How to Crop an Image with ImageMagick Convert?

Using the ImageMagick convert command to crop an image to a specific size requires the -crop geometry option. This powerful command-line utility allows you to define the exact width and height of the output image, along with optional X and Y offsets to pinpoint the exact area you want to extract. Whether you need a quick center-crop or a precise slice from the top-left corner, mastering the basic geometry syntax ensures fast and efficient image manipulation directly from your terminal.

The Basic Syntax

The fundamental syntax for cropping an image with ImageMagick relies on specifying the target dimensions and the starting coordinates.

convert input.jpg -crop WidthxHeight+X+Y output.jpg

• Width: The desired width of the cropped image in pixels.
• Height: The desired height of the cropped image in pixels.
• X (Horizontal Offset): The distance in pixels from the left edge to start the crop.
• Y (Vertical Offset): The distance in pixels from the top edge to start the crop.

Note: If you omit the +X+Y offsets (e.g., convert input.jpg -crop 300x200 output.jpg), ImageMagick will tile the entire image into multiple 300x200 pixel segments. Always include offsets if you only want a single, specific cut.

Practical Examples

Here are the most common scenarios you will encounter when cropping images.

1. Cropping from a Specific Coordinate

To extract a 400x300 pixel area starting 50 pixels from the left and 100 pixels from the top, use the following command:

convert photo.png -crop 400x300+50+100 cropped_photo.png

2. Cropping from the Center

Cropping from the exact center of an image is a frequent requirement for creating thumbnails. By combining the -gravity option with -crop, you can change the origin point from the top-left corner to the center.

convert photo.png -gravity Center -crop 500x500+0+0 center_cropped.png

When using -gravity Center, setting the offsets to +0+0 ensures the crop happens perfectly dead-center.

3. Using Different Gravity Anchors

The -gravity option supports various compass directions, allowing you to crop relative to different edges of the image.

For example, to crop a 300x300 square from the bottom-right corner of an image:

convert photo.png -gravity SouthEast -crop 300x300+0+0 bottom_right.png

Handling Image Canvas Reset

ImageMagick sometimes preserves the original image’s canvas size metadata (virtual canvas) after a crop, which can cause unexpected layout behavior in certain viewers or web browsers. To completely discard the original canvas data and set the new image boundaries as the absolute layout, append the +repage option immediately after the crop command:

convert photo.jpg -crop 600x400+10+20 +repage final_output.jpg