A new method and data encapsulation arrangement are disclosed for over-ranging color image data. The resulting data storage format renders color image data sets encoded in the over-ranging format compatible with in-range color image systems. Thus, color images including over-ranging portions will be readable by legacy systems that handle only in-range color data. The new arrangement of the color image data storage comprises a file header segment describing contents of a color image file. The new arrangement also includes an image data segment comprising digital image data representing a set of color image elements encoded in a signed over-ranged color space. A multi-partitioned color image bitmap data segment is created. A first partition in the multi-partitioned bitmap data segment includes image data corresponding to a first color image data word portion associated with an in-range color space. A second partition in the multi-partitioned bitmap data segment includes image data corresponding to a second color image data word portion associated with an over-ranging color space. The second partition may optionally include additional precision bits that are concatenated with the lowest precision in-range color channel data of the first partition.