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post #1 of 6 Old 12-30-2019, 09:39 AM - Thread Starter
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Gamma calculator help

Hey guys,

I have recently recalibrated my JVC projector since the bulb has aged. I typically calibrate to 2.4 but wanted to calibrate to BT. 1886 this time. I use HCFR for my calibration software. The issue is, I don't know how to calculate the correct luminance for each of the display patches (e.g., 10%, 20%, ... etc.). I have always used an Excel sheet that has floated around here that I can define a gamma log function (like 2.4), give it my maximum light output, and it tells me what each luminance is supposed to be. That is, if my 100% max luminance is 16 cd/m^2, then my 50% should be 3.03 cd/m^2, 90% should be 12.43 cd/m^2, etc.

I cant seem to find a similar calculator for dialing in my BT. 1886. Obviously it will have to be more complex than the typical gamma calculation since it takes into account non-zero black level. Can anyone direct me in the right direction as to how to calculate each luminance range so I can dial in my gamma with HCFR and my JVC? The JVC has a 12 point gamma correction. Perhaps there is an updated and even more automated way to calibrate my gamma to BT. 1886 with HCFR that doesn't require this kind of manual calculation?

Thanks for the direction.
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post #2 of 6 Old 12-30-2019, 12:42 PM - Thread Starter
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Am I just way off here? If I'm not asking the right kind of question or there is an obvious answer, please point me in the right direction.
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post #3 of 6 Old 12-31-2019, 07:38 AM
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As I recall HCFR will calculate the Y values at each point based on your max nits if you have the xyY page up; it will do this for 1886, 2.4, or whatever based on your gamma settings.

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Am I just way off here? If I'm not asking the right kind of question or there is an obvious answer, please point me in the right direction.
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post #4 of 6 Old 01-02-2020, 09:25 AM
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Originally Posted by jsmith967 View Post
Am I just way off here? If I'm not asking the right kind of question or there is an obvious answer, please point me in the right direction.
HCFR shows the Target Y automatically according on the gamma/EOTF you choose, and the measured 0% and 100% levels. No spreadsheet is required.

Last edited by Dominic Chan; 01-03-2020 at 07:41 AM.
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post #5 of 6 Old 01-04-2020, 02:58 PM - Thread Starter
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Quote:
Originally Posted by jqmn View Post
As I recall HCFR will calculate the Y values at each point based on your max nits if you have the xyY page up; it will do this for 1886, 2.4, or whatever based on your gamma settings.
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Originally Posted by Dominic Chan View Post
HCFR shows the Target Y automatically according on the gamma/EOTF you choose, and the measured 0% and 100% levels. No spreadsheet is required.
I see, so I will have to go through all measurements (0,...100) in order for it to know how to calculate the target Y for each, right? Otherwise, it would not know the 100% levels, which is required for the intermediate (e.g., 10%, 20%, 30%, etc)?
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post #6 of 6 Old 01-04-2020, 03:09 PM
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Quote:
Originally Posted by jsmith967 View Post
I see, so I have to go through all measurements (0,...100) in order for it to know how to calculate the target Y for each, right? Otherwise, it would not know the 100% levels, which is required for the intermediate (e.g., 10%, 20%, 30%, etc)?
Not really. Just a single measurement at 100% will populate the target values for all columns, unless you select a gamma option that also depends on 0% (BT.1886, Black Compensation etc), in which case you need to measure 0% as well.

Regardless, it’s always advisable to do a complete greyscale sweep as baseline prior to making any adjustments, so the above is more or less moot.

Last edited by Dominic Chan; 01-04-2020 at 06:02 PM.
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