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couple of calibration questions

 
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Arcsaber



Joined: 15 Apr 2015
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PostLink    Posted: Wed Apr 22, 2015 8:56 am    Post subject: couple of calibration questions Reply with quote


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1. My old i1D is, I think, out of kilter - I can't seem to reach 0.06 on the blue primary no matter how much I mess with the hues and saturations of any display I try to calibrate. Don't know about the red and green filters; they get very close to reference.

Is there a way to check for this and, of so, account for it? Some kind of primary-coloured cards I can measure and use in place of the CIE values?


2. I've just read a review of a TV in which I'm very interested, wherein they mention "repurposing the 10-point white balance controls for 10-point gamma".

They got the gamma absolutely flat across the full IRE range - how would one do this? Is there some way to use the 10-point WB controls to change the relative luminances of the IREs?


If these have already been answered, feel free to direct me to the approriate posts/threads:).

M.
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kal
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PostLink    Posted: Wed Apr 22, 2015 12:42 pm    Post subject: Re: couple of calibration questions Reply with quote

Arcsaber wrote:
Is there a way to check for this and, of so, account for it? Some kind of primary-coloured cards I can measure and use in place of the CIE values?

Not really. See my response when someone asked about this a couple of days ago here: http://www.curtpalme.com/forum/viewtopic.php?p=439328#439328

It needs to be recalibrated. This is done by measuring it against a known good meter and then creating offsets. We offer this service for ChromaPure users. See: http://www.curtpalme.com/ChromaPure.shtm

Quote:
2. I've just read a review of a TV in which I'm very interested, wherein they mention "repurposing the 10-point white balance controls for 10-point gamma".

They got the gamma absolutely flat across the full IRE range - how would one do this?

Not sure. Sounds odd/doesn't make much sense. You'd have to ask the reviewer. If a TV has controls that do one thing, there's no way the user can re-assign the controls to do something completely different themselves. Has to be something built into the TV that allows this. I don't understand why they'd do that however - just provide two sets of controls. Do you have a link to this review?

Kal

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Arcsaber



Joined: 15 Apr 2015
Posts: 16



PostLink    Posted: Wed Apr 22, 2015 1:06 pm    Post subject: Re: couple of calibration questions Reply with quote

kal wrote:
Not sure. Sounds odd/doesn't make much sense. You'd have to ask the reviewer. If a TV has controls that do one thing, there's no way the user can re-assign the controls to do something completely different themselves. Has to be something built into the TV that allows this. I don't understand why they'd do that however - just provide two sets of controls. Do you have a link to this review?

Kal


Review is here, along with my question:).

I was confused as well - surely the white balance controls don't include a way to set the luminances for each grey level... boy, if that option were in there...
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kal
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PostLink    Posted: Wed Apr 22, 2015 2:50 pm    Post subject: Reply with quote

Thanks for the link. I don't really understand what he means by repurposed. Hopefully they'll be able to explain.

Kal

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HogPilot



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PostLink    Posted: Thu Apr 23, 2015 3:43 pm    Post subject: Re: couple of calibration questions Reply with quote

Arcsaber wrote:
2. I've just read a review of a TV in which I'm very interested, wherein they mention "repurposing the 10-point white balance controls for 10-point gamma".

They got the gamma absolutely flat across the full IRE range - how would one do this? Is there some way to use the 10-point WB controls to change the relative luminances of the IREs?

M.


I do this with my Lumagen Radiance. As long as you have controls for all three colors at each point, and they have a sufficient amount of +/- range, you should be able to simultaneously adjust white balance and luminance using the WB controls. Adjusting one color allows you to adjust WB at a given %; adjusting all three simultaneously by the same amount adjusts the luminance at that same %.

Here's an example: you're adjusting 50% white, and the default for the RGB controls are 0/0/0, with a +/- range of 20 units in 0.1 increments. You adjust the white balance to D65, and your end values are R: 5.7, G: 0, B: -1.3. As long as you know what your peak luminance is at 100% white, you can use a simple gamma calculator to tell you what the luminance values should be at each %. Let's say your calculator tells you your luminance should be 4.5 ftL at 50% white, but you're measuring 5.5 ftL. You can reduce all 3 RGB controls by the same amount (-1.0 let's say) to lower the luminance at 50% until you measure 4.5ftL output - a parametric gamma control would do the exact same thing, just with a single control instead of adjusting all 3 simultaneously. In fact, on the Radiance, when you adjust the Gamma/luminance control at a given %, you can see it simultaneously raising/lowering the RGB controls as a result. After that you'll have to re-tweak your WB, and probably re-tweak your luminance, but that's much quicker since you're already in the ballpark.

Your job will be easier if your overall display gamma is set to something that measures close to your target so you don't run out of range on your WB controls, and you have to know your 100% luminance before so you can calculate your target luminance at each % ahead of time.

Clear as mud?

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Arcsaber



Joined: 15 Apr 2015
Posts: 16



PostLink    Posted: Thu Apr 23, 2015 3:56 pm    Post subject: Re: couple of calibration questions Reply with quote

HogPilot wrote:
I do this with my Lumagen Radiance. As long as you have controls for all three colors at each point, and they have a sufficient amount of +/- range, you should be able to simultaneously adjust white balance and luminance using the WB controls. Adjusting one color allows you to adjust WB at a given %; adjusting all three simultaneously by the same amount adjusts the luminance at that same %.

Here's an example: you're adjusting 50% white, and the default for the RGB controls are 0/0/0, with a +/- range of 20 units in 0.1 increments. You adjust the white balance to D65, and your end values are R: 5.7, G: 0, B: -1.3. As long as you know what your peak luminance is at 100% white, you can use a simple gamma calculator to tell you what the luminance values should be at each %. Let's say your calculator tells you your luminance should be 4.5 ftL at 50% white, but you're measuring 5.5 ftL. You can reduce all 3 RGB controls by the same amount (-1.0 let's say) to lower the luminance at 50% until you measure 4.5ftL output - a parametric gamma control would do the exact same thing, just with a single control instead of adjusting all 3 simultaneously. In fact, on the Radiance, when you adjust the Gamma/luminance control at a given %, you can see it simultaneously raising/lowering the RGB controls as a result. After that you'll have to re-tweak your WB, and probably re-tweak your luminance, but that's much quicker since you're already in the ballpark.

Your job will be easier if your overall display gamma is set to something that measures close to your target so you don't run out of range on your WB controls, and you have to know your 100% luminance before so you can calculate your target luminance at each % ahead of time.

Clear as mud?


Makes perfect sense - keep the colours balanced, and shift them ALL up or down to get the required luminance at each IRE. This is pretty much exactly what I suspected, but this review was done by some ISF calibrators, and I think they were being intentionally obtuse to protect their "trade secrets"!

The top-end IRE white balances seem to have an effect on the lower ones, but not vice versa, so I always go top-down.
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kal
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PostLink    Posted: Thu Apr 23, 2015 5:56 pm    Post subject: Reply with quote

Ah! Thanks Hog. That makes a lot of sense. Pretty straightforward idea too.

Kal

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CIR Engineering



Joined: 25 Aug 2008
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PostLink    Posted: Thu Apr 23, 2015 6:46 pm    Post subject: Re: couple of calibration questions Reply with quote

HogPilot wrote:
Arcsaber wrote:
2. I've just read a review of a TV in which I'm very interested, wherein they mention "repurposing the 10-point white balance controls for 10-point gamma".

They got the gamma absolutely flat across the full IRE range - how would one do this? Is there some way to use the 10-point WB controls to change the relative luminances of the IREs?

M.


I do this with my Lumagen Radiance. As long as you have controls for all three colors at each point, and they have a sufficient amount of +/- range, you should be able to simultaneously adjust white balance and luminance using the WB controls. Adjusting one color allows you to adjust WB at a given %; adjusting all three simultaneously by the same amount adjusts the luminance at that same %.

Here's an example: you're adjusting 50% white, and the default for the RGB controls are 0/0/0, with a +/- range of 20 units in 0.1 increments. You adjust the white balance to D65, and your end values are R: 5.7, G: 0, B: -1.3. As long as you know what your peak luminance is at 100% white, you can use a simple gamma calculator to tell you what the luminance values should be at each %. Let's say your calculator tells you your luminance should be 4.5 ftL at 50% white, but you're measuring 5.5 ftL. You can reduce all 3 RGB controls by the same amount (-1.0 let's say) to lower the luminance at 50% until you measure 4.5ftL output - a parametric gamma control would do the exact same thing, just with a single control instead of adjusting all 3 simultaneously. In fact, on the Radiance, when you adjust the Gamma/luminance control at a given %, you can see it simultaneously raising/lowering the RGB controls as a result. After that you'll have to re-tweak your WB, and probably re-tweak your luminance, but that's much quicker since you're already in the ballpark.

Your job will be easier if your overall display gamma is set to something that measures close to your target so you don't run out of range on your WB controls, and you have to know your 100% luminance before so you can calculate your target luminance at each % ahead of time.

Clear as mud?

Perfect explanation.

Just watch out for banding as some built in 10-point gamma system can introduce a lot of irregularities in the luma response. If you have a ramp pattern look at it before and after you adjust the gamma to make sure you haven't made things worse. Look at any bands in the pattern and try not to create more of them.
craigr

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HogPilot



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PostLink    Posted: Fri Apr 24, 2015 11:27 am    Post subject: Re: couple of calibration questions Reply with quote

CIR Engineering wrote:
HogPilot wrote:
Arcsaber wrote:
2. I've just read a review of a TV in which I'm very interested, wherein they mention "repurposing the 10-point white balance controls for 10-point gamma".

They got the gamma absolutely flat across the full IRE range - how would one do this? Is there some way to use the 10-point WB controls to change the relative luminances of the IREs?

M.


I do this with my Lumagen Radiance. As long as you have controls for all three colors at each point, and they have a sufficient amount of +/- range, you should be able to simultaneously adjust white balance and luminance using the WB controls. Adjusting one color allows you to adjust WB at a given %; adjusting all three simultaneously by the same amount adjusts the luminance at that same %.

Here's an example: you're adjusting 50% white, and the default for the RGB controls are 0/0/0, with a +/- range of 20 units in 0.1 increments. You adjust the white balance to D65, and your end values are R: 5.7, G: 0, B: -1.3. As long as you know what your peak luminance is at 100% white, you can use a simple gamma calculator to tell you what the luminance values should be at each %. Let's say your calculator tells you your luminance should be 4.5 ftL at 50% white, but you're measuring 5.5 ftL. You can reduce all 3 RGB controls by the same amount (-1.0 let's say) to lower the luminance at 50% until you measure 4.5ftL output - a parametric gamma control would do the exact same thing, just with a single control instead of adjusting all 3 simultaneously. In fact, on the Radiance, when you adjust the Gamma/luminance control at a given %, you can see it simultaneously raising/lowering the RGB controls as a result. After that you'll have to re-tweak your WB, and probably re-tweak your luminance, but that's much quicker since you're already in the ballpark.

Your job will be easier if your overall display gamma is set to something that measures close to your target so you don't run out of range on your WB controls, and you have to know your 100% luminance before so you can calculate your target luminance at each % ahead of time.

Clear as mud?

Perfect explanation.

Just watch out for banding as some built in 10-point gamma system can introduce a lot of irregularities in the luma response. If you have a ramp pattern look at it before and after you adjust the gamma to make sure you haven't made things worse. Look at any bands in the pattern and try not to create more of them.
craigr


Thanks for the input, I never thought of the banding issue. Say one does get banding on a grey ramp after calibration - what is the likelihood that it will be visible in real-world material? I would guess the answer would partially depend on the material and how bad the banding is, but I ask because I don't know.

I guess if it was bad enough that you could see it in regular material, you'd have to compromise between a lower gamma and the banding - essentially find a happy medium?

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Curt Palme wrote:
Interesting, Mac isn't returning my emails. Go figure.

He's mad at us for making Hog a moderator. He took his ball and went home.

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CIR Engineering



Joined: 25 Aug 2008
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PostLink    Posted: Sun Apr 26, 2015 10:48 pm    Post subject: Reply with quote

The first primary point to looking at the ramp is to see if there are large dramatic brightness jumps between any of the incremental luma increases in the ramp pattern. For example, if you see a single brighter band between two darker bands than you may want to try and correct it.

The second primary point in looking at the ramp is for dramatic color shift between two graduations in the ramp pattern. If there is / are cyan or magenta tinted greys than you should try and correct them.

Correcting the issues can sometimes be easy and is sometimes very difficult. It is easier to correct at higher IRE levels, but it can be fixed everywhere.

Let's say you have a 10 or 11 point greyscale system. If you have one or more abnormal bands between say 30 and 40 IRE, what I do is go to the 30 IRE and / or 40 IRE adjustments in the parametric gamma and experiment. If the band(s) are magenta, try lowering the red at 30 and / or 40 IRE. Often several clicks will have zero impact, but once you hit the threshold one click more will suddenly have a dramatic impact. I go through and work with these until bands are reduced or removed.

Making this adjustment is done by eye and will usually result in a greyscale that measures technically worse with higher dE. That said, the dE in between the measurement points will be reduced even if your calibration report looks worse at the end... the image will be better.

As you suggest how easy it is to see the deleterious impact of the banding depends entirely on content. For the most part on BD there is very little banding if a disc is played natively without digital gamma and greyscale correction. That said, many samples are on the verge of banding, but are just barely not banding. Making adjustments in a digital CMS or greyscale can push these verge portions of the video past the edge and then you can see banding in real world video that was not there before correction.

A good example is the Universal Studios logo at the beginning of their BD's. The blue in the globe is often of very low quality and is close to banding. After full correction, this is often an easy place to detect errors that you can see in real world video.

Another thing to keep in mind with the Radiance processors is that it's better to increase luma in the parametric greyscale than to decrease it or lower luma (this is opposite to the old VisionHDP line). The reason for this is that increasing luma (and that goes for RGB too) allows the Radiance to upsample the colors. Decreasing luma values is accomplished by basically throwing away data.

So with that all in mind, it's best with a Radiance to start with a projector native gamma that is too high, and then to lower it with the parametric greyscale. With other manufacturer's greyscale functions you should try both ways and see which looks better. In most cases the method that creates the least amount of banding in the ramp pattern is the way to go.

Hopefully that was all concise and not to much information Wink

craigr

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Arcsaber



Joined: 15 Apr 2015
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PostLink    Posted: Mon Apr 27, 2015 12:04 pm    Post subject: Reply with quote

When calibrating the gamma, I've seen some reviewrs use 2.2 for the blacks and 2.4 elsewhere - is this worth trying? 2.2 for, say, IRE 0 to 30, and 2.4 for the rest?

This would probably be for daytime viewing only, so I don't crush the blacks.
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CIR Engineering



Joined: 25 Aug 2008
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PostLink    Posted: Mon Apr 27, 2015 1:18 pm    Post subject: Reply with quote

Arcsaber wrote:
When calibrating the gamma, I've seen some reviewrs use 2.2 for the blacks and 2.4 elsewhere - is this worth trying? 2.2 for, say, IRE 0 to 30, and 2.4 for the rest?

This would probably be for daytime viewing only, so I don't crush the blacks.

You can try it. It will boost the low IRE details without totally compromising the depth of the image. Higher gamma gives a more saturated and three dimensional looking picture, but low gamma will also make compression artifacts stand out in low IRE images. But for daytime use this should be totally fine.

craigr

_________________
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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
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www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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Arcsaber



Joined: 15 Apr 2015
Posts: 16



PostLink    Posted: Mon Apr 27, 2015 1:40 pm    Post subject: Reply with quote

CIR Engineering wrote:
Arcsaber wrote:
When calibrating the gamma, I've seen some reviewrs use 2.2 for the blacks and 2.4 elsewhere - is this worth trying? 2.2 for, say, IRE 0 to 30, and 2.4 for the rest?

This would probably be for daytime viewing only, so I don't crush the blacks.

You can try it. It will boost the low IRE details without totally compromising the depth of the image. Higher gamma gives a more saturated and three dimensional looking picture, but low gamma will also make compression artifacts stand out in low IRE images. But for daytime use this should be totally fine.

craigr


I'd probably stick with straight 2.4 gamma for night - the blacks can be a bit darker then, anyway.

What kind of peak luminances are recommended for day vs night, by the way? 120 seems to be common, but is it worth adding a bit on for daytime?
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CIR Engineering



Joined: 25 Aug 2008
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PostLink    Posted: Mon Apr 27, 2015 8:54 pm    Post subject: Reply with quote

Arcsaber wrote:
CIR Engineering wrote:
Arcsaber wrote:
When calibrating the gamma, I've seen some reviewrs use 2.2 for the blacks and 2.4 elsewhere - is this worth trying? 2.2 for, say, IRE 0 to 30, and 2.4 for the rest?

This would probably be for daytime viewing only, so I don't crush the blacks.

You can try it. It will boost the low IRE details without totally compromising the depth of the image. Higher gamma gives a more saturated and three dimensional looking picture, but low gamma will also make compression artifacts stand out in low IRE images. But for daytime use this should be totally fine.

craigr


I'd probably stick with straight 2.4 gamma for night - the blacks can be a bit darker then, anyway.

What kind of peak luminances are recommended for day vs night, by the way? 120 seems to be common, but is it worth adding a bit on for daytime?

What kind of display device are you asking about? 120 flt would really be for something in a sun room.

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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Arcsaber



Joined: 15 Apr 2015
Posts: 16



PostLink    Posted: Mon Apr 27, 2015 9:52 pm    Post subject: Reply with quote

CIR Engineering wrote:
What kind of display device are you asking about? 120 flt would really be for something in a sun room.

craigr


LED LCD.
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HogPilot



Joined: 21 Jan 2010
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TV/Projector: Vizio P702ui-B3, Pioneer Elite Pro-151FD & 111FD


PostLink    Posted: Mon Apr 27, 2015 10:34 pm    Post subject: Reply with quote

Craig - thanks for the answers to my questions! Definitely not too detailed, just lots of great info - thanks for taking the time to share some insider calibration knowledge with the rest of us Smile
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ecrabb wrote:
Curt Palme wrote:
Interesting, Mac isn't returning my emails. Go figure.

He's mad at us for making Hog a moderator. He took his ball and went home.

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Arcsaber



Joined: 15 Apr 2015
Posts: 16



PostLink    Posted: Tue Apr 28, 2015 7:08 pm    Post subject: Reply with quote

Well, I bought the TV in question, and have just finished calibrating it. Did exactly what @Hogpilot suggested: get the greyscale sorted first, then move down the IRE's shooting for the right luminance. I did pretty well - results here:



I had to compromise between gamma tracking and greyscale accuracy, but all dE's under 3 after 10%... and all under 2 after 20%... and all under 1 after 40% is nothing to be sniffed at!
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