1. Introduction to User Filters

1.1 What is User Filter

User Filter is a Gimp plugin that allows for user defined algorithms to be applied to a Gimp drawable (i.e. an image layer or a selection). It is in this aspect similar to, yet allows for more complex filters, the convolution matrix filter of Gimp (in fact, you can also do a convolution matrix filter with User Filter, but the normal convolution matrix filter is better optimized for that task).

User filter allows for users with no real programming skill (or patience to work on graphical user interfaces) to quickly develop new effects. The difficulty of creating a new user defined filter ranges from „easy“ (simple colour manipulation) to „complex“ (applying complex mathematical formulas to the image).

1.2 Usages of User Filter

The possible applications tat this filter can be used with are many. We will list the most interesting here.

1.2.1 Creating Gradients with User Filter

This can be considered a „rendering“ filter where you can apply a simple formula to change the colour values in an image depending on the current horizontal and vertical position the filter is working on. You can create nice gradients and save them for later use, or you can also develop a general-purpose gradient editor.

1.2.2 Creating Patterns with User Filter

Sometimes, one needs patterns to be applied to the images one is working with. Normally, one would then create such a pattern in an external program which is better fit for this task and import it into Gimp. With User Filter, you can write a filter that can create patterns of all sorts, adjustable by parameters – that way you don't have to draw the patterns by hand but only to adjust a couple of sliders to control the outcome of the filter.

1.2.3 Creating Image Borders with User Filter

Image borders are similar to the pattern application (used as a mask). You can use User Filter to write a filter that creates borders (bevels or masks) for an image.

1.2.4 Manipulating Images User Filter

You can also directly manipulate an image with a user defined filter. This means that you can manipulate the colours of the image as well as its bitmap.

1.2.4.1 Color Effects

This is the easiest application of all...

1.2.4.2 Bitmap Effects

2. Creating Filters with User Filter

1. Introduction to User Filters

1.1 What is User Filter

1.2 Usages of User Filter

1.2.1 Creating Gradients with User Filter

1.2.2 Creating Patterns with User Filter

1.2.3 Creating Image Borders with User Filter

1.2.4 Manipulating Images User Filter

1.2.4.1 Color Effects

1.2.4.2 Bitmap Effects

2. Creating Filters with User Filter

2.1 Creating New Filters

2.2 Filter Expressions

2.2.1 Constants

2.2.2 Variables

2.2.3 Functions

2.2.4 Operators

2.3 Saving / Exporting Filters

2.4 Loading Existing Filters

2.5 Examples

2.5.1 (simple Filter Name here)

2.5.2 (more complex Filter Name here)

2.5.3 (even more complex Filter Name here)