From bd0eb609e7e81a1130587a120fe413e6234c1044 Mon Sep 17 00:00:00 2001
From: Michele Cereda <cereda.michele@gmail.com>
Date: Sun, 9 Jul 2023 14:49:46 +0200
Subject: [PATCH] chore: added a way to find visually similar images

---
 knowledge base/imagemagick.md              | 58 +++++++++++++++++-----
 knowledge base/parallel.md                 |  6 +++
 knowledge base/resize an image from cli.md |  6 +--
 3 files changed, 55 insertions(+), 15 deletions(-)

diff --git a/knowledge base/imagemagick.md b/knowledge base/imagemagick.md
index 8f6b49d..5d60c2f 100644
--- a/knowledge base/imagemagick.md	
+++ b/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
diff --git a/knowledge base/parallel.md b/knowledge base/parallel.md
index 75b6b29..ff1da28 100644
--- a/knowledge base/parallel.md	
+++ b/knowledge base/parallel.md	
@@ -35,6 +35,12 @@ parallel --group --jobs 100% --tag \
    | jq -r '.items[] | .metadata.name + \"\t\" + .spec.nodeName' -" \
   ::: "${NAMESPACES}" \
 | column -t
+
+# Given  a collection of images in the same working directory, find all those
+# that are at least 90% similar, but not equal, to another.
+parallel --tag "magick compare -metric NCC -quiet {} NULL: 2>&1; echo" \
+  ::: *.jpg *.jpeg *.png *.webp ::: *.jpg *.jpeg *.png *.webp \
+| grep '0\.9'
 ```
 
 ## Further readings
diff --git a/knowledge base/resize an image from cli.md b/knowledge base/resize an image from cli.md
index 35f6e94..9aa8240 100644
--- a/knowledge base/resize an image from cli.md	
+++ b/knowledge base/resize an image from cli.md	
@@ -1,12 +1,12 @@
 # Resize images using the CLI
 
-Leverages `convert` from `imagemagick`.
+Leverage `convert` from `imagemagick`:
 
 ```sh
-convert input.jpg -adaptive-resize 50% output.jpg
+magick convert -adaptive-resize '50%' 'in.jpg' 'out.jpg'
 
 # Scale down all images in a folder.
-ls -1 | xargs -I{} convert {} -adaptive-resize 50% {}_scaled.jpg
+ls -1 | xargs -I{} magick convert -adaptive-resize '50%' {} {}_scaled.jpg
 ```
 
 Further readings