Showing papers on "High dynamic range published in 2010"

Generalized Assorted Pixel Camera: Postcapture Control of Resolution, Dynamic Range, and Spectrum

Abstract: We propose the concept of a generalized assorted pixel (GAP) camera, which enables the user to capture a single image of a scene and, after the fact, control the tradeoff between spatial resolution, dynamic range and spectral detail. The GAP camera uses a complex array (or mosaic) of color filters. A major problem with using such an array is that the captured image is severely under-sampled for at least some of the filter types. This leads to reconstructed images with strong aliasing. We make four contributions in this paper: 1) we present a comprehensive optimization method to arrive at the spatial and spectral layout of the color filter array of a GAP camera. 2) We develop a novel algorithm for reconstructing the under-sampled channels of the image while minimizing aliasing artifacts. 3) We demonstrate how the user can capture a single image and then control the tradeoff of spatial resolution to generate a variety of images, including monochrome, high dynamic range (HDR) monochrome, RGB, HDR RGB, and multispectral images. 4) Finally, the performance of our GAP camera has been verified using extensive simulations that use multispectral images of real world scenes. A large database of these multispectral images has been made available at http://wwwl.cs.columbia.edu/ CAVE/projects/gap_camera/ for use by the research community.

Capturing and rendering high dynamic range images

Abstract: Some embodiments of the invention provide a mobile device that captures and produces images with high dynamic ranges. To capture and produce a high dynamic range image, the mobile device of some embodiments includes novel image capture and processing modules. In some embodiments, the mobile device produces a high dynamic range (HDR) image by (1) having its image capture module rapidly capture a succession of images at different image exposure durations, and (2) having its image processing module composite these images to produce the HDR image.

Noise-optimal capture for high dynamic range photography

Abstract: Taking multiple exposures is a well-established approach both for capturing high dynamic range (HDR) scenes and for noise reduction. But what is the optimal set of photos to capture? The typical approach to HDR capture uses a set of photos with geometrically-spaced exposure times, at a fixed ISO setting (typically ISO 100 or 200). By contrast, we show that the capture sequence with optimal worst-case performance, in general, uses much higher and variable ISO settings, and spends longer capturing the dark parts of the scene. Based on a detailed model of noise, we show that optimal capture can be formulated as a mixed integer programming problem. Compared to typical HDR capture, our method lets us achieve higher worst-case SNR in the same capture time (for some cameras, up to 19 dB improvement in the darkest regions), or much faster capture for the same minimum acceptable level of SNR. Our experiments demonstrate this advantage for both real and synthetic scenes.

Coded rolling shutter photography: Flexible space-time sampling

Abstract: We propose a novel readout architecture called coded rolling shutter for complementary metal-oxide semiconductor (CMOS) image sensors. Rolling shutter has traditionally been considered as a disadvantage to image quality since it often introduces skew artifact. In this paper, we show that by controlling the readout timing and the exposure length for each row, the row-wise exposure discrepancy in rolling shutter can be exploited to flexibly sample the 3D space-time volume of scene appearance, and can thus be advantageous for computational photography. The required controls can be readily implemented in standard CMOS sensors by altering the logic of the control unit. We propose several coding schemes and applications: (1) coded readout allows us to better sample time dimension for high-speed photography and optical flow based applications; and (2) row-wise control enables capturing motion-blur free high dynamic range images from a single shot. While a prototype chip is currently in development, we demonstrate the benefits of coded rolling shutter via simulation using images of real scenes.

Globally Optimized Linear Windowed Tone Mapping

Abstract: This paper introduces a new tone mapping operator that performs local linear adjustments on small overlapping windows over the entire input image. While each window applies a local linear adjustment that preserves the monotonicity of the radiance values, the problem is implicitly cast as one of global optimization that satisfies the local constraints defined on each of the overlapping windows. Local constraints take the form of a guidance map that can be used to effectively suppress local high contrast while preserving details. Using this method, image structures can be preserved even in challenging high dynamic range (HDR) images that contain either abrupt radiance change, or relatively smooth but salient transitions. Another benefit of our formulation is that it can be used to synthesize HDR images from low dynamic range (LDR) images.

The Rehabilitation of MaxRGB

Abstract: The poor performance of the MaxRGB illuminationestimation method is often used in the literature as a foil when promoting some new illumination-estimation method. However, the results presented here show that in fact MaxRGB works surprisingly well when tested on a new dataset of 105 high dynamic range images, and also better than previously reported when some simple pre-processing is applied to the images of the standard 321 image set [1]. The HDR images in the dataset for color constancy research were constructed in the standard way from multiple exposures of the same scene. The color of the scene illumination was determined by photographing an extra HDR image of the scene with 4 Gretag Macbeth mini Colorcheckers at 45 degrees relative to one another placed in it. With preprocessing, MaxRGB’s performance is statistically equivalent to that of Color by Correlation [2] and statistically superior to that of the Greyedge [3] algorithm on the 321 set (null hypothesis rejected at the 5% significance level). It also performs as well as Greyedge on the HDR set. These results demonstrate that MaxRGB is far more effective than it has been reputed to be so long as it is applied to image data that encodes the full dynamic range of the original scene. Introduction MaxRGB is an extremely simple method of estimating the chromaticity of the scene illumination for color constancy and automatic white balancing based on the assumption that the triple of maxima obtained independently from each of the three color channels represents the color of the illumination. It is often used as a foil to demonstrate how much better some newly proposed algorithm performs in comparison. However, is its performance really as bad as it has been reported [1,3-5] to be? Is it really any worse than the algorithms to which it is compared?1 The prevailing belief in the field about the inadequacy of MaxRGB is reflected in the following two quotations from two different anonymous reviewers criticizing a manuscript describing a different illumination-estimation proposal: “Almost no-one uses Max RGB in the field (or in commercial cameras). That this, rejected method, gives better performance than the (proposed) method is grounds alone for rejection.” “The first and foremost thing that attracts attention is the remarkable performance of the Scale-by-Max (i.e. White-Patch) algorithm. This algorithm has the highest performance on two of the three data sets, which is quite remarkable by itself.”   Paper’s title inspired by Charles Poynton, “The Rehabilitation of Gamma,” Proc. of Human Vision and Electronic Imaging III SPIE 3299, 232-249, 1998. We hypothesize that there are two reasons why the effectiveness of MaxRGB may have been underestimated. One is that it is important not to apply MaxRGB naively as the simple maximum of each channel, but rather it is necessary to preprocess the image data somewhat before calculating the maximum, otherwise a single bad pixel or spurious noise will lead to the maximum being incorrect. The second is that MaxRGB generally has been applied to 8-bit-per-channel, non-linear images, for which there is both significant tone-curve compression and clipping of high intensity values. To test the pre-processing hypothesis, the effects of preprocessing by median filtering, and resizing by bilinear filtering, are compared to that of the common pre-processing, which simply discards pixels for which at least one channel is maximal (i.e., for n-bit images when R=2n-1 or G=2n-1 or B=2n-1). To test the dynamic-range hypothesis, a new HDR dataset for color constancy research has been constructed which consists of images of 105 scenes. For each scene there are HDR2 (high dynamic range) images with and without Macbeth mini Colorchecker charts, from which the chromaticity of the scene illumination is measured. This data set is now available on-line. MaxRGB is a special and extremely limited case of Retinex [6]. In particular, it corresponds to McCann99 Retinex [7] when the number of iterations is infinite, or to path-based Retinex [8] without thresholding but with infinite paths. Retinex and MaxRGB both depend on the assumption that either there is a white surface in the scene, or there are three separate surfaces reflecting maximally in the R, G and B sensitivity ranges. In practice, most digital still cameras are incapable of capturing the full dynamic range of a scene and use exposures and tone reproduction curves that clip or compress high digital counts. As a result, the maximum R, G and B digital counts from an image generally do not faithfully represent the corresponding maximum scene radiances. Barnard et al. [9] present some tests using artificial clipping of images that show the effect that lack of dynamic range can have on various illumination-estimation algorithms. To determine whether or not MaxRGB is really as poor as it is report to be in comparison to other illumination-estimation algorithms, we compare the performance of several algorithms on the new image database. We also find that two simple preprocessing strategies lead to significant performance improvement in the case of MaxRGB. Tests described below show that MaxRGB performs as well on this new HDR data set as other representative and recently published algorithms. We also find that two simple pre-processing strategies lead to significant performance improvement. The results reported here extend those of an earlier study [10] in a number of ways: the size of the dataset   2 Note that the scenes were not necessarily of high dynamic range. The term HDR is used here to mean simply that that full dynamic range of the scene is captured within the image. 3 www.cs.sfu.ca/~colour/data  Page 1 of 4

A low-noise, high-dynamic-range, digital receiver for radio astronomy applications: an efficient solution for observing radio-bursts from Jupiter, the Sun, pulsars, and other astrophysical plasmas below 30 MHz

Abstract: A new two-channel digital receiver that can be used for observing both stationary and sporadic radio sources in the decameter wave band is presented. Current implementation of the device operating at the sampling frequency of 66 MHz is described in detail, including the regimes of waveform capture, spectrogram analysis, and coherence analysis (cross covariance between the two inputs). Various issues pertaining to observational methods in the decameter waveband affected significantly by man-made interferences have been taken into account in the receiver design, as well as in the architecture of the interactive software that controls the receiver parameters in real time. Two examples of using the receiver with the UTR-2 array (Ukraine) are reported: S-bursts from Jupiter and low-frequency wide-band single pulses from the pulsar PSR0809+74

A reassessment of the simultaneous dynamic range of the human visual system

Abstract: The dynamic range of the human visual system should be an important parameter in the design of high dynamic range (HDR) display devices. A good display should at least approximate this range. However, the literature reports a simultaneous dynamic range between 2 and 4 log units of luminance, leaving ambiguity as to what dynamic range HDR display devices should cater for. In this paper we present a sequence of psychophysical experiments, carried out with the aid of a high dynamic range display device, to determine the simultaneous dynamic range of the human visual system under full adaptation to a given background luminance. Our findings show that the human visual system is capable of distinguishing contrasts over a range of 3.7 log units under specific viewing conditions. Further, we show how the dynamic range is affected by stimulus duration, contrast of the stimulus as well as background illumination, thereby accounting for the differences reported in the literature and providing guidance for display design.

An adaptive Logluv transform for High Dynamic Range video compression

Abstract: High Dynamic Range (HDR) imaging represents a wide range of intensity levels found in real scenes ranging from direct sunlight to shadows. However, raw HDR sequences require very huge memory space for storage. In this work, we present an approach of how an existing encoder can be used for encoding HDR video sequence with our proposed adaptive LogLuv transform. The proposed method shows considerable improvement when compared with non-adaptive LogLuv transform.

Performance verification of symbol-based OFDM radar processing

Abstract: In this paper a recently proposed novel processing approach for OFDM radar is verified with measurements. This processing algorithm directly calculates a radar image from the transmitted and received modulation symbols that compose the OFDM signal without the need for performing correlation operations. The implementation of a suitable system setup is described. The measurement results confirm that with this approach a very high dynamic range can be obtained. Moreover, the SNR in the measured radar images is investigated. The results prove that the proposed algorithm provides high processing gain.

Single-shot, high-dynamic-range measurement of sub-15 fs pulses by self-referenced spectral interferometry.

Abstract: We explore theoretically and numerically the temporal contrast limitation of a self-referenced spectral interferometry measurement. An experimental confirmation is given by characterization and fine compression of hollow-core fiber generated sub-15fs pulses, yielding an accurately measured coherent contrast of 50dB on a ±400fs time range.

Evalution of High Dynamic Range Image-Based Sky Models in Lighting Simulation

Abstract: High Dynamic Range (HDR) Photography is used to capture 180° images of the sky dome and provide data for image-based lighting in lieu of CIE sky models.

Recent advances in high dynamic range imaging technology

Abstract: Recently, visual representations using high dynamic range (HDR) images become increasingly popular, with advancement of technologies for increasing the dynamic range of image. HDR image is expected to be used in wide-ranging applications such as digital cinema, digital photography and next generation broadcast, because of its high quality and its powerful expression ability. HDR imaging technologies will spread its sphere of influence in imaging industry. In this paper, we review the state-of-the-art studies and the trends of the HDR imaging, in terms of the following three points: (1) HDR imaging sensor and HDR image generation techniques as image acquisition technologies, (2) encode method of HDR images for efficient transmission and storage, (3) human visual system issues associated with reproduction of HDR image.

HDR image construction from multi-exposed stereo LDR images

Abstract: In this paper, we present an algorithm that generates high dynamic range (HDR) images from multi-exposed low dynamic range (LDR) stereo images. The vast majority of cameras in the market only capture a limited dynamic range of a scene. Our algorithm first computes the disparity map between the stereo images. The disparity map is used to compute the camera response function which in turn results in the scene radiance maps. A refinement step for the disparity map is then applied to eliminate edge artifacts in the final HDR image. Existing methods generate HDR images of good quality for still or slow motion scenes, but give defects when the motion is fast. Our algorithm can deal with images taken during fast motion scenes and tolerate saturation and radiometric changes better than other stereo matching algorithms.

Zone-based tone mapping

Abstract: A method of tone mapping high dynamic range images for display on low dynamic range displays wherein a high dynamic range image is first accessed. The high dynamic range image is segmented into different regions such that each region is represented by a matrix, where each element of the matrix is a weight or probability of a pixel. An exposure of each region is determined or calculated and the exposure values are applied to the regions responsive to the weight or probability. The different regions are then fused together to obtain a final tone mapped image.

Swept-source polarization-sensitive optical coherence tomography based on polarization-maintaining fiber.

Abstract: We present a swept-source polarization-sensitive optical coherence tomography system based on a polarization-maintaining fiber interferometer. The system produces reflectivity and birefringence information along a depth profile with a single sweep of the optical spectrum. Unlike single-mode fiber systems, retardance and relative optical axis orientation images are calculated without compensation. The source is a 45 mW polygon-based swept-source centered at 1290 nm and tuned at a rate of 28 kHz. The interferometer consists of a single polarization-maintaining coupler that utilizes balanced detection for improved performance. Characterization data shows that this system yields accurate measurements with high sensitivity (106.2 dB) comparable to conventional setups. Images of biological tissues with high dynamic range are demonstrated.

Low resistance, high dynamic range reconfigurable phase change switch for radio frequency applications

Abstract: A GeTe reconfigurable phase change switch for radio frequency applications is presented Low ON state resistance (180 Ω) and large dynamic range (7×103 X) were achieved through low resistance electrode design and high current A partial crystallization and partial reamorphization model is proposed to explain the differences between the measured and calculated device ON (set) and OFF (reset) state resistances, respectively The dependency between ON state resistance and reset current was estimated using a first order thermal design in steady state which suggests lower reset current by choosing materials of lower melting temperature and structures with better thermal isolation

Laser flare measuring device and measuring method thereof

Abstract: The invention relates to a laser facula measuring device and a measuring method thereof. The device consists of a DMD micro-mirror array, a digital camera, an exposure control unit and a picture digital processor. The exposure control unit is provided with two output ends which respectively output signals to control the DMD micro-mirror array and the digital camera; and the input end of the picture digital processor is connected with the video signal output end of the digital camera. In the method, DMD micro-mirror array components are utilized, so the characteristics of an incident light path can be changed at different times and in different regions so as to accurately control the exposure process and obtain a laser beam detection image with high dynamic range; and by means of data processing, diameter, ellipticity, position, center, three-dimensional outline, power, and other parameters of the facula can be obtained. As the whole process happens within a short time, the defect thatthe position and the energy state of the laser facula changes as time goes by can be avoided, and light beam quality of the laser beam can be more accurately measured.

High dynamic range video with ghost removal

Abstract: We propose a new method for ghost-free high dynamic range (HDR) video taken with a camera that captures alternating short and long exposures. These exposures may be combined using traditional HDR techniques, however motion in a dynamic scene will lead to ghosting artifacts. Due to occlusions and fast moving objects, a gradient-based optical flow motion compensation method will fail to eliminate all ghosting. As such, we perform simpler block-based motion estimation and refine the motion vectors in saturated regions using color similarity in the adjacent frames. The block-based search allows motion to be calculated directly between adjacent frames over a larger search range, yet at the cost of decreased motion fidelity. To address this, we investigate a new method to fix registration errors and block artifacts using a cross-bilateral filter to preserve the edges and structure of the original frame while retaining the HDR color information. Results show promising dynamic range expansion for videos with fast local motion.

DEPFET sensor with intrinsic signal compression developed for use at the XFEL free electron laser radiation source

Abstract: A new DEPFET detector-amplifier structure with strongly non-linear characteristics is presented. It will be used as basic element of an X-ray pixel detector at the new XFEL free electron laser radiation source to be constructed in Hamburg, Germany, providing at the same time single X-ray photon detection and high dynamic range even when operated at readout frequency up to 5 MHz. This is possible due to the new detector concept that adds to the excellent DEPFET properties – combined function of detector amplifier and data storage, full sensitivity over whole bulk, non-destructive readout, low serial noise and absence of reset noise – the new features of very large charge handling capability and signal compression. Concept and design will be presented and properties demonstrated by extended computer simulations.

High dynamic velocity range particle image velocimetry using multiple pulse separation imaging.

Abstract: The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods.

Solid-state ultrafast all-optical streak camera enabling high-dynamic-range picosecond recording.

Abstract: We demonstrate an ultrafast optical recording system based on a novel optical beam deflection technique. An optical pump temporarily creates an array of prisms that deflect an optical signal beam within a GaAs/AlGaAs planar waveguide. The fabricated device yielded, to our knowledge, the fastest sustained optical deflection reported to date and was used to create spatial representations of ultrafast temporal waveforms. A conventional camera was then used to record single-shot waveforms with a 2.5 ps resolution over a 50 ps record with a dynamic range in excess of 3000:1. Through further development, this all-optical streak camera could provide insight into previously unmeasurable phenomena in many fields.

A multiple target doppler estimation algorithm for OFDM based intelligent radar systems

Abstract: In this paper an approach will be presented that allows for estimating the velocity of multiple reflecting objects with standard OFDM communication signals. The proposed technique does not require any specific coding of the transmit signal and provides high dynamic range and low sidelobe levels. This allows for an efficient acquisition of velocity information in joint communication and radar systems. The paper discusses the developed algorithm and a possible OFDM system concept for automotive applications. Measurement results are provided that prove the operability in practical scenarios.

Exposure control for high dynamic range image capture

Abstract: A device and methods are provided for producing a high dynamic range (HDR) image of a scene are disclosed and claimed. In one embodiment, method includes setting an exposure period of an image sensor of the digital camera and capturing image data based on the exposure period. The method may further include checking the image data to determine whether the number of saturated pixels exceeds a saturation threshold and checking the image data to determine whether the number of cutoff pixels exceeds a cutoff threshold. The method may further include generating a high dynamic range image based on image data captured by the digital camera, wherein the high dynamic range image is generated based on a minimum number of images to capture a full dynamic range of the scene.

A robust and fast anti-ghosting algorithm for high dynamic range imaging

Abstract: This paper presents a robust and fast algorithm for automatically generating high dynamic range (HDR) images in presence of camera movement and moving objects. This scheme comprises five modules: 1) image alignment, 2) estimation of camera response function (CRF) in dynamic scenes, 3) moving object detection, 4) progressive image correction, and 5) construction of HDR images. The key advantage of the algorithm is the ability to generate HDR images without ghost artifact. The proposed algorithm is fast as it is a one-shot solution without iterative computation and post-processing or even manual operation. Experimental results demonstrate that the proposed method outperforms the existing commercial products.

Multi-modal tone-mapping of images

Abstract: A system for multi-modal mapping of images is described. Embodiments are described where the image mapping system is used for visualizing high dynamic range images such as medical images, satellite images, high dynamic range photographs and the like and also for compressing such images. In examples, high bit-depth images are tone-mapped for display on equipment of lower bit-depth without loss of detail. In embodiments, the image mapping system computes statistics describing an input image and fits a multi-modal model to those statistics efficiently. In embodiments, the multi-modal model is a Gaussian mixture model and a plurality of sigmoid functions corresponding to the multi-modal model are obtained. In an embodiment the sigmoid functions are added to form a tone-mapping function which is used to transform a high bit-depth image such as 16 or 12 bits per pixel to a low bit-depth image such as 8 bits per pixel.

High Dynamic Range image tone mapping based on local Histogram Equalization

Abstract: High Dynamic Range (HDR) images can represent the acquired scene with a greater dynamic range of luminance than classical Low Dynamic Range (LDR) ones. Despite the recent diffusion of some HDR camera models, HDR displays are not yet in the market. For this reason HDR images need to be adapted in order to be properly rendered through conventional devices. This operation mainly consists in a dynamic range compression realized by applying a Tone Mapping Operator (TMO). In this work, a new tone map algorithm, derived from the Contrast Limited Adaptive Histogram Equalization (CLAHE) technique, is presented. With respect to the original CLAHE, in the proposed implementation an adaptive contrast limit and a new strategy for the determination of local tone mapping functions have been introduced. The comparison between the obtained LDR images, and those produced by applying State of the Art TMOs, evidences how the main characteristic of the proposed algorithm is the ability to equally enhance visibility in both dark and bright areas. This could be, for example, a key feature in video surveillance applications and automotive safety camera systems.

Automated Broadband High-Dynamic-Range Nonlinear Distortion Measurement System

Abstract: This paper presents an intermodulation distortion measurement system based on automated feedforward cancellation that achieves 113 dB of broadband spurious-free dynamic range for discrete tone separations down to 100 Hz. For 1-Hz tone separation, the dynamic range is 106 dB, limited by carrier phase noise. A single-tone cancellation formula is developed requiring only the power of the probing signal and the power of the combined probe and cancellation signal so that the phase shift required for cancellation can be predicted. The technique is applied to a two-path feedforward cancellation system in a bridge configuration. The effects of reflected signals and of group delay on system performance is discussed. Spurious frequency content and interchannel coupling are analyzed with respect to system linearity. Feedforward cancellation and consideration of electromagnetic radiation coupling and reverse-wave isolation effects extends the dynamic range of spectrum and vector analyzers by at least 40 dB. Application of the technique to the measurement of correlated and uncorrelated nonlinear distortion of an amplified wideband code-division multiple-access signal is presented.