Krita plugin for cleaning up scanned paper notes. There's an action variant for notes written with a pencil (graphite) and one for notes written with a pen (ink).

This plugin was written in a day to integrate my paper notes into my Obsidian vault. It is only tested on Linux, and only as far as "it works on my machine." Please exercise caution and back-up your files before you can verify that you are able to get a workflow with this plugin working.

Comparison

Input:

Output with added white background:

Installation

1. Copy the contents of this project's krita folder into your krita folder. On Linux, this is usually $HOME/.local/share/krita/. You can find the folder by pressing Settings -> Manage resources... -> Open Resource Folder.

2. Go to Settings -> Configure Krita... -> Python Plugin Manager and check the box for Clean paper notes to enable the plugin.

You can also install the files using GNU Stow as done in the included install.sh and uninstall.sh scripts.

Usage

1. The action cannot be undone so I recommend keeping your originals backed up and saving a processed copy instead of overwriting the original.

2. Before running the actions, clean up your image by cropping as close to the content area as possible and draw white over any elements you want to remove.

3. Select the appropriate action under Tools -> Scripts -> Clean paper notes. The action designed for pencil will darken the text a lot more than the one for ink, while the one for ink has some adjustments to retain colour.

4. To crop your picture afterwards, press Select -> Select Opaque -> Select Opaque (Replace) followed by Image -> Trim to Selection.

5. Export a copy of your image.

How it works

The plugin works by first altering levels to pull white closer to true white and the darkest colours towards black. It then converts white to alpha, and finally adjusts alpha so that all pixels below a certain opacity threshold are made fully transparent. In the ink version, this step also restores some brightness to colours.

Possible future improvements

There's room for improvement in this project, though it is admittedly unlikely that I make them as this project is a big ol' yak shave.

Batch processing

Batch processing should be doable, but was skipped due to trouble getting set active document to actually work.

Automatic cropping

Cropping is currently quite easy to do by just selecting opaque and cropping to selection. Unfortunately this has problems with race conditions and is quite unpredictable overall when automated.

Customisable filters

The project in its current iteration is written based on what I thought looked given the paper, pencils, inks, and scanner I used. This is almost definitely not something universal.