chore: added a way to find visually similar images

knowledge base/imagemagick.md

@@ -2,36 +2,70 @@
 
 Components:
 
+- `compare`: diff tool
 - `convert`: image conversion tool
 
+## Table of contents <!-- omit in toc -->
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+1. [Sources](#sources)
+
 ## TL;DR
 
 ```sh
-# scale an image to 50% its original size
-convert IMG_20200117_135049.jpg -adaptive-resize 50% IMG_20200117_135049_resized.jpg
+# Scale images to 50% its original size.
+magick convert -adaptive-resize '50%' 'in.jpg' 'out.jpg'
 
-# create a gif using images
-magick *.jpg images.gif
+# Create GIFs from single images.
+magick *.jpg 'out.gif'
 
-# convert n images to individual pdf pages
-magick *.jpg +adjoin page-%d.pdf
+# Convert N images into individual PDF documents.
+magick *.jpg +adjoin 'page-%d.pdf'
 
-# convert n images to a single pdf document
-magick *.png out.pdf
+# Convert N images into pages of a single PDF document.
+magick *.png 'out.pdf'
+
+# Calculate the percentage of *similarity* between 2 images.
+# Avoid saving the diff.
+magick compare -metric 'NCC' 'in_1.jpg' 'in_2.jpg' NULL:
+
+# Output only the differences between 2 images.
+magick compare -compose 'src' -fuzz '5%' 'in_1.jpg' 'in_2.jpg' 'diff.jpg'
 ```
 
 ## Further readings
 
 - [Website]
-- [cheat.sh/convert]
-
-[cheat.sh/convert]: https://cheat.sh/convert
-[website]: https://imagemagick.org
+- [image similarity comparison]
 
 ## Sources
 
+All the references in the [further readings] section, plus the following:
+
+- [cheat.sh/convert]
+- [cheat.sh/compare]
 - [Converting Multiple Images into a PDF File]
 - [How to Quickly Resize, Convert & Modify Images from the Linux Terminal]
+- [Diff an image using ImageMagick]
+- [ImageMagick compare without generating diff image]
 
+<!--
+  references
+  -->
+
+<!-- upstream -->
+[image similarity comparison]: https://imagemagick.org/script/compare.php
+[website]: https://imagemagick.org
+
+<!-- article sections -->
+[further readings]: #further-readings
+
+<!-- knowledge base -->
+<!-- others -->
+[cheat.sh/compare]: https://cheat.sh/compare
+[cheat.sh/convert]: https://cheat.sh/convert
 [converting multiple images into a pdf file]: https://legacy.imagemagick.org/discourse-server/viewtopic.php?p=144157&sid=e7706233f81874af86ffbbf3e57b1e76#p144157
+[diff an image using imagemagick]: https://stackoverflow.com/questions/5132749/diff-an-image-using-imagemagick
 [how to quickly resize, convert & modify images from the linux terminal]: https://www.howtogeek.com/109369/how-to-quickly-resize-convert-modify-images-from-the-linux-terminal/
+[imagemagick compare without generating diff image]: https://unix.stackexchange.com/questions/612067/imagemagick-compare-without-generating-diff-image