One-Shot HDR Imaging via Stereo PFA Cameras

Abstract

High Dynamic Range (HDR) imaging techniques aim to increase the range of luminance values captured from a scene. The literature counts many approaches to get HDR images out of low-range camera sensors, however most of them rely on multiple acquisitions producing ghosting effects when moving objects are present.In this paper we propose a novel HDR reconstruction method exploiting stereo Polarimetric Filter Array (PFA) cameras to simultaneously capture the scene with different polarized filters, producing intensity attenuations that can be related to the light polarization state. An additional linear polarizer is mounted in front of one of the two cameras, raising the degree of polarization of rays captured by the sensor. This leads to a larger attenuation range between channels regardless the scene lighting condition. By merging the data acquired by the two cameras, we can compute the actual light attenuation observed by a pixel at each channel and derive an equivalent exposure time, producing a HDR picture from a single polarimetric shot. The proposed technique results comparable to classic HDR approaches using multiple exposures, with the advantage of being a one-shot method.

Exploiting Light Polarization for Deep HDR Imaging from a Single Exposure

“…Similar to the aforementioned single LDR to HDR techniques, PFA-based HDR methods also encounter the challenge of poor performance in underexposed areas. In [ 15 ], we introduced a novel stereo PFA camera setup, which provides a significant increase in the dynamic range of the HDR image, compared to using single PFA cameras. The HDR images computed with [ 15 ] are visually more pleasing and closer to the ground truth when compared to other existing methods.…”

“…PFA cameras are also shown to be useful for HDR imaging [ 3 , 13 , 14 , 15 ]: these cameras can capture four images simultaneously with polarizers at different orientations. Since each linear polarizer reduces the observed intensity according to the degree of polarization of incoming light, the filter acts as an exposure time reduction and, thus, an equivalent exposure time can be computed to perform HDR reconstruction.…”

“…Since the degree of polarization in a real-world scene is generally low, the usage of a plain PFA camera is limited. In [ 15 ], we proposed an HDR reconstruction method with a PFA stereo camera setup. In these settings, we used two PFA cameras, with only one of them equipped with an extra linear polarizer positioned outside the lenses.…”

“…In this paper, we build on top of the method proposed in [ 15 ], with the goal of removing one camera and obtaining a simpler yet effective system to perform HDR reconstruction using one PFA camera. We propose a novel HDR reconstruction setup involving a single PFA camera with an additional linear polarizer outside the lenses, paired with a tailored data-driven model, which is trained to simulate the response of the missing camera (i.e., the one with no filter on).…”

“…An extensive experimental study supports the effectiveness of the proposed method, including a comparison with state-of-the-art techniques. The rest of the paper is organized as follows: Section 2 describes the most relevant works connected to our method, then Section 3 briefly summarizes polarimetric basics and the stereo HDR reconstruction presented in [ 15 ]. The proposed technique is then presented in detail in Section 4 , and finally both qualitative and quantitative experimental results are discussed in Section 5 .…”