Warp and weft density is commonly considered as one of the most important index for estimating the quality of fabrics.
However, the detecting method adopted is basically base on manually counting. It is rather inefficient. This article
demonstrates how to construct efficient system to achieve automatically detection. Fabric is first coupled into the image
sensor by a specific optical system, whose resolution matching is carefully designed. And other component parameters
are also well considered. What is more, the system contains a light source to provide uniformed illumination. A circuit
board with camera module is constructed to perform the role of image processing platform. With amazingly agile
performance provide by an ARM920T processor, and featuring an incredible breadth of peripheral interfaces, the
platform is well suit for fabric density detection. The periodicity within the captured image furnishes convenience for
analysis in frequency domain. After FFT the intensity peaks ranked orderly around the original point. However, the peaks
in the spectrum are always blurred by severe interference whose form is usually an image or a pattern on the fabric. For
this reason, a specific algorithm should be worked out to erode the peaks from the blurred edge to the center. Sometimes,
the central peak is so severely blurred and the central peak is actually useless for us, a unique algorithm is employed to
kick off the central peak. By this way, the position of the surround peaks can be easily located. And the density can also
be easily worked out.
The roughness of the surface is an important parameter that reflects the quality of the object. Optical methods are the
usual ways to measure the surface roughness including scattering method, speckle method, interferometric method and
optical stylus method. But they are highly required the precision of the mechanism and they are not convenient to realize
the automatic measurement. To improve the structure and the automatic performance, this surface roughness
measurement system is based on the theory of two-dimensional phase unwrapping that is widely used in
aerophotogrammetry. With the theory, the three dimensional data can be calculated from the images detected. The
difference is that the image is captured by radar in aerophotogrammetrytly while it is got by using optical structure in this
system. The images are got through the optical structure with the structured light. To control the phase of the light, the
gratings is used in the system controlled by the piezoelectric ceramics. The phase information is contained in the image
and captured by the CCD camera. To analyze the images captured through the optical system, the phase should be
extracted from the images through complex operation to generate the phase map. The quality-guided algorithm is the
main algorithm in this system. LabVIEW is the main software development environment and the massive calculation is
accomplished in the dynamic linked library complied by Visual C++ to realize the image processing. Through the
stereogram showed in the software we can clearly get the three dimensional information of the surface.
Eccentric photorefraction (EPR), which is used to determine the refractive error of eye, is greatly relied on the crescent pattern of the pupil image or on the intensity gradient in the principal meridian across the pupil. The vignetting image of the pupil, which is formed by a camera lens aperture with an eccentric light source, and contains a lot of refractive information of the subject eye, has been studied by many authors expecting to get more accurate measurement. In this paper, we have investigated the formation of the crescent image of the pupil. A mathematical expression that calculates the relative intensity in the whole pupil is derived. The intensity distribution is shown in a topography figure that gives a more clear understanding of the pupil image. Based on the discussion of the point light source, light sources are then further extended to other shapes such as line, circle or rectangular form for more general cases, simply by integrating the point source over the scale of the actual geometric form. The analysis and calculation presented are based on Gaussian optics for simplicity. The investigation results show that line source with 0 eccentricity at its one end is suggested in the EPR, in which the intensity slope is much sensitive to the refractive states.
Eccentric photorefraction is an objective refraction technique that, by taking a picture of the pupil of the subject, can measure refractive errors in human eyes. The method assessing the refractive errors is mainly from the size and orientation of the crescent of the pupil image. Because of the effects of the light source and the vignetting of the optical system’s aperture, the boundary of the crescent is not sharp so as to accurately determine its size. This uncertainty reduces the accuracy of the EPR system and limits its extensive application. In this paper, analysis on the light intensity distribution across the pupil is presented. It aims to determine the size of the crescent based on the aperture opening in the form of straight edge, rectangle and slit are also included in discussion. The analysis shows that the EPR system with a line source and a rectangular aperture opening will give a good linear light distribution profile across the pupil, which may be helpful to automatically determine the size of the crescent. The method will effectively improve the measurement accuracy of EPR.
The inverted telephoto lens consisting of two groups is required when a long back focal length and a wide field of view are needed. Varying the air space between these two groups would change the effective focal length. In this paper, power allocation for this varifocal lens affected by aperture, field of view and amount of variation of air space is analyzed. The solution of power allocation is introduced, from which large aperture, wide field of view, and small volume is benefit. Six equations, i.e. power region equation, aperture equation, field of view equation, back focal length equation, movable region equation, speed equation, are derived to guide power allocation of this kind of optical system.
We introduce a Gaussian Optical analysis method for a common five-components zoom lens, namely “3+2”. This model has covered a great many type of zoom lens forms by regarding some of components as dummy ones. Taking each component as a paraxial one, “3+2” program calculates the geometric optics through the whole zooming range. The output report will show the moving curve of each element. “3+2” can mutually share the information with ZEMAX through the extension feature of ZEMAX.
The diffraction of volume holographic gratings follows the Bragg law, and narrow wavelength selectivity and angle selectivity can be achieved with certain thickness of hologram. Multiple volume holographic gratings formed in Fe : LiNbO3 have high diffraction efficient and stability performance, which can be used for compact dense multiplexer/demultiplexer (MUX/DMUX). In this paper, we identify that it is feasible to record 16 volume holographic gratings by a special recording ways. The calculated results show the insertion losses and crosstalk at 1 .55µm waveband with channel separation 0.8nm is 0.66dB and —26dB respectively.
A kind of super larger, aperture combined, reflective plane wavefront is recommended in this paper. Structure principle and the method of forming accurate plane wavefront are described. Accuracy is analyzed, and several results of local experiments for arguments are discussed. All these prove that the SLAPW with accuracy higher than λ/20(λ-wavelength) can be constructed, which will be used in testing astronomic instruments with any super large aperture.
It is difficult to detect ametropia and anisometropia for children. Image sensor for testing refractive error of eyes does not need the cooperation of children and can be used to do the general survey of ametropia and anisometropia for children. In our study, photographs are recorded by a CCD element in a digital form which can be directly processed by a computer. In order to process the image accurately by digital technique, formula considering the effect of extended light source and the size of lens aperture has been deduced, which is more reliable in practice. Computer simulation of the image sensing is made to verify the fineness of the results.
In this paper, we introduce a new method to inspect the soft and smooth surface, especially the corneal topography. The method is based on the fact that smooth surfaces have the property of reflecting light. Special-shaped gratings are used as projecting device, that is, different grating for different inspected object, according to the topographic condition. For example, a grating with the form of a series of concentric circular rings is good for corneal topography inspection. When the image which contains the topographic information of the object being tested is reflected, it is recorded by a CCD camera. Then the 2D image obtained is processed and calculated by a computer to make out a 3D profile of the surface. This article emphatically reckons a new algorithm which can deduce the corneal topography.
Two phenomena which are different form traditional observation results in holographic imaging are reported in this paper. They are double virtual images and so-called virtual pseudomorphic image. It is shown that here exists an appropriate condition for Fresnel hologram upon which two virtual images can be reconstructed. And it is also shown that the virtual pseudomorphic image could not be physical, but only psychological.