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.

Color Tone-Mapping Circuit for a Focal-Plane Implementation

“…The tone-mapping curve of the operator described in [5] is adjusted at each pixel, according to its local luminance value and to the average luminance value of the scene. Each pixel cell contains two photodiodes, which store the local luminance value for different purposes: the capture photodiode, whose photocurrent determines the actual pixel value; and the control photodiode, whose photocurrent is used to calculate the average luminance value of the scene.…”

“…The digital tone-mapping operators are typically expressed in terms of parameters that control output image perceptual attributes. Therefore, in a digital simulation of the tonemapping operator from [5], six parameters must be set: V mid , C, m ph , m c , T max , and T s .…”

“…al. [5] is not digital: it is implemented inside the focal plane of the camera, before analog-to-digital conversion, and immediately maps the HDR image to the 8-bit range, as soon as it is acquired. The (grayscale) image is then readily available for display, without requiring further processing or multiple exposures of the scene.…”