Resize Image Skill

This skill allows you to resize images using ImageMagick's convert command when they are too large to view or process.

When to Use

• When reading an image file fails due to token limits
• When an image is too large to process
• When you need to create a thumbnail or smaller version of an image
• When a user provides a mockup or screenshot that's too large

Prerequisites

ImageMagick must be installed. Check with:

which convert || echo "ImageMagick not installed"

If not installed, suggest the user install it:

• Ubuntu/Debian: sudo apt-get install imagemagick
• macOS: brew install imagemagick

Instructions

Step 1: Check the original image size

identify "/path/to/image.png"

This shows dimensions and file size.

Step 2: Resize the image

Resize to a maximum width/height while maintaining aspect ratio:

convert "/path/to/original.png" -resize 800x600\> "/tmp/resized-image.png"

The \> flag ensures the image is only shrunk, never enlarged.

Common resize options:

• -resize 800x600 - Fit within 800x600, maintain aspect ratio
• -resize 50% - Scale to 50% of original size
• -resize 400x - Set width to 400px, auto-calculate height
• -resize x400 - Set height to 400px, auto-calculate width

Step 3: Reduce quality/colors for smaller file size (optional)

For PNG files, reduce colors:

convert "/path/to/original.png" -resize 800x600\> -colors 256 "/tmp/resized-image.png"

For JPEG files, reduce quality:

convert "/path/to/original.jpg" -resize 800x600\> -quality 80 "/tmp/resized-image.jpg"

Step 4: Read the resized image

# Verify the new size
ls -la /tmp/resized-image.png
identify /tmp/resized-image.png

Then use the Read tool to view the resized image:

Read /tmp/resized-image.png

Examples

Example 1: Resize a large mockup

# Check original size
identify "/mnt/c/Users/user/mockup.png"
# Output: mockup.png PNG 2400x1800 ...

# Resize to fit within 800x600
convert "/mnt/c/Users/user/mockup.png" -resize 800x600\> "/tmp/mockup-small.png"

# Verify
identify "/tmp/mockup-small.png"
# Output: mockup-small.png PNG 800x600 ...

Example 2: Create a thumbnail

convert "/path/to/screenshot.png" -resize 400x -colors 128 "/tmp/thumbnail.png"

Example 3: Batch resize multiple images

for img in /path/to/images/*.png; do
  convert "$img" -resize 800x600\> "/tmp/$(basename "$img")"
done

Output Location

Always save resized images to /tmp/ with a descriptive name:

• /tmp/resized-mockup.png
• /tmp/thumbnail-screenshot.png
• /tmp/small-diagram.png

Troubleshooting

"convert: command not found" ImageMagick is not installed. Ask the user to install it.

"convert: unable to open image" Check the file path. Windows paths under WSL should use /mnt/c/... format.

Image still too large after resize Try reducing colors or quality, or resize to smaller dimensions.