dilate

Apply morphological dilation to expand bright regions and fill small gaps.

Usage

Terminal

$ mediaproc image dilate <input> [options]

The dilate command applies morphological dilation, a fundamental operation in image processing that expands bright (high-value) regions while shrinking dark (low-value) regions. This is the opposite of erosion. Dilation is useful for:

Filling holes: Close small gaps and holes in objects
Connecting components: Join nearby objects or features
Expanding boundaries: Enlarge object boundaries
Noise removal: Remove small dark noise spots
Strengthening edges: Make weak edges more prominent

Uses a 3×3 kernel that examines each pixel and its 8 neighbors, replacing the center pixel with the maximum value in the neighborhood.

Options

Option	Type	Default	Description
`<input>`	string	required	Input image file path
`-o, --output`	string	`<input>_dilated.<ext>`	Output file path
`-q, --quality`	number	`90`	Output quality 1-100
`--dry-run`	boolean	`false`	Show what would be done without processing
`-v, --verbose`	boolean	`false`	Enable verbose logging

Examples

Basic Dilation

Apply dilation to expand bright regions:

# Dilate binary mask
mediaproc image dilate mask.png -o dilated_mask.png

# Expand white regions
mediaproc image dilate binary.jpg -o expanded.jpg

# Fill small gaps
mediaproc image dilate document.png -o filled.png

# Strengthen edges
mediaproc image dilate edges.jpg -o strong_edges.jpg

Quality Control

# High quality output
mediaproc image dilate mask.png -q 95 -o high_quality.png

# Standard quality
mediaproc image dilate image.jpg -q 90 -o dilated.jpg

# Lower quality for previews
mediaproc image dilate binary.png -q 80 -o preview.png

Multiple Dilations

Apply dilation multiple times for stronger effect:

# Single dilation
mediaproc image dilate mask.png -o dilated1.png

# Double dilation (stronger effect)
mediaproc image dilate mask.png -o temp.png
mediaproc image dilate temp.png -o dilated2.png
rm temp.png

# Triple dilation
mediaproc image dilate mask.png -o temp1.png
mediaproc image dilate temp1.png -o temp2.png
mediaproc image dilate temp2.png -o dilated3.png
rm temp1.png temp2.png

Morphological Closing

Combine dilation then erosion to close holes:

# Closing operation: dilate → erode
# Fills small holes while preserving size
mediaproc image dilate mask.png -o temp_dilated.png
mediaproc image erode temp_dilated.png -o closed.png
rm temp_dilated.png

# Stronger closing (multiple iterations)
mediaproc image dilate noisy.png -o temp1.png
mediaproc image dilate temp1.png -o temp2.png
mediaproc image erode temp2.png -o temp3.png
mediaproc image erode temp3.png -o closed_strong.png
rm temp1.png temp2.png temp3.png

Connecting Nearby Objects

Join components that are close together:

# Connect nearby text characters
mediaproc image dilate text.png -o connected_text.png

# Join fragmented objects
mediaproc image dilate fragments.jpg -o joined.jpg

# Connect broken lines
mediaproc image dilate lines.png -o continuous_lines.png

Batch Processing

Apply dilation to multiple images:

# Dilate all masks
for file in masks/*.png; do
  mediaproc image dilate "$file" -o "dilated/${file##*/}"
done

# Process binary images
for img in binary/*.jpg; do
  mediaproc image dilate "$img" -o "processed/${img##*/}"
done

# Dilate with quality setting
for file in *.png; do
  mediaproc image dilate "$file" -q 95 -o "output/${file}"
done

Edge Enhancement

Detect edges by subtracting original from dilated:

# Edge detection workflow
mediaproc image dilate image.jpg -o dilated.jpg
# Then use external tool to subtract original from dilated
# Result shows object boundaries

Mask Expansion

Expand selection masks:

# Expand mask for compositing
mediaproc image dilate selection_mask.png -o expanded_mask.png

# Grow selection area
mediaproc image dilate region.png -o larger_region.png

# Expand alpha channel mask
mediaproc image dilate alpha_mask.png -o expanded_alpha.png

Document Processing

Process scanned documents:

# Fill gaps in scanned text
mediaproc image dilate scan.jpg -o filled_text.jpg

# Connect broken characters
mediaproc image dilate old_document.png -o restored.png

# Strengthen faded text
mediaproc image dilate faded.jpg -o strengthened.jpg

Dry Run Testing

Test dilation before processing:

# Preview dilation
mediaproc image dilate mask.png --dry-run

# Test batch operation
for file in *.png; do
  mediaproc image dilate "$file" --dry-run
done

Verbose Processing

Monitor dilation operations:

# See processing details
mediaproc image dilate mask.png -v -o dilated.png

# Debug batch processing
for file in *.jpg; do
  mediaproc image dilate "$file" -v -o "output/${file}"
done

How Dilation Works

Morphological Operation

Dilation examines each pixel and its 8 neighbors in a 3×3 grid:

Kernel:
1  1  1
1  1  1
1  1  1

Operation:
For each pixel, replace with MAXIMUM value in 3×3 neighborhood

Effect:

Bright pixels expand into neighboring dark pixels
Dark regions shrink
Small gaps and holes get filled
Objects grow in size

Visual Example

Before (binary):           After dilation:
0 0 0 0 0                 0 0 0 0 0
0 1 1 0 0                 1 1 1 1 0
0 1 0 1 0    →           1 1 1 1 1
0 0 1 1 0                 0 1 1 1 1
0 0 0 0 0                 0 0 1 1 0

Notice: Gap filled, regions connected, size increased

Common Use Cases

Hole Filling

# Fill small holes in binary mask
mediaproc image dilate mask_with_holes.png -o filled.png

# Close gaps in object
mediaproc image dilate broken_object.jpg -o complete_object.jpg

Text Processing

# Connect broken text characters
mediaproc image dilate degraded_text.png -o readable.png

# Thicken thin text
mediaproc image dilate thin_text.jpg -o bold_text.jpg

Medical Imaging

# Connect tissue regions
mediaproc image dilate tissue_scan.png -o connected_tissue.png

# Fill gaps in vessel detection
mediaproc image dilate vessels.jpg -o continuous_vessels.jpg

Object Detection Preparation

# Expand objects before detection
mediaproc image dilate objects.png -o expanded_objects.png

# Connect nearby features
mediaproc image dilate features.jpg -o connected_features.jpg

Best Practices

Work with Binary/Grayscale: Dilation works best on high-contrast or binary images
Multiple Iterations: Apply multiple times for stronger effects
Combine with Erosion: Use closing (dilate→erode) to fill holes without size change
Quality for Masks: Use PNG format for binary masks to preserve sharp edges
Test First: Use dry-run to verify operation before batch processing
Preserve Originals: Always keep original files for comparison
Monitor Results: Use verbose mode for troubleshooting

Morphological Workflows

Closing (Fill Holes)

# Remove small holes while preserving size
mediaproc image dilate input.png -o temp_dilated.png
mediaproc image erode temp_dilated.png -o closed.png
rm temp_dilated.png

Gradient (Edge Detection)

# Morphological gradient = dilated - eroded
# Highlights object boundaries
mediaproc image dilate input.png -o dilated.png
mediaproc image erode input.png -o eroded.png
# Subtract eroded from dilated using external tool

Top-Hat Transform

# Morphological top-hat = original - opened
# Extracts small bright features
# (opening = erode then dilate)
mediaproc image erode input.png -o temp1.png
mediaproc image dilate temp1.png -o opened.png
# Subtract opened from original

Performance Tips

Format Selection: PNG for binary masks, JPEG for grayscale
Quality Settings: Use lower quality for intermediate results
Batch Efficiency: Process similar images together
Iteration Control: More iterations = more processing time
File Size: Dilation doesn't significantly increase file size

Troubleshooting

Objects Too Large After Dilation

Problem: Dilated objects are too big.

Solutions:

# Use single dilation instead of multiple
mediaproc image dilate mask.png -o dilated.png

# Apply erosion after to shrink back
mediaproc image dilate mask.png -o temp.png
mediaproc image erode temp.png -o balanced.png
rm temp.png

Unwanted Regions Connected

Problem: Separate objects merged together.

Solutions:

# Use erosion to separate first
mediaproc image erode mask.png -o separated.png

# Apply weaker dilation (single pass only)
mediaproc image dilate separated.png -o result.png

Not Enough Effect

Problem: Gaps still visible after dilation.

Solutions:

# Apply multiple dilations
mediaproc image dilate mask.png -o temp1.png
mediaproc image dilate temp1.png -o temp2.png
mediaproc image dilate temp2.png -o strong_dilated.png
rm temp1.png temp2.png

# Use morphological closing
mediaproc image dilate mask.png -o temp_d.png
mediaproc image erode temp_d.png -o closed.png
rm temp_d.png

Quality Loss

Problem: Output looks pixelated.

Solutions:

# Increase quality
mediaproc image dilate mask.png -q 95 -o high_quality.png

# Use PNG for binary images
mediaproc image dilate binary.jpg -o dilated.png

# Ensure source is high resolution

Processing Grayscale Images

Problem: Dilation effect unclear on grayscale.

Solutions:

# Convert to binary first (use external tool for threshold)
# Then apply dilation
mediaproc image dilate binary.png -o dilated.png

# Or apply multiple dilations for stronger effect
mediaproc image dilate grayscale.jpg -o temp.jpg
mediaproc image dilate temp.jpg -o stronger.jpg
rm temp.jpg