We report a module employing shearing interferometry with constant off-axis angle (SICA) that works both for coherent light sources and low-coherence light sources, in which the shearing distance in uncoupled to the off-axis angle. In the module, two laterally sheared sample beams are generated by a grating, and the part of the sample area containing no sample details serves as the reference beam, as in any shearing interferometer. However, in our module, the shearing distance can be flexibly adjusted by controlling the axial location of the grating, while the off-axis interference angle remains constant.
The value range of AoP (angle of polarization) is physically limited to [0, π]. However, for most programing languages such as Matlab and C/C++, the range of inverse tangent function is commonly limited to [-π/2, -π/2]. Therefore, this paper derives a practical formula for AoP calculation based on the inverse tangent function of common programming languages. Because AoP is a periodical function, the conventional gray image cannot effectively display the AoP levels. The hue component of HSV (hue, saturation and value) color space is also periodical. Therefore, this paper maps the AoP to hue component and then transforms HSV space to RGB space. Different AoP reference orientations will produce different false color displays. In our experiment, polarization images of a fishbowl scene are captured by a DoFP (division of focal plane) polarization camera, and a sequence of false RGB images with different reference orientations are produced.
Structural Similarity Index (SSIM) is a common and useful image assessment method, and is better than mean square error (MSE) and peak signal to noise ratio (PSNR). However, when evaluating the quality of blur images and noise images, the correlation coefficient between the assessment results of SSIM and the subjective ones is low. A method based on visual structural similarity (VSSIM) for image quality assessment is proposed in this paper. The method is based on the multichannel properties of the log-polar Gabor filter and contrast sensitivity function. Multi-channel visual feature of distorted and reference images with log-polar Gabor transformation is extracted, and then the value of each channel’s SSIM is calculated, and finally, all the SSIM are mixed together according to the weight calculated by the contrast sensitivity function. Experimental results show that VSSIM can assess the blur and noise image quality precisely.
The modulation transfer function (MTF) is the tool most commonly used for quantifying the performance of an electro-optical imaging system. Recently, trapezoid-shaped pixels were designed and used in a retina-like sensor in place of rectangular-shaped pixels. The MTF of a detector with a trapezoidal pixel array is determined according to its definition. Additionally, the MTFs of detectors with differently shaped pixels, but the same pixel areas, are compared. The results show that the MTF values of the trapezoidal pixel array detector are obviously larger than those of rectangular and triangular pixel array detectors at the same frequencies.
A method of encoding eight objects simultaneously in a detour computer generated hologram(CGH) is
proposed. In the method, we divide eight objects into two groups and multiple objects are encoded
through synthesized spectrum. The simulation demonstrated the effectiveness of the method. In the
reconstruction two groups of objects were reconstructed around the same diffraction order along x, y directions, respectively. The result showed that the method can improve the information capacity in
a CGH efficiently.
The aspheric technology has been largely restricted by testing methods. In particular, the acquisition of the dynamic
measurement for different aspheric surface is still a challenge. The reconstruction of the reference wavefront based on
spatial light modulator is studied in this paper. Computer-generated hologram is been loaded into the SLM and the
standard wavefront is reconstructed. Considering the effect of the SLM grid structure on wavefront accuracy, the theory
model of SLM diffraction is analyzed and the elimination methods of SLM structure influence are proposed. Then based
on theory analysis, the reconstructed wavefront is demonstrated by using computer simulation. Finally, the
corresponding experimental apparatus is built and the wavefront accuracy is analyzed. The experiment results show that
the method has achieved worthy measurement precision and has great development potential for optical shape
measurement.
It is important to accurately obtain micro displacement in industry, especially in numerical controlled
machine. But traditional methods encountered some difficulties in high-precision measurement. A new
approach based on moiré fringes digital image processing technique (DIP) is proposed in this paper. A
smartly designed experiment is done to grasp moiré fringes from two same gratings, so complicated
equipments are not necessary which has obvious advantages. A CCD is used to acquire digital images.
Then the images are done by digital image processing, including filtering and gray-scale transformation,
fringes identification. A smart way to calibrate the distance represented by each pixel is given in this
paper with DIP technique. The distance of a certain fringe between two images is obtained to display
the micro displacement of any object. The result of this approach is compared with a higher accurate
micro displacement, their similarity identify the correct of this method. We are sure that the result will
be more satisfactory if higher accurate equipment is applied in inspection.
Optical transfer function (OTF) of optical system is an important character to show optical system's
imaging quality. It is important to accurately obtain the OTF in optical measurement. But traditional
methods encountered some difficulties in high-precision measurement. A new approach based on
digital image processing technique (DIP) is proposed in this paper. An experiment is done to acquire
the image of a pill and a CCD is used to acquire digital images. Optical-electronic focal plane fixing
technology is adopted to obtain a more accurate image. Then the images are done by digital image
processing, including filtering and Fast Fourier Transform, and the 2-dimension modulated transfer
function (MTF) is obtained. The MTF of this detected lens derived from this way is compared with a
higher accurate equipment to measure the OTF of the same lens, the results have some differences.
The reason is analyzed in this paper. This method will be widely used in optical inspection.
Resolution of optical system is a critical index to judge the quality of optical system. Measuring the
resolution of optical system has become more and more important in optical measurement. But
traditionally the method to evaluate the resolution of optical system is mainly subjective because of
man's eye seeing. Although this method is simple and intuitive, it is very easy for the introduction of
the subjective error. To solve this problem, an approach based on digital image processing technique is
brought out to achieve this subjective processing in this paper. An experiment is done to grasp image of
resolving power test target formed by a teleobjective, its extreme resolution is obtained. The result
matches ideal resolution by calculation. This way has the advantage of rapid processing and objective.
It is the tendency of measuring resolution in the future.
A novel method of using Thin Film Transistor-Liquid Crystal Display(TFT-LCD) as phase filter in Zernike phase
contrast method is introduced. First, theoretical analysis of using TFT-LCD as programmable phase modulator instead of
conventional phase contrast plate to filter the spectrum is conducted. Then the phase modulation property curve of the
used TFT-LCD is measured which is function of gray scales in modified Mach-Zehnder interferometer, and frequency
filtering is used to eliminate interferogram's noise and the correlation method is adopted to determine the
mini-displacement of interference fringe. At last, Experiment conducted in 4F system. The result showed that the method
is effective in qualitative observation of phase distribution for a small phase object.
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