A study of dark current in digital imagers in digital single- lens reflex (DSLR) and compact consumer-grade digital cameras is presented. Dark current is shown to vary with temperature, expo- sure time, and ISO setting. Further, dark current is shown to in- crease in successive images during a series of images. DSLR and compact consumer cameras are often designed such that they are contained within a densely packed camera body, and therefore the digital imagers within the camera frame are prone to heat generated by the sensor as well as nearby elements within the camera body. It is the scope of this work to characterize the dark current in such cameras and to show that the dark current, in part due to heat gen- erated by the camera itself, can be corrected by using hot pixels on the imager. This method generates computed dark frames based on the dark current indicator value of the hottest pixels on the chip. We compare this method to standard methods of dark current correction. © 2010 SPIE and IS&T. DOI: 10.1117/1.3358365 mation. However, there are problems associated with this method of correction. Foremost, this method is time con- suming, as it is required after every exposure. Furthermore, the camera will not be under identical conditions for the second frame due to the generation of the first image itself. As is shown in this work, the dark current is not consistent from frame to frame and shows increasing dark current with increasing number of frames taken in succession. This is likely due to an increase in the internal temperature of the camera. In addition, due to the statistical nature of the dark current, even dark frames taken under identical condi- tions will not necessarily have the same amount of dark noise. The very attributes that define the compact consumer class of camera, their affordability and compact size, are likely indicators that dark noise is a greater issue in this class of camera. Dark noise is caused by defects and impu- rities within the silicon of the pixel. 3-5 The price point of compact consumer cameras would seem to indicate that the best digital imagers, in terms of lowest impurities and therefore lowest dark noise, would be selectively chosen for more expensive, higher-end cameras. Consumer cam- eras are generally not cooled, and therefore heat will be
['Justin Charles Dunlap', 'Erik Bodegom', 'Ralf Widenhorn']
Correction of dark current in consumer cameras