Logarithmic Footage

Definition

Log Footage is video material encoded with a logarithmic transfer function to preserve maximum dynamic range in the recording. Logarithmic encodings compress visual data into a flat, contrastless form similar to unprocessed film negative in cinematography. This encoding allows optimal capture of highlights and shadows but requires mandatory color grading to produce the final, visually appealing image.

Physico-Optical Fundamentals

Logarithmic Transfer Function

The logarithmic curve follows the formula:

Output = log(Input + offset) / log(2)

Characteristics of the Log Curve:

• Flat Shadows: Shadow areas are not suppressed, maximum information retained
• Compressed Highlights: Highlights are compressed to maximize detail preservation
• Linear Perception: Human eyes perceive brightness differences logarithmically (Weber-Fechner Law)

Comparison: Linear vs. Gamma vs. Logarithmic

Log Formats by Camera Manufacturer

Red Digital RedLogFilm

Characteristics:

• Dynamic Range: 16+ Stops
• Transformation: Specific mathematical curve for Red sensors
• Color Space: Native Red color space
• Standard LUT: RedLogFilm to Rec.709 or DCI-P3

Workflow in DaVinci Resolve:

1. Set project to Red Color Science v2 or v3
2. Decode Quality: Full (Half-Res can be chosen for 8K material)
3. Timeline Color Space: DaVinci Wide Gamut RGB
4. LUT: RedLogFilm to Rec.709

Arri LogC and Alexa Wide Gamut

LogC Versions:

• LogC.V2: Classic Arri format (Alexa XT/SXT)
• LogC.V3: Optimized for modern Alexa Mini LF
• LogC.V4: Latest version with extended highlights

Characteristics:

• Dynamic Range: 15-16 Stops
• Color Space: Alexa Wide Gamut RGB (larger than DCI-P3)
• ASC CDL Integration: Color Decision Lists automatically importable
• Standard LUT: LogC to Rec.709

Workflow in DaVinci Resolve:

1. Input Color Space: Select Arri LogC (correct version!)
2. Decoding: Automatic with correct illuminant
3. Input Transform LUT: Apply Arri standard
4. Grade in Wide Gamut RGB

Sony S-Log and S-Log3

S-Log Family:

• S-Log: Original Sony Log (Alpha7S)
• S-Log2: Improved version
• S-Log3: Modern version with improved shadow handling (a7S III, FX30, etc.)
• HLG (Hybrid Log-Gamma): For HDR recording

Characteristics:

• Dynamic Range: 14-16 Stops (S-Log3 optimized for highlights)
• Color Space: S-Gamut3.Cine (camera-specific)
• Standard LUT: S-Log3 to Rec.709

Workflow in DaVinci Resolve:

1. Input Color Space: Select Sony S-Log
2. Gamma: S-Log3 (correct version)
3. Color Gamut: S-Gamut3.Cine
4. Input Transform: Apply Sony Standard LUT

Panasonic V-Log

Characteristics:

• Dynamic Range: 14+ Stops
• Color Space: V-Gamut (larger than Rec.2020)
• Available on: Lumix S Series, Varicam
• Standard LUT: V-Log to Rec.709

Dynamic Range and Practical Implications

Stops Conversion and Exposure Latitude

A "stop" is a doubling or halving of brightness:

Recording with Log:

• Sunlight on snow (very bright): ~+6 Stops above midtone
• Midtone (Caucasian skin, 18% gray): 0 Stops (reference)
• Black objects in shadow: ~-6 Stops below midtone

Total Dynamics with Log: ~12-16 Stops available

This extra dynamic range enables:

• Exposure Error Tolerance: ±1-2 Stops under/overexposure still correctable
• Creative Options: Bright and dark scenes combinable in single take
• HDR Preparation: Material convertible for different output formats

Practical Exposure Guidelines for Log

Best Practices:

• Exposure Index (EI): Use native sensor sensitivity (Red ISO 320, Alexa 800, Sony 2500)
• Zebra/Waveform: Use for clipping control (highlights should not be clipped)
• Light Meter/Spotmeter: Measure critical areas (skin, highlights)
• Overexposure Tolerance: Log cameras handle +0.5-1 Stop overexposure without quality loss

Log-to-Rec.709 Decoding in DaVinci Resolve

Input Transform (Automatic)

DaVinci Resolve offers automatic Input Transforms for various Log formats:

Process:

1. Import clip
2. Open Clip Inspector
3. Select "Input Color Space"
4. Set camera/Log format correctly
5. DaVinci automatically selects matching Input LUT

Result:

• Log footage automatically converted to Rec.709 or DCI-P3
• Standard viewing conditions applied
• Ready for grading and editing

Manual Color Management

Advanced Setup in Project Settings:

Color Management:
- Input LUT: Select camera-specific
- Timeline Color Space: DaVinci Wide Gamut RGB (internal)
- Output Transform: Rec.709 (Monitoring)
- Display: Rec.709 + Gamma 2.4

Grading Workflow with Log Material

Phase 1: Primary Color Correction

After Input Transform (Log to Rec.709):

1. Exposure Adjustment: Correct basic brightness
2. Contrast Adjustment: Optimize tonality with curve
3. Color Balance: White balance and basic color cast
4. Check Clipping: Review histogram for clipping

Phase 2: Secondary Correction

After primary grade is correct:

1. Isolate Luminance Ranges: Grade shadows, midtones, highlights separately
2. Isolate Color Ranges: Correct specific colors (e.g., skin, sky)
3. Local Adjustments: Power Windows for spatial corrections
4. Effects: Vignetting, softness, film grain

Phase 3: Window Masking and Power Windows

Log material has neutral colors enabling Power Windows for selective grading:

• Face Windows: Skin tone corrections
• Sky/Background Windows: Grade sky or background separately
• Moving Windows: Motion tracking for moving objects
• Qualitative Feathering: Smooth transitions between window and surroundings

Storage and Archiving

Log Proxies and Final Exports

Workflow:

1. Proxy Generation: Smaller Log files for fast editing (ProRes, DNxHR)
2. Grade on Proxies: Timing and pre-corrections
3. Conform to Masters: Final timeline with full-res Log originals
4. Final Grade: Color grading on full-res
5. Deliver: Export to Rec.709, DCI-P3, Rec.2020 (depending on medium)

Archive Standards

Best Practice:

• Original Log Material: Archive (uncompressed or minimal compression)
• Mezzanine ProRes: For quick access
• Grading Session: Save DaVinci project for future adjustments

Common Errors and Solutions

Practical Scenarios

Scenario 1: Multi-Format Production

Production with Red Komodo (RedLogFilm) + Arri Alexa Mini LF (LogC.V3):

1. Import both footage types into project
2. Set Input Color Space for each camera individually
3. Create master grade on one camera
4. Generate matching LUT and apply to other camera
5. Perform fine-tuning

Scenario 2: Extreme Lighting Situations

Scenes with bright outdoor light and dark interiors:

1. Choose Log format for maximum dynamic range (Red RedLogFilm or Arri LogC)
2. Set exposure so highlights just don't clip
3. In grading, lift shadows and compress highlights
4. Apply creative grade

Scenario 3: Creating HDR Versions

From Log master to SDR and HDR:

1. Grade Log master in DCI-P3 (Rec.2020 for HDR)
2. SDR Version: Curve adjustment for Rec.709 levels
3. HDR Version: Rec.2020 with extended gamut and dynamic range
4. Export both versions as separate deliverables

Summary

Log Footage is the gold standard for professional film production. The increased dynamic range and grading flexibility justify the additional complexity in post-production. Correct setting of the Log format and Input Transform in grading software is essential for optimal results.