We present a novel technique for capturing spatially or temporally resolved light probe sequences, and using them for image based lighting. For this purpose we have designed and built a real-time light probe, a catadioptric imaging system that can capture the full dynamic range of the lighting incident at each point in space at video frame rates, while being moved through a scene. The real-time light probe uses a digital imaging system which we have programmed to capture high quality, photometrically accurate color images of 512×512 pixels with a dynamic range of 10000000:1 at 25 frames per second. By tracking the position and orientation of the light probe, it is possible to transform each light probe into a common frame of reference in world coordinates, and map each point and direction in space along the path of motion to a particular frame and pixel in the light probe sequence. We demonstrate our technique by rendering synthetic objects illuminated by complex real world lighting, first by using traditional image based lighting methods and temporally varying light probe illumination, and second an extension to handle spatially varying lighting conditions across large objects and object motion along an extended path.

This work presents a survey and a user evaluation of tone mapping operators (TMOs) for high dynamic range (HDR) video, i.e. TMOs that explicitly include a temporal model for processing of variations in the input HDR images in the time domain. The main motivations behind this work is that: robust tone mapping is one of the key aspects of HDR imaging [Reinhard et al. 2006]; recent developments in sensor and computing technologies have now made it possible to capture HDR-video, e.g. [Unger and Gustavson 2007; Tocci et al. 2011]; and, as shown by our survey, tone mapping for HDR video poses a set of completely new challenges compared to tone mapping for still HDR images. Furthermore, video tone mapping, though less studied, is highly important for a multitude of applications including gaming, cameras in mobile devices, adaptive display devices and movie post-processing. Our survey is meant to summarize the state-of-the-art in video tonemapping and, as exemplified in Figure 1 (right), analyze differences in their response to temporal variations. In contrast to other studies, we evaluate TMOs performance according to their actual intent, such as producing the image that best resembles the real world scene, that subjectively looks best to the viewer, or fulfills a certain artistic requirement. The unique strength of this work is that we use real high quality HDR video sequences, see Figure 1 (left), as opposed to synthetic images or footage generated from still HDR images. / VPS

No / In recent years inverse tone mapping techniques have been proposed for enhancing low-dynamic range (LDR) content for a high-dynamic range (HDR) experience on HDR displays, and for image based lighting. In this paper, we present a psychophysical study to evaluate the performance of inverse (reverse) tone mapping algorithms. Some of these techniques are computationally expensive because they need to resolve quantization problems that can occur when expanding an LDR image. Even if they can be implemented efficiently on hardware, the computational cost can still be high. An alternative is to utilize less complex operators; although these may suffer in terms of accuracy. Our study investigates, firstly, if a high level of complexity is needed for inverse tone mapping and, secondly, if a correlation exists between image content and quality. Two main applications have been considered: visualization on an HDR monitor and image-based lighting.

Image based lighting, (IBL), is a computer graphics technique for creating photorealistic renderings of synthetic objects such that they can be placed into real world scenes. IBL has been widely recognized and is today used in commercial production pipelines. However, the current techniques only use illumination captured at a single point in space. This means that traditional IBL cannot capture or recreate effects such as cast shadows, shafts of light or other important spatial variations in the illumination. Such lighting effects are, in many cases, artistically created or are there to emphasize certain features, and are therefore a very important part of the visual appearance of a scene. This thesis and the included papers present methods that extend IBL to allow for capture and rendering with spatially varying illumination. This is accomplished by measuring the light field incident onto a region in space, called an Incident Light Field, (ILF), and using it as illumination in renderings. This requires the illumination to be captured at a large number of points in space instead of just one. The complexity of the capture methods and rendering algorithms are then significantly increased. The technique for measuring spatially varying illumination in real scenes is based on capture of High Dynamic Range, (HDR), image sequences. For efficient measurement, the image capture is performed at video frame rates. The captured illumination information in the image sequences is processed such that it can be used in computer graphics rendering. By extracting high intensity regions from the captured data and representing them separately, this thesis also describes a technique for increasing rendering efficiency and methods for editing the captured illumination, for example artificially moving or turning on and of individual light sources.

We describe the design and implementation of a high dynamic range (HDR) imaging system capable of capturing RGB color images with a dynamic range of 10,000,000 : 1 at 25 frames per second. We use a highly programmable camera unit with high throughput A/D conversion, data processing and data output. HDR acquisition is performed by multiple exposures in a continuous rolling shutter progression over the sensor. All the different exposures for one particular row of pixels are acquired head to tail within the frame time, which means that the time disparity between exposures is minimal, the entire frame time can be used for light integration and the longest expo- sure is almost the entire frame time. The system is highly configurable, and trade-offs are possible between dynamic range, precision, number of exposures, image resolution and frame rate.

Typical consumer digital cameras capture the scene by generating a mosaic-like grayscale image, known as a color filter array (CFA) image. One obvious challenge in digital photography is the storage of image, which requires the development of an efficient compression solution. This issue has become more significant due to a growing demand for high dynamic range (HDR) imaging technology, which requires increased bandwidth to allow realistic presentation of visual scene. This thesis proposes two digital camera pipelines, efficiently encoding CFA image data represented in HDR format. Firstly, a lossless compression scheme exploiting a predictive coding followed by a JPEG XR encoding module is introduced. It achieves efficient data reduction without loss of quality. Secondly, a lossy compression scheme that consists of a series of processing operations and a JPEG XR encoding module is introduced. Performance evaluation indicates that the proposed method delivers high quality images at low computational costs.

Typical consumer digital cameras capture the scene by generating a mosaic-like grayscale image, known as a color filter array (CFA) image. One obvious challenge in digital photography is the storage of image, which requires the development of an efficient compression solution. This issue has become more significant due to a growing demand for high dynamic range (HDR) imaging technology, which requires increased bandwidth to allow realistic presentation of visual scene. This thesis proposes two digital camera pipelines, efficiently encoding CFA image data represented in HDR format. Firstly, a lossless compression scheme exploiting a predictive coding followed by a JPEG XR encoding module is introduced. It achieves efficient data reduction without loss of quality. Secondly, a lossy compression scheme that consists of a series of processing operations and a JPEG XR encoding module is introduced. Performance evaluation indicates that the proposed method delivers high quality images at low computational costs.

Ο τομέας της ψηφιακής φωτογράφισης εξελίσσεται διαρκώς. Το γεγονός αυτό, καθιστά τη ψηφιακή φωτογραφία χρήσιμο εργαλείο για διάφορες επιστημονικές και όχι μόνο εφαρμογές. Για αυτό τον λόγο, γίνεται απαραίτητη η λεπτομερέστερη αποτύπωση της πληροφορίας. Η λεπτομερέστερη αποτύπωση της πληροφορίας αποτελεί αντικείμενο της εικονοποίησης υψηλής δυναμικής περιοχής(High Dynamic Range Imaging). Ο σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της εικονοποίησης υψηλής δυναμικής περιοχής και η υλοποίηση ενός αλγορίθμου, κάνοντας χρήση πολλαπλών λήψεων για την παραγωγή τελικής εικόνας με διευρυμένη δυναμική περιοχή. / The field of digital photography is constantly evolving. In fact, this makes digital photography a useful tool in various scientific applications. For this reason, a more detailed presentation of information is needed. The detailed presentation of information is the subject of high dynamic range (High Dynamic Range Imaging). The purpose of this thesis is to study the field of high dynamic range imaging and the implementation of an algorithm, making use of multiple shots to produce a final image with extended dynamic range.

High dynamic range (HDR) imaging is a rapidly growing field in computer graphics and image processing. It allows capture, storage, processing, and display of photographic information within a scene-referred framework. The HDR imaging pipeline consists of the major steps an HDR image is expected to go through from capture to display. It involves various techniques to create HDR images, pixel encodings and file formats for storage, tone mapping for display on conventional display devices and direct display on HDR capable screens. Each of these stages have important open problems, which need to be addressed for a smoother transition to an HDR imaging pipeline. We addressed some of these important problems such as noise reduction in HDR imagery, preservation of color appearance, validation of tone mapping operators, and image display on HDR monitors. The aim of this thesis is thus, to present our findings and describe the research we have conducted within the framework of optimizing the HDR imaging pipeline.

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