Image Based Keyer – a powerful keying toolset in Nuke compositing software that analyzes the screen color from a clean plate to create highly accurate keys, particularly effective for difficult situations like uneven green screens, spill, and fine detail preservation.
What is IBK?
IBK (Image Based Keyer) is a powerful keying system in Nuke that analyzes a clean plate to determine the exact greenscreen color. Unlike traditional keyers that assume a uniform color, IBK works with the actual, varying screen color.
Basic Principle
| Aspect | Description |
|---|---|
| Clean Plate | Reference without subject |
| Analysis | Exact screen color |
| Pixel-by-Pixel | Individual values |
| Result | More precise key |
Components in Nuke
| Node | Function |
|---|---|
| IBKColour | Analyze screen color |
| IBKGizmo | Main keyer |
| Additional | Refinement tools |
IBKColour
| Function | Description |
|---|---|
| Input | Clean Plate |
| Output | Screen Color Map |
| Analysis | Color variation |
| Usage | For IBKGizmo |
IBKGizmo
| Element | Description |
|---|---|
| FG Input | Footage with subject |
| Screen Input | From IBKColour |
| Output | Key + Despill |
| Controls | Fine-tuning |
Workflow
| Step | Description |
|---|---|
| Clean Plate | Load |
| IBKColour | Analyze screen |
| IBKGizmo | Connect with FG |
| Refine | Fine-tune |
Clean Plate Requirements
| Requirement | Description |
|---|---|
| Identical | Same camera position |
| Same Lighting | As FG |
| Empty | Screen only |
| High Quality | No artifacts |
Advantages of IBK
| Advantage | Description |
|---|---|
| Uneven Screens | Handles variation |
| Spill | Effective despill |
| Fine Detail | Hair, transparency |
| Edge Quality | Clean edges |
Problems IBK Solves
| Problem | IBK Solution |
|---|---|
| Wrinkles in Screen | Pixel-wise analysis |
| Shadows | Individual values |
| Hotspots | Local correction |
| Color Variation | Automatic |
Despill
| Aspect | Description |
|---|---|
| Integrated | In IBKGizmo |
| Quality | High quality |
| Controls | Adjustable |
| Color Replace | Options |
IBK vs. Other Keyers
| Aspect | IBK | Primatte/Keylight |
|---|---|---|
| Method | Clean Plate | Color Sample |
| Uneven Screens | Excellent | More difficult |
| Setup | Requires Clean Plate | Faster |
| Quality | Often better | Good |
When to Use IBK?
| Situation | Recommendation |
|---|---|
| Clean Plate available | IBK ideal |
| Uneven Screen | IBK preferred |
| Difficult Spill | IBK good |
| No Clean Plate | Other keyer |
Combined Workflows
| Combination | Purpose |
|---|---|
| IBK + Keylight | Backup key |
| IBK + Primatte | Edge refinement |
| IBK + Roto | Hybrid approach |
| IBK + Bezier | Garbage matte |
Parameters
| Control | Function |
|---|---|
| Screen Type | Green/Blue |
| Patch Black/White | Levels |
| Erode/Dilate | Edge adjust |
| Screen Gain | Intensity |
Troubleshooting
| Problem | Solution |
|---|---|
| Black spots | Adjust Patch Black |
| White holes | Adjust Patch White |
| Edge Issues | Adjust Erode/Dilate |
| Spill remaining | Adjust Despill |
Performance
| Aspect | Consideration |
|---|---|
| Render Time | Fast |
| Memory | Moderate |
| Optimization | Bounding Box |
| Caching | Recommended |
On-Set for IBK
| Shot | Importance |
|---|---|
| Clean Plate | Essential |
| Locked Off | Ideal |
| Same Settings | Camera |
| Same Lighting | Identical |
Plate Creation
| Method | Description |
|---|---|
| Before Take | Best option |
| After Take | Acceptable |
| Motion Control | Moving camera |
| Patch | Partially possible |
Best Practices
| Practice | Reason |
|---|---|
| Clean Plate always | Maximum options |
| Same setup | Best results |
| Multiple Keys | Combine |
| QC thoroughly | Check edges |
Today
IBK has revolutionized keying in Nuke – what previously required difficult roto work can now often be solved automatically. The clean-plate-based analysis enables keys that traditional keyers cannot achieve. For VFX artists, IBK is an indispensable tool in the compositing arsenal.