Sentence:  Indeed, this latter process may have begun during the seventeenth century: Muizelaar and Van de Wetering have suggested that <WSD>'formatizing</WSD>' (the term sometimes used to describe the cutting down or adding to a picture, or changing its shape from oval to rectilinear as part of a predetermined scheme) may have been ... 
Meaning of the word marked with <WSD> tags:  To trim or add to a picture in order to make it fit into a standard frame size.