Single-Exposure HDR Technique Based on Tunable Balance Between Local and Global Adaptation

Abstract

This paper describes a high dynamic range technique that compresses wide ranges of illuminations into the available signal range with a single exposure. An on-line analysis of the image histogram provides the sensor with the necessary feedback to dynamically accommodate changing illumination conditions. This adaptation is accomplished by properly weighing the influence of local and global illumination on each pixel response. The main advantages of this technique with respect to similar approaches previously reported are: i) standard active pixel sensor circuitry can be used to render the pixel values; ii) the resulting compressed image representation is ready either for readout or for early vision processing at the very focal plane without requiring any additional peripheral circuit block. Experimental results from a prototype smart image sensor achieving a dynamic range of 102dB are presented.

Image Sensing Scheme Enabling Fully-Programmable Light Adaptation and Tone Mapping With a Single Exposure

“…The labels max and min refer to those pixels where the maximum and minimum photocurrents, respectively, are generated. The rest of pixels would evolve along curves in between.The parameter T S constitutes a simplification with respect to the multiple samplings of the mean illumination proposed in [3]. We prove next that this simplification permits programmable adaptation to any possible illumination conditions.…”

“…The pixel to be considered is the same as in [3]. The extra elements required with respect to the pixel in [2] are depicted with a thicker red line in Fig 1. The image capture stage is governed by three temporal parameters: a reset period T RST , a maximum photo-integration period T max and a period T S where the ambient illumination is sensed.…”

“…where M × N is the image resolution, C is the sensing capacitance and m, equal to 1 in our prototype, is an area scale factor as described in [3]. Note that V rst = vfrd if hard reset is applied.…”

“…We recently proposed a two-photodiode HDR technique as well [3]. A major asset of our technique is that, unlike in [2], tone mapping is inherent to the adaptation process.…”

“…On the flip side, some extra transistors are needed with respect to the pixel in [2] and global shutter is mandatory. In this letter, we describe how the technique introduced in [3] can be further simplified. More importantly, we mathematically demonstrate that the resulting simplified sensing scheme can accommodate any possible illumination conditions.…”