GCD - Gamut Calibration Disk - Page 19 - AVS Forum
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post #541 of 633 Old 12-17-2012, 06:33 PM
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Quote:
Originally Posted by zoyd View Post

For software that assumes integer stimulus levels (which I believe HCFR does), I've calculated the %error mismatch in luminance that both the AVSHD and GCD disks will generate assuming pretty typical values of 2.2 gamma/120 cd/m^2 peak white. Again, software which assumes typical rounding will be perfect for GCD and software which assumes "round down" will be perfect for AVSHD.
Hello zoyd,
Thanks for the clarification. Now I hope Sotti and Tom will chip in to explain how their software does it and then to achieve a common standard.
To me the correct way seems to be to use bit level stimulus for the calculation
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post #542 of 633 Old 12-17-2012, 07:52 PM
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Quote:
Originally Posted by zoyd View Post

For software that assumes integer stimulus levels (which I believe HCFR does), I've calculated the %error mismatch in luminance that both the AVSHD and GCD disks will generate assuming pretty typical values of 2.2 gamma

Here is another mathematical way to represent the same sort of idea, where rounding to the nearest 8-bit luma value puts an error in the middle of the grayscale, and rounding-down places any discrepancy near black. The idea of the following spreadsheet is to relate the "Actual Percent" with the "Target Luminance" and look at how it would affect display gamma. I used http://www.avsforum.com/t/843411/how-to-calculate-gamma#post_10469695 to calculate the "Point Gamma" columns and compared the point gammas using the "Gamma Change" column. I'm not really sure if the trend toward a lower gamma near black on the round-down video is explicitly an issue in relation to question 6 at http://www.poynton.com/PDFs/GammaFAQ.pdf

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post #543 of 633 Old 12-18-2012, 06:07 AM
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Without getting into the math, the message I take from this is that patterns need to match what the calibration software is expecting? I'll have to reread this thread more carefully to quantify the impact in terms of dE.
Perhaps it is more accurate to let calibration software output its own patterns via a laptop with HDMI. At least then there should not be any mismatch.

Perhaps only semi-appropriate here, but where does this leave people with video processors that can output their own patterns? How do we verify whether patterns match now:(

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post #544 of 633 Old 12-18-2012, 06:35 AM
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Quote:
Originally Posted by Jeroen1000 View Post

Without getting into the math, the message I take from this is that patterns need to match what the calibration software is expecting?

that's what I'm thinking too. Just use the levels the software expects and everything should be fine. Guess that all calculations the software does is based on what is expected and not on what's mathematical correct. See:
http://www.avsforum.com/t/1441407/grayscale-variances-different-patterns-plasma-calibration/120#post_22687374

what calman expects can easy be seen by turning on the "pattern change prompts" option.


As I'm also working on a pattern disc (5% and 6.5% windows) for testing my VT50:
Quote:
Originally Posted by visca blaugrana View Post

Simple answer.. no
I cannot stress enough before any release I verify all patterns.
the verification process is the following:
RBG->4:2:0 YCbCr->Video->4:2:0 YCbCr->RGB
where the RBG's are compared in both ends

how is the process from Video to 4:2:0 YCbCr and what authoring software do You use?

thanks!
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post #545 of 633 Old 12-18-2012, 07:35 AM
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Quote:
Originally Posted by Jeroen1000 View Post

Without getting into the math, the message I take from this is that patterns need to match what the calibration software is expecting?

no, just the opposite since the patterns are limited to 8 bit integers and the software is not. From the above gamma error calculations you can see that at most we are talking about 1-1.5% errors in gamma (do you care if your real gamma is 2.2 or 2.22 at 10% stimulus and correct at all others?) While this error is measurable it will not be noticeable to the user, so I don't expect anyone changing their software and/or patterns to be completely consistent.
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post #546 of 633 Old 12-18-2012, 09:39 AM
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You are conflating two different issues, let me try and separate them for you.

1. The discussion above concerns the values used to generate the pattern's luma value (loosely, it's intensity). Because you can't have 10 (or 20) equal integer intervals to cover the 219 possible steps you have to drop 1 step somewhere in the sequence. The only inconsistency between DVE/AVSHD and the GCD disks is where they drop that step. The end result of this choice depends on what intervals your calibration software assumes but will be no larger than ~0.02 in gamma and only for the interval with the skipped code. This is simply a non-issue.

2. The other issue has to do with what pattern size is appropriate for your display technology and also systematic errors in your own methods and equipment usage and the equipment itself. That belongs in another thread.
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post #547 of 633 Old 12-18-2012, 11:31 AM
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Quote:
Originally Posted by H Stevens View Post

There doesn't appear to be any consistency between calibration disc. If you take a gamma reading with the Chromapure disc, AVSHD and then GCD you will get three different results. Also, the results are different among window sizes and of course normal vs. APL.

Basically you're measuring how your display responds differently depending on the displayed image. If you were to use an LCD-based display with a fixed backlight, you would find that DVE and AVS HD 709 are in complete agreement within the limits of the meter and the stability of the backlight. In such a situation with a contact meter, the expectation is that it doesn't matter if you measure a field, a window of various sizes, or an APL series, because the patterns all contain the same digital information in the measurement area.
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And the most puzzling is that none of the results from any of the disc will be close to the setting you selected in the user menu which is why, I assume, that calibrators set the gamma to 2.4 in the display when they want an end result of 2.2.

Again you're talking about the display, rather than the calibration pattern.
Quote:
Also, in the past week or so, there has been an effort by some members, to create a set of patterns with a smaller window size, so that they can get an accurate reading with their plasma panels.

It's been discussed before, and personally I haven't seen data that suggests choosing a particular size window increases the correlation among various displays. If anyone had provided a data-backed argument I was willing to consider changing the window size, but I never saw anyone working on data that concentrated to show if a particular size window actually tended to bring various displays more into agreement. I don't see how it would, but I also don't care to concentrate on plasma or CRT displays.
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Why isn't there a standard? Or is there one?

My cynical side says there's no standard because it might not be good for business if people really started concentrating on just how much observable display to display variation there can be after "calibration". My practical side says that as long as there are various displays that operate somewhat differently, the sort of accuracy people think they're achieving may not really be possible.
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Shouldn't all of this have been ironed out along time ago or is it that most are using pattern generators and have not come across these issues?

Pattern generators have to conform to the same 8-bit world that they attempt to calibrate. From an end-user perspective they can't achieve anything that couldn't also be done with video.
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post #548 of 633 Old 12-18-2012, 01:01 PM
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If the noob invasion is not allowed (or dilluting this thread) please do say so and I'll take it in a separate one. I understand 8-bit integers cannot represent a decimal value.

For instance: 5%: (235-16) * 5 / 100 = 10.95 or presented as 8-bit binary 0000 1011. Rounding up to 11 would be the mathematically correct thing to do. Rounded down to 10, the binary represenation changes to 0000 1010.
This is essentially what we are discussing.
How Zoyd and Alluring get to 26 and 27 as luma values then is still a bit (no pun intended) beyond my understanding (I'm talking about the Excel spreadsheet screenshots posted). Maybe someone can round this up (sorry, small joke:-)) for those still struggeling to understand (including myself).

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post #549 of 633 Old 12-18-2012, 01:08 PM
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post #550 of 633 Old 12-18-2012, 11:52 PM
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Quote:
Originally Posted by zoyd View Post

For software that assumes integer stimulus levels (which I believe HCFR does), I've calculated the %error mismatch in luminance that both the AVSHD and GCD disks will generate assuming pretty typical values of 2.2 gamma/120 cd/m^2 peak white. Again, software which assumes typical rounding will be perfect for GCD and software which assumes "round down" will be perfect for AVSHD.


Ah thanks, I missed that. In the Excel screenshot you posted, the AVSHD error as % luminance is actually quite large from 5% to let's say 20% stimulus?

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post #551 of 633 Old 12-19-2012, 03:20 AM
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Quote:
Originally Posted by zoyd View Post

no, just the opposite since the patterns are limited to 8 bit integers and the software is not.
As Shakespeare said:"Tom and sotti: where areth thou?"

zoyd is right. Patterns are limited, software is not. So the software has to follow the pattern to make things correct. So far in this discussion, we did not see a response from Sotti and Tom yet.

But of course, software following patterns only makes sense when patterns are the same, and now it is not.
Is it too much to ask that zoyd, visca, alluringreality, Tom and sotti put their heads together to agree on a standard?

And don't say it is only a small error. Because to me it looks also like just a small effort to put it right.
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post #552 of 633 Old 12-19-2012, 07:57 AM
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Quote:
Originally Posted by turboman123 View Post

Because to me it looks also like just a small effort to put it right.

conceptually quite simple but to remake either of these disks would take many hours of work. Every pattern using 5% through 50% luma would have to be remastered
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post #553 of 633 Old 12-20-2012, 07:11 AM
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What size are the small windows on this disc?
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post #554 of 633 Old 12-21-2012, 08:55 AM
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Never mind, I found the answer to my last question when I checked the disk. I actually found an issue unique to myself. I could only achieve hitting a peak output target with my contrast control using the smallest windows on the GCD disk. Using any other sized window (both normal and APL) on GCD or any other disk would give me an inaccurate reading. I would try to achieve a target of 35fL and I would actually end up north of 40fL. Everything improved when I moved to the other windows
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post #555 of 633 Old 12-21-2012, 10:34 AM
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Quote:
Originally Posted by HD-Master View Post

Never mind, I found the answer to my last question when I checked the disk. I actually found an issue unique to myself. I could only achieve hitting a peak output target with my contrast control using the smallest windows on the GCD disk. Using any other sized window (both normal and APL) on GCD or any other disk would give me an inaccurate reading. I would try to achieve a target of 35fL and I would actually end up north of 40fL. Everything improved when I moved to the other windows

I have a pn51d6500 samsung plasma and with the Cell Light set to 20 and Contrast at 95 i get 32fL once the set is calibrated. If I push the contrast to 100 then I get 35fL. Also I noticed on my set that what I thought was "pinking "to my eye was in fact that at a contrast of 95 was actually my 2pt wb Red gain being way too high. In default movie mode with a meter my Red was over 130% appearing very pink/redish in the greyscale this falsely led me to adjust the contrast to a lower setting. Now my Red gain is at 0 and it is closer to 100% for RGB balance and I have left contrast at 95 .
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post #556 of 633 Old 01-01-2013, 11:37 AM
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I noticed something odd about the white clipping pattern on the AVCHD a5.0.0 version of the disc. It has spaces for flashing bars at digital 255 and 254 even though the background of the pattern cannot exceed 254 on a disc. It should go up to 253 only, just like on the AVSHD709 disc.
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post #557 of 633 Old 01-02-2013, 03:12 AM - Thread Starter
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Sorry for the absebt lately, but hve a few comemnts

1: Project is still on hold, due to my attention is required elseware
2:@PlasmaPZ80U when using Calman5 with generic calibration disk I would use AVSHD709 unless you are calibrating with 100% luminance, if so both disk are usable - the reason behind this is that the RGB's requested by Calman does not match the one used on GCD (GCD uses fixed luminance patterns and Calman5 ask for variable lumininace patterns) - I am working with SpectraCal to find a solution on this.
3: @DrFaxe "how is the process from Video to 4:2:0 YCbCr and what authoring software do You use?" please see here for deails http://www.avsforum.com/t/948496/avs-hd-709-blu-ray-mp4-calibration/3180#post_21583899
4: Regarding Pattern Sizes: I will await some final conclutions, from tests elseware but it look like the following (this is subject to confirmation) 6% 10% and fields 6% and 10% windows will also be created as 23%APL windows
5: since most software(as far as I can gather) uses % values to gamma I will countinue to use normal mathematical roundings
6: Regarding white clip pattern. Since 109% white is 255,255,255 why would you limit it to 253,253,253? also why is a disk limited to 254? am I missing something here?
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post #558 of 633 Old 01-02-2013, 08:40 AM
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Quote:
Originally Posted by visca blaugrana View Post

when using Calman5 with generic calibration disk I would use AVSHD709 unless you are calibrating with 100% luminance, if so both disk are usable - the reason behind this is that the RGB's requested by Calman does not match the one used on GCD (GCD uses fixed luminance patterns and Calman5 ask for variable lumininace patterns) - I am working with SpectraCal to find a solution on this.

I'm not sure I follow. Are you talking about grayscale when you say 100% luminance or the dynamic range tool or gamut/saturation sweeps? What do you mean by fixed luminance patterns vs. variable luminance patterns? Are you saying I should use the AVSHD709 disc over the GCD one or select the AVS disc in CalMAN 5 over the Generic Calibration Disc option?
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post #559 of 633 Old 01-02-2013, 08:44 AM
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Quote:
Originally Posted by visca blaugrana View Post

6: Regarding white clip pattern. Since 109% white is 255,255,255 why would you limit it to 253,253,253? also why is a disk limited to 254? am I missing something here?

If the background is 255, having a bar for 255 is pointless since it will never flash as there is no difference in digital levels.

If the background is 254, having bars for 255 and 254 is pointless since they will never flash.

I believe awhile back Sotti mentioned somewhere here that you cannot encode a value higher than digital 254 on a disc but you can output 255 on a dedicated pattern generator.
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post #560 of 633 Old 01-02-2013, 09:15 AM - Thread Starter
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regarding the 100% luminance I'm talking about CMS work.

if you are calibrating to 100% luminance (again CMS work) either disk will work, then its just a matter of what pattern size you prefere.
if you are calibrating to lets say 75% luminance I would use AVSHD7090with calman reason why:

in calman for Red 75saturation/70% luminance it expect 180,64,64 this will give you the correct x,y values but not the correct amplitude (I.E. 75%) to get the 75% Amplitude it would be 167,60,60. Again this is not wrong but all about how the software work. GCD was at that point build for Chromapure. But as I said I am working with Calman so GCD will be incorperated


regarding the clip pattern the background is encoded at 255,255,255 correct the 255 willnever flash, but I do prefere to keep it that way (preferential Engineering)
I have never heard that you can have 255 levels on a disk, I will look in to this.
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post #561 of 633 Old 01-02-2013, 12:11 PM
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Quote:
Originally Posted by visca blaugrana View Post

regarding the 100% luminance I'm talking about CMS work.
if you are calibrating to 100% luminance (again CMS work) either disk will work, then its just a matter of what pattern size you prefere.
if you are calibrating to lets say 75% luminance I would use AVSHD7090with calman reason why:
in calman for Red 75saturation/70% luminance it expect 180,64,64 this will give you the correct x,y values but not the correct amplitude (I.E. 75%) to get the 75% Amplitude it would be 167,60,60. Again this is not wrong but all about how the software work. GCD was at that point build for Chromapure. But as I said I am working with Calman so GCD will be incorperated
regarding the clip pattern the background is encoded at 255,255,255 correct the 255 willnever flash, but I do prefere to keep it that way (preferential Engineering)
I have never heard that you can have 255 levels on a disk, I will look in to this.

I've found the Gamut Calibration Disc to work fine with the CMS portion of the CalMAN 5 Enthusiast Workflow with 100% saturation, 75% luminance/stim/amplitude test patterns... identical to the patterns on the AVSHD709 disc. Are you referring to 75% saturation, 75% stim patterns instead?
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post #562 of 633 Old 01-02-2013, 12:21 PM - Thread Starter
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Thinking about it. You are right 100% saturation will have no problem it's only when using patterns where both saturation Luminance different then 100%.
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post #563 of 633 Old 01-02-2013, 02:50 PM - Thread Starter
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Just confirming. Since the avshd709 disk don't contain the patterns (75/75) you should get the same results no matter what disk you use. However dont use the 75/75 patterns with Calman 5 just yet..
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post #564 of 633 Old 01-03-2013, 08:13 AM
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Quote:
Originally Posted by visca blaugrana View Post

regarding the clip pattern the background is encoded at 255,255,255 correct the 255 willnever flash, but I do prefere to keep it that way (preferential Engineering)
I have never heard that you can have 255 levels on a disk, I will look in to this.

check this thread out

http://www.spectracal.com/forum/viewtopic.php?f=94&t=4279&p=28820#p28813
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post #565 of 633 Old 01-03-2013, 08:38 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

If the background is 255, having a bar for 255 is pointless since it will never flash as there is no difference in digital levels.
If the background is 254, having bars for 255 and 254 is pointless since they will never flash.
I believe awhile back Sotti mentioned somewhere here that you cannot encode a value higher than digital 254 on a disc but you can output 255 on a dedicated pattern generator.

I have almost all available disks, i have scanned each contrast pattern, all disks are using 254 level at the background with 253 and lower flashing.

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post #566 of 633 Old 01-03-2013, 09:01 AM
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Originally Posted by ConnecTEDDD View Post

I have almost all available disks, i have scanned each contrast pattern, all disks are using 254 level at the background with 253 and lower flashing.

That sounds right and is what I noticed on the AVSHD709 disc.
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post #567 of 633 Old 01-03-2013, 11:07 AM
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Quote:
Originally Posted by visca blaugrana View Post

Sorry for the absebt lately, but hve a few comments
4: Regarding Pattern Sizes: I will await some final conclutions, from tests elseware but it look like the following (this is subject to confirmation) 6% 10% and fields 6% and 10% windows will also be created as 23%APL windows

I'm not following this one. Do you mean to create 6% windows (on black) in additional to the 10% already available? Because 6% windows on 23% APL backgrounds will not measure any differently than 10% windows on 23% backgrounds. As far as gamma calibration on plasmas is concerned the existing APL patterns are optimal based on measurement that both Tom and I did last year.
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post #568 of 633 Old 01-03-2013, 08:04 PM
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Quote:
Originally Posted by visca blaugrana View Post

why is a disk limited to 254? am I missing something here?

You can find the video specifications if you Google the following:

6.11 Quantization level assignment (8-bit coding)

Video data: 1 through 254
Timing references: 0 and 255
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post #569 of 633 Old 01-04-2013, 09:33 AM
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Quote:
Originally Posted by PlasmaPZ80U View Post

I noticed something odd about the white clipping pattern on the AVCHD a5.0.0 version of the disc. It has spaces for flashing bars at digital 255 and 254 even though the background of the pattern cannot exceed 254 on a disc. It should go up to 253 only, just like on the AVSHD709 disc.

Quote:
Originally Posted by PlasmaPZ80U View Post

If the background is 255, having a bar for 255 is pointless since it will never flash as there is no difference in digital levels.
If the background is 254, having bars for 255 and 254 is pointless since they will never flash.
I believe awhile back Sotti mentioned somewhere here that you cannot encode a value higher than digital 254 on a disc but you can output 255 on a dedicated pattern generator.

Quote:
Originally Posted by ConnecTEDDD View Post

I have almost all available disks, i have scanned each contrast pattern, all disks are using 254 level at the background with 253 and lower flashing.

Quote:
Originally Posted by alluringreality View Post

You can find the video specifications if you Google the following:
6.11 Quantization level assignment (8-bit coding)
Video data: 1 through 254
Timing references: 0 and 255

Quote:
Originally Posted by PlasmaPZ80U View Post

check this thread out
http://www.spectracal.com/forum/viewtopic.php?f=94&t=4279&p=28820#p28813

I'd say it would be helpful if the next release of the GCD got rid of the 255 and 254 bars since the background is 254. Otherwise, users might trying lowering Contrast in an effort to make those last two bars appear, but they never will for the reasons covered above. Since the pattern is effectively from/based on the White Clipping Pattern on the AVS disc, it makes sense to set it up in the same way. Also, something odd is going on with the dynamic range, clipping with peak white pattern for 109%, as shown in the link to the SpectraCal forum above.
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post #570 of 633 Old 01-05-2013, 04:01 AM - Thread Starter
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Quote:
Originally Posted by zoyd View Post

I'm not following this one. Do you mean to create 6% windows (on black) in additional to the 10% already available? Because 6% windows on 23% APL backgrounds will not measure any differently than 10% windows on 23% backgrounds. As far as gamma calibration on plasmas is concerned the existing APL patterns are optimal based on measurement that both Tom and I did last year.

okay that sounds goot, it was all based on what Chad B is doing at the moment.
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