OpenDRT: An Advanced Display Rendering Transform for Superior Color Grading in DaVinci Resolve

Cullen Kelly

Installing OpenDRT [0:51]

• OpenDRT is a free DCTL (DaVinci Color Transform Language) that offers advanced display rendering capabilities within DaVinci Resolve Studio.
  • To install, download the OpenDRT.dctl file from Jed Smith's GitHub repository.
  • Navigate to DaVinci Resolve Project Settings (Shift+9) > Color Management > Lookup Tables > Open LUT Folder.
  • Save the OpenDRT.dctl file directly into this folder.
  • Completely quit and restart DaVinci Resolve for the DCTL to be indexed and appear in your effects list.

Understanding OpenDRT's Core Features [2:50]

• OpenDRT operates as a Display Rendering Transform (DRT), converting scene-referred or timeline-referred color spaces to display-referred spaces.
• Key parameters to configure:
  • Input Gamut & Input Transfer Function: Typically set to DaVinci Wide Gamut and DaVinci Intermediate when working in a color-managed workflow.
  • Display Encoding Preset: Adjust based on your display; e.g., sRGB for YouTube viewing on gamma 2.2 displays, or Rec. 1886, Gamma 2.4, Rec. 709 for standard monitors.
• Additional parameters (initially can be left at default for SDR work):
  • Display Peak Luminance (for HDR).
  • HDR Gray Boost (for HDR).
  • HDR Purity (for HDR).
  • Clamp: Enabled by default, clamping values below 0 and above 1, which are outside the displayable range.
  • Creative White: Allows for baking in a warmer white point (e.g., D50 or D60) than the display's true white point (D65).
    • This creates a color shift where reds are boosted and blues are attenuated as luminance increases, imparting warmth.
    • Creative White Range: Controls how far down the tone scale the creative white point adjustment influences the image.
      • Moving the slider to the right extends the influence to darker pixels, while moving it to the left restricts it to highlights.

OpenDRT vs. DaVinci Resolve Color Space Transform (CST) [9:44]

• While a Resolve CST can function as a DRT, OpenDRT offers superior color handling, especially at higher saturations and luminances.
• Evaluating DRTs requires looking beyond a single image to understand how they handle all possible pixels and extreme conditions.
• Using an RGB Chips test pattern (a diagnostic DCTL by Thatcher Freeman) reveals the differences:
  • Resolve CST: Shows significant clipping and clumping of colors at the edges of the vectorscope, indicating aggressive handling of highly saturated colors.
  • OpenDRT: Demonstrates a much smoother "path to white" and gentler compression of colors, maintaining better color separation and integrity even with extreme saturations.
    • This smooth handling prevents harsh clipping and provides a more aesthetically pleasing and robust foundation for grading.

      

      

Creative Control with OpenDRT Look and Tone Scale Presets [13:59]

• OpenDRT provides four distinct Look Presets: Default, Colorful, Umbra, and Base, each offering a different baseline rendering.
• The Tone Scale Preset, by default, follows the selected Look Preset but can be independently chosen for greater control.
• Two primary approaches to using OpenDRT in your grading workflow ("The Print"):

1. Two-Step Print: Flat Baseline for Extensive Creative Grading [18:45]

• Goal: Start with a very flat, neutral image to maximize room for creative manipulation in subsequent nodes.
• Method:
  • Select a Look Preset (e.g., Default).
  • Choose a low-contrast Tone Scale Preset (e.g., ACES 2.0 or Low Contrast) to provide a conservative, light-touch baseline.
  • Apply a separate "creative look" (e.g., using a custom LUT, plugin like Contour, or manual grading) after the OpenDRT node.
• This allows the colorist to exert full authorship over contrast, saturation, and color shaping.

2. One-Step Print: Polished Baseline for Simpler Grading [19:55]

• Goal: Achieve a good-looking, polished baseline directly from the DRT, ready for subtle adjustments at the shot level.
• Method:
  • Select a Look Preset (e.g., Colorful).
  • Choose a more preferential, higher-contrast Tone Scale Preset (e.g., ACES 1.x).
• This approach consolidates the technical rendering and a significant portion of the aesthetic into a single OpenDRT node, reducing the need for extensive creative look development.

The "Base" Look Preset: Understanding the "Chalky" Effect [21:31]

• The "Base" look preset in OpenDRT is designed for maximum accuracy and neutrality, taking a very light touch.
• The "Chalky" Look: Unlike most DRTs that gradually desaturate colors as they approach white (a "path to white"), the "Base" preset maintains saturation even in highlights.
  • This can result in a "chalky" appearance, where there's less separation between key and fill sides of a subject, making the image feel less dimensional or "flat" in a less desirable way to the eye, even if it's technically more "accurate" to the scene's color.
• Mitigation: If you desire the traditional desaturation towards white with the "Base" preset:
  • Add a serial node before OpenDRT.
  • Use a Luminance vs. Saturation (Lum vs. Sat) curve.
  • Drag down the top portion of the curve to desaturate highlights as they increase in luminance, reintroducing the "path to white" behavior.
• This knowledge allows colorists to either embrace the unique aesthetic of the "Base" preset or actively control its behavior, offering more creative flexibility.

The Importance of the Print and DRT [15:25] [26:07]

• The "print" is the most crucial component of the imaging pipeline, transforming raw or graded data into a viewable image, analogous to an oven baking ingredients into food.
• The DRT is a key ingredient within that "print."
• A versatile DRT like OpenDRT, which handles edge cases gracefully and provides numerous options, significantly impacts the quality, consistency, and speed of color grading.