Extended use of incremental signal-to-noise ratio as reliability criterion for multiple-slope wide-dynamic-range image capture

摘要

Mobile applications present new image quality chal-nlenges. Automotive vision requires reliable capture of scene detail.nPhotospace measurements have shown that the extremely wide in-ntrascene dynamic range of traffic scenes necessitates wide-ndynamic-range (WDR) technology. Multiple-slope complementarynmetal-oxide semiconductor (CMOS) technology adaptively extendsndynamic range by partially resetting the pixel, resulting in a re-nsponse curve with piecewise linear slopes of progressively increas-ning compression. As compression and thus dynamic range increase,na trade-off against detail loss is observed. Incremental signal-to-nnoise ratio (iSNR) has been proposed in ISO/TC42 standards forndetermining dynamic range, and this work describes how to adaptnthese to WDR. Measurements and computer simulations reveal thatnthe observed trade-off between WDR extension and the loss of localndetail can be explained by a drop in iSNR at each reset point. If anreset is not timed optimally, then iSNR may drop below the detectionnlimit causing an iSNR hole to appear within the dynamic range. ThusniSNR has extended utility: it not only determines the dynamic rangenlimits but also defines dynamic range as the luminance range wherendetail detection is reliable. It has become the critical criterion whennmaximizing dynamic range to maintain the minimum necessary levelnof detection reliability.