Computer-implemented methods and apparatus for converting a computer graphics illustration that includes a plurality of overlapping artwork elements from an input format to an output format that differs from the input format. The overlapping artwork elements are classified as transparent or non-transparent artwork elements. The transparent artwork elements are classified as being compatible or incompatible with the output format. The incompatible transparent artwork elements and any of the artwork elements that are at least partially overlapped by any of the incompatible transparent artwork elements are transformed into transformed artwork elements, without transforming any compatible artwork element that is not overlapped by an incompatible transparent artwork element. The transformed artwork elements are compatible with the output format.