Color calibration of multi-projector displays through automatic optimization of hardware settings

We describe a system that performs automatic, camera- based photometric projector calibration by adjusting hard- ware settings (e.g. brightness, contrast, etc.). The approach has two basic advantages over software-correction meth- ods. First, there is no software interface imposed on graph- ical programs: all imagery displayed on the projector ben- efits from the calibration immediately, without render-time overhead or code changes. Secondly, the approach benefits from the fact that projector hardware settings typically are capable of expanding or shifting color gamuts (e.g. trad- ing off maximum brightness versus darkness of black lev- els), something that software methods, which only shrink gamuts, cannot do. In practice this means that hardware settings can possibly match colors between projectors while maintaining a larger overall color gamut (e.g. better con- trast) than software-only correction can. The prototype system is fully automatic. The space of hardware settings is explored by using a computer- controlled universal remote to navigate each projector's menu system. An off-the-shelf camera observes each projec- tor's response curves. A cost function is computed for the curves based on their similarity to each other, as well as in- trinsic characteristics, including color balance, black level, gamma, and dynamic range. An approximate optimum is found using a heuristic combinatoric search. Results show significant qualitative improvements in the absolute colors, as well as the color consistency, of the display.