---
title: "Min/Max"
slug: "minmax-filter"
updated: 2026-02-26T08:03:47Z
published: 2026-02-26T08:03:47Z
---

> ## 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.

# Min/Max

The Min/Max Filter performs morphological operations on images. These are fundamental image processing operations useful for noise removal, edge detection, and mask/matte refinement.

## Overview

Morphological operations use a "structuring element" (kernel) that slides across the image. At each position, the operation examines all pixels within the kernel and selects the minimum or maximum value.

## Operations

| Operation | Description | Use Case |
|-----------|-------------|----------|
| **Minimum (Erosion)** | Selects darkest pixel in kernel. Shrinks bright areas, expands dark areas. | Remove small bright noise, shrink masks |
| **Maximum (Dilation)** | Selects brightest pixel in kernel. Expands bright areas, shrinks dark areas. | Fill small holes, expand masks |
| **Open** | Min then Max. Removes small bright spots while preserving overall shape. | Remove salt noise, smooth contours |
| **Close** | Max then Min. Removes small dark spots while preserving overall shape. | Remove pepper noise, fill small holes |
| **Gradient** | Max minus Min. Highlights edges/boundaries. | Edge detection, outline extraction |

## Settings

### Operation

| Setting | Description |
|---------|-------------|
| **Operation** | The morphological operation to perform |
| **Iterations** | Number of times to apply the operation (1-10). More = stronger effect. |

### Kernel

| Setting | Description |
|---------|-------------|
| **Radius X** | Horizontal radius of the kernel (1-100 pixels) |
| **Radius Y** | Vertical radius of the kernel (1-100 pixels) |
| **Link radii** | When ON, Radius Y follows Radius X for uniform kernel |
| **Shape** | Shape of the structuring element |

### Kernel Shapes

| Shape | Description | Best For |
|-------|-------------|----------|
| **Box** | Square/rectangular kernel | General purpose, fast |
| **Ellipse** | Circular/elliptical kernel | Isotropic operations, natural look |
| **Cross** | Plus-shaped kernel (+) | Directional operations |
| **Diamond** | Diamond-shaped kernel (◇) | Compromise between box and ellipse |

### Processing (Advanced)

| Setting | Description |
|---------|-------------|
| **Channel mode** | Per-Channel: process R, G, B independently. Luminance: select whole pixel by brightness. |
| **Process channels** | Which channels to process (see below) |

### Process Channels

| Option | Description |
|--------|-------------|
| **RGB** | Process color channels only, preserve original alpha |
| **RGBA** | Process all channels including alpha |
| **Alpha Only** | Process only the alpha channel, preserve RGB colors |

The **Alpha Only** option is particularly useful for:
- Refining mattes and masks
- Choking/spreading alpha edges without affecting color
- Cleaning up keyed footage alpha

## Keyboard Shortcuts

| Key | Function |
|-----|----------|
| **F1** | Cycle through operations |
| **F2** | Cycle through kernel shapes |
| **F3** | Toggle channel mode (Per-Channel/Luminance) |
| **F4** | Cycle process channels (RGB/RGBA/Alpha) |
| **F5** | Toggle link radii |
| **R** | Reset all settings to defaults |

## Reset

Click the **Reset all** button or press **R** to restore all settings to their default values:
- Operation: Maximum
- Iterations: 1
- Radius X/Y: 3
- Link radii: On
- Shape: Ellipse
- Channel mode: Per-Channel
- Process channels: RGB

## Use Cases

### Noise Removal

**Salt noise (bright spots):**
- Use **Open** operation (Min then Max)
- Small radius (1-3)
- 1-2 iterations

**Pepper noise (dark spots):**
- Use **Close** operation (Max then Min)
- Small radius (1-3)
- 1-2 iterations

### Mask/Matte Refinement

**Shrink mask (choke):**
- Use **Minimum** operation
- Adjust radius to desired shrink amount
- Use Ellipse shape for smooth edges

**Expand mask (spread):**
- Use **Maximum** operation
- Adjust radius to desired expansion
- Use Ellipse shape for smooth edges

**Clean up mask edges:**
- Use **Open** then **Close** (or vice versa)
- Small radius (1-2)
- Removes small artifacts

### Edge Detection

- Use **Gradient** operation
- Adjust radius for edge thickness
- Works like a simple edge detector

### Creating Outlines

1. Apply **Maximum** to expand the shape
2. Subtract original from expanded version
3. Result is an outline of the original shape

## Channel Modes

### Per-Channel Mode
Processes R, G, B channels independently. Each channel gets its own min/max calculation. This is the standard mode and works well for most cases.

### Luminance Mode
Calculates brightness (luminance) for each pixel in the kernel and selects the entire pixel with the minimum/maximum luminance. This preserves color relationships better but may produce different results.

## Performance Notes

- Larger radii are slower (O(r²) complexity)
- Box shape is slightly faster than Ellipse
- Multiple iterations are slower than single iteration with larger radius, but may produce different results
- Processing alpha adds minimal overhead

## Comparison with Median Filter

| Feature | Min/Max | Median |
|---------|---------|--------|
| **Noise removal** | Good for impulse noise | Better for mixed noise |
| **Edge preservation** | Can shift edges | Better edge preservation |
| **Speed** | Faster | Slower |
| **Compound ops** | Open/Close/Gradient | N/A |
| **Use case** | Mask refinement, morphology | General denoising |

## Technical Details

The structuring element (kernel) determines which pixels are considered at each position:

```
Box 3x3:        Ellipse 3x3:    Cross 3x3:      Diamond 3x3:
■ ■ ■           · ■ ·           · ■ ·           · ■ ·
■ ■ ■           ■ ■ ■           ■ ■ ■           ■ ■ ■
■ ■ ■           · ■ ·           · ■ ·           · ■ ·
```

For non-square kernels (Radius X ≠ Radius Y), the shapes scale proportionally.