Rec.709 vs DCI P3

[Alex Prohorushkin]

Hi everyone.

Lot of us know (or have heard) that in cinema and theatre p3 color space is usually used when projecting images to screens. 

It is very different from Rec 709 color space. Should i pay much of my attention and spend money for P3>Rec.709 adaption if people anyway can't see it on the screens of their home TVs?

Talking with one of my collabs i heard something quite interesting. He said that much of the color guys all over the world work inside Rec.709 color space because when Rec709 is converted to P3 almost nothing changes for the eyes of the audience because p3s range is much wider than the Rec709s one. What can't be said about P3 to Rec709 converting because it takes much effort to place wide range of P3s in Rec709.

Understanding that this approach is quite wrong, I guess that for many movies this way is viable.

What would you say?

Here is comparative graph of the color spaces.

 

[Margus Voll]

Point is that you can get REC709 perfectly calibrated on reasonable price and work like this and then later when doing DCP converting it perfectly you get accurate results comparing with cheap monitor not doing accurate P3.

You could work on P3 with projection but i would say you need to buy "cheap" projection starting from 20 to 30 thousand € or USD. Not very feasible for many so REC 709 workflow is used. If you have budget for good projection calibration and such then sure go P3 if not then good monitor like FSI is my suggestion. 

I do all my features on 709 displays and it is perfect in cinema.

[Abby Bader]

If you want and can afford the extra range that can be stored inside P3, go for P3. If you can't afford it, live with the restrictions and grade in REC 709 and convert it in DCP delivery.

[Nicolas Hanson]

You could always work r709 color space and do the final adjustments in a p3 studio / theatre before final delivery. 

[Daniele Siragusano]

When looking into projectors the Colour Gamut is not the only aspect you need to look at.
Most "cheap" projectors do not meet other criteria, which are needed to judge a picture in a meaningful way:
Most importantly:
• Sequential and intra frame contrast
• Luminance Uniformity
• Colour Uniformity
• Greyscale Tracking
and more…
There is a SMPTE Recommendation for Reference Projectors that describe all this:
“SMPTE Recommended Practice for Digital Cinema” DC28.30

As suggested above I would rather do a first pass on a good monitor and then do a final trim in a proper grading theater.
About Gamut Compression (because this is what you need to convert from P3 to 709 ) . Not many colours of a typical scene are outside of Rec709. Most of the pointer gamut  (gamut of all surface colours)  are within 709, so your image typically does not contain a great amount of data which cannot be represented in 709. visually the biggest impact is in Reds (attached a diagram in uv which is more visually meaningful than xy, the purple triangle is 709, green is p3 and red is 2020).  You can have special highly saturated objects which have colours outside of 709 but humans are not very good in detecting errors in highly saturated colours. So if those special object look a bit different in the TV Version that is normally ok.
Gamut Compression is normally used to convert from P3 to 709. This avoids gamut clipping which is much more unpleasing.
best
Daniele   

[Abby Bader]

Great insight Daniele, and nice to see you here!

Reviewing the final grade in a proper grading theater is important, and especially today when delivering specialized versions like for IMAX etc. And don't forget, there are many other reasons to run the movie through a large screen as well.

Edited November 13, 2016 by Abby Bader

[Tom Evans]

Thank you for your clarifications Daniele!

[Thomas Singh]

On 12.11.2016 at 2:38 PM, Daniele Siragusano said:

• Sequential and intra frame contrast

Can someone please explain what this means? 

[Andy Minuth]

Contrast measurements are about the dynamic range of the projector. 

Sequential contrast is determined by comparing a completely black frame with the maximum brightness in another frame. It describes kind of the the maximum contrast of the device.

Intra-frame contrast in comparison describes the maximum contrast within one frame, which is usually much lower. It is usually measured with a black/white checkerboard pattern or with a small white patch in a mainly black frame. Important to note is that the lower intra-frame performance of DCI compliant projectors is NOT due to an adaptive iris or dynamic light dimming (which mess up images in consumer displays). The reason lies mainly in the imperfection of the projection lens, which lifts the blacks because of flare. We know the effect from camera lenses: If there is a very bright object in the frame, the black level even of technically decent lenses like Master Primes is lifted a lot.  

To throw in some numbers, the DCI minimum specs and tolerances for example are:

Sequential contrast:

nominal 2000:1

review rooms (e.g. grading) 1500:1

theatres 1200:1

 

Intra-frame contrast:

nominal 150:1

review rooms and theatres 100:1

 

[Thomas Singh]

Thank you for this great insight!

[Ibrahim Ziazadeh]

If I want to send a film to a festival what should my project settings be in my NLE when dealing with color grading 1080p 14-bit cinemaDNG footage in After effects? i.e. If I have understood this the working space I must select is P3 DCI gamma 2.6 and depth at 32bpc? Or do I keep my working space to rec 709 gamma 2.4?

I have openDCP or DCP-o-matric at my disposal for the DCP conversion. Since I cannot directly export to DCP in AE what is the best intermediate format to export to resulting in no quality loss?

 

 

[Tom Evans]

Ask the festival for their specifications. Normally you can deliver DNxHR/ProRes as their setup isn't neccessarily professionalized enough to receive DCP's and treat the signal the way it should. Most cinemas today even create a hybrid 5.1 from stereo tracks. The digital age is evolving, not neccessarily for the best.

Edited April 2, 2019 by Tom Evans

[Ibrahim Ziazadeh]

They want the film either non-encrypted DCP or Apple prores 4444. 

[Tom Evans]

Then you deliver ProRes 4444

[Ibrahim Ziazadeh]

1 minute ago, Tom Evans said:

Then you deliver ProRes 4444

Isn't prores 4444 in a lower quality than DCP?
My source film is a 14-bit RAW at 1080p.

 

[Tom Evans]

No it is not, don't make your life harder than it is.

[Ibrahim Ziazadeh]

Ok, thanks man. What about the working space isn't DCI p3 better to color grade in rather than rec709 if I choose apple prores 4444? or apple prores 4444 XQ.

Edited April 3, 2019 by Ibrahim Ziazadeh

[Tom Evans]

That's a completely different discussion and a complicated topic, but if you don't have an established P3 color workflow with proper P3 monitoring you don't need to think about these things at all. 

[Soumitra Sarkar]

On 11/2/2016 at 12:49 PM, Margus Voll said:

Point is that you can get REC709 perfectly calibrated on reasonable price and work like this and then later when doing DCP converting it perfectly you get accurate results comparing with cheap monitor not doing accurate P3.

You could work on P3 with projection but i would say you need to buy "cheap" projection starting from 20 to 30 thousand € or USD. Not very feasible for many so REC 709 workflow is used. If you have budget for good projection calibration and such then sure go P3 if not then good monitor like FSI is my suggestion. 

I do all my features on 709 displays and it is perfect in cinema.

If I am wrong... P3 in 2.6 gamma and rec709 in 2.4..when you grade in rec709 and project in theaters how its look as same as grade.. I think it would be  gamma issue 

[Margus Voll]

It will be adjusted accordingly and it will look spot on.