How To Crop Images Using Command Line Tools Only

In this modern age, image manipulation is a common task that we perform almost daily. While there are numerous graphical tools available to perform such tasks, sometimes you might need to automate these tasks or use a command-line interface (CLI) due to the lack of a graphical interface. This article will guide you on how to crop images using command-line tools only. We will be using a powerful tool called ImageMagick.

Introduction to ImageMagick

ImageMagick is a robust collection of tools and libraries to read, write, and manipulate an image in any of the more popular image formats. It can crop, resize, rotate, apply various effects, and do much more. In this article, we will focus on how to use ImageMagick to crop images.

Installing ImageMagick

Before we start cropping images, we need to ensure that ImageMagick is installed on our system. You can install it using the package manager of your Linux distribution. For Ubuntu, you can use the following command:

sudo apt-get install imagemagick

For other distributions or operating systems, you can refer to the official ImageMagick installation instructions.

Cropping Images Using ImageMagick

ImageMagick provides two commands for cropping images: convert and mogrify.

Using the convert command

The convert command allows you to crop an image and save it as a new file. The syntax for the command is as follows:

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

In this command:

• input.jpg is the original image that you want to crop.
• W is the width of the crop rectangle.
• H is the height of the crop rectangle.
• X is the horizontal offset (distance from the left edge of the image to the left edge of the crop rectangle).
• Y is the vertical offset (distance from the top edge of the image to the top edge of the crop rectangle).
• output.jpg is the file name of the cropped image.

For example, if you want to crop a 100×100 pixel area from the top left corner of an image, you would use the following command:

convert input.jpg -crop 100x100+0+0 output.jpg

Using the mogrify command

The mogrify command is similar to the convert command, but it modifies the original image file instead of creating a new one. The syntax for the command is as follows:

mogrify -crop WxH+X+Y input.jpg

The parameters are the same as the convert command.

Using a Python Script

For more complex tasks, you might want to use a script. Here is an example of a Python script that uses ImageMagick to crop an image:

#!/usr/bin/env python3
import subprocess
import sys

img = sys.argv[1]
left = sys.argv[2]
right = sys.argv[3]
top = sys.argv[4]
bottom = sys.argv[5]

img_base = img[:img.rfind(".")]
extension = img[img.rfind("."):]
path = img[:img.rfind("/")]
img_out = img_base + "[cropped]" + extension

data = subprocess.check_output(["identify", img]).decode("utf-8").strip().replace(img, "")
size = [int(n) for n in data.replace(img, "").split()[1].split("x")]

w = str(size[0] - int(left) - int(right))
h = str(size[1] - int(top) - int(bottom))
x = left
y = top

cmd = ["convert", img, "-crop", w + "x" + h + "+" + x + "+" + y, "+repage", img_out]
subprocess.Popen(cmd)

This script takes five arguments: the image file path, and the number of pixels to crop from the left, right, top, and bottom. It then calculates the size of the crop rectangle and its offset, and uses the convert command to crop the image.

Conclusion

ImageMagick is a powerful tool that allows you to manipulate images directly from the command line. This can be very useful for automating tasks or working on systems without a graphical interface. With the knowledge from this article, you should now be able to crop images using command-line tools only.