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Grading Light Illusion Forums / Grading /

How do you define a color space?

Author Chuckycheez
Mono
#1 | Posted: 16 Mar 2013 14:13 
Hi,

Someone once said that there's no such thing as a stupid question... So here we go!

Let's say I'm grading a feature film shot on Alexa with Pro-Res 4444 files, in LOG-C on a P3 projector...

My first question would be: is colorspace 100% display dependent? I'm asking this because I heard somewhere that Pro-Res is only Rec709 compliant. Does that make any sense?

Let me elaborate... I'm grading a film in PR 4444 (log-c) on a P3 projector. I push my grade towards an "illegal" Rec709 cyan... Render and take it to a Rec709 setup. We all know what will happen at that point... Normally I would do a P3 to 709 lut (with out of gamut activated) and do a trim pass...

So by that logic, is the display the only thing dictating my color-space? Cause I never defined anywhere that this footage is P3. How can the LUT dertermine which colors are illegal if the only things that are interacting in this scenario are my eyes and the projector?

What I don't understand is where in a certain format or file are things defined? For example, I cannot tell Resolve I'm working in P3... Or for that matter I cannot set up a R3D file to be in P3.

Is this a philosophical thing? ;)

And finally, should I be weary of certain files that cannot extend to P3?

Any insight would be great!

Author Steve
Scene
#2 | Posted: 16 Mar 2013 14:24 
Yep - the display is the only relevance.

ProRes is not at all 'just' Rec709 capable... (no image format has any real idea of colour space).

So, any image can be converted to display in any colour space.
But, when going from a larger space to a smaller one some colours will not show accurately - hence the OOG LUT and a trim pass.

Steve

Author Chuckycheez
Mono
#3 | Posted: 16 Mar 2013 14:42 
It just seems so untangible... I don't see how it can be written in a file that a certain cyan cannot be represented in Rec709. But I guess I'm thinking to hard!

Ok just for the hell of it: i'm grading on a rec709 setup and I saturate to the point I habe pure primaries in my image... But I add a node and keep going and going and going... I will never get a OOG color? What will happen if I take that to a P3 projector without converting it? It'll look green and the gamma will be off and the colors will be slightly less saturated?

What if you saturate the hell out of a P3 grade? How will that look like on a rec709 display (without conversion)?

And the OOG lut must absolutely be viewed on a Rec709 monitor rigth?

Thanks!!

Author Steve
Scene
#4 | Posted: 16 Mar 2013 15:04 | Edited by: Steve 
Eeeek - I think your really 'over-thinking' this.

Colours are just digital values - so RGB 0,255,0 in 8 bit is pure Green.
When that value is seen on a Rec709 calibrated display it looks a certain way.
When the same colour value is seen on a P3 display it looks different... as the display will 'map' 255,0,0 to a different Green colour.

Rec709_P3.png

Make sense?

When grading pushing a colour can't go beyond the peak value, so 0,255,0 is max Green - there is no more.

And OOG LUTs can be made for any colour space.

Author Chuckycheez
Mono
#5 | Posted: 16 Mar 2013 15:11 
This missing link... Now I understand!

Thanks Steve!!

Author Steve
Scene
#6 | Posted: 16 Mar 2013 18:23 
Great - glad to have helped!


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