Showing papers on "High-dynamic-range imaging published in 2007"

Model of retinal local adaptation for the tone mapping of color filter array images

Abstract: We present a tone mapping algorithm that is derived from a model of retinal processing. Our approach has two major improvements over existing methods. First, tone mapping is applied directly on the mosaic image captured by the sensor, analogous to the human visual system that applies a nonlinearity to the chromatic responses captured by the cone mosaic. This reduces the number of necessary operations by a factor 3. Second, we introduce a variation of the center/surround class of local tone mapping algorithms, which are known to increase the local contrast of images but tend to create artifacts. Our method gives a good improvement in contrast while avoiding halos and maintaining good global appearance. Like traditional center/surround algorithms, our method uses a weighted average of surrounding pixel values. Instead of being used directly, the weighted average serves as a variable in the Naka-Rushton equation, which models the photoreceptors' nonlinearity. Our algorithm provides pleasing results on various images with different scene content and dynamic range.

Tone mapping for high-dynamic range displays

Abstract: We address the problem of re-rendering images to high dynamic range (HDR) displays, which were originally tone-mapped to standard displays. As these new HDR displays have a much larger dynamic range than standard displays, an image rendered to standard monitors is likely to look too bright when displayed on a HDR monitor. Moreover, because of the operations performed during capture and rendering to standard displays, the specular highlights are likely to have been clipped or compressed, which causes a loss of realism. We propose a tone scale function to re-render images first tone-mapped to standard displays, that focuses on the representation of specular highlights. The shape of the tone scale function depends on the segmentation of the input image into its diffuse and specular components. In this article, we describe a method to perform this segmentation automatically. Our method detects specular highlights by using two low-pass filters of different sizes combined with morphological operators. The results show that our method successfully detects small and middle sized specular highlights. The locations of specular highlights define a mask used for the construction of the tone scale function. We then propose two ways of applying the tone scale, the global version that applies the same curve to each pixel in the image and the local version that uses spatial information given by the mask to apply the tone scale differently to diffuse and to specular pixels.

A framework for inverse tone mapping

Abstract: In recent years many tone mapping operators (TMOs) have been presented in order to display high dynamic range images (HDRI) on typical display devices. TMOs compress the luminance range while trying to maintain contrast. The inverse of tone mapping, inverse tone mapping, expands a low dynamic range image (LDRI) into an HDRI. HDRIs contain a broader range of physical values that can be perceived by the human visual system. We propose a new framework that approximates a solution to this problem. Our framework uses importance sampling of light sources to find the areas considered to be of high luminance and subsequently applies density estimation to generate an expand map in order to extend the range in the high luminance areas using an inverse tone mapping operator. The majority of today’s media is stored in the low dynamic range. Inverse tone mapping operators (iTMOs) could thus potentially revive all of this content for use in high dynamic range display and image based lighting (IBL). Moreover, we show another application that benefits quick capture of HDRIs for use in IBL.

High Dynamic Range Imaging Pipeline : Perception-Motivated Representation of Visual Content

Abstract: The advances in high dynamic range (HDR) imaging, especially in the display and camera technology, have a significant impact on the existing imaging systems. The assumptions of the traditional low-dynamic range imaging, designed for paper print as a major output medium, are ill suited for the range of visual material that is shown on modern displays. For example, the common assumption that the brightest color in an image is white can be hardly justified for high contrast LCD displays, not to mention next generation HDR displays, that can easily create bright highlights and the impression of self-luminous colors. We argue that high dynamic range representation can encode images regardless of the technology used to create and display them, with the accuracy that is only constrained by the limitations of the human eye and not a particular output medium. To facilitate the research on high dynamic range imaging, we have created a software package (http://pfstools.sourceforge.net/) capable of handling HDR data on all stages of image and video processing. The software package is available as open source under the General Public License and includes solutions for high quality image acquisition from multiple exposures, a range of tone mapping algorithms and a visual difference predictor for HDR images. Examples of shell scripts demonstrate how the software can be used for processing single images as well as video sequences.

High Dynamic Range Imaging and its Application in Building Research

Abstract: This article describes the theory and application of high dynamic range imaging (HDRI). HDRI is a recent technology allowing the capture of images with a much extended dynamic range whose values represent real-world luminance rather than just arbitrary pixel values. This article lays out the steps necessary to create HDR images, and highlights recent developments in the technology and its applications for building research.

High-dynamic-range video for photometric measurement of illumination

Abstract: 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 ...

Gradient Domain Tone Mapping of High Dynamic Range Videos

Abstract: A gradient domain tone mapping algorithm is proposed to display high dynamic range (HDR) video sequences in low dynamic range (LDR) devices in this work. The proposed algorithm obtains a pixelwise motion vector field and incorporates the motion information into the Poisson equation. Then, by attenuating large spatial gradients, the proposed algorithm can yield a high-quality tone-mapped result without flickering artifacts. Simulation results show that the proposed algorithm provides a better performance than the frame-based method, which processes each frame independently.

Veiling glare: the dynamic range limit of HDR images

Abstract: High Dynamic Range (HDR) images are superior to conventional images However, veiling glare is a physical limit to HDR image acquisition and display We performed camera calibration experiments using a single test target with 40 luminance patches covering a luminance range of 18,619:1 Veiling glare is a scene-dependent physical limit of the camera and the lens Multiple exposures cannot accurately reconstruct scene luminances beyond the veiling glare limit Human observer experiments, using the same targets, showed that image-dependent intraocular scatter changes identical display luminances into different retinal luminances Vision's contrast mechanism further distorts any correlation of scene luminance and appearance There must be reasons, other than accurate luminance, that explains the improvement in HDR images The multiple exposure technique significantly improves digital quantization The improved quantization allows displays to present better spatial information to humans When human vision looks at high-dynamic range displays, it processes them using spatial comparisons

Self-calibrating wide color gamut high dynamic range display

Abstract: High Dynamic Range displays offer higher brightness, higher contrast, better color reproduction and lower power consumption compared to conventional displays available today. In addition to these benefits, it is possible to leverage the unique design of HDR displays to overcome many of the calibration and lifetime degradation problems of liquid crystal displays, especially those using light emitting diodes. This paper describes a combination of sensor mechanisms and algorithms that reduce luminance and color variation for both HDR and conventional displays even with the use of highly variable light elements.

High dynamic range imaging device

Abstract: The present invention relates to improved imaging devices having high dynamic range and to monitoring and automatic control systems incorporating the improved imaging devices.

High dynamic range imaging with a single-mode pupil remapping system: a self-calibration algorithm for redundant interferometric arrays

Abstract: The correction of the influence of phase corrugation in the pupil plane is a fundamental issue in achieving high dynamic range imaging. In this paper, we investigate an instrumental set-up which consists of applying interferometric techniques on a single telescope, by filtering and dividing the pupil with an array of single-mode fibres. We developed a new algorithm, which makes use of the fact that we have a redundant interferometric array, to completely disentangle the astronomical object from the atmospheric perturbations (phase and scintillation). This self-calibrating algorithm can also be applied to any - diluted or not - redundant interferometric set-up. On an 8-m telescope observing at a wavelength of 630 nm, our simulations show that a single-mode pupil remapping system could achieve, at a few resolution elements from the central star, a raw dynamic range up to 10 6 , depending on the brightness of the source. The self-calibration algorithm proved to be very efficient, allowing image reconstruction of faint sources (magnitude = 15) even though the signal-to-noise ratios of individual spatial frequencies are of the order of 0.1. We finally note that the instrument could be more sensitive by combining this set-up with an adaptive optics system. The dynamic range would however be limited by the noise of the small, high-frequency displacements of the deformable mirror.

Research on temperature distribution of combustion flames based on high dynamic range imaging

Abstract: The imaging-based three-color method is widely used in the field of non-contact temperature measurement of combustion flames. In this paper, by analyzing the imaging process of a combustion flame in detail, we re-derivate the three-color method by adopting a theory of high dynamic range imaging. Instead of using white balanced, gamma calibrated or other algorithms applied 8-bit pixel values, we use irradiance values on the image plane; these values are obtained by combining two differently exposed raw images into one high dynamic range irradiance map with the help of the imaging system's response function. An instrumentation system is presented and a series of experiments have been carried out, the results of which are satisfactory.

Spatially varying image based lighting by light probe sequences: Capture, processing and rendering

Abstract: 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.

On Geometric and Photometric Registration of Images

Abstract: Finding geometric and photometric relation among images is crucial in many computer vision tasks such as panoramic imaging, high dynamic range imaging, stereo imaging, and change detection. Most photometric registration algorithms require accurate geometric registration of images. On the other hand, geometric registration may fail when images are not aligned photometrically. There are two contributions of this paper: (i) A contrast invariant feature detection algorithm is proposed. This would allow geometric registration of images without photometric registration, (ii) A photometric registration algorithm that can handle scene occlusions is presented.

Accuracy of Luminance Maps Obtained from High Dynamic Range Images

Abstract: High dynamic range images can be converted into luminance maps if the response curve of the camera is known. Previous results for a consumer grade CCD camera have shown luminance errors as a function of Munsell hue and value. New measurements with a digital SLR camera with a CMOS sensor find two problems. First, saturated hues, especially blue, blue green, and purple are still difficult to measure. Second, surfaces with low reflectance below Munsell value N4 can be significantly overestimated, especially in spherical images obtained from the photography of mirror spheres. Nevertheless, it appears that HDR imaging is a suitable tool for luminance measurement if the scene contains luminance reference values such as calibrated matte color checkers and gray cards, and if dark surfaces and saturated hues are excluded. Spherical HDR images obtained from mirror spheres capture nearly the entire environment, but resolution and decreased sensitivity for surfaces with very low reflectance are still problems.

Testing tone mapping operators with human-perceived reality

Abstract: A number of successful tone mapping operators for con- trast compression have been proposed due to the need to visualize high dynamic range (HDR) images on low dynamic range (LDR) devices. They were inspired by fields as diverse as image process- ing, photographic practice, and modeling of the human visual sys- tems (HVS). The variety of approaches calls for a systematic per- ceptual evaluation of their performance. We conduct a psychophysical experiment based on a direct comparison between the appearance of real-world scenes and HDR images of these scenes displayed on an LDR monitor. In our experiment, HDR im- ages are tone mapped by seven existing tone mapping operators. The primary interest of this psychophysical experiment is to assess the differences in how tone mapped images are perceived by hu- man observers and to find out which attributes of image appearance account for these differences when tone mapped images are com- pared directly with their corresponding real-world scenes rather than with each other. The human subjects rate image naturalness, overall contrast, overall brightness, and detail reproduction in dark and bright image regions with respect to the corresponding real-world scene. The results indicate substantial differences in the perception of images produced by individual tone mapping operators. We ob- serve a clear distinction between global and local operators—in fa- vor of the latter—and we classify the tone mapping operators ac- cording to naturalness and appearance attributes. © 2007 SPIE and

Acquisition and Encoding of High Dynamic Range Images using Inverse Tone Mapping

Abstract: A two layer coding algorithm for high dynamic range images is discussed. In the first layer, a low dynamic range image is encoded by a conventional codec, and then the residual information that represents the difference between an original and the decoded images in the first layer is encoded in the second layer, which realizes compatibility with conventional image file formats. Our method utilizes the approximation of an inverse tone mapping function that reduces the high dynamic range to a displayable range. Our algorithm significantly improves a compression performance, compared to conventional methods.

Multidimensional image enhancement from a set of unregistered and differently exposed images

Abstract: If multiple images of a scene are available instead of a single image, we can use the additional information conveyed by the set of images to generate a higher quality image. This can be done along multiple dimensions. Super-resolution algorithms use a set of shifted and rotated low resolution images to create a high resolution image. High dynamic range imaging techniques combine images with different exposure times to generate an image with a higher dynamic range. In this paper, we present a novel method to combine both techniques and construct a high resolution, high dynamic range image from a set of shifted images with varying exposure times. We first estimate the camera response function, and convert each of the input images to an exposure invariant space. Next, we estimate the motion between the input images. Finally, we reconstruct a high resolution, high dynamic range image using an interpolation from the non-uniformly sampled pixels. Applications of such an approach can be found in various domains, such as surveillance cameras, consumer digital cameras, etc.

A multicurve tone mapping operator for the display of high dynamic range image and video

Abstract: This paper presents a novel method for tone mapping high dynamic range images and videos for display in conventional low dynamic range devices. The new multi-curve method uses tone mapping curves that are adaptive to local luminance levels. The new method has the computational simplicity of curve based tone mapping methods and achieves results comparable to spatial operator methods. When applying the operator to render high dynamic range video, we introduce a bilateral style temporal filtering which successfully avoids undesirable shot noise and ghosting effects. It is also shown that our HDR tone mapping operator is a useful image enhancement method for standard format (8 bits/pixel) images. (7 pages)

Optimizing the high dynamic range imaging pipeline

Abstract: 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.

Display HDR Image using a Gain Map

Abstract: In this paper, we present a novel method for the display of high dynamic range images. The new method first computes a gain map image using a computational approach inspired by a machine learning algorithm and sums the gain map and the original image together; it then linearly scales the sum image to fit the dynamic range of the display devices. Results are presented to demonstrate the effectiveness of this new method and it is also shown that the new approach is an effective method for enhancing standard (8 bits/pixl) images.

Active Aperture Control and Sensor Modulation for Flexible Imaging

Abstract: In the paper, we describe an optical system which is capable of providing external access to both the sensor and the lens aperture (i.e., projection center) of a conventional camera. The proposed optical system is attached in front of the camera, and is the equivalent of adding externally accessible intermediate image plane and projection center. The system offers controls of the response of each pixel which could be used to realize many added imaging functions, such as high dynamic range imaging, image modulation, and optical computation. The ability to access the optical center could enable a wide variety of applications by simply allowing manipulation of the geometric properties of the optical center. For instance, panoramic imaging can be implemented by rotating a planar mirror about the camera axis; and small base-line stereo can be implemented by shifting the camera center. We have implemented a bench setup to demonstrate some of these functions. The experimental results are included.

Color high dynamic range imaging: The luminance–chrominance approach

Abstract: This article presents a novel and efficient approach to color in high dynamic range (HDR) imaging. In contrast to state-of-the-art methods, we propose to move the complete HDR imaging process from RGB to a luminance–chrominance color space. Our aim is to get a computationally efficient technique and to avoid any possible color distortions originating from the three RGB color channels processed separately. To achieve this, we build a camera response function for the luminance channel only and weight and compose the HDR luminance accordingly, while for the chrominance channels we apply weighting in relation with the saturation level. We demonstrate that our technique yields natural and pleasant to perceive tone-mapped images and is also more robust to noise. © 2007 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 17, 152–162, 2007

Hyperspectral imaging and spectral unmixing of stained tissue sections using a spectrally programmable light engine

Abstract: A series of hyperspectral transmission images of hematoxylin and eosin stained tissue sections from cervical biopsies were acquired at 10 nm intervals and assembled into a hyperspectral image cube. Custom software providing extraction of spectra at each pixel allows selection of images with maximum contrast for determination of selected features and differentiation of tissue features. Illumination profiles were created using a spectrally and temporally programmable light engine based on a spatial light modulator that can dynamically create any narrow or broadband spectral profile was used to select illumination wavelengths. Images were acquired with a monochrome CCD camera. Several methods of combining images from individual or composite spectral bands to recreate color images for pathologist review are shown. Unlike current "mechanical" illumination systems employing optical filters, filter wheels, motors, shutters and multiple control interfaces, the light engine integrates the lamp, wavelength control, intensity control and exposure control in a simple MEMS based system, where the only moving part is the lamp cooling fan. Illumination can now be programmed dynamically with digital control of all illumination parameters allowing wavelengths and intensities to be changed much faster than with filter wheels, and providing exposure control orders of magnitude more precise than mechanical shutters. This system can be integrated with digital imaging systems. Digitally controlled illumination is bit additive with image data providing high dynamic range imaging with monochrome or with color imaging devices. Performance of image analysis software for nuclear morphometric and tissue architecture analysis are compared for different wavelength regions.

High dynamic range imaging and display.

Abstract: A method is provided for treating gum base to improve its resistance to oxidation without the need for antioxidants wherein air or oxygen is swept from the gum base by means of an inert gas, and the oxygen-free gum base, in particulate form, is coated with a highly oxygenated substance, such as molten sugar, sorbitol solution or hydrogenated starch hydrolysate which acts as a barrier against oxygen. The gum base produced by the above method and chewing gum containing such gum base are also provided.

High Dynamic Range Imaging: Towards the Limits of the Human Visual Perception

Abstract: Vast majority of digital images and video material stored today can capture only a fraction of visual information visible to the human eye and does not offer sufficient quality to reproduce them on the future generation of display devices. The limitating factor is not the resolution, since most consumer level digital cameras can take images of higher number of pixels than most of displays can offer. The problem is a limited color gamut and even more limited dynamic range (contrast) that cameras can capture and that majority of image and video formats can store. For instance, each pixel value in the JPEG image encoding is represented using three 8-bit integer numbers (0-255) using the YCrCb color space. Such color space is able to store only a small part of visible color gamut (although containing the colors most often encountered in the real world), as illustrated in Figure 1-left, and even smaller part of luminance range that can be perceived by our eyes, as illustrated in Figure 1-right. The reason for this is that the JPEG format was designed to store as much information as can be displayed on the majority of displays, which were Cathode Ray Tube (CRT)