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CGI Lighting and Compositing Workflow

Aug 16, 2024

Visual Effects Shot Workflow

Introduction

  • Challenge: Matching lighting between footage and CGI elements
  • Old method: Guessing and tweaking in compositing
  • New workflow: Confidently match lighting using simple tools and Asus color system
  • Resources: Workflow graphic, footage, photo, and Blender assets available for free download

Filming Process

  • Main Camera: Panasonic GH5 with V-log color space for flat footage
    • Constant white balance to avoid changes during the shot
  • Color Checker: X-rite Color Checker Classic shot after main footage
    • Alternatives: White balance card or none (best results with Color Checker)
  • 360 Camera Setup: Near CG elements' scene location
    • Capture multiple exposures

Creating HDRI

  • Merge 360 photos into one image using Photoshop's Merge to HDR Pro
    • Ignore alignment option since the camera is stationary
    • Save as a Radiance file

Color Space Conversion with Aces

  • Convert HDRI and footage to same color space using Aces
  • Nuke Software: Used for color management
    • Set project settings to use Aces
    • Import footage and HDRI
    • Apply appropriate Aces IDT (Input Display Transform)
  • Testing IDT: Exposure test with different stops to validate correct IDT

Matching Exposure and White Balance

  • Sample RGB values from gray patch in both footage and HDRI
  • Multiply HDRI by values to match footage RGB values
  • Maintain linear workflow; avoid major color grading at this stage

Blender Workflow

  • Setup:
    • Configure Blender for Aces
    • Camera alignment and background set to footage
    • Apply same color correction to HDRI in Blender as in Nuke
  • Material Adjustments:
    • Correct Aces IDT for materials in Blender
    • Use appropriate settings for diffuse, roughness, metalness, etc.

Rendering Process

  • Issue: Most 360 cameras cannot capture low exposure for sun detail
  • Solution:
    • Cover sun in HDRI and create a separate sun object in Blender
    • Align shadows using sun object and adjust strength to match reference footage

Final Composition

  • Blender Compositing:
    • Use shadow pass for color and darkness
    • Adjust shadows and car color for realistic match
  • Rendering: Save as open EXR multi-layer file

Final Color Grading

  • DaVinci Resolve:
    • Set Aces color science and input transform
    • Apply final color grading and export

Conclusion

  • Encouragement to try the workflow with provided assets
  • Opportunity to share results for feedback

This workflow simplifies the process of integrating CGI elements into live footage by ensuring consistent lighting and color space management, making compositing more straightforward and reliable.

Full transcript