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Author Topic: DCP luminance levels issue on simulation  (Read 2538 times)

fredjeang2

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DCP luminance levels issue on simulation
« on: November 19, 2017, 08:23:48 AM »

I'm doing a DCP simulation from the NLE to see before/after convertion.

Edit is in REC709, corrected

1) I apply the Rec709 to DCI-XYZ lut: it appears as it should
but then, when I
2) apply on top of that the DCIXYZ to Rec709
the luminance levels became slighlty darker with a subtle colder look.

The idea that I have in mind is trying to color correct previous those 2 Luts in order to optimize the footage for DCP,
by simulating the way the footage will actually be viewed.
then disable those 2 luts when exporting so that it would be done by the DCP creator.

The question is that in my simulation done in Lightworks and PP to check, I got this darker luminance levels and the slightly colder look.
So I would be tempted to color correct from what my simulation is telling me. But the dilema is:
How do I know that I can trust the fact that the luminance gets slightly darker and the look slighly colder (and so color correct considering this) or that I'm doing something wrong?
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #1 on: November 19, 2017, 01:03:12 PM »

I'm doing a DCP simulation from the NLE to see before/after convertion.

Edit is in REC709, corrected

1) I apply the Rec709 to DCI-XYZ lut: it appears as it should
but then, when I
2) apply on top of that the DCIXYZ to Rec709
the luminance levels became slighlty darker with a subtle colder look.

The idea that I have in mind is trying to color correct previous those 2 Luts in order to optimize the footage for DCP,
by simulating the way the footage will actually be viewed.
then disable those 2 luts when exporting so that it would be done by the DCP creator.

The question is that in my simulation done in Lightworks and PP to check, I got this darker luminance levels and the slightly colder look.
So I would be tempted to color correct from what my simulation is telling me. But the dilema is:
How do I know that I can trust the fact that the luminance gets slightly darker and the look slighly colder (and so color correct considering this) or that I'm doing something wrong?

From my experience, you should do the color correction in REC709 and let the DCP creator person do the transform to XYZ and DCP.  Make sure you tell the DCP people your timeline specs, such as "REC709, gamma 2.2, full range data".  The gamma is very important or you could end up with a DCP that is darker or lighter than you expect.  Check the DCP in a calibrated DCP projection theater to make sure all is correct.

When will we see your movie in the theater?  I'll buy a ticket :)
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fredjeang2

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Re: DCP luminance levels issue on simulation
« Reply #2 on: November 20, 2017, 03:27:40 AM »

From my experience, you should do the color correction in REC709 and let the DCP creator person do the transform to XYZ and DCP.  Make sure you tell the DCP people your timeline specs, such as "REC709, gamma 2.2, full range data".  The gamma is very important or you could end up with a DCP that is darker or lighter than you expect.  Check the DCP in a calibrated DCP projection theater to make sure all is correct.

When will we see your movie in the theater?  I'll buy a ticket :)
I agree to let do the experienced DCP people for important projects.
It is more a matter of educational question in this case.
Adquiring awareness on the processes involved.
The key point is to get the right people for the right task.
But at the same time having a knowledge base.
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #3 on: November 20, 2017, 01:00:09 PM »

I agree to let do the experienced DCP people for important projects.
It is more a matter of educational question in this case.
Adquiring awareness on the processes involved.
The key point is to get the right people for the right task.
But at the same time having a knowledge base.
I did a test, just for fun a few weeks ago.  I created 3d display LUT for DCI/xyz, output to DCIxyz, and opened the rendered file and viewed on the DCI/xyz LUT.Gamma looked about right, but there was a whitepoint shift due to the DCI whitepoint being different. There may be a way to build the DCI/xyz display LUT with d65 white point, and that would probably fix the discrepancy.  Since I didn't want to fool around with that, I just decided to let the DCP house handle all the conversion.  But, with some testing, I think you can do this.  I would test the resulting DCP though to make sure it looks right before committing to the DYI workflow.
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #4 on: November 20, 2017, 01:01:37 PM »

I did a test, just for fun a few weeks ago.  I created 3d display LUT for DCI/xyz, output to DCIxyz, and opened the rendered file and viewed on the DCI/xyz LUT.Gamma looked about right, but there was a whitepoint shift due to the DCI whitepoint being different. There may be a way to build the DCI/xyz display LUT with d65 white point, and that would probably fix the discrepancy.  Since I didn't want to fool around with that, I just decided to let the DCP house handle all the conversion.  But, with some testing, I think you can do this.  I would test the resulting DCP though to make sure it looks right before committing to the DYI workflow.

And don't forget about frame rate conversions for picture and sound.  DCP is 24fps.  Your project may well be 23.98fps or 25 fps.  So I also let the DCP house handle the frame rate conversions.
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fredjeang2

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Re: DCP luminance levels issue on simulation
« Reply #5 on: November 20, 2017, 04:12:54 PM »

I would test the resulting DCP though to make sure it looks right before committing to the DYI workflow.
Indeed!
By the way, I like the DP reel ! Great work there.
And, correct me if I'm wrong, but it seems that you've changed the layout of your web site. Much better like that! ;)

Ps: about frame rate, fortunatly I always work from the very roots in 24p and 2k DCI 1.85 projects. Never in 25 nor 23.98.
« Last Edit: November 20, 2017, 04:22:51 PM by fredjeang2 »
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #6 on: November 20, 2017, 06:47:49 PM »

Indeed!
By the way, I like the DP reel ! Great work there.
And, correct me if I'm wrong, but it seems that you've changed the layout of your web site. Much better like that! ;)

Ps: about frame rate, fortunatly I always work from the very roots in 24p and 2k DCI 1.85 projects. Never in 25 nor 23.98.
We've been shooting 23.98 because the post production sound mixers wanted that.  The last project was shot 25fps as it was originally for TV in PAL land, but things changed and now it's going to the cinema...

Thanks for the feedback about the website.  I need to rebuild it though with different authoring software as there's some bad code in it that makes my ISP think they're under attack, and they block it for half an hour...  I'm not good with code and can't just fix it.

And the latest project that I've been grading opens January 4.  The trailer has just been released.


Night Shift trailer
« Last Edit: November 20, 2017, 06:54:22 PM by smthopr »
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fredjeang2

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Re: DCP luminance levels issue on simulation
« Reply #7 on: November 21, 2017, 01:38:05 PM »



And the latest project that I've been grading opens January 4.  The trailer has just been released.


Night Shift trailer
Very nice! I like the grading very much.

PS: I've checked a DCP created with Adobe Media encoder and the MXF file opnened in Scratch play is just fine, all parameters correct, without the luminance shift that I obtain when I try to simulate the all process using Luts. I don't want to fool around either with Luts honestly because it's time consuming.
In fact, I color correct just in rec709, then I don't know what the program does internaly but in the end the resulting MXF looks exactly like the grade.
All we'd need is a way to simulate with reliability from color without the need to go to theaters, because that is a complete hassle and old school.
« Last Edit: November 21, 2017, 01:53:31 PM by fredjeang2 »
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #8 on: November 21, 2017, 03:57:02 PM »

Very nice! I like the grading very much.

PS: I've checked a DCP created with Adobe Media encoder and the MXF file opnened in Scratch play is just fine, all parameters correct, without the luminance shift that I obtain when I try to simulate the all process using Luts. I don't want to fool around either with Luts honestly because it's time consuming.
In fact, I color correct just in rec709, then I don't know what the program does internaly but in the end the resulting MXF looks exactly like the grade.
All we'd need is a way to simulate with reliability from color without the need to go to theaters, because that is a complete hassle and old school.

Well, checking in a calibrated projection theater may be "old school", but if you're about to send out a DCP to hundreds or thousands of theaters, you'll want to really be able to say that all is ok before they ship.  If you don't, and the distributor is not pleased, only the colorist will be to blame. You can be certain that the DCP house will blame you, and not themselves, if they make a mistake.  I've been there and done that. There is also a little perceptual difference between an emissive display and a projector.  There's really no way to see that without a projector.  But for most projects, this won't be too much of an issue I think.
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fredjeang2

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Re: DCP luminance levels issue on simulation
« Reply #9 on: November 21, 2017, 04:47:52 PM »

Well, checking in a calibrated projection theater may be "old school", but if you're about to send out a DCP to hundreds or thousands of theaters, you'll want to really be able to say that all is ok before they ship.  If you don't, and the distributor is not pleased, only the colorist will be to blame. You can be certain that the DCP house will blame you, and not themselves, if they make a mistake.  I've been there and done that. There is also a little perceptual difference between an emissive display and a projector.  There's really no way to see that without a projector.  But for most projects, this won't be too much of an issue I think.
Yes, but it comes to the question that:
If there is no way to figure-out the result except in a calibrated projection theater (and I understand it), and let's say that you see an issue. Then we are back to the departure zone in the sense that the correction would be done in the studio, hours later considering traffic jam, coffee pause, beer stops... and hours later brain can easily fool the senses. Then redo a corrected DCP that has to be checked again to see if now it displays correctly. If there is no way to have this facility in the studio I don't see how the fine tuning could be done, or endless studio-theater trips?
This is where I'm lost.
"I see a luminance shift" in theater...but as long as I can not process live to correct, a luminance shift may be vague. So the correction involved.
« Last Edit: November 21, 2017, 04:51:03 PM by fredjeang2 »
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #10 on: November 21, 2017, 06:51:00 PM »

Yes, but it comes to the question that:
If there is no way to figure-out the result except in a calibrated projection theater (and I understand it), and let's say that you see an issue. Then we are back to the departure zone in the sense that the correction would be done in the studio, hours later considering traffic jam, coffee pause, beer stops... and hours later brain can easily fool the senses. Then redo a corrected DCP that has to be checked again to see if now it displays correctly. If there is no way to have this facility in the studio I don't see how the fine tuning could be done, or endless studio-theater trips?
This is where I'm lost.
"I see a luminance shift" in theater...but as long as I can not process live to correct, a luminance shift may be vague. So the correction involved.

There is a middle ground.   Create a test DCP.  It need not be more than 5 minutes.  Select an average scene, and a couple more extreme light or dark scenes. Show each shot at slightly different gamma, and maybe saturation.  View the test in a calibrated theater and pick the best overall approach.  Then you can make 1 or 2 corrections to the entire project if desired.  Perhaps your DCP house has such a theater to check their work.  They may not charge extra for the short test.  I've done this approach myself and ended up adding something like 5% saturation to the project.  I might have made the overall gamma slightly darker as well, but I'm nervous about dark projection in many multiplexes...
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fredjeang2

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Re: DCP luminance levels issue on simulation
« Reply #11 on: November 22, 2017, 03:03:19 AM »

There is a middle ground.   Create a test DCP.  It need not be more than 5 minutes.  Select an average scene, and a couple more extreme light or dark scenes. Show each shot at slightly different gamma, and maybe saturation.  View the test in a calibrated theater and pick the best overall approach.  Then you can make 1 or 2 corrections to the entire project if desired.  Perhaps your DCP house has such a theater to check their work.  They may not charge extra for the short test.  I've done this approach myself and ended up adding something like 5% saturation to the project.  I might have made the overall gamma slightly darker as well, but I'm nervous about dark projection in many multiplexes...
Very usefull approach. Thanks for the tip. Great to have experienced pros in the forum.
Well, I only did one DCP 3 years ago. It was for an advertising campaign. I used at that time something called openDCP.
It worked fine. The AD talked to the dcp people in the theater it was tested with a reference clip. If dcp created was
Corrupted then they would tell the guys to do it but it played all ok with just a slightly gamma (almost undetectable
If not viewed side by side with original). Big luck.
I remember that the cost in the case it went wrong was very affordable.
So indeed it might not be a so good calculation to DIY considering that prices went down.
I also see the same corrections as you mention. Sort of 5%.
But I prefer a slightly lighter gamma than the opposite.
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smthopr

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Re: DCP luminance levels issue on simulation
« Reply #12 on: November 22, 2017, 04:12:41 PM »

Very usefull approach. Thanks for the tip. Great to have experienced pros in the forum.
Well, I only did one DCP 3 years ago. It was for an advertising campaign. I used at that time something called openDCP.
It worked fine. The AD talked to the dcp people in the theater it was tested with a reference clip. If dcp created was
Corrupted then they would tell the guys to do it but it played all ok with just a slightly gamma (almost undetectable
If not viewed side by side with original). Big luck.
I remember that the cost in the case it went wrong was very affordable.
So indeed it might not be a so good calculation to DIY considering that prices went down.
I also see the same corrections as you mention. Sort of 5%.
But I prefer a slightly lighter gamma than the opposite.

Yes.  I lean towards liking projection a tiny bit darker than my reference display at home.  I think it has to do with the slightly lower contrast of the projection. But, in the end, I'm afraid of dark cinemas in the wild :)
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