Novel Degrees of Flexibility in Computational Cameras

    

    

Text Box: Top-Left: Two shiftable layers of CMY color filter arrays (CFAs) and their effective combination (bottom most layers). The combination is (a) CMY CFA before shift, (b) RGB CFA after a horizontal shift, (c) RGBCMY after a diagonal shift. Top-Right: Our prototype camera that can switch between RGB and CMY modes using a mechanical shift. Bottom-left: Our prototype camera that can switch between LDR and HDR modes using the same concept. Bottom-right: Images captured with the camera in LDR and HDR modes; the higher dynamic range achieved at the price of sacrificed resolution.

Camera consumers are forced to live with several trade-offs originating from conflicting demands on the quality. For example, broad-band filters (e.g. CMY), being more light efficient than narrow-band filters (e.g. RGB), are desired for low-illumination scenes (e.g. night/dark scenes). But, they result in more noise in lighted scenes and have lower color fidelity. However, since current cameras come with fixed RGB or CMY CFAs, users have to accept sub-optimal image quality either for dark or bright scenes.

Similarly, faithful capture of colourful scenes demand more than three primaries that trades off the spatial resolution making it not suitable for architectural scenes with detailed patterns and facades. However, since current cameras come with a fixed number of primaries, users cannot change the spatial and spectral resolution as demanded by the scene conditions. Single shot HDR cameras suffer from a similar trade-off, sacrificing the resolution to achieve a higher dynamic range.

Switchable Modes Using Shiftable CFAs

We tried to overcome such limitations by offering new degrees of flexibility using novel optical designs and computational methods. We observed that by using multiple layers of color filter arrays that can precisely move on top of each other, one can switch between different color primaries (e.g. RGB/CMY/RGBCMY) or generally, different operational modes (e.g. LDR/HDR). This allows the photographers to choose different trade-offs based on the nature of the scene and the purpose of the photography. We demonstrated this concept using several preliminary prototypes that can encourage the use of such ideas in consumer level cameras.

Publications:

Behzad Sajadi, Aditi Majumder, Kazuhiro Hiwada, Atsuto Maki, Ramesh Raskar, Switchable Primaries Using Shiftable Layers of Color Filter Arrays, ACM Siggraph, 2011 ( Video, Presentation)