On Being `undigital' with Digital Cameras: Extending Dynamic Range by Combining Differently Exposed Pictures

Most everyday scenes have a far greater dynamic range than can be recorded on a photographic lm or electronic imaging apparatus (whether it be a digital still camera, video, etc.). However, a set of pictures, that are identical except for their exposure, collectively show us much more dynamic range than any single picture. The dark pictures show us highlight details of the scene that would be washed out in a \properly exposed" picture, while the light pictures show us some shadow detail that would also not appear in a \properly exposed" picture. We propose a means of combining diierently exposed pictures to obtain a single picture of extended dynamic range, and improved color delity. Given a set of digital pictures, we may produce a single picture which is, for all practical purposes, `undigital', in the sense that it is a oating point image, with the kind of dynamic range we are accustomed to seeing in typical oating point representations, as opposed to the integer images from which it was generated. The method is completely automatic; it requires no human intervention, and it requires no knowledge of the response function of the imaging device. It works reliably with images from a digital camera of unknown response, or from a scanner with unknown response, scanning an unknown lm type.