Genlock

Genlock for LED Display Production

Genlock represents critical technology for any LED installation involving camera capture. Without proper synchronization, LED walls produce visible artifacts in video footage that cannot be corrected in post-production.

Understanding the Problem

LED displays refresh by scanning through pixel rows or groups. At any instant, different parts of the display are at different brightness levels during the scan cycle. This is invisible to human eyes due to persistence of vision.

Cameras, however, capture discrete frames. If camera exposure happens while the LED display is mid-scan:

• Horizontal black bars appear in footage
• Brightness varies frame-to-frame (flickering)
• Color banding may occur if RGB doesn't scan simultaneously

How Genlock Solves This

Genlock synchronizes the LED refresh cycle to camera timing:

1. Camera outputs reference signal (or uses house sync) 2. Reference feeds to LED processor genlock input 3. Processor aligns LED refresh to reference timing 4. LED refresh completes during camera blanking period 5. Camera captures fully-lit frame

Reference Signal Types

Blackburst: SD-era analog reference (still widely used)

Tri-Level Sync: HD timing reference (720p, 1080i, 1080p)

SDI Video: Any SDI signal can serve as reference

LTC Timecode: Some systems accept timecode for sync

LED Processor Genlock Features

Reference Input: BNC connector for sync signal

Phase Adjustment: Fine-tune timing alignment

Automatic Detection: Recognize reference format

Free-Run Fallback: Continue operating if reference lost

Status Indication: Show lock status

Genlock Configuration

Basic setup steps:

1. Connect reference from camera/switcher to processor 2. Enable genlock in processor settings 3. Select correct reference format 4. Adjust phase offset if banding persists 5. Verify on camera monitor

Advanced Considerations

Multiple Cameras: All cameras should share the same reference for consistent results across angles.

Frame Rate Matching: LED content playback should match camera frame rate (23.976, 24, 25, 29.97, 30, 50, 60).

Shutter Angle: Camera shutter settings interact with LED timing; some shutter angles work better than others.

Virtual Production: ICVFX requires extremely precise genlock with camera tracking systems.

When Genlock Isn't Enough

Even with genlock, some artifact sources remain:

Moiré: Geometric interference from pixel grid (solved by camera positioning/lens)

PWM Flicker: Some LED driving methods create camera issues

Rolling Shutter: Camera sensor type affects artifact appearance

Genlock-Free Alternatives

For situations where genlock isn't possible:

• Use LED displays with very high refresh rates (7680Hz+)
• Adjust camera shutter speed/angle
• Accept some artifacts in non-critical footage
• Use global shutter cameras