In 1971 Frederic Rossif made "Georges Matthieu ou la fureur d'être", a film about the French painter. Not only is the score by Vangelis throughout, there's a long segment in which Vangelis improvises on keyboards and other instruments while Matthieu paints, drawing parallels between the two art forms.
Last year, to mark the film's 25th anniversary, it was issued on DVD. As well as having half an hour of Vangelis music, it's an interesting watch. It's in French but has English subtitles. I bought it direct from the distributor, from http://www.georgesmathieu-themovie.com/en_buy.html
paying by PayPal. They were very efficient and I had the DVD within a few days. Highly recommended.