German geometric abstraction

I have been following contemporary German art for the past few years.  The early 20th century Russian avant garde pioneer of geometric abstraction Kazimir Malevich has been a major inspiration for the German artist Imi Knoebel's artistic creations.  While Malevich's approach to art is almost religious, Knoebel's is apparently more playful.  I was ecstatic to find Knoebel's installation Genter Raum at Duesseldorf's K21 last summer:

Another German artist Gerhard Richter's artistic practice is more diversified.  He has simultaneously produced abstract and photorealistic works.  I saw the paintings from his Colour Charts series at Duisburg's Museum Küppersmühle für Moderne Kunst in 2009: