High-dynamic-range imaging

About: High-dynamic-range imaging is a research topic. Over the lifetime, 766 publications have been published within this topic receiving 22577 citations.

Simplified fixed pattern noise correction and image display for high dynamic range CMOS logarithmic imagers

Abstract: Biologically inspired logarithmic CMOS sensors offer high dynamic range imaging capabilities without the difficulties faced by linear imagers. By compressing dynamic range while encoding contrast information, they mimic the human visual system’s response to photo stimuli in fewer bits than those used in linear sensors. Despite this prospect, logarithmic sensors suffer poor image quality due to illumination dependent fixed pattern noise (FPN), making individual pixels appear up to 100 times brighter or darker. This thesis is primarily concerned with alleviating FPN in logarithmic imagers in a simple and convenient way while undertaking a system approach to its origin, distribution and effect on the quality of monochrome and colour images, after FPN correction. Using the properties of the Human visual system, I propose to characterise the errors arising from FPN in a perceptually significant manner by proposing an error measure, never used before. Logarithmic operation over a wide dynamic range is first characterised using a new model; yi j =aj +bj ln(exp sqrt(cj +djxi)−1), where yi j is the response of the sensor to a light stimulus xi and aj, bj, cj and dj are pixel dependent parameters. Using a proposed correction procedure, pixel data from a monochromatic sensor array is FPN corrected to approximately 4% error over 5 decades of illumination even after digitisation - accuracy equivalent to four times the human eyes ability to just notice an illumination difference against a uniform background. By evaluating how error affects colour, the possibility of indiscernible residual colour error after FPN correction, is analytically explored using a standard set of munsell colours. After simulating the simple FPN correction procedure, colour quality is analysed using a Delta E76 perceptual metric, to check for perceptual discrepancies in image colour. It is shown that, after quantisation, the FPN correction process yields 1−2 Delta E76 error units over approximately 5 decades of illumination; colour quality being imperceptibly uniform in this range. Finally, tone-mapping techniques, required to compress high dynamic range images onto the low range of standard screens, have a predominantly logarithmic operation during brightness compression. A new Logr'Gb' colour representation is presented in this thesis, significantly reducing computational complexity, while encoding contrast information. Using a well-known tone mapping technique, images represented in this new format are shown to maintain colour accuracy when the green colour channel is compressed to the standard display range, instead of the traditional luminance channel. The trade off between colour accuracy and computation in this tone mapping approach is also demonstrated, offering a low cost alternative for applications with low display specifications.

Touch HDR: photograph enhancement by user controlled wide dynamic range adaptation

Abstract: High Dynamic Range (HDR) technology enables photographers to capture a greater range of tonal detail. HDR is typically used to bring out detail in a dark foreground object set against a bright background. HDR technologies include multi-frame HDR and single-frame HDR. Multi-frame HDR requires the combination of a sequence of images taken at different exposures. Single-frame HDR requires histogram equalization post-processing of a single image, a technique referred to as local tone mapping (LTM). Images generated using HDR technology can look less natural than their non- HDR counterparts. Sometimes it is only desired to enhance small regions of an original image. For example, it may be desired to enhance the tonal detail of one subject’s face while preserving the original background. The Touch HDR technique described in this paper achieves these goals by enabling selective blending of HDR and non-HDR versions of the same image to create a hybrid image. The HDR version of the image can be generated by either multi-frame or single-frame HDR. Selective blending can be performed as a post-processing step, for example, as a feature of a photo editor application, at any time after the image has been captured. HDR and non-HDR blending is controlled by a weighting surface, which is configured by the user through a sequence of touches on a touchscreen.

Augmented reality using high fidelity spherical panorama with HDRI

Abstract: This paper presents an experimental method and apparatus for producing spherical panoramas with high dynamic range imaging (HDRI). Our method is optimized for providing high fidelity augmented reality (AR) image-based environment recognition for mobile devices. Previous studies have shown that a pre-produced panorama image can be used to make AR tracking possible for mobile AR applications. However, there has been little research on determining the qualities of the source panorama image necessary for creating high fidelity AR experiences. Panorama image production can have various challenges that can result in inaccurate reproduction of images that do not allow correct virtual graphics to be registered in the AR scene. These challenges include using multiple angle photograph images that contain parallax error, nadir angle difficulty and limited dynamic range. For mobile AR, we developed a HDRI method that requires a single acquisition that extends the dynamic range from a digital negative. This approach that needs least acquisition time is to be used for multiple angles necessary for reconstructing accurately reproduced spherical panorama with sufficient luminance.

Use of fractional packet counting for high dynamic range imaging applications

Abstract: An asynchronous self-reset with residue conversion scheme for the readout electronics of an image sensor, further referred to as Fractional Packet Counting (FPC), is proposed. The basic concept of the FPC is to increase the resolution of the conversion both by using a switched integrator and by quantifying its output at the end of the signal integration time. A circuit implementing this principle for CT applications is proposed and simulated. In particular, in the proposed circuit a constant relative resolution is used: this means to use floating point representation with a constant number of significant bits. Simulations show that a dynamic range of 117 dB is achieved, working at 2 kHz frequency. The detectable signal range goes from 24 fA to ∼ 400 nA . The simulation results have been used to develop a mathematical model for the SNR accounting the different noise sources. The model shows that the floating point representation has no visible impact on the SNR of the circuit.

Ghost-free dual-exposure HDR for dynamic scenes

Abstract: High Dynamic Range Imaging (HDRI) and Exposure Fusion (EF) are methods of choice to computationally extend the dynamic range of images depicting real world scenes. Unfortunately, those methods are still prone to certain artifacts. Among others, the so-called Ghost Effect is the most critical HDR limitation when it comes to dealing with motion (camera or scene motion) in input Low Dynamic Range (LDR) images. This problem becomes more challenging when the input LDR image stack contains only a couple of images with large color differences, which is the case in the mobile phone domain. To address this issue, a de-ghosting step is required to preserve the quality of the final HDR images. In this paper, we propose a robust de-ghosting approach based on the detection and the elimination of the motion induced effects on the final HDR images. The proposed method performs efficiently in all cases even on scenarios where only two differently exposed images with large illumination variations are available as input. Compared to the state-of-the-art, our results exhibit significant visual improvement and artifact reduction. Furthermore, our approach has low computational cost and complexity, which enables an efficient implementation especially for mobile phone-related applications.