The Official ChromaPure thread - Page 221 - AVS | Home Theater Discussions And Reviews
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post #6601 of 6612 Unread 06-25-2015, 08:32 PM
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Originally Posted by TomHuffman View Post
A much higher amount of light gets into the meter, which allows it to spend more time in its ideal operating range.

I think I undersold the results in my previous post. I'm flat out shocked by the difference I'm seeing. The image went from borderline unwatchable to deeply immersive and pleasing. In the few movies I demoed all the shades of gray seemed perfectly rendered. I saw practically nothing in the way of uniformity errors.

If these kind of results are here to stay I will remain a very happy viewer.
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post #6602 of 6612 Unread 06-25-2015, 08:39 PM
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Originally Posted by subliminac View Post
I think I undersold the results in my previous post. I'm flat out shocked by the difference I'm seeing. The image went from borderline unwatchable to deeply immersive and pleasing. In the few movies I demoed all the shades of gray seemed perfectly rendered. I saw practically nothing in the way of uniformity errors.

If these kind of results are here to stay I will remain a very happy viewer.
You weren't by any case using the meter's diffuser when facing the screen? I might expect some improvement when correctly doing a lens calibration. I wouldn't expect the kind of dramatic night-and-day difference that you describe. I am suspicious that something else was going on.

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post #6603 of 6612 Unread 06-26-2015, 09:12 PM
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The Official ChromaPure thread

No the diffuser wasn't covering the meter previously. As I said before, color films always looked fine. It was with B&W films where I was the most disappointed, where grayscale inaccuracies and uniformity issues would be the most prominent. In this case a subtle shift could make a big difference. Whatever I did seemed to take away the red tint. The end result isn't as good as what a DLP projector would produce (since there should be no alignment issues) but it is very watchable and frequently stunning.

Any chance not having whiter than white set properly could have contributed to the problem? I know I made an adjustment which made the bars visible where they weren't before. I believe I also plugged in the 100% and 0% luminance values when setting up the software before dialing in the grayscale. Could that have helped? The only other thing I did differently was take my readings directly off the projector. Everything else was the same.

Last edited by subliminac; 06-27-2015 at 03:57 AM.
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post #6604 of 6612 Unread 06-27-2015, 10:03 AM
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Maybe the meter wasn't placed properly when you measured from the screen. Did you put up a 100% white pattern and ensure the meter was level and positioned properly in order to maximize the fL reading? You could have been picking up some of the meter's shadow.
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post #6605 of 6612 Unread 06-27-2015, 10:08 AM
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Originally Posted by Kilgore View Post
Maybe the meter wasn't placed properly when you measured from the screen. Did you put up a 100% white pattern and ensure the meter was level and positioned properly in order to maximize the fL reading? You could have been picking up some of the meter's shadow.

No it was properly positioned.
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post #6606 of 6612 Unread 06-27-2015, 10:18 AM
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Originally Posted by subliminac View Post
Any chance not having whiter than white set properly could have contributed to the problem? I know I made an adjustment which made the bars visible where they weren't before. I believe I also plugged in the 100% and 0% luminance values when setting up the software before dialing in the grayscale. Could that have helped? The only other thing I did differently was take my readings directly off the projector. Everything else was the same.
Sure. If your contrast setting resulted in not being able to see some of the bars in the white PLUGE test pattern, then that means that contrast was set too high. Lowering contrast would reveal those bars and end the white crush. The other issue is irrelevant. That is just for calculating BT.1886 gamma.

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post #6607 of 6612 Unread Today, 01:01 AM
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Hi all,

Please can I request some guidance on my calibration. There's a couple of points I want to raise, and I'm hoping someone can chime in with some thoughts.

This is a gamma 2.22 / Rec .709 / 120 cd/m2 calibration, using a Samsung HU9000 LED TV with a i1D3 Pro w/ corrections from Tom. No issues with greyscale at all. When it comes to colour, I always have a luminance / saturation issue with Dark Skin and Light Skin, which seems to dictate inaccurate skin tones.

Please allow me to try an explain one anomaly which I can't quite understand. If I try to calibrate with a higher gamma figure such as 2.4, I get huge luminance errors on all of the ColourChecker colours. If I try to dial them out by increasing the luminance of the colours in the CMS, it starts to bring all the saturation points (25%, 50%, 75%, 100%) of said colour closer together. So, as an example, a 25% saturation pattern of red would appear nearer 35% in the CIE chart.75% saturation pattern would appear nearer 60% and a 100% pattern would be nearer 85%. If it helps, look at the Moderate Red and Red plots on the CIE. They line up well. If this were a 2.4 gamma calibration, they would be close to touching each other.

I've attached some pictures. Please ignore the Pre-ColourChecker figures and only note the Post details. I've also added a picture of Luminance results when targeting Gamma @ 2.4. Can anyone offer some insight please? Thanks!
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post #6608 of 6612 Unread Today, 01:23 AM
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Quote:
Originally Posted by Toadus View Post
Hi all,

Please can I request some guidance on my calibration. There's a couple of points I want to raise, and I'm hoping someone can chime in with some thoughts.

This is a gamma 2.22 / Rec .709 / 120 cd/m2 calibration, using a Samsung HU9000 LED TV with a i1D3 Pro w/ corrections from Tom. No issues with greyscale at all. When it comes to colour, I always have a luminance / saturation issue with Dark Skin and Light Skin, which seems to dictate inaccurate skin tones.

Please allow me to try an explain one anomaly which I can't quite understand. If I try to calibrate with a higher gamma figure such as 2.4, I get huge luminance errors on all of the ColourChecker colours. If I try to dial them out by increasing the luminance of the colours in the CMS, it starts to bring all the saturation points (25%, 50%, 75%, 100%) of said colour closer together. So, as an example, a 25% saturation pattern of red would appear nearer 35% in the CIE chart.75% saturation pattern would appear nearer 60% and a 100% pattern would be nearer 85%. If it helps, look at the Moderate Red and Red plots on the CIE. They line up well. If this were a 2.4 gamma calibration, they would be close to touching each other.

I've attached some pictures. Please ignore the Pre-ColourChecker figures and only note the Post details. I've also added a picture of Luminance results when targeting Gamma @ 2.4. Can anyone offer some insight please? Thanks!
I guess I don't understand. Your average CIE94 error for skin tones is 1.2. That's really all you need to concern yourself with and that's a very good number. Even the luminance error is just 7.6%. Anything +- 5% for luminance is fine, so you are off that just a little.

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post #6609 of 6612 Unread Today, 01:35 AM
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Originally Posted by TomHuffman View Post
I guess I don't understand. Your average CIE94 error for skin tones is 1.2. That's really all you need to concern yourself with and that's a very good number. Even the luminance error is just 7.6%. Anything +- 5% for luminance is fine, so you are off that just a little.
Thanks for the reply Tom.

I'm trying to increase my knowledge so I can get better at what I'm doing. Settling for good results is fine, but I would like to understand more. I touched upon calibrating with gamma @ 2.4. I can't get accurate colours with this and was hoping I could learn more to try and resolve it. As my current understanding goes, I can't see any reason as to why I get poor results with gamma higher than 2.22.
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post #6610 of 6612 Unread Today, 01:47 AM
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Originally Posted by Toadus View Post
Thanks for the reply Tom.

I'm trying to increase my knowledge so I can get better at what I'm doing. Settling for good results is fine, but I would like to understand more. I touched upon calibrating with gamma @ 2.4. I can't get accurate colours with this and was hoping I could learn more to try and resolve it. As my current understanding goes, I can't see any reason as to why I get poor results with gamma higher than 2.22.
First, if you are getting poor results with 2.4, then you should post screen shots showing this. I can only comment on the screenshots you did post and they didn't show any issues.

Second, I don't know what calibration tools you have available to you. If all you have is what the Samsung provides, it may be that the Samsung's calibration tools simply do not provide the needed adjustments to get to the gamma you have targeted. All CP does is measure the results. You have to make the adjustments yourself with the tools you have available.

Third, to precisely dial in performance with the precision you seem to be aiming for, you should consider a dedicated calibration instrument, such as a Lumagen video processor. The calibration adjustments within displays are often somewhat crude and not very flexible.

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post #6611 of 6612 Unread Today, 02:13 AM
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Originally Posted by TomHuffman View Post
First, if you are getting poor results with 2.4, then you should post screen shots showing this. I can only comment on the screenshots you did post and they didn't show any issues.

Second, I don't know what calibration tools you have available to you. If all you have is what the Samsung provides, it may be that the Samsung's calibration tools simply do not provide the needed adjustments to get to the gamma you have targeted. All CP does is measure the results. You have to make the adjustments yourself with the tools you have available.

Third, to precisely dial in performance with the precision you seem to be aiming for, you should consider a dedicated calibration instrument, such as a Lumagen video processor. The calibration adjustments within displays are often somewhat crude and not very flexible.
Thanks again for your reply.

I posted just one screen shot of the ColourChecker results with gamma @ 2.4. It's the last one in the list, please take a look at my previous post. Luminance is low throughout, and if I try to correct the luminance, it starts to bring the saturation points closer together, so I can't win either way. I.e., a 75% saturation test pattern will read under-saturated and a 25% saturation test pattern will read over-saturated.

The Samsung has a decent and comprehensive CMS, but it doesn't work in a linear fashion unfortunately. But this doesn't explain to me why it wouldn't calibrate well at a gamma setting above 2.22. Leads me to think it's more my lack of knowledge..

Agreed, a Lumagen would be ideal, but just trying to get the best out of what I've got for the time being.
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post #6612 of 6612 Unread Today, 03:19 AM
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Originally Posted by Toadus View Post
I posted just one screen shot of the ColourChecker results with gamma @ 2.4. It's the last one in the list, please take a look at my previous post. Luminance is low throughout, and if I try to correct the luminance, it starts to bring the saturation points closer together, so I can't win either way. I.e., a 75% saturation test pattern will read under-saturated and a 25% saturation test pattern will read over-saturated.
Yes, that's the one I referred to that was off by 7.6%. That is just not that bad. In any case, the dE figure is what you should focus on rather than a single component. BTW, you can raise color luminance often by raising the main color conrol a few ticks.

Quote:
Originally Posted by Toadus View Post
The Samsung has a decent and comprehensive CMS, but it doesn't work in a linear fashion unfortunately. But this doesn't explain to me why it wouldn't calibrate well at a gamma setting above 2.22. Leads me to think it's more my lack of knowledge.
I wouldn't assume that. It could very well be that this is how the Samsung was engineered. BTW, you can use the G control in the 10-pt grayscale for multi-point gamma adjustment. Just be sure to use the R and B controls afterwards to restore white balance.

2.4 gamma throughout will not look good and will provide poor shadow detail. Try BT.1886 instead. Either that or a flat 2.22 power law would be preferable to a 2.4 power law.

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