGB LowEnd. If you have such a display, we recommend adjusting back and forth at the 80% and 20% points as described here as it'll likely give you 90% of what you need. Then use the 10-point system for minor touch-ups only at the specific problem points (i.e. If after doing a full sweep as mentioned below in 2.4.8 it is determined that the 10% point is off, put up a 10% test pattern and adjust the point that corresponds to 10% in the display).


Kal

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dcchan2



Joined: 20 Mar 2015
Posts: 3
Location: Mississauga, ON


PostLink    Posted: Fri Apr 03, 2015 6:32 pm    Post subject: Reply with quote

kal wrote:
I updated the tip to be clearer:

Quote:
TIP: Some displays will offer the ability to adjust grayscale at 10 points, instead of simply the standard RGB HighEnd and RGB LowEnd. If you have such a display, we recommend adjusting back and forth at the 80% and 20% points as described here as it'll likely give you 90% of what you need. Then use the 10-point system for minor touch-ups only at the specific problem points (i.e. If after doing a full sweep as mentioned below in 2.4.8 it is determined that the 10% point is off, put up a 10% test pattern and adjust the point that corresponds to 10% in the display).


Kal


Thanks Kal. That indeed makes the use of 10-point calibration very clear.

A further question on this - 2.5.9 states that "you will almost certainly have to touch-up the grayscale (STEP 2.4) once you have finished with gamma. Fortunately, changes in gamma have a much larger affect on the grayscale than changes in grayscale have on gamma".

That being the case, wouldn't it be easier to do the 10-point fine-tuning after 2.5.8 instead of during 2.4?
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kal
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PostLink    Posted: Sat Apr 04, 2015 1:14 am    Post subject: Reply with quote

I would get the grayscale as perfect as possible before moving on to gamma, which will then require you to likely go back and re-tweak grayscale.
As you've noticed, it's a very iterative process. You'll like tweak both a few times, going back and forth. At the end of the day it may also not make any difference. I don't think you can say it's necessarily easier.

Kal

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