The Spill Suppression operator removes green or blue color contamination from chroma key footage. When filming against a green or blue screen, the screen color often reflects onto the subject's hair, skin, clothing, and other surfaces. This filter detects and removes that color "spill" while optionally replacing it with a more natural tone.
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Overview
Spill occurs because:
- Light bounces off the green/blue screen onto the subject
- Semi-transparent materials (hair, fabric edges) pick up the screen color
- The screen color bleeds into edge pixels during keying
Spill suppression works by detecting where the green (or blue) channel is abnormally high compared to the other channels, then reducing it to a natural level.
Quick Start
- Add the Spill Suppression operator after your chroma key effect
- Select Screen type (Green or Blue) to match your footage
- Adjust Amount to control overall suppression strength
- Use Show spill map to visualize detected spill areas
- Fine-tune with Method and Replace mode for best results
Settings
Screen
| Setting | Description |
|---|---|
| Screen type | The color of your chroma key screen - Green or Blue. |
Suppression
| Setting | Description |
|---|---|
| Amount (%) | Overall spill suppression strength. 0% = no suppression, 100% = full suppression. |
| Method | Algorithm for detecting spill. See Suppression Methods below. |
| Core strength (%) | Suppression intensity on obviously spilled areas (strong green/blue contamination). |
| Edge strength (%) | Suppression intensity on subtle edge spill. Often needs to be lower to avoid artifacts. |
Suppression Methods
| Method | Description |
|---|---|
| Light | Subtle suppression. Green/blue shouldn't exceed the maximum of the other two channels. Good for minor spill. |
| Medium | Balanced suppression. Green/blue shouldn't exceed the average of the other channels. Best general-purpose option. |
| Aggressive | Strong suppression. Uses a weighted average that's more restrictive. Good for heavy spill. |
| Max | Maximum suppression. Green/blue shouldn't exceed the minimum of the other channels. Can cause color shifts on legitimate green/blue objects. |
Spill Replacement
When spill is removed, you can optionally replace it with another color to compensate for the lost luminance and maintain natural skin tones.
| Setting | Description |
|---|---|
| Replace mode | What to do with removed spill. See Replace Modes below. |
| Tint strength (%) | How strongly to apply the replacement color. |
| Replace color (R/G/B) | Custom replacement color when using Custom mode. |
Replace Modes
| Mode | Description |
|---|---|
| None | Just remove spill without replacement. Can darken affected areas. |
| Gray | Add neutral gray to compensate. Maintains luminance without color shift. |
| Complement | Add the complementary color (magenta for green, yellow for blue). Most natural-looking for skin. |
| Custom | Blend toward a custom color. Useful for specific color correction needs. |
Fine Tuning (Advanced)
| Setting | Description |
|---|---|
| Spill range (%) | How sensitive the spill detection is. Higher values detect more subtle spill but may affect legitimate colors. |
| Protect skin tones | Reduces suppression on detected skin tones to prevent unnatural color shifts. Recommended to keep ON. |
| Preserve luminance (%) | Maintains original brightness after suppression. Prevents darkening of affected areas. |
Output
| Setting | Description |
|---|---|
| Output mode | What to display. See Output Modes below. |
Output Modes
| Mode | Description |
|---|---|
| Final | The processed result with spill suppression and alpha adjustment applied. |
| Foreground | The original input image before any processing. |
| Spill Map | Colored visualization of detected spill (green or blue depending on screen type). |
| Alpha | Grayscale view of the alpha channel, including any alpha adjustments. |
| Spill Matte | Grayscale visualization showing the amount of spill detected per pixel. |
Alpha Adjustment (Advanced)
These settings reduce the alpha channel in areas where spill is detected. This makes spill areas more transparent, which is useful for cleaning up semi-transparent edges (like hair) or removing fringe artifacts.
| Setting | Description |
|---|---|
| Alpha adjust (%) | Maximum alpha reduction in spill areas. 0% = no change, 100% = fully transparent where spill is strongest. |
| Alpha threshold (%) | Minimum spill level required before alpha is affected. 0% = any spill affects alpha, higher = only strong spill affects alpha. |
| Alpha softness (%) | Transition range above threshold. 0% = hard cutoff, higher = gradual transition from no effect to full effect. |
How it works:
- The filter detects spill amount per pixel (visible in Spill Matte output mode)
- If spill > threshold, alpha reduction begins
- Softness controls how gradually the effect ramps up
- Alpha adjust controls the maximum reduction at full effect
Keyboard Shortcuts
| Key | Function |
|---|---|
| F1 | Toggle Green/Blue screen type |
| F2 | Cycle through suppression methods |
| F3 | Cycle through replace modes |
| F4 | Toggle protect skin tones |
| F5 | Cycle through output modes |
Workflow Guide
Step 1: Identify Spill
- Enable Show spill map to see where spill is detected
- Bright areas indicate strong spill
- If spill map doesn't match visible spill, adjust Spill range
Step 2: Choose Method
Start with Medium method, then:
- If spill remains: Try Aggressive or Max
- If colors look wrong: Try Light
Step 3: Adjust Strength
- Set Core strength high (80-100%) for obvious spill
- Set Edge strength lower (30-60%) to preserve edge detail
- Adjust Amount for overall control
Step 4: Color Compensation
- If skin looks gray/dead: Use Complement replace mode
- Increase Tint strength until skin looks natural
- Enable Preserve luminance to prevent darkening
Step 5: Alpha Adjustment (Optional)
If you have semi-transparent edges that look too solid due to spill:
- Set Output mode to Alpha to see the current alpha channel
- Increase Alpha adjust gradually (start with 20-40%)
- Adjust Alpha threshold to only affect spill areas
- Use Alpha softness for smooth transitions
- Switch back to Final to see the result
Step 6: Final Tweaks
- Enable Protect skin tones if not already on
- Zoom in on hair and fabric edges to check for artifacts
- Compare with original to ensure no over-correction
Common Scenarios
Hair Fringe / Flyaway Hair
Hair edges often pick up significant spill:
- Use Medium or Aggressive method
- Keep Edge strength moderate to preserve detail
- Complement replace mode helps maintain natural hair color
Skin Near Screen Edge
When skin is close to the screen, it can pick up green/blue cast:
- Enable Protect skin tones
- Use Complement replace mode
- Increase Tint strength for natural skin
White or Light Clothing
White fabrics easily pick up spill:
- Medium method usually works well
- Use Gray replace mode to maintain neutral whites
- High Preserve luminance to keep brightness
Transparent/Translucent Objects
Glass, plastic, fabric with transparency:
- Often needs Aggressive method
- May need to accept some spill on truly transparent areas
- Consider masking and treating separately
Troubleshooting
| Problem | Solution |
|---|---|
| Skin looks magenta/purple | Reduce Tint strength, or switch to Gray replace mode |
| Skin looks gray/lifeless | Enable Complement mode, increase Tint strength |
| Spill still visible | Increase Amount, try Aggressive method, increase Spill range |
| Legitimate green/blue objects affected | Lower Spill range, use Light method, or mask those objects |
| Dark edges after suppression | Increase Preserve luminance, use Gray replace mode |
| Hair looks unnatural | Reduce Edge strength, enable Protect skin tones |
| Spill map shows nothing | Wrong Screen type selected, or very low spill in footage |
| Edges too transparent after alpha adjust | Reduce Alpha adjust, increase Alpha threshold |
| Alpha adjustment affects wrong areas | Increase Alpha threshold, reduce Spill range |
Tips for Best Results
Prevention at Shoot
- Keep subjects away from the screen (reduces spill)
- Use proper lighting to minimize screen reflection
- Consider spill-suppression lighting (magenta/yellow fill)
Order of Operations
Apply spill suppression after chroma keying but before:
- Color correction
- Final compositing
- Other effects
Multiple Passes
For difficult footage, consider two passes:
- First pass: Aggressive method, low strength, targeting obvious spill
- Second pass: Light method, targeting subtle remaining spill
Preserve the Original
Keep an unprocessed version of your footage to compare against. Over-suppression can look worse than some spill.
Technical Notes
- Spill detection compares the screen color channel against the other two channels
- Skin tone protection uses hue and saturation analysis to identify skin-colored pixels
- All processing is done per-pixel on the GPU in real-time
- The filter preserves the alpha channel from the input