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

Abstract

This letter presents new insights into a High Dynamic Range (HDR) technique recently reported. We demonstrate that two intertwined photo-diodes per pixel can perform tone mapping under unconstrained illumination conditions with a single exposure. Experimental results attained from a prototype chip confirm the proposed theoretical framework. It opens the door to the realization of imagers providing HDR images free of artifacts without requiring any digital post-processing at all.Index Terms-high dynamic range, split-diode, automatic adaptation, single exposure, tone mapping.

Comparison between Digital Tone-Mapping Operators and a Focal-Plane Pixel-Parallel Circuit

“…They can be implemented using post-processing resources embedded either in smart CMOS image sensor chips [7] or in smart camera boards [8], [9]. Alternatively, tone mapping can be implemented as an early vision task, by using dedicated mixed-signal circuitry embedded per pixel [4], [10]. Tone mapping runs in this latter case concurrently with image acquisition, and prior to image readout and digital coding.…”

“…However, to the best of our knowledge, there are no reported comparisons between FPTMOs and DTMOs. Our work main contribution is to provide a novel systematic comparison between a large set of typical DTMOs and the FPTMO architecture previously reported in [10] and [13]. We choose this FPTMO because its mapping function is calculated using only information from the frame being captured (i.e.…”

“…The chosen FPTMO was demonstrated through a proof-of-concept grayscale sensor chip in [10], and then extended to color sensors in [13]. All comparisons in this paper are for color sensors and employ behavioral models of the corresponding pixels.…”

“…These models include all relevant circuit nonidealities and have been parameterized by using data taken from the physical implementation of the pixels in the CADENCE design framework, including layout parasitics. For completeness, the tasks underlying the pixel operation in [10] have also been implemented as DTMO post-processing tasks.…”

“…This paper is organized as follows. Section 2 briefly describes the operating principle of the chosen FPTMO [10], and the modifications in its original circuit that are proposed in [13], which allow color image processing and reduce the circuit area. Section 3 describes the methodology adopted to objectively assess the tone-mapped image quality achieved by each TMO considered in this work, and compares the TMO performances using statistical analysis techniques.…”