Prism-based color separation for professional digital photography

In the field of silver-halide photography, color separation was explored about a century ago, using filter mosaics, dichroic mirrors, three-shot filtration, and other techniques, before the dominant technology of multi-layered color film emerged. In the field of digital photography, the same techniques are being explored now in conjuction with silicon sensor technology. The three-shot technique, and the related tri-linear scanning technique, can deliver excellent images, but are awkward to employ and unsuitable for subjects that move. The filter-mosaic aproach is currently dominant in the digital camera market, but its inevitable aliasing artifacts limit its applicability in the professional end of the business. The use of dichroic mirrors, embedded in prisms as in color-TV cameras, has been attempted by a few camera vendors, so far with limited success. The demand for better digital images, however, has provided a continuing incentive to work on making this three-sensor approach feasible. Several key problems must be solved to make a viable professional camera using this approach: first, sensors with high enough resolution and image quality must be made at a cost that allows three of them to be included in a product; second, a prism must be designed for good color reproduction fidelity and must be economically and precisely manufactured; third, the three sensors must be optically aligned to the prism in a way that avoids ghost reflections and other problems; and finally, a whole new camera system needs to be designed around such a three-channel sensor assembly. This paper recounts some of the ways in which these problems are addressed in the design of the recently introduced Foveon Studio Camera, and provides qualitative assessments of the resulting advantages in image quality and usability.