Generating pictures using random permitting context

We use random context picture grammars to generate pictures through success ive refinement. At any stage a picture consists of a shape divided into sma ller shapes, each containing a variable or terminal. A variable may be rewr itten according to a production of the underlying grammar, which entails ei ther dividing the shape containing it into smaller shapes, or substituting a variable or terminal for it. A production may depend on context randomly distributed in the intermediate picture. Context is classified as either pe rmitting or forbidding, the former enabling the application of a production , the latter inhibiting it. For visualization purposes every terminal is as sociated with a color, and its shape filled with that color. We show examples of pictures generated with random context picture grammars . Then we concentrate on grammars which use permitting context only and pre sent a pumping lemma for the corresponding picture sets.