---
title: "Difference Matte"
slug: "difference-matte"
updated: 2026-02-26T08:02:43Z
published: 2026-02-26T08:02:43Z
---

> ## Documentation Index
> Fetch the complete documentation index at: https://composer.docs.vindral.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Difference Matte

The **Difference Matte operator** compares the current frame against a "clean plate" (background image without the subject) to automatically generate a matte that isolates the foreground. This technique is ideal for locked-off camera shots where you need to extract a subject from a known background.

![Image](https://cdn.document360.io/94808959-fd66-406c-ab5e-4691ce952a14/Images/Documentation/image(236).png)

---

## Overview

Difference matting works by comparing each pixel in your footage to the corresponding pixel in the clean plate. Where the pixels differ significantly, that area is considered foreground; where they're similar, it's considered background.

```
Clean Plate     Current Frame     Difference      Matte
(empty room)  - (room + person) = (person shape) → (alpha channel)
```

## Quick Start

1. Add the **Difference Matte** operator to your composition (found in Chroma Keying)
2. Click on **Clean plate image** and select your background image (a frame from your footage without the subject)
3. Adjust **Threshold** until the subject is cleanly separated from the background
4. Adjust **Softness** to smooth the matte edges

## When to Use Difference Matte

**Ideal scenarios:**

- Locked-off camera shots (camera doesn't move)
- Consistent lighting between clean plate and footage
- Subject doesn't cast strong shadows on the background
- Quick extraction without setting up a green screen

**Not ideal for:**

- Moving camera shots
- Changing lighting conditions
- Subjects that closely match the background color
- Complex shadows that should be preserved

## Settings

### Clean Plate

| Setting | Description |
| --- | --- |
| **Clean plate image** | Select the background image file. This should be a frame from your footage (or a separately captured image) showing the background without the subject. |
| **Reload** | Button to reload the clean plate if the file has changed on disk. |

### Matte Generation

| Setting | Description |
| --- | --- |
| **Threshold (%)** | Minimum difference to consider as foreground. Lower values = more sensitive, higher values = less sensitive. Start around 10% and adjust. |
| **Softness (%)** | Edge softness / feather amount. Higher values create smoother transitions between foreground and background. |
| **Pre-blur** | Blur the input before comparison to reduce noise sensitivity. Useful for noisy footage. 0 = no blur. |
| **Difference mode** | How to calculate the difference. See Difference Modes below. |

#### Difference Modes

| Mode | Description |
| --- | --- |
| **RGB** | Average difference across all color channels. Best general-purpose option. |
| **Luminance** | Difference in brightness only, ignoring color. Good when subject differs mainly in brightness. |
| **Max Channel** | Uses the maximum difference from any single channel. More sensitive to small color shifts. |

### Color Tolerance (Advanced)

These settings allow you to ignore small differences in specific color channels, useful when there's slight color shift between clean plate and footage due to lighting variations.

| Setting | Description |
| --- | --- |
| **Red tolerance (%)** | Ignore red channel differences below this amount. |
| **Green tolerance (%)** | Ignore green channel differences below this amount. |
| **Blue tolerance (%)** | Ignore blue channel differences below this amount. |

### Matte Refinement (Advanced)

| Setting | Description |
| --- | --- |
| **Expand / Contract** | Positive values grow the matte outward, negative values shrink it inward. Use to include/exclude edge pixels. |
| **Denoise** | Remove small isolated pixels that are likely noise. Higher values remove larger noise clusters. |

### Output

| Setting | Description |
| --- | --- |
| **Output mode** | What the filter outputs. See Output Modes below. |
| **Invert matte** | Swap foreground and background. |

#### Output Modes

| Mode | Description |
| --- | --- |
| **Composite** | Original image with matte in the alpha channel. Use this to composite over a new background. |
| **Matte Only** | Grayscale image showing just the matte. White = foreground, black = background. |
| **Foreground Only** | Premultiplied foreground (RGB multiplied by alpha). |
| **Difference** | Raw difference visualization - useful for debugging and setting threshold. |

### Debug

| Setting | Description |
| --- | --- |
| **Show clean plate** | Display the loaded clean plate image. Useful to verify it loaded correctly and matches the footage. |

## Keyboard Shortcuts

| Key | Function |
| --- | --- |
| **F1** | Cycle through output modes |
| **F2** | Cycle through difference modes |
| **F3** | Toggle invert matte |
| **F4** | Toggle show clean plate |
| **F5** | Reload clean plate |

## Creating a Clean Plate

### From Your Footage

If you have a frame in your footage where the subject is not present:

1. Navigate to that frame
2. Export it as an image (PNG recommended)
3. Load it as the clean plate

### Shooting a Separate Clean Plate

For best results:

1. After filming your shot, have the subject leave the frame
2. Keep the camera in exactly the same position
3. Keep lighting identical
4. Capture a frame or short clip of the empty background
5. Export and use as clean plate

### Tips for Better Clean Plates

- **Same resolution** - Clean plate must match footage resolution exactly
- **Same exposure** - Any exposure differences will affect the matte
- **Same white balance** - Color shifts will cause problems
- **No camera movement** - Even tiny shifts will misalign the comparison

## Workflow Tips

### Setting Threshold

1. Start with **Output mode: Difference** to see the raw difference
2. Brighter areas in difference view = more difference from clean plate
3. Adjust **Threshold** so your subject is bright and background is dark
4. Switch to **Output mode: Matte Only** to see the resulting matte
5. Fine-tune threshold until edges look clean

### Dealing with Noise

If your footage is noisy:

1. Increase **Pre-blur** to 1-3 to smooth out noise before comparison
2. Use **Denoise** to remove isolated pixels in the matte
3. Slightly increase **Threshold** to ignore noise-level differences

### Dealing with Shadows

Shadows are challenging because they're "different" from the clean plate:

1. If you want to **include** shadows: Lower threshold, but this may include noise
2. If you want to **exclude** shadows: Use **Luminance** mode which is less sensitive to darkening
3. Consider using **Color tolerance** to ignore the darkening effect of shadows

### Edge Refinement

1. Use **Softness** for natural-looking edges (20-40% typically)
2. Use **Expand/Contract** to fine-tune edge position:
  - Positive values if you're losing edge detail
  - Negative values if background is bleeding through

## Troubleshooting

| Problem | Solution |
| --- | --- |
| **Matte is all white or all black** | Threshold is set too low or too high. Use Difference output mode to calibrate. |
| **Clean plate doesn't load** | Check file path, ensure image exists and is a supported format. |
| **Size mismatch error** | Clean plate resolution must exactly match input footage resolution. |
| **Noisy/speckled matte** | Increase Pre-blur and/or Denoise. Slightly raise Threshold. |
| **Edges are jagged** | Increase Softness. |
| **Thin halo around subject** | Use negative Expand/Contract to shrink matte slightly. |
| **Missing parts of subject** | Subject color is too similar to background in those areas. Try different Difference mode, or lower Threshold. |
| **Shadows included in matte** | Switch to Luminance mode, or increase threshold, or add tolerance. |

## Technical Notes

- The filter requires the clean plate and input to have identical dimensions
- Processing is done entirely on GPU for real-time performance
- Matte is generated per-frame; there is no temporal smoothing
- For moving camera shots, consider using a different keying approach (Chroma Key, Roto, etc.)