Methods, apparatuses, and computer readable storage mediums for generating an object representation from a bitmap image by selecting a set of regions, including a background region, from the bitmap image. Color and partial transparency parameters of a first graphical object with partial transparency that overlaps a second graphical object are estimated according to colors of the set of regions. The estimated color and partial transparency are consistent with a transparency compositing model. Geometric models of the first and second graphical objects are constructed from the set of regions and the estimated color and transparency parameters of the first graphical object. The object representation is generated dependent upon the geometric models. The object representation may be an electronic document and the bitmap image may be a scanned version of a document.