Gimp

Basic actions

• Create squares, ellipses, circles
  • This is done by stroking paths. Eg. to create a rectangle:
    1. If needed, create a new layer.
    2. Create a rectangle using the Rectangle Select Tool.
    3. Transform selection into path with Select → To Path.
    4. Stroke the path with Edit → Stroke Path.
  • Instead of stroking the path, the selection can be stroked as well with Edit → Stroke Selection. 3rdd step above can be skipped in that case.
  • The GIMP keeps track of all used path, so converting to path is handy to reuse previous paths. Check the dialog box Layers, Channels, Paths, Undos.

Plugins and scripts

Fourier plugin

• Download the fourier plugin.
• Install a few packages:

sudo apt-get install libfftw3-dev libgimp2.0-dev

• Build and install the plugin:

make
make install

Descreen scriptfu

• Download the Descreen plugin.
• Copy the script into ~/.gimp-2.8/scripts.
• Restart gimp or select Scriptfu → refresh scripts. The script appears in Enhance → Descreen.

How-To

Remoe Moiré effect on a photo scan

• Apply Filter → Blur → Gaussian Blur effect.

• Pick method RLE, and adapt radius until the moiré disappear (4 or 5 px, possibly more).