“Using a P3-D65 CST followed by a Rec.2020 CST does not limit the gamut to P3. Since this is a requirement by all studios and clients today, we recommend using a Rec.2020 CST followed by a P3-D65 Gamut Limiter which will constrain the color gamut to P3 within the Rec.2020 container.” – Dolby Labs
Matthias Tomasi, a colorist from Austria with over 70 credits to his name ranging from short films to movies to TV series, instructs another colorist on the liftgammagain colorist forum on how to go about limiting Rec. 2020 to P3-D65 in a node-based workflow, but even after being presented with the proper workflow, he’d sooner lead a colleague astray rather than acknowledge his stunning lack of expertise. Tomasi writes:
- Set your display rendering (this could be a CST node or ACES node or custom DRT) to go from DWG/DI to P3-D65 ST2084 1000 nit.
- Add as a last node a CST that goes from P3-D65 ST2084 1000 nit to Rec2020 ST2084 1000 nit, with Tone Mapping and Gamut Mapping set to None.
- Set your mastering display to P3-D65 ST2084 1000 nit.
How can industry professionals get the basics so wrong? Don’t follow in Tomasi’s steps. Instead, follow the advice below.
See here for an article that succinctly explains why Rec. 2020 has not normally been used as a display color space for cinematic productions.
Many seem to be unaware that there is a tool in Resolve FX that performs the same function as the one found in RCM – the Gamut Limiter – which was designed specifically for instances where a deliverable with a larger gamut restricted to a smaller one is required.
Here’s a description of the setting in RCM, from the DaVinci Resolve manual:
This control is only visible while the Resolve Color Management presets menu is set to Custom Settings. In the emerging world of larger gamuts for distribution, it’s increasingly common for delivery specifications to specify output to a large gamut, such as Rec. 2020, yet require that image values be restricted to a smaller gamut, such as P3. This is to allow delivery to “future-proofed” delivery standards, while preventing saturation values that are too high to be displayed on consumer displays that aren’t capable of implementing the full scope of those standards.
In this case, you’ll choose a larger gamut in Output Color Space, but you’ll then choose a smaller gamut in “Limit Output Gamut To.” When you do this, all image values falling outside the “Limit Output Gamut To” standard specified will be hard clipped. This setting defaults to None.
And here’s a description of the Gamut Limiter in Resolve FX:
Lets you limit the gamut to a specified standard. Useful in situations where the delivery color space is a large gamut such as Rec. 2020, but the QC specification requires limiting to a smaller gamut such as P3, in order to limit the amount of saturation allowable in the final output.This is a limiting operation, so out of bounds values are hard clipped. This plugin can be used regardless of whether or not Resolve Color Management is enabled. Because it’s a limiter, it should probably be one of the last operations in any node tree to prevent useful image data from being clipped.
— Current Gamut: Choose the timeline gamut currently being used by the image.
— Current Gamma: Choose the timeline gamma currently being used by the image.
— Limit Gamma to: Choose the gamut you want to restrict the image to here.
Worth noting is that ARRI provides a LogC4 LUT (ST2084 Rec.2100 P3-D65 Limited), not available in the LogC3 LUT package – something we wish it were possible to create in REDCINE-X for the RED KOMODO.
Be sure to calibrate your monitor to Rec. 2020.
The Daejeon Chronicles 