We report a novel device that the reflected intensity of Bragg grating (FBG) inscribed in a polarization-maintaing fewmode fiber (PM-FMF) is tuned by temperature from 56°C to 156°C with a wavelength shift of 1nm and intensity decrease of ~10dBm. The reflection spectrum and corresponding mode coupling are analyzed, the calcultated birefringence B for LPo1, LP11a and LP11b polarized modes are 4.3×10-4 , 4.6×10-4 and 4.7×10-4 , respectively, which agree with the specified birefringence of the PM-FMF, B ~5.0×10-4 .
Wavefront coding for athermal technique can effectively ensure the stability of the optical system imaging in large temperature range, as well as the advantages of compact structure and low cost. Using simulation method to analyze the properties such as PSF and MTF of wavefront coding athermal system under several typical temperature gradient distributions has directive function to characterize the working state of non-ideal temperature environment, and can effectively realize the system design indicators as well. In this paper, we utilize the interoperability of data between Solidworks and ZEMAX to simplify the traditional process of structure/thermal/optical integrated analysis. Besides, we design and build the optical model and corresponding mechanical model of the infrared imaging wavefront coding athermal system. The axial and radial temperature gradients of different degrees are applied to the whole system by using SolidWorks software, thus the changes of curvature, refractive index and the distance between the lenses are obtained. Then, we import the deformation model to ZEMAX for ray tracing, and obtain the changes of PSF and MTF in optical system. Finally, we discuss and evaluate the consistency of the PSF (MTF) of the wavefront coding athermal system and the image restorability, which provides the basis and reference for the optimal design of the wavefront coding athermal system. The results show that the adaptability of single material infrared wavefront coding athermal system to axial temperature gradient can reach the upper limit of temperature fluctuation of 60°C, which is much higher than that of radial temperature gradient.
Hilbert transform (HT) is widely used in temporal speckle pattern interferometry, but errors from low modulations might propagate and corrupt the calculated phase. A spatio-temporal method for phase retrieval using temporal HT and spatial phase unwrapping is presented. In time domain, the wrapped phase difference between the initial and current states is directly determined by using HT. To avoid the influence of the low modulation intensity, the phase information between the two states is ignored. As a result, the phase unwrapping is shifted from time domain to space domain. A phase unwrapping algorithm based on discrete cosine transform is adopted by taking advantage of the information in adjacent pixels. An experiment is carried out with a Michelson-type interferometer to study the out-of-plane deformation field. High quality whole-field phase distribution maps with different fringe densities are obtained. Under the experimental conditions, the maximum number of fringes resolvable in a 416×416 frame is 30, which indicates a 15λ deformation along the direction of loading.
A measurement region extended differential laser Doppler velocimeter with multipoint illumination was proposed. The arrangement used two types of ruled diffraction gratings to form the extended region with several independent measuring volumes. The measurement model was then given, demonstrating that a solid object passed through a single measuring volume or two measuring volumes simultaneously. Signal processing technique efficiently enhanced the signal-to-noise ratio. Experimental results showed that the measurement range along the optical axis could be extended to 109.73 mm with a beam angle of 9.557 deg. The mean error of velocity ranging from 7 to 13 m/s was 1.52% by using the frequency spectrum correction method. The results indicated that the proposed method has great potential for realizing the velocity measurement of solid objects in a large measuring region.
A modified Michelson interferometer for spatial phase shifting speckle shearography is presented. The interferometer consists of one slit aperture, one beam splitter, and two spherical mirrors. Spatial carrier frequency and shear are both generated by one translated spherical mirror. The slit aperture controls the speckle size. These arrangements make the system simple and easy to align. The shear is proportional to the translation of the spherical mirror. Shear distortion due to the rotated mirror in a traditional Michelson interferometer is avoided as well. The carrier frequency is proven to be constant in image plane and can be conveniently adjusted by translating the spherical mirror without changing imaging setup. Fourier analysis method is applied to accurately calibrate carrier frequency. Finally, experimental dynamic deformation results of a center loaded metal plate using the proposed method are provided.
Dynamic speckle pattern interferometry has been widely applied to measure vibration or continuously-deformation. As a
promising technique, temporal phase analysis reduces the 2D phase retrieval task to 1D and gives wider measurement
range. In this paper, some classical and recently proposed temporal phase retrieval techniques, such as windowed Fourier
transform, wavelet transform and Hilbert transform, are comparatively studied. The advantages and drawbacks of each
algorithm are discussed and evaluated in simulation experiments.
Dynamic speckle interferometry using temporal phase analysis has larger measurement range and is easier to setup over
phase-shifting based speckle interferometry. Hilbert transform (HT) is a widely used approach to implement analytic
method based phase retrieval. To fulfill the requirements of HT based phase retrieval, EMD (Empirical Mode
Decomposition) can be applied to remove the bias intensity. With the low noise assumption, the first IMF was taken as
the input for HT. However, according to our experiments, some dynamic speckle signals are not as good as assumed. In
many cases, the first IMF is not the proper one. To find the proper IMF, we proposed to adaptively find the IMF of
largest similarity with the input signal. And the similarity is evaluated by mutual information. Simulation experiments
were given to verify the validity of the proposed algorithm.
Detectors of infrared focal plane arrays are, in the nature of their photoresponse, nonuniform. Response curves are nonlinear. In view of this, a novel nonuniformity correction algorithm based on the S-curve nonlinear response model and its simplified correction algorithm is proposed. The algorithm is an essential calibration and interpolation correction based on an analytical formula. It requires calibrating in advance, but possesses higher correction precision and wider applicative response range, which is particularly applicable to uncooled infrared focal plane arrays. Borrowing ideas from look-up tables, a real-time hardware correction system, which provides an experimental platform for contrasting different algorithms, is expounded. Experimental results validate that the proposed S-curve model-based algorithm does much better than the two-point correction algorithm and the simplified S-curve model-based correction algorithm.
Uniform illumination plays an important role in Digital Speckle Pattern Interferometry (DSPI) of measuring a large
object. This paper presents a method that by designing a specified DOE with certain algorithm in front of laser diodes, a
large and uniform illumination could be achieved at the designed distance. The fluctuation of no more than 10% has been
analyzed for its influence on interferogram. Only 6 semiconductor lasers are necessary in the interferometer to lighting
its view in theory and the experiment with the simulated illumination has been done. The fringes of deformation at
different parts of the object show that this method is suitable for large area detection.
This paper proposed an interactive image segmentation algorithm that can tolerate slightly incorrect user constraints.
Interactive image segmentation was formulated as a constrained spectral graph partitioning problem. Furthermore, it was
proven to equal to a supervised classification problem, where the feature space was formed by rows of the eigenvector
matrix that was computed by spectral graph analysis. ν-SVM (support vector machine) was preferred as the classifier.
Some incorrect labels in user constraints were tolerated by being identified as margin errors in ν-SVM. Comparison with
other algorithms on real color images was reported.
In order to measure the 3D architecture of tire size code, Digital Speckle Pattern Interferometry (DSPI) and Phase
Shifting interferometry(PSI) were integrated to capture its phase. With capturing speckle pattern interferogram by
reference-wave interferometry, the illumination laser diodes of DSPI-PSI interferometer were arranged to enlarge the
illumination area; and the viewing field was also expanded by battery of lens containing field lens and imaging lens. To
generate a phase difference associated with height of test surface, the illumination beam was rotated by motor. The
experiment results show the viewing field was more than 60 degree, the resolution of surface profile match the tire size
code height as 1mm.
Using Digital Speckle Pattern Interferometry (DSPI) method measuring the large object in practice, the
primarily problem is uniform illumination. This paper presents a method that using multiple laser
beams to enlarge the illumination area and analysis the non-uniform illumination influences for
interferogram. We design an illumination model using 10 semiconductor lasers for interferometer, and
corresponding experiment shows that this method is suitable for industrial measurement in large area
detection.
The width of the crack is an important indicator in evaluation of the quality of the buildings. Hand-held embedded device used for measuring the width of the cracks can reduces the labor intensity of staff, improve the efficiency and reliability of measurement. In width measuring based on embedded image processing, some problems are existed, such as: "isolated island" noise, the edge of burr which reduce the accuracy of calculation result. The algorithm in the paper can solve these problems. By means of sub-block to increase the speed of image processing of the cracks, then searched
the edge of the crack in the blocks which contains crack. this way can reduce image processing time by at least one order of magnitude while getting the preliminary ruling edge of the crack. Additionally, presents a method that use the basic morphological operations and chain to smooth the edge, then obtains the correct edge of the crack. Finally, get the width of the cracks through "Fast hierarchical vector". Experiments confirmed that the correct width of the crack can be got with this algorithm, Accuracy is up to 50μm.
Tire size code (TSC) specifies the dimensions of the tire, and some of its key limitations, such as load-bearing ability and
maximum speed. The key challenge of vision based TSC identification is the low contrast of TSC to tire background. In
order to extract TSC from low-contrast tire images, this paper proposed to consider the contours of TSC as the symmetry
axes of the neighbor pixels along the contours. The symmetry axes were detected using local phase information which is
robust to image brightness and contrast. Firstly, the ring shaped tire region was segmented and then expanded to a
rectangular region, where all characters were upright. Due to the intensity values of the neighbor pixels along the
contours of TSC were symmetric, the contours in low-contrast tire image were enhanced using local phase information,
which is computed by Log-Gabor wavelets. Finally, the thin contours were extracted by non-maxima suppression and
thresholding with hysteresis. Experiments on real tire images showed that, in comparison with intensity based
algorithms, the proposed algorithm were robust to uneven illumination and low-contrast.
KEYWORDS: Monochromatic aberrations, Wavefronts, Modulation transfer functions, Optical transfer functions, Phase transfer function, Spatial frequencies, Signal to noise ratio, Optoelectronics, Image processing, Computer simulations
The phase mask plays a key role in wavefront coding systems. In order to find the phase coding device with better
performance, a new kind of phase mask - five times phase mask is proposed, based on cubic phase mask in common use,
and its coding properties are studied in the paper. First of all, the reason of depressing spherical aberration is analyzed by
deriving the asymptotic solution to OTF of the wavefront coding systems with five times phase mask. And then we
compare the effects of inhibition of spherical aberration when place the cubic and five times phase mask respectively.
Finally, the experimental simulation is done. The results show that on the specific threshold (MTF=0.1) the normalized
bandwidth of the system with five times phase mask can be reached 3 times of that with the cubic one; at the same
characteristic frequency (u = 0.5), the MTF value is 2 times of that in system with cubic one. Both the MTF consistency
in the low frequency region and the PTF consistency in the high frequency region of the system with a five times phase
mask are better than those with a cubic one in condition of different spherical aberration. Compared with the cubic phase
mask, the five times phase mask performs better in inhibition of spherical aberration.
High-power LEDs of different color have generated much enthusiasm because of the potential energy savings and
reduced maintenance cost due to long lifetimes compared with traditional light source. Two schemes are widely used for
LED dimming: continuous current dimming, or pulse-width modulation (PWM) dimming. The visual felling to the LEDs
is the most intuitive judgment in the LED illumination and display. But the apparent brightness of the LEDs under these
dimming ways has never been studied. In this paper, the research of the apparent brightness is approached through
experiments. The results show that when the average intensities are the same, the apparent brightness of the PWM
dimming LED is higher than that of the continuous dimming LED. In addition, to the PWM dimming LEDs, the contrast
apparent brightness of various color LEDs is obviously discrepant as the duty cycle is less than 40%, but when it is
above 40%, the gap between the contrast values becomes much smaller. Thus, in the LED applications, the LEDs using
PWM driving method has higher brightness efficacy, and the duty cycle of the PWM should be above 40% to achieve the
consistent apparent brightness between LEDs. The results have great availability to optimize the driver for the LEDs.
KEYWORDS: Image processing, Image filtering, Optical character recognition, Detection and tracking algorithms, Feature extraction, Pattern recognition, Edge roughness, Aluminum, Zoom lenses, Signal to noise ratio
To relieve the inefficient of traditional method on auto car tire character recognition based on
hand-copying, in this paper, we present an intellective method of fast recognition. Several algorithms
were involved in this method, including polar transformation, improved canny operator and distance
fast cluster.
The procedure was consisted of several steps. In first step, tire image was rotated by polar
transformation and mosaic to form a rectangle area by Bilinear Interpolation algorithm. Compared to
other methods this part can reduce system time expense greatly. Next, Histogram Equalization
algorithm was used to improve the gray distribution and image contrast, which always low on the
foreground and background of image for the curing process. Then, the real edge was extracted by
improved canny operator, which has advantages of smoothing image, binarizing image and suppressing
the big noise caused by rough surface. Subsequently, based on foregoing results, tire image was divided
into several small regions, and the judgment of each region whether belongs to real character region
was processed by utilizing the continued similarity and the ratio of black pixel number to white pixel
number. Furthermore distance fast cluster was utilized to filter noise and split image, and class merging
was also used to complete character split. Finally, character feature vectors were extracted and
character pattern recognition was completed using them.
This method was tested on a series of experiments, the result shows small time expenses and high
recognition ratio, which demonstrated that this method can satisfy the special requirement of fast and
effective recognition of autocar tire character.
This paper deals with the problem that a great number of rotary joints are suffering the conflict between high efficiency of signal dynamic coupling and low requirement of precision mechanism. As a solution, a specific design of the infrared spatial interconnection rotary joint is presented accompanying with the discussion of requirements for the mechanism and the circuit. Benefit from infrared data interconnection between the stator and the rotor, the security of data transfer is ensured and the off-axis angle can vary from 0º to 30º, which contribute to a simpler mechanism and a compact rotary joint. Relative experiment shows that with this rotary joint, signals can be transmit securely, and the efficient data transmission speed is up to 1.4Mbps under Windows 2000 circumstance.
Accurate object location is a key problem in image measurement system and the basis of other image processing procedures. In our project, we aim to locate some chromatic round objects in a large field. In this paper, the regions where the objects lie are isolated firstly from the original image using their color information, in which the edges of objects are detected. A novel fast method for fitting an
ellipse to the edge points in the region is presented, by which the geometric distortion is calibrated by the ellipse model calculated linearly according to the position of the region. And the position of object with the precision of one pixel is obtained through edge fitting. Finally the accurate data in 1/5 pixel result from subpixel subdivision.
KEYWORDS: Video, Image processing, Digital image processing, Image compression, Data processing, Optoelectronics, Video processing, Video compression, Instrumentation engineering, Pattern recognition
The movement of an object can be detected by subtracting the successive two frames of the object's video sequence. On the image after subtraction, there is a larger difference in the object area while a smaller one in the background part. So the track of a moving object can be detected by calculating the position of its gravity center on the image. But if there are several moving objects or the background is moving too, the gravity center of the image is not the real one of any objects. In this paper, we divided the image into 16 by 16 equals 256 parts and calculate the gravity center of each one. Then we get rid of parts with small average weight according to a certain threshold. The parts belong to the same moving object should be grouped in space, and a new gravity center is obtained. It is quite easy to get rid of the parts belong to the background because their differences are small and their moving vector are same. On the condition of 768 by 576 resolution and 25f/s video frequency, we are able to detect the tracks of several moving objects against a moving background and display them on a PC screen in real time.
Using JPEG standard, color still images can be compressed in high ratios while good quality can be guaranteed. The framework of the JPEG is specified, but the recommended quantization table and the Huffman table can be pruned according to the image's characteristic. In this paper, we put forward an adaptive-quantization approach which is compatible for the baseline JPEG. In our approach, we statistically calculate the image's average probability distributivity, which used as the threshold for the quantization. The quanti-table recommended by JPEG can then be justified with the characteristic of images and the average code-rate is noticeably dropped.
A real-time hybrid joint transform correlator (JTC) with parallel processing architecture that use two liquid crystal light valves spatial light modulators, two VP32 image boards and two optical wavefront-division multiplexers as the key parts was presented. Using this hybrid JTC< real-time high- efficiency joint transform correlation, high-speed joint transform correlation and four-channel joint transform correlation were realized. The hybrid JTC system has also been used in the domain of morphological complex-valued kernel scale-space image processing. In this paper, the principles of the above experiments are described, experimental results are also given and analyzed.
A nonlinear joint transform correlation (NLJTC) used for moving object tracking was proposed in this paper. In the proposed NLJTC, a high contrast liquid crystal light valve was used to implement real-time joint power spectrum nonlinear processing. Moving object tracking principle is described. Experimental results were given and analyzed.
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