Showing papers on "High-dynamic-range imaging published in 2005"

High Dynamic Range Imaging: Acquisition, Display, and Image-Based Lighting (The Morgan Kaufmann Series in Computer Graphics)

Abstract: This landmark book is the first to describe HDRI technology in its entirety and covers a wide-range of topics, from capture devices to tone reproduction and image-based lighting. The techniques described enable you to produce images that have a dynamic range much closer to that found in the real world, leading to an unparalleled visual experience. As both an introduction to the field and an authoritative technical reference, it is essential to anyone working with images, whether in computer graphics, film, video, photography, or lighting design. New material includes chapters on High Dynamic Range Video Encoding, High Dynamic Range Image Encoding, and High Dynammic Range Display Devices Written by the inventors and initial implementors of High Dynamic Range Imaging Covers the basic concepts (including just enough about human vision to explain why HDR images are necessary), image capture, image encoding, file formats, display techniques, tone mapping for lower dynamic range display, and the use of HDR images and calculations in 3D rendering Range and depth of coverage is good for the knowledgeable researcher as well as those who are just starting to learn about High Dynamic Range imaging Table of Contents Introduction; Light and Color; HDR Image Encodings; HDR Video Encodings; HDR Image and Video Capture; Display Devices; The Human Visual System and HDR Tone Mapping; Spatial Tone Reproduction; Frequency Domain and Gradient Domain Tone Reproduction; Inverse Tone Reproduction; Visible Difference Predictors; Image-Based Lighting.

Predicting visible differences in high dynamic range images : Model and its calibration

Abstract: New imaging and rendering systems commonly use physically accurate lighting information in the form of high-dynamic range (HDR) images and video. HDR images contain actual colorimetric or physical values, which can span 14 orders of magnitude, instead of 8-bit renderings, found in standard images. The additional precision and quality retained in HDR visual data is necessary to display images on advanced HDR display devices, capable of showing contrast of 50,000:1, as compared to the contrast of 700:1 for LCD displays. With the development of high-dynamic range visual techniques comes a need for an automatic visual quality assessment of the resulting images. In this paper we propose several modifications to the Visual Difference Predicator (VDP). The modifications improve the prediction of perceivable differences in the full visible range of luminance and under the adaptation conditions corresponding to real scene observation. The proposed metric takes into account the aspects of high contrast vision, like scattering of the light in the optics (OTF), nonlinear response to light for the full range of luminance, and local adaptation. To calibrate our HDR VDP we perform experiments using an advanced HDR display, capable of displaying the range of luminance that is close to that found in real scenes.

Perceptual evaluation of tone mapping operators with real-world scenes

Abstract: A number of successful tone mapping operators for contrast compression have been proposed due to the need to visualize high dynamic range (HDR) images on low dynamic range devices. They were inspired by fields as diverse as image processing, photographic practice, and modeling of the human visual systems (HVS). The variety of approaches calls for a systematic perceptual 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 a low dynamic range monitor. In our experiment, HDR images 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 human observers and to find out which attributes of image appearance account for these differences when tone mapped images are compared 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 perception of images produced by individual tone mapping operators. We observe a clear distinction between global and local operators in favor of the latter, and we classify the tone mapping operators according to naturalness and appearance attributes.

Transfer function and high dynamic range images

Abstract: Methods and apparatuses to derive at least one exposure function for high dynamic range imaging from images of different exposure durations. In one aspect, a method to generate a high dynamic range image from a plurality of images taken with a plurality of exposure durations respectively, includes: computing an exposure function from the plurality of images; and combining the plurality of images into a high dynamic range (HDR) image using the exposure function. In one example of an embodiment, the exposure function is evaluated through: evaluating first data representing a derivative of the exposure function from pixel values of the plurality of images; and integrating the first data to generate second data representing the exposure function.

Validation of High Dynamic Range Imaging to Luminance Measurement

Abstract: High dynamic range imaging is a set of techniques that allows for a far greater dynamic range of exposure than normal digital imaging techniques. The intention is to accurately represent the dynamic range of lighting levels found in real scenes, ranging from direct sunlight to deep shadows. Various software packages have emerged that translate these HDR images into high resolution luminance maps. This paper tests the accuracy of one such package, taking into consideration different Munsell hues, values and chroma. It investigates the impact of different light spectra, spatial frequency, vignetting, and thermal noise on the accuracy of luminance measurements and determines the potential errors.

Hierarchical tone mapping for high dynamic range image visualization

Abstract: In this paper, we present a computationally efficient, practically easy to use tone mapping techniques for the visualization of high dynamic range (HDR) images in low dynamic range (LDR) reproduction devices. The new method, termed hierarchical nonlinear linear (HNL) tone-mapping operator maps the pixels in two hierarchical steps. The first step allocates appropriate numbers of LDR display levels to different HDR intensity intervals according to the pixel densities of the intervals. The second step linearly maps the HDR intensity intervals to theirs allocated LDR display levels. In the developed HNL scheme, the assignment of LDR display levels to HDR intensity intervals is controlled by a very simple and flexible formula with a single adjustable parameter. We also show that our new operators can be used for the effective enhancement of ordinary images.

High dynamic range CMOS image sensor with pixel level ADC and in-situ image enhancement

Abstract: We describe a CMOS image sensor with pixel level analog to digital conversion (ADC) having high dynamic range (>100db) and the capability of performing many image processing functions at the pixel level during image capture. The sensor has a 102x98 pixel array and is implemented in a 0.18um CMOS process technology. Each pixel is 15.5um x15.5um with 15% fill factor and is comprised of a comparator, two 10 bit memory registers and control logic. A digital to analog converter and system processor are located off-chip. The photodetector produces a photocurrent yielding a photo-voltage proportional to the impinging light intensity. Once the photo-voltage is less than a predetermined global reference voltage; a global code value is latched into the pixel data buffer. This process prevents voltage saturation resulting in high dynamic range imaging. Upon completion of image capture, a digital representation of the image exists at the pixel array, thereby, allowing image data to be accessed in a parallel fashion from the focal plane array. It is demonstrated that by appropriate variation of the global reference voltage with time, it is possible to perform, during image capture, thresholding and image enhancement operations, such as, contrast stretching in a parallel manner.

Multispectral endoscopy and microscopy imaging system using a spectrally programmable light engine

Abstract: We report a spectrally and temporally programmable light engine based on a spatial light modulator that can dynamically create any narrow or broadband spectral profile for hyperspectral, fluorescence, or principal component imaging. Most hyperspectral or multispectral imaging systems use wavelength selection devices such as acousto-optic tunable filters (AOTFs), tunable grating or prism-based monochromators, or filter wheels. While these devices can select wavelengths they cannot create arbitrary spectral profiles. This simple and economical system can be controlled at high speed (up to 5000 illumination profiles per second). Digitally controlled illumination is bit additive with image data providing high dynamic range imaging with monochrome or color imaging devices. This is especially advantageous for endoscopes employing small well CCD or CMOS sensors since the dynamic range now can extend beyond the limits of the sensor itself. In this report we show multispectral images of in vivo tissue and in vitro tissue samples using endoscopes, surgical microscopes and conventional microscopes.

Mosaicing with interferometers: An Efficient Algorithm for Imaging and Image Plane Corrections

Abstract: The imaging dynamic range of an aperture synthesis telescope for mosaicing and for fields with significant flux throughout the antenna primary beams can be limited by the knowledge of the individual primary beams projected on the sky. For high dynamic range imaging of such fields, one requires an accurate measurement of the shape of the primary beams and the pointing offsets as a function of time. The effect of antenna pointing errors remain separable in the visibility domain. With at least two, well separated sources along the RA and Dec axis each to constrain the solutions, it is possible to solve for these errors in an antenna based fashion in the visibility domain. Here we describe an algorithm to solve for these errors using a model for the sky brightness distribution. For a typical L-band eVLA simulation with typical pointing errors for the VLA antennas, the RMS noise can be reduced by a factor of ∼ 10 using this algorithm. The improvement in the image fidelity is even larger.

Single-mode filtering and pupil remapping

Abstract: Correction of the in.uence of phase corrugation in the pupil plane is a fundamental issue in achieving high dynamic range imaging. It can be done in real-time with a deformable mirror, but also by post-detection data processing. We present here an imaging system which, thanks to non-redundant pupil remapping and spatial filtering by single mode fibers, allows perfect calibration of the Modulation Transfer Function (MTF). Using phase closure, we have then precise knowledge of the complex values filling the spatial frequency plane of the telescope. We do show that such a system would be free from phase perturbations, photon noise limited, and would allow processed imaging with very high dynamic range. This at the price of loosing the convolution operation between the focal plane and the object.