Image Collages with ImageMagick

Create Professional Academic Figures with Labeled Subfigures

Author

Dr. Md Abdus Samad

Published

January 24, 2026

Why ImageMagick for Academic Figures?

NoteIntroduction

Image collages are essential for academic papers, presentations, and technical documentation. ImageMagick provides powerful command-line tools to create professional multi-panel figures with labeled subfigures like (a), (b), (c) - perfect for journal submissions.

What We’ll Create

A collage layout with:

  • Top row: Two images side by side (labeled a and b)
  • Bottom row: One centered image (labeled c)
  • Labels positioned below each image
  • Consistent spacing between images
  • High resolution output (1500 DPI)
  • Clean borders and professional appearance

Prerequisites

  • ImageMagick installed on your system
  • Three source images: Fig_1x.png, Fig_1y.png, Fig_1z.png

The Complete Command

VS Code: Open integrated terminal with Ctrl+ ` (backtick)

magick Fig_1x.png -background white -gravity center -extent "%[fx:w]x%[fx:h+200]" -pointsize 80 -gravity South -annotate +0+20 '(a)' a_labeled.png && magick Fig_1y.png -background white -gravity center -extent "%[fx:w]x%[fx:h+200]" -pointsize 80 -gravity South -annotate +0+20 '(b)' b_labeled.png && magick Fig_1z.png -background white -gravity center -extent "%[fx:w]x%[fx:h+200]" -pointsize 80 -gravity South -annotate +0+20 '(c)' c_labeled.png && magick a_labeled.png b_labeled.png +append -background white -gravity center -extent "%[fx:w+20]x%[fx:h]" top_row.png && magick c_labeled.png -background white -gravity center -extent "%[fx:max(w,3000)]x%[fx:h]" bottom_row.png && magick top_row.png bottom_row.png -background white -append -gravity center -extent "%[fx:w]x%[fx:h+20]" -resize 3000x3000\> temp_collage.png && magick temp_collage.png -trim +repage -bordercolor white -border 50 -density 1500 -units PixelsPerInch Fig_1_collage.png

Step-by-Step Breakdown

Step 1: Add Labels to Each Image

magick Fig_1x.png -background white -gravity center -extent "%[fx:w]x%[fx:h+200]" -pointsize 80 -gravity South -annotate +0+20 '(a)' a_labeled.png
Option Description
-extent "%[fx:w]x%[fx:h+200]" Adds 200 pixels of white space below the image
-pointsize 80 Sets the label font size to 80 points
-gravity South Positions text at the bottom center
-annotate +0+20 '(a)' Places the label “(a)” 20 pixels from the bottom

This process repeats for figures (b) and (c).

Step 2: Create the Top Row

magick a_labeled.png b_labeled.png +append -background white -gravity center -extent "%[fx:w+20]x%[fx:h]" top_row.png
Option Description
+append Combines images horizontally (side by side)
-extent "%[fx:w+20]x%[fx:h]" Adds 20 pixels horizontal gap between images

Step 3: Prepare the Bottom Row

magick c_labeled.png -background white -gravity center -extent "%[fx:max(w,3000)]x%[fx:h]" bottom_row.png

Centers the single bottom image with proper width matching.

Step 4: Combine Rows and Finalize

magick top_row.png bottom_row.png -background white -append -gravity center -extent "%[fx:w]x%[fx:h+20]" -resize 3000x3000\> temp_collage.png
Option Description
-append Stacks images vertically
-extent "%[fx:w]x%[fx:h+20]" Adds 20 pixels vertical gap between rows
-resize 3000x3000\> Ensures maximum dimension is 3000 pixels (only shrinks if larger)

Step 5: Final Touch-ups

magick temp_collage.png -trim +repage -bordercolor white -border 50 -density 1500 -units PixelsPerInch Fig_1_collage.png
Option Description
-trim +repage Removes excess white space from edges
-border 50 Adds clean 50-pixel white border around the entire collage
-density 1500 -units PixelsPerInch Sets output to high-resolution 1500 DPI

Customization Options

Adjust Label Position

Change the annotate offset to move labels:

-annotate +0+40 '(a)'  # Further from image
-annotate +0+10 '(a)'  # Closer to image

Modify Label Size

-pointsize 60   # Smaller labels
-pointsize 100  # Larger labels

Change Spacing Between Images

-extent "%[fx:w+40]x%[fx:h]"  # 40px horizontal gap
-extent "%[fx:w]x%[fx:h+40]"  # 40px vertical gap

Adjust Border Size

-border 100  # Thicker border
-border 20   # Thinner border

Removing Metadata from Images

WarningWhy Remove Metadata?

When publishing images, especially for academic or professional use, you may want to remove metadata (EXIF data, GPS coordinates, camera settings, software information) for privacy or to reduce file size.

Reasons to Remove Metadata

  • Privacy: EXIF data can contain location information, timestamps, and device details
  • File Size: Removing metadata reduces file size
  • Clean Output: Professional publications often require clean images without embedded metadata
  • Security: Prevents unintended information disclosure

Quick Metadata Removal

Remove Metadata from Single Image:

magick input.png -strip output.png

Remove Metadata from Multiple Images:

magick Fig_1x.png -strip Fig_1x.png
magick Fig_1y.png -strip Fig_1y.png
magick Fig_1z.png -strip Fig_1z.png

In-Place Metadata Removal (Overwrite Original):

magick mogrify -strip *.png
CautionWarning

This overwrites original files. Make backups first!

Integrate Stripping into Collage Creation

Add -strip to your collage command to ensure the final output has no metadata:

magick temp_collage.png -trim +repage -bordercolor white -border 50 -density 1500 -units PixelsPerInch -strip Fig_1_collage.png

Verify Metadata Removal

Method 1: Using ImageMagick

magick identify -verbose Fig_1_collage.png | head -50

Stripped images show minimal information (just dimensions, format, and basic properties).

Method 2: Using ExifTool

exiftool Fig_1_collage.png

Output should show very minimal metadata.

Method 3: Compare File Sizes

ls -lh original.png stripped.png

The stripped version is typically smaller.

Method 4: Count Metadata Lines

# Before stripping
magick identify -verbose original.png | wc -l

# After stripping
magick identify -verbose stripped.png | wc -l

Stripped images will have significantly fewer lines of output.

What Gets Removed with -strip?

The -strip option removes:

Metadata Type Description
EXIF data Camera settings, timestamps
GPS coordinates Location information
Thumbnail images Embedded previews
Color profiles ICC profiles
Comments Annotations and notes
Software information Editing software details
Copyright metadata Rights information
XMP data Extensible metadata
IPTC data Press and media metadata

When NOT to Strip Metadata

TipKeep Metadata When Needed

Don’t remove metadata if you need:

  • Color profiles for accurate color reproduction
  • Copyright information for attribution
  • Camera settings for photography analysis
  • GPS data for mapping applications

Selective Metadata Removal

If you want to keep color profiles but remove other metadata:

magick input.png -define png:exclude-chunks=date,time input.png

Or preserve only specific metadata:

magick input.png -strip -set comment "My custom description" output.png

Batch Processing Script

For processing many images at once:

#!/bin/bash
for img in *.png; do
    magick "$img" -strip "cleaned_$img"
done

This creates new files with the cleaned_ prefix.

Quick Reference

Task Command
Label an image magick img.png -pointsize 80 -gravity South -annotate +0+20 '(a)' labeled.png
Horizontal append magick a.png b.png +append row.png
Vertical append magick top.png bottom.png -append collage.png
Add border magick img.png -border 50 bordered.png
Set DPI magick img.png -density 1500 -units PixelsPerInch output.png
Remove metadata magick img.png -strip clean.png
Batch strip magick mogrify -strip *.png
TipKey Takeaways
  • Use -extent and -annotate for precise label positioning
  • Use +append for horizontal and -append for vertical combinations
  • Always set appropriate DPI with -density for print quality
  • Use -strip to remove all metadata from final outputs
  • Verify metadata removal with identify -verbose or exiftool