Issues with common assumptions about the camera pipeline and their impact in hdr imaging from multiple exposures

Multiple-exposure approaches for high dynamic range (HDR) image generation share a set of building assumptions: that color channels are independent and that the camera response function (CRF) remains constant while changing the exposure. The first contribution of this paper is to highlight how these assumptions, which were correct for film photography, do not hold in general for digital cameras. As a consequence, results of multiexposure HDR methods are less accurate, and when tonemapped they often present problems like hue shifts and color artifacts. The second contribution is to propose a method to stabilize the CRF while coupling all color channels, which can be applied to both static and dynamic scenes, and yield artifact-free results that are more accurate than those obtained with state-of-the-art methods according to several image metrics.The work of the authors was supported by the European Unions Horizon 2020 research and innovation programme grant 761544 (project HDR4EU) and grant 780470 (project SAUCE) and by the Spanish government and FEDER fund grant TIN2015-71537-P (MINECO/FEDER,UE). The work of the second author was supported by the Spanish government under grant IJCI-2014-19516