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Grading Light Illusion Forums / Grading /

Color Space Conversion in practice

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Author medavoym
Mono
#16 | Posted: 29 Apr 2013 20:37 
Hi Steve,

Thanks!

As per my second point... why do people always talk about the dynamic range limitations of the REC 709 environment?

A very quick google search:

www.google.com/search?client=safari&rls=en&q=rec+709+dynamic+range&ie=UTF-8&oe=UTF-8

I am missing something, probably...

Thanks again! Much appreciated,
Mike

Author Steve
Scene
#17 | Posted: 29 Apr 2013 21:34 
Camera range is a different issue...

The Rec709 profile is very different to a 'Log' camera.

See the curves here: http://www.lightillusion.com/sony_curves.html
Look at the 'profile graphs'.
They should be self explanatory.

Steve

Author medavoym
Mono
#18 | Posted: 29 Jun 2013 06:33 
Dear Steve,

Apart from the color loss (which - as stated before in this thread - is too small to be noticeable/important), are there any other disadvantages to grading in REC 709 vs P3? Disadvantages of any kind.

Thanks!
Mike

Author Steve
Scene
#19 | Posted: 29 Jun 2013 08:01 
It all depends on the display you have - can it really do P3 - and the expected delivery requirement.
If TV mainly there is no benefit working P3 at all, and actually some negative as you will need to drop back to Rec709.
If DCP delivery is the main format, either will work 100%.

Steve

Author medavoym
Mono
#20 | Posted: 29 Jun 2013 14:54 | Edited by: medavoym 
Thank you Steve!

I am learning and so your replies are greatly appreciated!

When grading in REC 709 (using a display LUT) and then converting to P3... do we remove the original Log-to-REC 709 display LUT and replace it with a Log-to-P3 LUT (thus basically applying the conversion to the graded log material), or do we simply apply a REC 709-to-P3 conversion LUT at the end of the chain, over everything?

Thanks!
Mike

Author Steve
Scene
#21 | Posted: 29 Jun 2013 15:21 
Mike, that depends entirely on your specific workflow, and what 'display LUT' you are using.

There is no single answer, and I would have to see you workflow to be able to tell you what you need to do in your case.

For example, is the LUT a simple Log to to TV gamma LUT, or does it have a display calibration component?

Steve

Author medavoym
Mono
#22 | Posted: 29 Jun 2013 16:12 
Dear Steve,

Yes, it is a "generic" film emulation Cineon to REC 709 LUT - it was not generated based on a specific monitor profile.

I think I see what you are saying. If the Cineon to REC 709 display LUT was generated based on a specific monitor profile, then you can easily remove the LUT and replace it with a Cineon to P3 LUT, which would also have to be calibrated to that specific monitor. Everything will match since the two LUTs are in accordance with one another, and with the monitor.

But if the Cineon to REC 709 LUT is just a generic one, there is no point to go the above route, things will not match anyway - one would simply convert the final REC 709 result to P3.

Of course, the first approach is the best one. However, talking about the second option... is it still acceptable to use a calibrated (not profiled - just calibrated) REC 709 monitor with a generic Cineon to REC 709 LUT? And finishing on that monitor.

I guess my question pertains to what I see around me. Many people choose the low budget approach, using generic Cineon to REC 709 on calibrated HD monitors (no probes, no profiling etc). This reduces the options, but given that any calibrated REC 709 HD monitor is a known target more or less, an the generic LUT is made for that target, wouldn't that yield good results?

Mike

Author Steve
Scene
#23 | Posted: 29 Jun 2013 16:45 
If a display has not been profiled and accurately calibrated it is unlikely to be Rec709 accurate.
Very, very few 'Rec709 displays' are accurate at all as supplied...


Author medavoym
Mono
#24 | Posted: 29 Jun 2013 17:05 
I understand.

In that case, why are people selling/providing generic Cineon to REC 709 LUTs (not based on a specific monitor profile)?
Do these LUTs have any use at all?

Author Steve
Scene
#25 | Posted: 29 Jun 2013 17:11 
The LUT will assume you have an accurately calibrated display.
Without that no colour decisions are valid.
Also, is the LUT a simple gamma curve, or does it try to emulate 'film' colour?
Send me the LUT to look at if you want.

Steve

Author medavoym
Mono
#26 | Posted: 29 Jun 2013 18:02 
Dear Steve,

The two LUTs I have try to emulate film colors.
I just sent them to you - thanks for the offer to take a look at them!
I appreciate the help,
Mike

Author Steve
Scene
#27 | Posted: 29 Jun 2013 18:26 
Hi Mike,

As I say in the e-mail I sent to you directly, those LUTs are bollox!



They are inaccurate for what they say they are - and the w-adapt one is just a drop in peak white.
They in no way represent film, and will be excessively clipping shadow and highlight detail - badly!!!

Steve

Author Steve
Scene
#28 | Posted: 29 Jun 2013 19:07 
Oh, to answer your original questions you need to leave any creative LUT (as you have there) in the chain when making the DCP, as it is an integral part of the final look.

Steve

Author medavoym
Mono
#29 | Posted: 29 Jun 2013 19:40 
Got your e-mail Steve and replied - thanks again for taking a look!

Thanks also for answering the question.

So, to conclude, one would need an accurately calibrated REC 709 monitor, and a correct generic Cineon to REC 709 LUT to achieve good results. Do you have some documents on the website showing how to accurately calibrate a REC 709 monitor?

Mike

Author Steve
Scene
#30 | Posted: 29 Jun 2013 20:23 
Hi Mike,

Have a look at the LightSpace CMS pages.
All is explained there.

Start with the 'Idiot's Guide to Display Calibration'

Steve

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