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Color Space Conversion in practice

 
 
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Author aprilliasky
ZRO
#1 | Posted: 3 Mar 2013 21:24 | Edited by: aprilliasky 
Hello!

"This Colour Space Conversion capability has obvious usage, especially when looking to deliver finals in a different colour space to that within which the DI was performed."

I was wondering, what this could mean in practice, if my grading color space is "smaler" than the final one. For example I don't have the budget for a P3 display, and I'm grading in Rec.709. The result would be bad, because what I see is not what I get, right? Or maybe is Lightspace using a matrix to "rescale" Rec.709 to P3 for example?

I know that the movie Prometheus had around 8 graded versions: 3D, standard movie, Blu-Ray, DVD, web (trailer) etc.
Because they had the budget, they graded all delivery formats one by one. But when you don't have the time and money, what do you do if they ask you a Rec.709, P3, and sRGB??

Thank you!

George

Author Steve

INF
Male
#2 | Posted: 3 Mar 2013 21:41 
Correct - grading in Rec709, and then converting to P3 or XYZ for the DCI deliverables will be 100% perfect!

We do that all the time.



Steve
Steve Shaw
Mob Boss at Light Illusion

Author aprilliasky
ZRO
#3 | Posted: 3 Mar 2013 23:01 
Thank you! Steve!

Author waltervolpatto
ZRO
#4 | Posted: 9 Mar 2013 02:43 
when you go from a color space that is "smaller" that the one that will contain it you will not loss in fidelity ( as close as technologically possible ) The problem is when you go from a larger one (like XYZ with a full spectrum) to a small one (like rec.709...)

Author aprilliasky
ZRO
#5 | Posted: 9 Mar 2013 11:06 
I thought it is more problematic to "upscale" something.

What I'm planning to do is grade lets say an Alexa Log C file on a REC. 709 monitor, and probably deliver a DCI P3 copy. I wish I could have the money for a large sized wide gamut monitor, but I don't. So I have to convert up and down between these spaces.

Author Steve

INF
Male
#6 | Posted: 9 Mar 2013 12:06 
As I said above, converting from Rec709 to P3 or DCI XYZ is 100% accurate, as all the Rec709 colour space fits inside the larger P3 or XYZ space.



When converting from P3 to Rec709 you have areas of the P3 space that are not within Rec709, so something has to be done, such as clipping the colours, or compressing the larger space into the smaller, so changing the actual 'colour look' of the images.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author aprilliasky
ZRO
#7 | Posted: 9 Mar 2013 13:55 
Thank you all for the answers! I don't want to overtalk this topic, I just rarely find a forum where I get answers. So I just speak out loud.

There is a very good article on ARRI's site about grading. "Log C and Rec 709 Video". I can not paste the link because I'm a newbie, but it covers this conversation.

Lets get back to my example. I accept a job to grade Log C files. The client comes, and we grade in Rec 709 on a large client display. They are asking Rec 709 for HDTV, Rec 601 for DVD and P3 for DCI cinema.

We do the grading session. After that I have my Rec. 709 version. Then I convert my Rec.709 Display LUT to a P3 Output LUT so I can use my grading settings in the grading software, and do the render again.
- After this, maybe I could buy a small (cheap) P3 monitor for quality checking the result (basicly skipping a large size P3 display as client monitor). I have my P3 version.

Right after this, I convert my Rec. 709 display LUT to a Rec 601 LUT. I perform the quality checking with my Rec. 709 monitor, but with a Rec. 601 display LUT applied. After correcting the "color shifts" I export the job with the Rec 601 LUT.
Is this a correct operation workflow? Did anyone tried this before? Or it is better to buy a Rec. 601 QC display as well?

Author Steve

INF
Male
#8 | Posted: 9 Mar 2013 14:12 
You don't convert your display LUT.
You generate a Rec709 to Rec601 transform LUT, and apply that to the entire project for the Rec601 deliverable.
You also generate a Rec709 to DCI XYZ transform LUT, and again apply to the whole project for the DCI deliverable.

Job done.

We do this all the time, with no errors at all.
The converted colour space versions will match the original Rec709 version when displayed on accurate Rec601 and XYZ displays.

There will be nothing to correct, as there will be no errors. The conversion will be 'clean' and accurate.

And you wont find a cheap display that can do P3 accurately - they don't exist.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author badams
ZRO
#9 | Posted: 20 Apr 2013 15:40 
Hello everyone!
I have similar questions about color space conversion. I think this thread can help me figure it out.
We are going to build our own color grading system recently. Our goal is to digital cinema presented in theater but we don't have budget for really high-end monitor or projector.

1. If grading in a proper Rec 709 monitor/system.
As your discussion above, I can grade my desire 709 look and later apply a 709toP3 LUT to the DCI deliverable. On the theater screen, I can see the same accurate 709 look. The disadvantage is that we can never represent any color out of 709 gamut, is it right?

2. If I have a DCI-P3 monitor(like FSI,TVlogic,Eizo... maybe not 100% DCI compatible)
I shall see "more color" than 709 monitor however the inaccuracy may occurs, as well as in the theater.

We want to grade in p3 space and slight deviation is acceptable. Could you suggest any monitor or projector which meet the minimum requirement? I hope the price not over $10,000....

Author Steve

INF
Male
#10 | Posted: 22 Apr 2013 19:56 
Hi Badams,

We tend to use FSI and Penta displays, and ProjectionDesign and SIM2 projectors.

No display(other than the Dolby) can really do P3, so we suggest working in Rec709 and convert at the end to P3/DCI-XYZ.
The results are perfect, and any loss in potential colour using Rec709 vs. P3 is really, really small.

With LightSpace CMS such conversion is very, very easy.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author badams
ZRO
#11 | Posted: 24 Apr 2013 07:15 
Thank you Steve!
It seems to build an accurate P3 grading environment really go beyond our capability right now. I will try get a good rec.709 display solution instead. Also hope new display or projector will reinforce better P3 compatibility.

Author waltervolpatto
ZRO
#12 | Posted: 26 Apr 2013 00:09 
badams

99% of the color representation of a normal exposed scene will fall within the rec709 gamuth. only Cartoons (like Pixar Cars) or laser color will not be represented correctly.

Most of the feature movies i time normally (and I have done quite a few) fall anywhere from 10% to 60% of the gamut and still be gorgeous.

if you cannot afford the P3DCI environment, as long as your viewing environment is setup correctly and strictly calibrated you will be fine.

Author badams
ZRO
#13 | Posted: 27 Apr 2013 15:16 
It seems like rec 709 gamut is sufficient for most practical case then why go DCI-P3? What is the benefit to master our film in DCI-P3 space?

Nowaday new digital camera like Sony F65/F55 claim the ultra wide gamut capability. The cameras can "capture" much wider color than P3 or 709 space. Future laser projectors will also reproduce wider gamut. Will there be a new standard (better than P3) then?

Author medavoym
ZRO
#14 | Posted: 29 Apr 2013 19:29 
Hi!

Reading over this thread, it seems totally feasible to color correct in a RED 709 environment (properly calibrated) and then simply convert to the P3 space for DCP deliverables.

It seems that what you lose in terms of color is only marginal information, not worth the extra trouble/expense (for most projects, of course) of going the P3 route.

Quick question - if in terms of color we are fine, how about the dynamic range? Would we lose some stops in the process, if we grade in 709 instead of P3? Is there any difference in terms of the dynamic range?

Thanks!
Mike

Author Steve

INF
Male
#15 | Posted: 29 Apr 2013 19:46 | Edited by: Steve 
Your first point is correct - obviously, there is some difference when capturing with wide gamut cameras, but it is a very small difference. So the result is very little loss in 'real' colour information working Rec709 and converting to P3.


As for dynamic range, that has noting to do with the colour space used at all.
DR is not specified for a given colour space, with regard to image display.
If you want to maintain DR the best approach is to grade through a 'roll-off' LUT; one that soft-clips highlights.

So, no, there is no difference for a given set-up.

Hope this helps,

Steve
Steve Shaw
Mob Boss at Light Illusion

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