I had a set of many scanned images from magazine pages, the sizes were varying and I wanted to apply the GIMP erode filter to enhance the text readability. Generally for image batch processing I use Imagemagick from the command line, but I was not able to reproduce the erode filter with Imagemagick, so I searched the recipe to do batch processing with the GIMP.

You can apply the erode filter in GIMP from menu Filters ⇒ Generic ⇒ Erode. There is no dialog box to control the filter parameters, but it turned out that when you want to call the plug-in-erode function from a script you have to pass several parameters.

To inspect the required parameters go to menu Filters ⇒ Script-Fu ⇒ Console ⇒ Browse. Here you are into the Script-Fu Procedure Browser and you can search for the plug-in-erode procedure. For each parameter you have the type (e.g. float or integer) and a brief description:

• run-mode
• image
• drawable
• propagate-mode
• propagating-channel
• propagating-rate
• direction-mask
• lower-limit
• upper-limit

It is not simple to have an explanation of each paramter, so I proceeded by trials. It turned out that the wanted result is obtaiuned by passing propagate-mode = O:white. I set to zero the other parameters too.