High dynamic range imaging by varying exposure time, gain and aperture of a video camera

Abstract

To generate high dynamic range (HDR) images usually the exposure time is the only parameter varied when acquiring the low dynamic range (LDR) image series. In this paper the f-number and the gain of the camera are also considered to be variable as exposure defining parameter. This enables HDR imaging for image acquisition systems with limited exposure time range to prevent motion blur. The impacts of the added parameters gain and f-number are analyzed. Since common HDR image generating algorithms require the exposure time as input, an approach to estimate an equivalent exposure time by the used parameter set (exposure time, f-number and camera gain) is shown. Further this equivalent exposure time can also be estimated without a priori knowledge of the parameter set. At the end of the paper a quality assurance application is shown, where this extended parameter set was used and proved necessary for the HDR image acquisition.