Showing papers on "High dynamic range published in 2008"

Automatic High-Dynamic Range Image Generation for Dynamic Scenes

Abstract: Automatic high-dynamic range image generation from low- dynamic range images offers a solution to conventional methods, which require a static scene. The method consists of two modules: a camera-alignment module and a movement detector, which removes the ghosting effects in the HDRI created by moving objects.

Dynamic range independent image quality assessment

Abstract: The diversity of display technologies and introduction of high dynamic range imagery introduces the necessity of comparing images of radically different dynamic ranges. Current quality assessment metrics are not suitable for this task, as they assume that both reference and test images have the same dynamic range. Image fidelity measures employed by a majority of current metrics, based on the difference of pixel intensity or contrast values between test and reference images, result in meaningless predictions if this assumption does not hold. We present a novel image quality metric capable of operating on an image pair where both images have arbitrary dynamic ranges. Our metric utilizes a model of the human visual system, and its central idea is a new definition of visible distortion based on the detection and classification of visible changes in the image structure. Our metric is carefully calibrated and its performance is validated through perceptual experiments. We demonstrate possible applications of our metric to the evaluation of direct and inverse tone mapping operators as well as the analysis of the image appearance on displays with various characteristics.

Extending Quality Metrics to Full Luminance Range Images

Abstract: Many quality metrics take as input gamma corrected images and assume that pixel code values are scaled perceptually uniform. Although this is a valid assumption for darker displays operating in the luminance range typical for CRT displays (from 0.1 to 80 cd/m2), it is no longer true for much brighter LCD displays (typically up to 500 cd/m2), plasma displays (small regions up to 1000 cd/m2) and HDR displays (up to 3000 cd/m2). The distortions that are barely visible on dark displays become clearly noticeable when shown on much brighter displays. To estimate quality of images shown on bright displays, we propose a straightforward extension to the popular quality metrics, such as PSNR and SSIM, that makes them capable of handling all luminance levels visible to the human eye without altering their results for typical CRT display luminance levels. Such extended quality metrics can be used to estimate quality of high dynamic range (HDR) images as well as account for display brightness.

Correcting direction-dependent gains in the deconvolution of radio interferometric images

Abstract: Astronomical imaging using aperture synthesis telescopes requires deconvolution of the point spread function as well as calibration of instrumental and atmospheric effects. In general, such effects are time-variable and vary across the field of view as well, resulting in direction-dependent (DD), time-varying gains. Most existing imaging and calibration algorithms assume that the corruptions are direction independent, preventing even moderate dynamic range full-beam, full-Stokes imaging. We present a general framework for imaging algorithms which incorporate DD errors. We describe as well an iterative deconvolution algorithm that corrects known DD errors due to the antenna power patterns (including errors due to the antenna polarization response) as well as pointing errors for high dynamic range full-beam polarimetric imaging. Using simulations we demonstrate that errors due to realistic primary beams as well as antenna pointing errors will limit the dynamic range of upcoming higher sensitivity instruments like the EVLA and ALMA and that our new algorithm can be used to correct for such errors. We show that the technique described here corrects for effects that can be described as approximate unitary operators in the interferometric measurement equation, such as those due to antenna pointing errors and non-azimuthally symmetric antenna power patterns. We have applied this algorithm to VLA 1.4 GHz observations of a field that contains two “4C” sources and have obtained Stokes I and V images with systematic errors that are one order of magnitude lower than those obtained with conventional imaging tools. Residual systematic errors that are seen at a level slightly above that of the thermal noise are likely due to selfcalibration instabilities that are triggered by a combination of unknown pointing errors and errors in our assumption of the shape of the primary beam of each antenna. We hope to present a more refined algorithm to deal with the fully general case in due course. Our simulations show that on data with no other calibration errors, the algorithm corrects pointing errors as well as errors due to known asymmetries in the antenna pattern.

High dynamic range image sensor with reduced line memory for color interpolation

Abstract: An image sensor has an array of pixels organized into a row and column format. Pixels are read out in a line-by-line sequence and buffered in a line image buffer. An extended dynamic range is supported by varying a column exposure time according to a periodic sequence. As a result, the pixel exposure times vary within each row. A high dynamic range is generated by combining pixel data of adjacent pixels within the same row that are of the same filter type but having different exposure times. Color interpolation is performed on the combined line data.

An asynchronous time-based image sensor

Abstract: In this paper we propose a fully asynchronous, time- based image sensor, which is characterized by high temporal resolution, low data rate (near complete temporal redundancy suppression), high dynamic range, and low power consumption. Autonomous pixels asynchronously communicate the detection of relative changes in light intensity, and the time from change detection to the threshold crossing of a photocurrent integrator, so encoding the instantaneous pixel illumination shortly after the time of a detected change. The chip is being implemented in a standard 0.18 mum CMOS process and measures less than 10times8 mm2 at 304times240 pixel resolution.

High Dynamic Range Microwave Photonic Links for RF Signal Transport and RF-IF Conversion

Abstract: Two different techniques were used to extend the dynamic range of analog optical links operating at microwave frequencies. The link noise figure was reduced by adjusting the bias point of an external Mach-Zehnder intensity modulator. The link distortion was reduced by linearizing the transfer function of the intensity modulator. Frequency conversion was implemented using an additional optical modulator and electrical local oscillator rather than a conventional electronic mixer. A microwave frequency signal transport link was demonstrated with a spur-free dynamic range (SFDR) of 71 dB in a 500-MHz noise bandwidth. A link with down-conversion from a microwave frequency to an intermediate frequency was demonstrated with an SFDR of 64 dB in a 500-MHz noise bandwidth.

Dynamic Backlight Gamma on High Dynamic Range LCD TVs

Abstract: A high dynamic range liquid crystal display (HDR-LCD) can enhance the contrast ratio of images by utilizing locally controlled dynamic backlight. We studied the HDR-LCD as a dual-panel display: a backlight module and a liquid crystal (LC) cell. As the gamma of the LC signal, the backlight module was also endowed with a gamma function to control the contrast ratio of HDR images. The inverse of a mapping function (IMF) method proposed as a dynamic gamma mapping curve for the backlight module, has been demonstrated to further improve in HDR image quality. By implementing the IMF method on a HDR-LCD TV with 88 backlight zones, the image contrast ratio can reach while maintaining high brightness, clear image detail, and an average power reduction of 30%.

High dynamic range sensor system and method

Abstract: A high dynamic range sensor assembly includes a plurality of sensing sets that are organized into a sensing array. Each of the sensing sets includes a set of sensing elements for sensing physical phenomena. Each set of sensing elements has a locally selectable integration time. An analog-to-digital (A/D) converter operatively connected to the set of sensing elements acquires and converts an analog signal from each of the sensing elements into a digital signal. A processor operatively connected to the A/D converter and to the set of sensing elements manages the selectable integration time for the set of sensing elements and analyzes the digital signals from each of the sensing elements in the set of sensing elements. The digital signals from each of the sensing elements are measured by the processor and an integration scaling factor for the set of sensing elements is computed and controlled by the processor to adjust the integration time. The integration scaling factor for the set of sensing elements is mathematically combined with a value of the digital signal from the A/D converter to form a larger data word than what is generated by the A/D converter. The larger data word is utilized to represent a magnitude of each of the sensing elements. If a substantial number of A/D values have saturated, the integration time is decreased; and, if a substantial number of A/D values are below a predetermined threshold, the integration time is increased.

Bit-depth scalable coding for high dynamic range video

Abstract: This paper presents a technique for coding high dynamic range videos. The proposed coding scheme is scalable, such that both standard dynamic range and high dynamic range representations of a video can be extracted from one bit stream. A localized inverse tone mapping method is proposed for efficient inter-layer prediction, which applies a scaling factor and an offset to each macroblock, per color channel. The scaling factors and offsets are predicted from neighboring macroblocks, and then the differences are entropy coded. The proposed inter-layer prediction technique is independent of the forward tone mapping method and is able to cover a wide range of bit-depths and various color spaces. Simulations are performed based on H.264/AVC SVC common software and core experiment conditions. Results show the effectiveness of the proposed method.

Towards large scale CMOS single-photon detector arrays for lab-on-chip applications

Abstract: Single-photon detection is useful in many domains requiring time-resolved imaging, high sensitivity and high dynamic range. In this paper the miniaturization and performance potential of solid-state single-photon detectors are discussed in the context of lab-on-chip applications where high accuracy and/or high levels of parallelism are suited. Technological and design trade-offs are discussed in view of recent advances in integrated LED matrix technology and the emergence of new multiplication based architectures.

XPAD3-S: A fast hybrid pixel readout chip for X-ray synchrotron facilities

Abstract: At X-ray synchrotron facilities, scattering experiments require detectors with a large sensitive surface, an high count rate capability, a large counter dynamics, a fast readout system and an adjustable energy threshold. X-ray pixel chip with adaptable dynamics (XPAD3) is a new pixellized photon detector based on hybrid pixel technology, which provides low noise data readout at high speed. It is designed in 0.25 μm IBM technology and contains 9600 pixels (130 μm×130 μm) distributed into 80 columns of 120 elements each. Its features have been optimized to fulfill a count rate capability up to 10+6 photons/pixel/s, an high dynamic range over 35 keV, a very low noise of 130e−, and a threshold adjustment well below 4 keV. Fast data readout below 2 ms/frame is expected. To meet these requirements, an innovative architecture has been designed that makes possible the readout the circuit during acquisition while preserving the precise setting of the thresholds all over the pixel array. The XPAD3 circuit can be bump-bonded with Si, CdTe, or GaAs sensors to optimize its detection efficiency at high X-ray energies. XPAD3 detector modules will be tiled together to form the XPIX detector with a 8 cm×12 cm sensitive area. We present first results obtained using a single-chip prototype of the XPAD3 detector.

Expanding low dynamic range videos for high dynamic range applications

Abstract: In this paper we introduce an algorithm and related methods that expand the contrast range of Low Dynamic Range (LDR) videos in order to regenerate missing High Dynamic Range (HDR) data. For content generated from single exposure LDR sequences, this is clearly an under constrained problem. We achieved the expansion by inverting established tone mapping operator, a process we term inverse tone mapping. This approach is augmented by a number of methods which help expand the luminance for the required pixels while avoiding artifacts. These methods may be used to convert the large libraries of available legacy LDR content for use, for instance, on new content-starved HDR devices. Moreover, these same methods may be used to provide animated emissive surfaces for image based lighting (IBL). We demonstrate results for all the above applications and validate the resultant HDR videos with original HDR references using the HDR Visual Difference Predictor (HDR-VDP) image metric.

High dynamic range scanning technique

Abstract: Measuring objects with high surface reflectivity variations (i.e., high dynamic range) is challenging for any optical method. This paper addresses a high dynamic range scanning (HDRS) technique that can measure this type of objects. It takes advantage of one merit of a phase-shifting algorithm: pixel-by-pixel phase retrieval. For each measurement, multiple shots of fringe images with different exposures are taken. And a sequence of fringe images with different overall brightness are captured: the brightest fringe images have good fringe quality for darker areas although the brighter areas may be saturated; while the darkest fringe images have good fringe quality in brighter areas although the fringes in the darker areas may be invisible. The sequence of fringe images is arranged from brighter to darker, i.e., from higher exposure to lower exposure. The final fringe images, used for phase retrieval, are produced pixel-by-pixel by choosing the brightest but the unsaturated corresponding pixel from one shot. A phase-shifting algorithm is employed to compute the phase, which can be further converted to coordinates. Our experiments demonstrate that the proposed technique can successfully measure objects with high dynamic range of surface properties.

Dynamic-range compression and contrast enhancement in infrared imaging systems

Abstract: Third-generation thermal cameras have high dynamic range (up to 14 bits) and collect images that are difficult to visualize because their contrast exceeds the range of traditional display devices. Thus, sophisticated techniques are required to adapt the recorded signal to the display, maintaining, and possibly improving, objects' visibility and image contrast. The problem has already been studied in relation to images acquired in the visible spectral region, while it has been scarcely investigated in the infrared. In this work, this latter subject is addressed, and a new method is presented that combines dynamic-range compression and contrast enhancement techniques to improve the visualization of infrared images. The proposed method is designed to meet typical requirements in infrared sensor applications. The performance is studied through experimental data and compared with that yielded by three well-established algorithms. Evaluation is performed through subjective analysis, assigning each algorithm a score on the basis of the average opinion of human observers. The results demonstrate the effectiveness of the proposed technique in terms of perceptibility of details, edge sharpness, robustness against the horizon effect, and presence of very warm objects.

High-dynamic-range single-shot cross-correlator based on an optical pulse replicator.

Abstract: The operation of a single-shot cross-correlator based on a pulse replicator is described. The correlator uses a discrete sequence of sampling pulses that are nonlinearly mixed with the pulse under test. The combination of a high reflector and partial reflector replicates an optical pulse by multiple internal reflections and generates a sequence of spatially displaced and temporally delayed sampling pulses. This principle is used in a cross-correlator characterizing optical pulses at 1053 nm. A dynamic range higher than 60 dB is obtained over a temporal range larger than 200 ps.

The Eye-RIS CMOS Vision System

Abstract: Eye-RIS is the name of a family of vision systems which are conceived for single-chip integration using CMOS technologies. The Eye-RIS systems employ a bio-inspired architecture where image acquisition and processing are truly intermingled and the processing itself is realized in two steps. At the first step processing is fully parallel owing to the concourse of dedicated circuit structures which are integrated close to the sensors. These circuit structures handle basically analog information. At the second step, processing is realized on digitally-coded information data by means of digital processors. Overall, the processing architecture resembles that of natural vision systems, where parallel processing is made at the retina (first layer) and significant reduction of the information happens as the signal travels from the retina up to the visual cortex. This chapter outlines the concept of the Eye-RIS system and its main components and presents experimental data to illustrate its practical operation.

Agile Spectrum Imaging: Programmable Wavelength Modulation for Cameras and Projectors

Abstract: We advocate the use of quickly-adjustable, computer-controlled color spectra in photography, lighting and displays. We present an optical relay system that allows mechanical or electronic color spectrum control and use it to modify a conventional camera and projector. We use a diffraction grating to disperse the rays into different colors, and introduce a mask (or LCD/DMD) in the optical path to modulate the spectrum. We analyze the tradeoffs and limitations of this design, and demonstrate its use in a camera, projector and light source. We propose applications such as adaptive color primaries, metamer detection, scene contrast enhancement, photographing fluorescent objects, and high dynamic range photography using spectrum modulation.

High Dynamic Range Imaging by Fusing Multiple Raw Images and Tone Reproduction

Abstract: This paper presents an integrated color imaging system for taking images in extremely high dynamic range scenes. The system first fuses several differently exposed raw images to acquire more intensity information. The effective dynamic range of the image raw data can be extended to 256 times if five differently exposed images are fused. Then it runs edge detection iterations to extract the image details in different luminance levels. The proposed tone reproduction algorithm equalizes the histogram of the extracted fine edges which tends to assign larger dynamic range for highly populated regions. Finally, the local contrast enhancement is performed to further refine the image details. The experimental results show that the proposed high dynamic range imaging system has good performance on both tone and color reproduction.

A CMOS Integrable Oscillator-Based Front End for High-Dynamic-Range Resistive Sensors

Abstract: A new oscillating circuit is proposed to estimate the resistance and parallel parasitic capacitance of resistive chemical sensors. The circuit is able to reveal the resistance in a wide range (from tens of kiloohms to more than 100 GOmega) due to the adopted resistance-to-time technique. In addition, the parallel capacitance (up to 50 pF) can be estimated. The circuit, which does not need any initial calibration, is very simple and compact and is suitable to be integrated with a standard CMOS technology to obtain a low-cost and low-power device for a sensor array interface. Different kinds of post layout simulations concerning the CMOS integrated implementation have been conducted. Experimental results obtained using a discrete prototype board, both on passive components and on real sensors (metal-oxide sensors), have shown good linearity and reduced percentage error with respect to the theoretical expectations.

Superimposing dynamic range

Abstract: We present a simple and cost-efficient way of extending contrast, perceived tonal resolution, and color space of reflective media, such as paper prints, hardcopy photographs, or electronic paper displays. A calibrated projector-camera system is applied for automatic registration, radiometric scanning and superimposition. A second modulation of the projected light on the surface of such media results in a high dynamic range visualization. This holds application potential for a variety of domains, such as radiology, astronomy, optical microscopy, conservation and restoration of historic art, modern art and entertainment installations.

Methods and Systems for Inter-Layer Image Prediction Parameter Determination

Abstract: Aspects of the present invention are related to systems and methods for predicting a prediction parameter which may be used in the prediction of high dynamic range image elements from low dynamic range image data.

Sensor calibration and simulation

Abstract: We describe a method for simulating the output of an image sensor to a broad array of test targets. The method uses a modest set of sensor calibration measurements to define the sensor parameters; these parameters are used by an integrated suite of Matlab software routines that simulate the sensor and create output images. We compare the simulations of specific targets to measured data for several different imaging sensors with very different imaging properties. The simulation captures the essential features of the images created by these different sensors. Finally, we show that by specifying the sensor properties the simulations can predict sensor performance to natural scenes that are difficult to measure with a laboratory apparatus, such as natural scenes with high dynamic range or low light levels.

Consistent tone reproduction

Abstract: In order to display images of high dynamic range (HDR), tone reproduction operators are usually applied that reduce the dynamic range to that of the display device. Generally, parameters need to be adjusted for each new image to achieve good results. Consistent tone reproduction across different images is therefore difficult to achieve, which is especially true for global operators and to some lesser extent also for local operators. We propose an efficient global tone reproduction method that achieves robust results across a large variety of HDR images without the need to adjust parameters. Consistency and efficiency make our method highly suitable for automated dynamic range compression, which for instance is necessary when a large number of HDR images need to be converted.

Characterization for High Dynamic Range Imaging

Abstract: In this paper we present a new practical camera characterization technique to improve color accuracy in high dynamic range (HDR) imaging. Camera characterization refers to the process of mapping device-dependent signals, such as digital camera RAW images, into a well-defined color space. This is a well-understood process for low dynamic range (LDR) imaging and is part of most digital cameras — usually mapping from the raw camera signal to the sRGB or Adobe RGB color space. This paper presents an efficient and accurate characterization method for high dynamic range imaging that extends previous methods originally designed for LDR imaging. We demonstrate that our characterization method is very accurate even in unknown illumination conditions, effectively turning a digital camera into a measurement device that measures physically accurate radiance values — both in terms of luminance and color — rivaling more expensive measurement instruments.

Method for real-time implementable local tone mapping for high dynamic range images

Abstract: The present invention relates to a method capable of real-time implementable local tone mapping of high dynamic range images. In one embodiment, the present invention relates to a method capable of accomplishing real-time local tone mapping of high dynamic range images so that they have clear details without, for example, halo artifacts when viewed on standard display devices. In another embodiment, the present invention relates to a method capable of accomplishing real-time local tone mapping of high dynamic range images so that they have clear details without, for example, halo artifacts when viewed on standard display devices where such a method utilizes, in part, a modified Reinhard operator.

High dynamic range cascaded integration pixel cell and method of operation

Abstract: A cascaded imaging storage system for a pixel is disclosed for improving intrascene dynamic range. Charges accumulated in a first capacitor spill over into a second capacitor when a charge storage capacity of the first capacitor is exceeded. A third capacitor may also be provided such that charges accumulated by said second capacitor spill over into the third capacitor when the charge storage capacity of the second capacitor is exceeded.

Image characteristic oriented tone mapping for high dynamic range images

Abstract: This paper presents a novel and efficient tone mapping algorithm for converting high dynamic range (HDR) images back to low dynamic range (LDR) images for displaying purpose because of the limited contrast ratio of common displays and printers. As the ratio between the maximum and minimum values of common HDR images is always very large and also the population usually deflects to one side, for convenient processing, most researchers first take the logarithm on the luminance layer or use another adaptive mapping to shorter the range of the distribution in their tone mapping methods. However, these mappings have already distorted the original imagespsila characteristics. In this paper, there is no such adverse mapping applied on the luminance layer in the proposed tone mapping algorithm. The paper does produce a tone reproduction curve to convert HDR images to LDR images. Adaptive techniques are also manipulated to provide better visual quality. The whole process is automatic and no parameter is required for manual input. The result will be a superior visual quality tone mapped LDR image with original HDR imagepsilas characteristics.

A New Auto Exposure System to Detect High Dynamic Range Conditions Using CMOS Technology

Abstract: This paper proposes a new auto-exposure algorithm that can accurately detect high-contrast lighting conditions and improve the dynamic range of output images for a camera system. The proposed method calculates the difference between the mean value and the median value of the brightness level of captured images to estimate lighting conditions. After that, a multiple exposure mechanism is carried out to improve the details of output pictures. Simulation results show that the system works well with CMOS sensors used in mobile phones and surveillance cameras. Besides, the proposed algorithm is fast and simple and therefore can be fitted in most CMOS platforms that have limited capabilities.

Chaos light time domain reflectometer and measuring method thereof

Abstract: The invention relates to a chaotic optical time domain reflectometer and the measuring method in which chaotic laser signals from a chaotic light emitting device are divided into detecting light I and reference light II via an optical fiber coupler I; wherein the detecting light I is ejected to the optical fiber circuit under test via a circulator, and is then returned to a photodetector I, where a optical signal is converted to an electrical signal; the electrical signal is then converted to a digital signal via an A/D converter I and is inputted into a signal processor; the reference light II is received by a photodetector II where an optical signal is converted to an electrical signal; the electrical signal is inputted into the signal processor via an A/D converter II; the signal processor applies cross-correlation upon the two branches of digital signal input and comes out with a loss and the distance under test. By this means, position of a fault point is detected and as an output shown on the display unit. The chaotic optical time domain reflectometer provides possibilities of simultaneous improvement both for measuring a resolution and measuring a dynamic range; improves resolution of the optical time domain reflectometer and is provided with an anti-interference capability. Meanwhile, the chaotic optical time domain reflectometer is characterized with big noise tolerance, high dynamic range, simple structure, low cost, etc.