Single CCD Research Articles

Simultaneous dual directional strain measurement using spatial phase-shift digital shearography

This paper presents a Dual Directional Sheared Spatial Phase-Shift Digital Shearography (DDS-SPS-DS) system for simultaneous measurement of strains/displacement derivative in two directions. Two Michelson Interferometers are used as the shearing device to create two shearograms, one in the x-shearing direction and one in the y-shearing direction, which are recorded by a single CCD camera. Two lasers with different wavelengths are used for illumination, and corresponding band pass filters are applied in front of each Michelson Interferometer to avoid cross-interference between the two shearing direction channels. Two perpendicular shearing directions in the two measurement channels introduce two different spatial frequency carriers whose spectrums are orientated in different directions after Fourier Transform. Phase maps of the recorded two shearograms can be obtained by applying a windowed inverse Fourier transform, which enables simultaneous measurement of dual directional strains/displacement derivatives. The new system is well suited for nondestructive testing and strain measurement with a continuous or dynamic load. The capability of the dual directional spatial phase-shift digital shearography system is described by theoretical discussions as well as experiments.

Error Optimization of Machine Vision based Tool Movement using a Hybrid CLONALG and PSO Algorithm

A machine vision system with single monochrome CCD camera and backlight was developed for tool positioning and verification. While evaluating the performance of the developed vision system, the experiments showed that the output of machine vision system was not comparable to the output of sensors embedded in motion stages. Inherent factors like Imaging setup, camera calibration, environmental effects etc. are responsible for the error. These errors must be minimized to achieve maximum efficiency of developed vision system. In this paper, a novel hybrid algorithm is proposed to optimize the tool position error. The proposed algorithm comprises of CLONALG (one of the techniques of Artificial Immune System) and Particle Swarm Optimization (PSO) (a global optimization algorithm). Hybrid algorithm is tested on tool movement ranging from 0.020 mm to 7 mm. Performance of proposed algorithm is evaluated and also compared with CLONALG and PSO algorithms individually.

Estimation of measurement uncertainty caused by surface gradient for a white light interferometer

Although the scanning white light interferometer can provide measurement results with subnanometer resolution, the measurement accuracy is far from perfect. The surface roughness and surface gradient have significant influence on the measurement uncertainty since the corresponding height differences within a single CCD pixel cannot be resolved. This paper presents an uncertainty estimation method for estimating the measurement uncertainty due to the surface gradient of the workpiece. The method is developed based on the mathematical expression of an uncertainty estimation model which is derived and verified through a series of experiments. The results show that there is a notable similarity between the predicted uncertainty from the uncertainty estimation model and the experimental measurement uncertainty, which demonstrates the effectiveness of the method. With the establishment of the proposed uncertainty estimation method, the uncertainty associated with the measurement result can be determined conveniently.

Compact and fully automated system for monitoring photodynamic therapy, based on two LEDs and a single CCD

Photodynamic therapy is one of the most promising methods for the treatment of oncological, inflammatory and degenerative diseases of the skin. This technique is based on light irradiation of a photosensitizer that has been injected into the patient’s body prior to the procedure, with determination of the efficacy of treatment requiring proper assessment of the drug concentration in the tissue lesion and the extent of sensitizer photobleaching during irradiation. We have developed a compact and low cost device based on a fluorescence imaging for localizing the tumor in the patient’s body, tracking the position of the tissue lesion during involuntary movements of the patient, estimating accumulation of the sensitizer in the tumor relative to the surrounding tissues and monitoring photobleaching of the sensitizer during laser irradiation. The system that has been created is compatible with any therapeutic laser and includes a single CCD camera and two LEDs, one in the excitation band and the other in the emission band of the ‘Photoditazin’ sensitizer. In this letter we also present the test results of the device in model experiments and in preliminary clinical trials. The results obtained clearly show the efficacy of the system for monitoring sensitizer photobleaching during photodynamic therapy.

Development and demonstration of table-top synchronized fast-scan femtosecond time-resolved spectroscopy system by single-shot scan photo detector array

Ultrafast dynamics is generally studied by pump–probe method with laser pulse, which scans optical delay by motorized stage step by step. Using ultrashort laser pulse shorter than typical molecular vibration periods, the pump–probe measurement can study both of electronic dynamics and vibration dynamics simultaneously. The probe wavelength dependence of the ultrafast electronic and vibration dynamics (UEVD) helps us to distinguish the signal contributions from the dynamics of the electronic ground state and that of the electronic excited states, which elucidates primary reaction mechanism after photoexcitation. Meanwhile, the measurement time of UEVD spectroscopy takes too long time to be used in realistic application. In our previous work, we have developed multi-channel lock-in amplifying (MLA) detectors to study UEVD at all probe wavelengths simultaneously, and synchronized it with laser and fast-scan delay stage to scan the data in five seconds. It enabled us to study UEVD spectroscopy even for photo-fragile materials. However, the home-made MLA detectors required for the measurement is expensive and massive in size and weight, thus not suitable for general researchers in the field of ultrafast time-resolved spectroscopy. In the present work, we have developed a table-top synchronized fast-scan femtosecond time-resolved spectroscopy system using single shot scan line CCD. This system measures time-resolved trace at all probe wavelengths simultaneously in five seconds. The CCD-based fast-scan time-resolved spectroscopy system enables us to study ultrafast dynamics of various materials even biomaterials, which have been thought to be hard or even impossible to be studied in previous methods.

Focal lengths of Venus Monitoring Camera from limb locations

The Venus Monitoring Camera (VMC) carried by European Space Agency’s Venus Express orbiter (Svedhem et al., 2007) consists of four optical units, each with a separate filter casting an image on a single CCD (Markiewicz et al., 2007a, 2007b). The desire to capture as much of the planet in a single frame during the spacecraft’s 24h, 0.84 eccentricity orbit led to optics with 18° field of view. Analysis of Venus images obtained by the VMC indicated that the computed limb radius and altitude of haze layers were somewhat inconsistent with prior knowledge and expectations. Possible causes include errors in the knowledge of image geometry, misalignment of the optic axis from the pointing direction, and optical distortion. These were explored and eliminated, leaving only deviations from the ground and pre-solar damage estimate of the focal length lengths as the most likely reason. We use the location of planet’s limb to estimate the focal length of each camera using images of the planet when the orbiter was more than 20,000km from planet center. The method relies on the limb radius to be constant at least over a small range of solar zenith angles. We were able to achieve better estimates for the focal lengths for all four cameras and also estimate small offsets to the boresight alignment.An outcome of this analysis is the finding that the slant unit optical depth varies more rapidly with solar zenith angle in the afternoon as compared to morning, with lowest values at local noon. A variation of this level is also observed with latitude. Both are indicative of the presence of overlying haze above the clouds, and the morning afternoon asymmetry suggests different photochemical processes in destruction and production of the haze.

English

This paper discusses about the design and fabrication of vision based Autonomous Underwater Cable Tracking (AUCT) system and its working principle based on the propulsion technique. The AUCT system consists of three levels of controllers namely, higher level controller, Middle level controller and the Lower level controller to navigate the Autonomous Underwater Vehicle (AUV). A single CCD camera and an Ultrasonic distance sensor are used to determine the relative position of the underwater cable with respect to the Autonomous Underwater Vehicle (AUV) in a 3 dimensional space. Visual data provides two dimensions and ultrasonic distance sensor data provides the 3rd dimension. An image filtering technique to reduce some undesirable features is underwater images, is used based on the morphological operator. A real-time algorithm is developed to determine the position of the cable in the image plane by cascading an estimator governed by AUV dynamics, with help of Hough transformation technique. The proposed system will perform very well other than in situations where the cable is covered by waterweeds for a long distance. This system can be used as a solution to the problem of underwater positioning especially in pre-determined areas.

Improvement of the dynamic range using background subtraction in single shot wide-field optical coherence tomography

We investigated on the signal in single shot wide-field optical coherence tomographic (SS-WF-OCT) system to improve the dynamic range (DR). The SS-WF-OCT system is based on two-dimensional (2D) polarization Michelson interferometer and superluminescent diode (center wavelength of 842.5 nm) as light source. Two π-phase-shifted interferograms were acquired simultaneously using a single CCD camera and after subtraction, the en-face OCT image (area (x) 4.0 mm × (y) 4.3 mm) is obtained using 2D Hilbert transform. The OCT signal including incoherent background noises was analyzed. To improve the DR, background noise subtraction has been introduced and its measurement process is presented. This method is valuable during the background noise is stable. Using the scattering samples, such as, grind metal and polymer sponge with background subtraction algorithm, a significant reduction in background noise and improvement in the DR was demonstrated .

单CCD彩色相机激光干扰模型及外场干扰实验

Out-field laser jamming experiment of single CCD colour imaging system irradiated by multi-wavelength laser( 750- 970 nm) was done. Laser jamming effects of colour CCD imaging system with different irradiating conditions were measured at 1. 3 km. Laser jamming model was set up,and theoretical proving and analysis on experimental results were completed. Theoretical and experimental results show that the jamming effect of laser on colour CCD imaging system is obvious,CCD surface appears obvious light saturation and crosstalk phenomena. The light saturation phenomenon is caused by laser diffraction effect. In addition,laser jamming effect and light saturation gradually enhance with the increasing of the laser power density to target. When the laser power density to target of single wavelength 750 nm laser is 4. 2 k W / cm2,the light saturation area of CCD surface is0. 88 mm × 0. 97 mm. When the laser power density to target of multi-wavelength laser is 20. 7 k W /cm2,CCD device appears the whole target saturation. The simulation results are coincident with the experimental results,and it proves that the laser jamming model is correct. The simulation results for far-field laser jamming show that the laser jamming effect gradually weakens with the increasingof laser jamming distance.

Fiber Specklegram-Multiplexed Sensor

In this study, several multiplexing techniques have been combined to achieve a fiber specklegram multiplexed sensor. Using a single CCD camera as detector, two lasers of different wavelengths have been launched into two multimode polymer optical fibers and then combined through a 2 x 2 coupler before their interrogation. Both coupler exit fibers have been projected to different CCD positions and by analyzing each color of the video sequence, the four fiber channels can be independently obtained. In addition, the speckle sensitivity has been also studied analyzing different properties of speckle patterns such as their contrast or the speckle size. The achieved results will be very useful to the development of new fiber specklegram sensors with several sensing areas using only a CCD camera as detector, making possible low cost sensing devices.

Study on Volumetric Tool Wear Measurement Using Image Processing

This paper presents a method of measuring the volumetric tool wear by use of the image processing technique. A single CCD camera based stereo vision system is built to acquire the image pair. The crater wear’s boundary of the cutting tool is then detected, and then the 3D volumetric shape of the worn region on the rake face is reconstructed through the developed image matching algorithms, and the crater’s volume and depth is estimated. A Matlab software system is developed to perform image acquisition, calibration, image rectification, image adjustment, stereo matching, crater’s depth estimation, and the representation of the volumetric tool wear. The feasibility of the proposed method is verified through experiments.

A video precipitation sensor for imaging and velocimetry of hydrometeors

Abstract. A new method to determine the shape and fall velocity of hydrometeors by using a single CCD camera is proposed in this paper, and a prototype of a video precipitation sensor (VPS) is developed. The instrument consists of an optical unit (collimated light source with multi-mode fibre cluster), an imaging unit (planar array CCD sensor), an acquisition and control unit, and a data processing unit. The cylindrical space between the optical unit and imaging unit is sampling volume (300 mm × 40 mm × 30 mm). As the precipitation particles fall through the sampling volume, the CCD camera exposes twice in a single frame, which allows the double exposure of particles images to be obtained. The size and shape can be obtained by the images of particles; the fall velocity can be calculated by particle displacement in the double-exposure image and interval time; the drop size distribution and velocity distribution, precipitation intensity, and accumulated precipitation amount can be calculated by time integration. The innovation of VPS is that the shape, size, and velocity of precipitation particles can be measured by only one planar array CCD sensor, which can address the disadvantages of a linear scan CCD disdrometer and an impact disdrometer. Field measurements of rainfall demonstrate the VPS's capability to measure micro-physical properties of single particles and integral parameters of precipitation.

New Optical Scanning Tomography using a rotating slicing for time-resolved measurements of 3D full field displacements in structures

In this paper, a new optical tomography process is presented. It has been developed for time-resolved measurement of kinematic fields in the whole volume of structure. This new process is based on the scan of the specimen by a plane laser beam submitted to a motion of rotation. Calibration and reconstruction steps have been established and are described in this document. Acquisition is achieved by illuminating successive slices in the specimen using a rotating plane laser beam and data are recorded with a single CCD camera. The recorded volumes are analyzed by Digital Volume Correlation to measure the three displacement components in the bulk. This new acquisition process is assessed by performing sub-voxel rigid body translations along the three axes. We discuss the quality of a reconstructed volume and also the measurement accuracy in terms of mean error and standard deviation through rigid body displacement tests. Results are compared with those obtained using classical Optical Scanning Tomography (OST) and using X-ray Tomography.

三种不同结构的无透镜鬼成像实验研究

To achieve stand-off sensing applications, ghost imaging experiments with pseudothermal light were performed from transmissive to reflective cases. First, ghost images of a transmissive double-slit aperture were retrieved in a setup that both the reference beam and signal beam were collected with two different regions of a single CCD. Then a CCD and a separate bucket detector were used to record the light intensity information of the reference beam and the signal beam, respectively. By calculating the intensity correlation function of the signal beam with no spatial light distribution and the spatial dependent reference beam that does not interact with the object, ghost images of a transmissive object and a reflective object were achieved. In order to design and develop prototype systems field applicable, detailed experimental investigations were performed to compare the effect of system parameters on the quality of imaging in the transmission configuration. The results show that enough high power of light source, large sample numbers, and proper exposure time and spatial frequency bandwidth can lead to ghost image with good resolution and visibility.

反射式光学像面拼接方法研究

The size of a single CCD cannot meet the requirements of modern optical system.To enlarge the field of optical system,a reflector based butting system was adopted.Aiming at the problems of vignetting and decline of modulation transfer function caused by butting,a reflector based butting system which has 6reflectors was investigated.By analyzing the feature of vignetting,a sub-image pixel overlapping method was proposed to reduce the vignetting.At the same time,vignetting at edge was restored,and the modulation transfer function was improved by compositive point spread function.The results show that though the cut-off frequency has not been increased,the value of modulation transfer function is improved obviously.

Polarization modulation polarimeter for measuring two-dimensional distribution of five cell parameters of a twisted nematic liquid crystal display

In this study, an intensity-sensitive polarization modulation polarimeter (IPMP) was proposed and set up in order to measure the cell parameters of a twisted-nematic liquid crystal display (TNLCD). Both Yeh and Gu's transfer matrix and Lien's transfer matrix of a TNLCD are used and they are able to characterize all five cell parameters of a TNLCD including the cell gap, pretilt angle, rubbing angle, twist angle and untwisted phase retardation simultaneously. The optical setup is based on a single CCD camera and the ratio of p- and s-linear polarization intensity signals whereas we rotate a calibrated quarter wave plate to produce the polarization modulation during measurement. Thus, all five cell parameters are determined numerically by use of the least square curve fitting algorithm between the measured data and theoretical prediction following Yeh & Gu's and Lien's models of a TNLCD at same time. Finally, the advantages of this proposed IPMP are discussed.

Dual-wavelength laser speckle imaging to simultaneously access blood flow, blood volume, and oxygenation using a color CCD camera

We developed a dual-wavelength laser speckle imaging system using a single industrial-grade color CCD camera with Bayer filters to simultaneously image changes in blood flow, blood volume, and oxygenation. One frame of a color image recorded with dual-wavelength laser illumination provides not only the intensity fluctuation of the speckle pattern, but also the dual-wavelength optical reflectance signal. The method was validated using a tissue phantom and cuff ischemia experiments in the human arm. This system achieves complete time synchronization, unlike conventional time-sharing systems. Compared with a multicamera system, it also avoids the problem of image registration and can be less expensive.

Measuring principle of vertical target density based on single linear array CCD camera

In consideration of the complexity and the high cost of the dual CCD intersection vertical target when it is used indoor. A novel measuring principle of one linear array CCD camera vertical target is presented. One low-power semiconductor sector-like laser with projection board is used to be the lamp-house of the CCD camera. The detection light screen of the CCD camera and the laser lamp-house are adjusted to same plane. When the projectile through the detection light screen, it blocks the part light of the laser and leaves a shadow of projectile on the board. The shadow and its coordinate are acquired and calculated by the CCD camera and computer, and the projectile coordinate of X and Y can be gotten through image processing and further calculation. The measuring principle and the formulas are given, and the measuring error is analyzed. The result indicates that the coordinate error of X and Y less than 1.5 and 2.2mm, respectively, when the detection light screens is 1m×1m, The principle presented has the advantages that measurement principle is simple, low cost and easy engineering.

Comparison about Stitching Algorithms for Sub-Images of Multiple TDI CCD Chips Based on Image Matching

Due to the limited pixel numbers in single TDI CCD chips, some TDI CCD chips are combined in the focal plane to reach a sufficient swath width. Basic imagery is delivered as one image data file per strip and how to convert those sub-images to a larger, accuracy equivalent image is an essential problem in satellite images’ processing. Some key factors that affect the imaging quality of TDI CCD images are discussed firstly. It shows that discrepancies in the along-track direction which caused by different viewing angle and topographic relief are the main problem to improve the stitching accuracy. Three basic image-oriented stitching strategies are discussed. Experimental results show that the RMS of shift transformation, single affine transformation and piecewise affine transformation is 1.4 pixels, 1.3 pixels and 0.2 pixels. Piecewise affine transformation fully meets the requirements of further processing.

Image demosaicing using content and colour-correlation analysis

Most digital cameras of today use a single CCD image sensor with alternating arrangement of red, blue and green colour filters in what is known as a Bayer pattern. To extract a full colour image, a demosaicing strategy has to be applied. In this paper we propose a content adaptive demosaicing strategy utilising structure analysis and correlation between the red, green and blue planes. These two aspects are used for the classification of a block of pixels to generated trained filters. The proposed method aims to reconstruct a high quality demosaiced image from a Bayer pattern in a colour filter array efficiently. Experimental results show that the proposed strategy performs comparatively as more expensive methods.