Author Topic: Greyscale/Gamma Calibration Tip  (Read 6170 times)

Offline KenMasters

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Greyscale/Gamma Calibration Tip
« on: September 19, 2015, 08:53:35 AM »
I was doing a bit of research yesterday and picked up a pretty damn handy tip I thought I'd share for those that use a meter and calibration software, working with 10 point white balance.

Traditionally when calibrating the greyscale you'd use two point white balance, say at 30% and 80% or whatever to get things in line and then iron things out using the 10 point white balance using an 11 point pattern. Now while this is obviously more time consuming, what you should do is first take a full 21 point pattern reading and look at the mid point readings, 5%, 15%, 25% and so on (I suppose you could also just measure those and work off that at first). Use the two point balance to flatten those points out as best you can and ignore the 10% stimuli. Then go to the 10 point adjustment and iron out the regular 10% intervals, there'll be a bit of back and forth between the 10 point and 2 point to fine tune but it actually works really well in the absence of a 20 point white balance option.

Besides the smoother greyscale, it really helps nail that difficult transition out of black when trying to implement BT. 1886 gamma tracking.

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #1 on: October 09, 2015, 05:13:26 PM »
Or you could implement a 3d colour cube generator and calibrate up to 64000 points automatically ;)

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #2 on: October 10, 2015, 01:55:23 PM »
Or you could implement a 3d colour cube generator and calibrate up to 64000 points automatically ;)

I can certainly see the value in a 3D LUT with a display that struggles to track well but I don't like the idea of a device between my devices - and I enjoy the manual calibration process. Would such a device add to input lag?

Come to think of it, a device like this would probably not work correctly with the Ultra HD standard, considering the gamma mapping system.

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #3 on: October 11, 2015, 11:09:51 AM »
What is the ultra hd standard, itu rec 2020 how many uhd displays reach that gamut and what spectro's (what price) are able to read it, or dci p3 that most uhd tv's use, how much uhd material is available without upscaling.

I am sure uhd 3d cube generators are available at a price.

http://www.lightillusion.com/manual_calibration_idiots_guide.html :thumbs:

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #4 on: October 11, 2015, 11:32:39 AM »
By the way, you need a 3 nano meter spectro to calibrate rec 2020, I think anything up from about R50 000 if not more. Becoming an expensive hobby this :stop:

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #5 on: October 11, 2015, 12:05:15 PM »
What is the ultra hd standard, itu rec 2020 how many uhd displays reach that gamut...

Yea, we're not there yet, but better to think of it as headroom for the future I think.

dci p3 that most uhd tv's use, how much uhd material is available without upscaling.

Yea, DCI-P3 is what they're aiming for at the moment, which is fantastic for the consumer I think, straight cinema conversions. There's no true Ultra HD content yet since offically Ultra HDTVs aren't out yet - though some of the current higher tier TVs are to be made compatible via firmware (can't say to what degree but there are a few that get within spitting distance of DCI and reach 1000 nits).

I am sure uhd 3d cube generators are available at a price.

Where I see a possible issue is with the new gamma tracking system, Ultra HD signals will contain EOTF metadata which displays will read then map according to their own light output characteristics.
« Last Edit: October 11, 2015, 12:24:47 PM by KenMasters »

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #6 on: October 12, 2015, 07:32:20 AM »
What meter and software do you use?

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #7 on: October 12, 2015, 08:05:33 AM »
What meter and software do you use?

I've got CalMAN 5 Control and an i1 Display Pro (can't justify the expense of a spectrophotometer).

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #8 on: October 12, 2015, 08:34:56 AM »
You may be interested in this: http://www.avsforum.com/forum/139-display-calibration/1303930-x-rite-eyeone-pro-i1-pro-recertification-now-available-spectracal-2.html

I have the i1pro2 and i1display pro, calman 5 enthusiast, have noticed a few similarities between the two meters. I will be writing a tutorial on how to overcome the inaccuracies of the two meters soon.

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #9 on: October 13, 2015, 07:53:19 PM »
By the way, you need a 3 nano meter spectro to calibrate rec 2020, I think anything up from about R50 000 if not more. Becoming an expensive hobby this :stop:

And ta-dah, sorted!



http://calman.spectracal.com/spectracal-c6-hdr.html

Not a spectro but good enough for me.

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #10 on: October 13, 2015, 11:05:49 PM »
I would have gone for the basic color discus in my personal opinion, it was designed for illuminant display callibrations where as the c6 is just a glorified i1d3 designed more for the printing industry. Congratulations if you have bought it, sorry do not meen to burst your bubble but, you are aware of the difference that a colorimeter is just like a comparator with reference filters and will likely return inaccurate readings if not profiled or compared to a spectro on the display in particular that is being calibrated? The i1pro and pro 2 can be used to measure in 3.3nm mode using the argyll cms drivers and hcfr.

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #11 on: October 14, 2015, 06:23:54 AM »
I would have gone for the basic color discus in my personal opinion, it was designed for illuminant display callibrations where as the c6 is just a glorified i1d3 designed more for the printing industry. Congratulations if you have bought it, sorry do not meen to burst your bubble but, you are aware of the difference that a colorimeter is just like a comparator with reference filters and will likely return inaccurate readings if not profiled or compared to a spectro on the display in particular that is being calibrated? The i1pro and pro 2 can be used to measure in 3.3nm mode using the argyll cms drivers and hcfr.

The Color Discus is only good to 500cd/m2, and what separates the C6 from the OEM i1 Display Pro is the fact that it's calibrated within +-0.002  of X & Y.

Don't have any plans to buy one yet, I'm sitting tight for a few more years before I pick up and Ultra HD display. I'm just glad to see such products on the market already.

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #12 on: October 14, 2015, 08:26:48 PM »
...will likely return inaccurate readings if not profiled or compared to a spectro on the display in particular that is being calibrated?

CalMAN hosts the display references.

Offline idm

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Re: Greyscale/Gamma Calibration Tip
« Reply #13 on: October 14, 2015, 10:14:02 PM »
Perhaps for all display technologies not for every display. And even the same display technology does not always measure the same, including the same display model.

Offline KenMasters

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Re: Greyscale/Gamma Calibration Tip
« Reply #14 on: October 15, 2015, 05:33:14 AM »
Perhaps for all display technologies not for every display. And even the same display technology does not always measure the same, including the same display model.

Perhaps one day I'll make the investment but currently it makes little sense to me for private use. I think my results look good and I trust my eyes. I would also hope given Spectracal's working relationship with Panasonic their EDRs are likely a good fit for their panels - my next display will likely also be a Panasonic. I do understand what you're saying though, and you are right that the ideal situation would be to have a good spectrophotometer / spectroradiometer for profiling the colorimeter but I can't justify the expense, it's money I'd rather spend on the display.
« Last Edit: October 15, 2015, 06:02:53 AM by KenMasters »