About Calibrating HDR-projectors on Calman

[YOUNGJUN WOO]

I have quetions on Calman when in HDR-Projectors.

First, the thing is about Offset setting 2084gamma for HDR-projectors on Calman. How can I judge what number is the best? I mean the ideal offset is the time when the EOTF will be onto Yellow-EOTF, and then adjusting Contrast. In this case, there might be different results depending on the Offset. Is it right?

Second, when in CMS, according to 50% targets of colours, I can do it as possible as the projector can be adjusted, but the reall projection was washed out without detail. So, I checked 80~100% saturation in bt2020. The things’ brightness wewre too high. It might be affecting on crushed-details. In this case, how can I adjust CMS?

Topic

[Gregg Loewen]

hello Johnny.

What projector are you calibrating? Some PJs can not do more than rec 709 in HDR (ie: Sony).

In regard to setting the HDR Gamma:
using 2084 (which is an absolute)… I start at considering 1000 nits. If the PJ max output is 150 nits, then take 1000 and divide by 150 = 6.6, so round up to 7. This is the value you will enter in the large Y value for screen offset. So every measurement you perform will be multiplied by 7. Adjusting the Contrast may affect the clipping point, and or roll off.

CalMan also has a BT2390 setting. Where you can select 1000 vs 4000 nits as a starting point. Tyler at CalMan recommends using this method for setting the EOTF on a PJ, Toshi at Sony does NOT recommend this, and suggests my method of creating a screen offset.

[YOUNGJUN WOO]

Thank you for your help!

VPL-VW270es, VPL-VW760es(Sony), UHZ65(optoma) were usually calibrated by me. Like you said, those of can cover the really small Rec.2020.
Do you mean I must take Rec.709 even though it is for HDR Mode for CMS?
Could you let me know about the good way for adjusting CMS for HDR-projectors?

When it comes to HDR gamma:
The 150 nits that you said is absolute maximum nits value(manufactures informed) or 100% white field pattern that I can measure with K10A? If second one is correct, then, how can I get the value on Calman? I was not able to find out the nits on Calman.

After setting offset which is your method, should I adjust Contrast as possible as the EOTF will be on the Yellow-EOTF(standard point)?

[Gregg Loewen]

Ive only calibrated 1 Optoma. It accepted an HDR signal but converted it to SDR, with a gamma of 2.2 – 2.4 (I dont remember). It do nothing beyond rec 709.

if in HDR mode, consider rec 2020 for your color space. But with the PJs you have listed, do not look for anything accurate beyond 40-50% of rec 2020.

the 150 nits (is my example), is what you would be measuring, with lamp on high and iris open. This is the PJ running at 100% capacity.

Start with the contrast at the default position. (on the Sony 60 is a good start, but will be clipping abit). Then look for Gamma presets or other settings that will move the EOTF to be brighter or darker to match the Calman reference.

[YOUNGJUN WOO]

1.
‘do not look for anything accurate beyond 40-50% of rec 2020.’ that means I only should focus on 50% targets of colors in CMS ignoring beyond 40~50% accuracy like what happened to beyond 60~100% of colors?

2
Please find attached the report of UHZ65.(peak luminance nit = 423.8)

In this case, according to your calculation way, the offset will be 3. However, due to a high gain screen in a perfect dark room, I set 5. Do you think it is ok or? Could you check this report? In my experience, the real projection was pretty good.
(In regard to setting CMS, I focused on 50% target, and considering 60~100% saturation were not too high DeltaE errors.)

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[Gregg Loewen]

1. correct. Remain to be aware of what you are doing at 40-50% and how that effects 75 -100. Do not go crazy with getting 40-50 perfect if 75-100 goes very bad.

2. When you select a screen offset, you are changing the target eotf. you are not changing the PJ. if you had selected the offset of 3, your reports would have looked better.

[YOUNGJUN WOO]

I finally got this report that is attached!

The Sony VPL-VW270ES was calibrated with 100 inch screen in a dark room.

According to your way, the nits of the projector was about 64 nits, and I set 16 of offset for the projector’s nits to be multiplied by.

Please check this out.

,and
I have question one more:
In order to get the offset value for being multiplied by. Like you said, the proejctors have to be 100% running at capacity. Color Temperature of Blue would attact on the nits, because of high Blue compared to Red, and Green. Before getting the 100% running at capacity, what Color temperature should I set? Should I set default setting for Color temperature? or Sould I find out which Color temperataure that affacts on high nits?

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[YOUNGJUN WOO]

I would like to know about Color banding when in HDR on projectors.

After the projector was perfectly calibrated, turning on Color Correction(CMS), there are Color Banding on the real picture such as a gradient sky or gray’ things.

Turning off Color Correction(CMS) on Sony VPL-VW270ES, then, the Color Banding is a bit less than turning on CMS. To get rid of, I set Smooth gradation with CMS on. It made a bit better, but the abnormal effects of Banding were never gone. In addition, the Blu-ray player was set with 4:2:0, and 24Hz to take it off. It cause same picture, though. Would you mind if you let me know about?

Please find attached the picture.

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[Gregg Loewen]

the Sony looks good.
Use the White Balance high controls to target about 50-65% stimulus for d65.

[YOUNGJUN WOO]

Use the White Balance high controls to target about 50-65% stimulus for d65:
Can you give me more details? What do you mean high controls? In this case, 50~65% RGB balances have under 20deltaE. I therefore set stimulus 50~65% on the setting?

[Gregg Loewen]

i saw a lot of banding on Sony 5000 PJ that I worked on a few months ago.
Engineers are still figuring some of this new technology out.
If CMS adjustments make banding worse, then do not use the CMS 🙁

[Gregg Loewen]

“high controls”
refers the the white balance controls for the brighter part of the gray scale.
Contrast, Gains, Drives, are all examples of high controls (RGB).

in the hdr workflow, select 50-65% of the gray scale as the target point for the RGB high balance point.

[YOUNGJUN WOO]

I will take 50~65% of the gray scale!

Is it always around 1000 nits which is a peak luminance for HDR projectors on the Calman report?

That means I set your way of offset calibrating.

Your way of calculation offset always affects peak luminance to around 1000 nits on the report?
(On the attached file, you can see the peak luminance that I draw red rectangle around it.)

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[Gregg Loewen]

report looks good!

the offset will make the target peak luminance around 1000 nits.

IF PEAK LUMINANCE IS AROUND 1000 NITS, then 50-65% will be at 400- 500 ? NITS (guessing ).

[YOUNGJUN WOO]

I would like to know the procedure time in HDR calibration workflow for projectors on Calman.

I understand how to measure the offset value.
However, in order to make a decision of the procedure time when measuring the maximum luminance, the procedure time is the time after adjusting Black level, and 2-point grayscale? or? I think the maximum luminance would be involved in Black level, and Color Temperature.

[Gregg Loewen]

use the HDR work flow.
Most likely do not adjust the black level and white level controls.
measure peak luminance and then enter the screen offset.
Do 2 point white balance and EOTF adjustment.
Consider multi point white balance.

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