How to wisely handle the Blue offset in projector calibration - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 14 Old 05-09-2020, 05:50 PM - Thread Starter
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How to wisely handle the Blue offset in projector calibration

Hi everyone I am sorry if allowed myself to open a new discussion here but I would really like to hear from experts how they suggest to handle the Blue offset in projector calibration. I owned and own now a JVC projector and any time I provide a calibration I try to not set the Blue offset in the RGB grayscale process at more than 0. In this way I would preserve the purity of blacks but at expense of a loss of brightness since I have to drop a lot the Red and Green offesets to keep the B at 0 or below. Would you recommend a slightly ‘positive’ set for the Blue or it is always better to keep it at 0 and below? Thank you for your assistance in advance
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post #2 of 14 Old 05-10-2020, 08:15 AM
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what you are asking is irrelevant.
you balance the RGB offsets to obtain a D65 balance.
After doing this you use the brightness control to correctly set the black level.

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post #3 of 14 Old 05-10-2020, 08:30 AM - Thread Starter
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Thank you for your answer. My question is not about the potential impact of the Blue offset on the black ‘level’ but on the blacks ‘quality’.In other words how the Blue offset can make the blacks a little more ‘blueish’. Is that a false question or there is a potential impact like that on the blacks? Thank you
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post #4 of 14 Old 05-10-2020, 08:42 AM
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quality = D65
level = setting the black level correctly.

If blue is increased to get to D65 then so be it.

Founder, Professional Video Alliance
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20 years of full time video calibration, consulting, and education.
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post #5 of 14 Old 05-10-2020, 10:03 AM
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Quote:
Originally Posted by jimmyp1974 View Post
Thank you for your answer. My question is not about the potential impact of the Blue offset on the black ‘level’ but on the blacks ‘quality’.In other words how the Blue offset can make the blacks a little more ‘blueish’. Is that a false question or there is a potential impact like that on the blacks? Thank you
If you use 20/80 or 30/70 to adjust RGB offsets and gains, your near black could be way off. Certainly your previously posted result showed that. It’s already way off the roof at 10%, and going off further at lower levels.


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Last edited by Dominic Chan; 05-10-2020 at 10:58 AM.
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post #6 of 14 Old 05-10-2020, 11:28 AM - Thread Starter
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Thank you Dominic. Yes I used 20/80 to adjust the RGB gains and offsets and while with the Rec.709 the grayscale is perfectly flat and delta below 1 from 10 to 100% here with the rec.2020 the lower levels are out. Do you have any suggestion about how to make them flat? I would make the attempt to use a positive Blue offset (+1 or +2) rather then dropping too much Red and Green to balance the low Blue levels at the starting point.Now I have these offesets R -21, G -11, B -2 which deliver the results you have seen. Thank you in advance.
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post #7 of 14 Old 05-11-2020, 08:24 AM - Thread Starter
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Hi Dominic and everyone. Attached the new grayscale graphic. The rest as to gamma and color temperature are perfect. Just me errors in some saturations, but overall under 3 for all colors together. I hope it is good now. I fixed the offsets with a +3 blue offset and I ended up with a luminance of 37.1 fL with iris at -10. Do you think it's too much? I watched some of the Greatest Showman HDR and it looked fantastic...
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post #8 of 14 Old 05-11-2020, 08:27 AM - Thread Starter
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Here the graphic. Sorry
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post #9 of 14 Old 05-11-2020, 08:33 AM
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Quote:
Originally Posted by jimmyp1974 View Post
Hi Dominic and everyone. Attached the new grayscale graphic. The rest as to gamma and color temperature are perfect. Just me errors in some saturations, but overall under 3 for all colors together. I hope it is good now. I fixed the offsets with a +3 blue offset and I ended up with a luminance of 37.1 fL with iris at -10. Do you think it's too much? I watched some of the Greatest Showman HDR and it looked fantastic...
It’s strange that you can fix the excess blue by increasing the blue offset from -2 to +3, unless you have also made changes to red and green offsets.

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Creating a basic HDR curve using Arve’s Tool;
Replacing JVC Bare Bulbs
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post #10 of 14 Old 05-11-2020, 08:43 AM - Thread Starter
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Yes of course I re-adjusted all the offsets but differently than ‘usual’ I tried the positive blue offset to +3 and basically it worked to fix the lower levels from 10 to 50% which were previously below. I ran a near black test too and it was perfectly under 1% error. Now my concern is about luminance, 37.1 fL which I thought it could be a lot but on screen with a 2.4 gamma is absolutely fine and actually I added too a +4 of the HDR optimazier from the Panasonic player and at least for my eyes the picture quality is really wonderful
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post #11 of 14 Old 05-11-2020, 10:19 AM - Thread Starter
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For some reason I am not able to generate the pdf of my calibration so allow my self to post some pics of the results. I would really be grateful if you could share your opinions about it. Thank you very much!
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post #12 of 14 Old 05-11-2020, 01:35 PM - Thread Starter
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Hi Dominic I would really be grateful if you could take a look at the pics and let me know your thoughts. I am try to learn and develop this passion. There’s so much to know though! Thank you
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post #13 of 14 Old 05-18-2020, 10:45 AM
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You may be obsessing about making changes to the display's settings in an attempt to get your calibration software to make a "pretty" graph of the resulting measurements. A problem arises if your adjustments are based on faulty data: if your meter does not perform well in low light, you may be making unnecessary changes.

The last step of any real world calibration workflow is to evaluate the results by eye while viewing reference material that you know well. I recommend you play a movie with a lot of dark scenes. If everything looks blue, then you should just go back to the settings you had previously and accept that your existing equipment is not helpful in making fine changes to settings near black.
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post #14 of 14 Old 05-18-2020, 12:38 PM - Thread Starter
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Many thanks yes this is a very wise advice. Real world rather than numbers which for some reason could be altered. I will play Oblivion the questioning scene with Morgan Freeman, still best dark/light scene ever
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