Lecture on Forgotten Visual Effects Technology: Sodium Vapor Process

Introduction

• Visual effects in old movies often seem superior to modern ones.
• Disney's 1960s invention, the Sodium Vapor Process, offered advantages over green screen.
• This technology has been largely forgotten.

Fundamentals of Visual Effects

• Layering one image over another is essential for visual effects.
• Common method: green screen or blue screen, but it has issues:
  • Can't film blurry or transparent objects well
  • Actors can't wear colors matching the screen
  • Color spill can ruin footage
• Example of a challenging scene unfriendly to green screen: A clown in colorful attire getting married on Mars.

The Sodium Vapor Process

Explanation by Dr. Paul Debevec

• Utilized a yellow screen with a specific yellow spectrum from a sodium vapor light (589 nm wavelength).
• Beam splitter prism split incoming light into two film strips:
  • Sodium vapor wavelength reflected off.
  • Rest of the spectrum passed through, capturing image of the actor.
• This resulted in a perfect matting without affecting other colors in the scene.
• Allowed for effects impossible with green screen, like keying out transparent items.

Challenges and Rediscovery

Why It's Not Used Today

• Replicating the custom beam splitter prism was difficult and costly.
• Only three prisms were made, which are now lost.
• This limitation hindered the practical application of the technology for modern use.

Recreating the Process

• Paul Debevec managed to recreate Disney’s prism using off-the-shelf components:
  • Used two filters instead of a custom beam splitter.
  • Two cameras simulated the two strips of film.
• Conducted test of the sodium vapor process after 30 years.

Experiment Details

Setup

• Sodium vapor lights still available; bulbs glow yellow after warming up.
• Used LED lights to illuminate actors without introducing unwanted colors.
• Spectral light meter used to confirm no side spill of sodium vapor light on subjects.
• Objective: Achieve perfect matte without color spill or transparency issues.

Execution and Results

• Created a challenging scene to test (e.g., clown getting married on Mars with various hues and transparent items).
• Compared sodium vapor process results to green screen:
  • Sodium vapor: No matting artifacts, perfect motion blur, excellent detail in transparent sections.
  • Green screen: Struggled with transparency, requiring extensive manual tweaking.

Conclusion

Advantages of Sodium Vapor Process

• Simulated the original filmic approach effectively with modern equipment.
• No need for extensive post-processing adjustments.
• Potential applications in today's film industry for complex compositing tasks.

Modern Implications and Future Use

• Despite technological advancements like LED volumes, some effects still benefit from perfect matting.

• Machine learning in compositing tools could benefit from sodium vapor process data.

• Reinforces the importance of blending classic techniques with modern advancements.

• Sodium vapor remains a valuable, though niche, technique for complex visual effects work.