Color Grading Q&A: Deep Dive on Display Rendering Transforms (DRTs)

Summary:

The video is a Q&A session on Display Rendering Transforms (DRTs) with Cullen Kelly, focusing on practical applications and conceptual understanding.

Discussion on when to use OpenDRT vs. JP2499, emphasizing control over the image.
DRTs offer a baseline technical rendering to get out to display.
Color and contrast are very interactive.
The benefits of using scene-referred LUTs.
Explanation of HSV (Hue, Saturation, Value) and its impact on color grading.

Cullen Kelly explaining controls in DaVinci Resolve [ 00:12:49 ]

OpenDRT vs. JP2499: Choosing the Right DRT [00:04:10]

The discussion begins with a comparison of OpenDRT and JP2499, two popular DRTs, focusing on their flexibility and control over image rendering.

There's no straightforward answer to which DRT is better.
The choice depends on the level of control a colorist wants to exert over the image and how they want to exert it.
A key consideration is understanding the levers of control that each DRT provides.

OpenDRT's primary controls lie in its look presets, tone scale presets, and creative white adjustments.

Look Presets: These presets dictate the overall color rendering of the image.
Tone Scale Presets: Control the contrast or tone scale, and by default, follow the look preset.
Creative White: Adjusts the warmth of the brighter areas of the image.

JP2499 offers control through sliders, providing a different approach compared to OpenDRT's drop-down menus.

Ten Sliders: The interface may seem overwhelming initially, but the controls can be broken down into four fundamental adjustments: density, overall rotate hue, highlight rotate hue, and purity.
RGB Chips Tool: This tool aids in auditing DRTs by visualizing the system-wide processing of various pixels, particularly through exposure sweeps across 36 hue bands.
The DRT does not offer explicit contrast control.

The video explores the possibility of combining different DRTs using composite modes to leverage their unique strengths.

An audience question proposes using JP2499 for its hue rotation properties and OpenDRT for its luminosity and contrast control.
Cullen expresses reservations about combining DRTs in this manner, comparing it to "Frankensteined toys" due to potential instability.
Instead, it's suggested to use one DRT for baseline rendering and creative looks for further adjustments.

The discussion shifts to how lookup tables (LUTs) interact with DRTs, particularly when a LUT is designed for a specific DRT setup.

A story about creating the Voyager LUT pack with Resolve CSTs is shared.
It's generally acceptable to use a LUT designed for one DRT with another DRT, but it's crucial to double-check the results and make adjustments as needed.
The aim is to achieve the best baseline rendering possible.

The video explores whether there are benefits to be gained from changing the way images are mapped into the grading space.

The basic process of color management involves two steps: moving from camera space to working space and then from working space to display space.
To remap sensitivity, this process involves:
Linearize
Apply a Matrix
Re-encode

It is concluded that attempting to forensically match one sensitivity to another can be complex and potentially problematic.

Cullen explores using HSV color models and whether different tools can affect them.

The color space is flipped.
Then it is stated that RGB now equals Hue, Saturation and Value, it is that red, green, and blue are now huge saturation and value.
Finally, custom curves are added.