_drafts | Setup ImageMagick

Setup ImageMagick

[last update: 02 Apr 2018]

tools

ImageMagick is a powerful open source commandline utility for processing image files that is used under the hood by numerous other tools and websites. Once you get the hang of it, you can use it directly to do a lot of interesting things, from simple batch conversions to complex rendering.

Note: ImageMagick commands made a major change between version 6 and 7+. The docs on the main website refer to version 7+, where all commands start with magick. Previous versions used several different commands, such as convert, instead. A mirror site contains all documentation about “legacy” ImageMagick.

Install ImageMagick

Install ImageMagick and Ghostscript (which enables it to work with PDFs). Setup is easy on Linux, however, it will likely be a legacy version (see note above):

Ubuntu: sudo apt install imagemagick ghostscript.
Fedora: sudo dnf install ImageMagick ghostscript.

On Windows:

Download the ImageMagick installer.
Run the installer with default options.
Download the Ghostscript installer (you probably want the AGPL Windows 64 bit version).
Run the installer with default options.

Also on Windows, if you want to follow the commands in this note, be sure to have a bash terminal, such as Git Bash (packaged with Git installer) or Cmder.

Using ImageMagick

The full ImageMagick docs do a nice job of introducing commandline processing concepts. However, here is the basics.

Basic pattern: <command> <image options> <input filename(s)> <image operator(s)> <output filename(s)>

First, use a built in pattern to create a test image: magick -size 640x480 pattern:checkerboard checkerboard.png

Convert into a JPEG: magick checkerboard.png output.jpg

Resize: magick checkerboard.png -resize 75% out2.png

Crop: magick checkerboard.png -crop 120x120+10+5 test-cr.png

Combine all PNG in the folder into a PDF: magick *.png test.pdf

Combine all JPEG in the folder into a GIF: magick *.jpg test.gif

Create an image from first page of PDF: magick test.pdf[0] new.jpg

Resize all PNG in a folder, convert to JPEG, and sequentially number: magick *.png -resize 200x200 thumb%d.jpg

Resize all PNG in a folder, convert to JPEG, but keep original file name: magick *.png -resize 300x300 -set filename:f '%t' '%[filename:f]-thumb.jpg'

Check the commandline options page for more details.

Create PDF Thumbs

In this example, I want to create an image representing a PDF by grabbing the first page from each PDF in a directory and creating a JPEG. A few approaches:

use Magick’s batch abilities: magick *.pdf[0] -resize x500 -set filename:f '%t' '%[filename:f]-thumb.jpg'
use simple Magick command in a Bash loop: for f in *.pdf; do magick "$f"[0] -resize x500 -flatten "${f%.pdf}.jpg"; done

For higher quality result, add -density 600, for example: for f in *.pdf; do magick -density 600 "$f"[0] -resize x500 -flatten "${f%.pdf}.jpg"; done. Before working with the PDF, Magick must render it at a specific resolution. The default density is 72 dpi, so bumping it up to 300 or 600 will greatly enhance the quality of most image, but also significantly slow processing.

If you need higher speed processing the PDFs, it might be faster to use Ghostscript or Xpdf directly to create the images:

Ghostscript: for f in *.pdf; do gs -q -o "${f%.pdf}.jpg" -sDEVICE=jpeg -dLastPage=1 -r300 "$f"; done gets the images.
Xpdf tools provides the pdftopng utility that can quickly create PNG images from PDFs. For example, for f in *.pdf; do pdftopng -l 1 -r 300 "$f" "${f%.pdf}"; done, would grab the first page at 300 dpi.

Then use magick to resize the JPEGs, something like for f in *.jpg; do magick "$f" -thumbnail x800 -flatten "${f%.jpg}-sm.jpg"; done.

If ImageMagick seems too slow, you can try GraphicsMagick which implements all the same tools and options, but is more optimized for speed. In the example commands above, the only difference is magick would be replaced with gm convert. When working with images of very large pixel dimensions, gm seems more efficient than magick.

PDF Error on Ubuntu

If you are using the older version of ImageMagick installed from Ubuntu repository (v. 6.9.x, and thus using convert), you will probably get an error trying to create images from PDFs. Version 6 had a security policy against using Ghostscript functions due to an security issue in gs. However, the Ghostscript version in the repositories is more up to date than the ImageMagick version–so the issue probably doesn’t apply.

Check your Ghostscript version:

gs -v

If you have > 9.24, you can safely override ImageMagick’s policy. Open the policy file:

sudo nano /etc/ImageMagick-6/policy.xml

Find this section:

<!-- disable ghostscript format types -->
  <policy domain="coder" rights="none" pattern="PS" />
  <policy domain="coder" rights="none" pattern="PS2" />
  <policy domain="coder" rights="none" pattern="PS3" />
  <policy domain="coder" rights="none" pattern="EPS" />
  <policy domain="coder" rights="none" pattern="PDF" />
  <policy domain="coder" rights="none" pattern="XPS" />

Then comment it out:

<!-- disable ghostscript format types -->
<!--
  <policy domain="coder" rights="none" pattern="PS" />
  <policy domain="coder" rights="none" pattern="PS2" />
  <policy domain="coder" rights="none" pattern="PS3" />
  <policy domain="coder" rights="none" pattern="EPS" />
  <policy domain="coder" rights="none" pattern="PDF" />
  <policy domain="coder" rights="none" pattern="XPS" />
-->

And save.

Random helpful things

Sometimes TIFF files have compression inside, which some other utilities can’t read. You can pass them through imagemagick to resave uncompressed: magick compressed.tif out.tif

Or as a batch:

for f in *.tif; do magick "$f" -set filename:f '%t' 'magick-%[filename:f].tif'; done