In recent years, endoscopic imaging has become the major diagnostic approach for early cancer. It is difficult to accurately obtain the information of lesions and components content by using conventional white light imaging (C-WLI). Multispectral imaging techniques such as narrowband imaging are widely used in endoscopic clinical because of their specificity on the surface structure of digestive tract mucosa. However, there is still a lack of multispectral techniques for tissue components specificity. Tissue components such as lipid, hemoglobin are closely related to the generation and development of tumors, but it is difficult to observe the characteristics of lipid and hemoglobin by conventional white light imaging. Therefore, we studied the multispectral endoscopic imaging technique for the analysis of digestive tract mucosal components. Based on the reflectance spectrum characteristics of these tissue components, we determined their specific wavelength, and comprehensively considered the absorption, scattering, oxygenation and others in order to determine the most appropriate optical band in the wavelength range of 365-660nm. Through experimental verification, we choose different narrow-band wavelength combinations for lipids and hemoglobin oxygen saturation respectively to achieve multispectral imaging. In order to simulate the optical properties of digestive tract surface, we made tissue optical phantom. At the same time, we tested and optimized the imaging system and algorithm by the experiments in vitro, and obtained the optimal multispectral image of tissue components, then realize the quantitative detection combined with the content analysis algorithm. Our pilots show that the multispectral imaging system can improve the contrast of endoscopy image, enhance the detail information, achieve high precision detection of tissue components content, and control the error within 10%.
Traditional endoscopes can only display common images of diseased tissues and difficultly detect early canceration in the digestive tract. With the continuous development of endoscopic technology, Fuji Intelligent Chromo Endoscopy (FICE) is widely used as a kind of simulated staining endoscopy technology. Compared to common images, FICE enhances the contrast of the image and can show the fine structure of the digestive tract mucosa more clearly. Because the white light illuminates the object, FICE is hard to observe capillaries in the superficial layers of the mucosa. In this paper, a bluewhite light imaging method is proposed, which combine a mixed light of a narrow-band blue light and a white light to illuminate the object with FICE technology to enhance the capillaries and maintain the images with certain brightness and background characteristics. Through the adjustment of the luminous intensity of blue light and white light, the optimal light intensity ratio range are determined by two evaluation indicators: the image’s pixel value difference and the blood vessel quantity difference. The results show that the deficiency of FICE technology can be compensated when the image’s pixel value difference is below 0.25 and the blood vessel quantity difference is below 0.1.
In the traditional 3D measurement systems based on phase shifted structured light, the structured light is usually generated by raster projection. But the optical system by using this method is a little big in size for the endoscope. This paper proposes a method for generating structured light based on bundled fibers, which can solve this problem. However, it was found in experiments that the structured light projected by this method is deviated greatly from the standard sinusoidal fringe. In order to compensate for the error caused by the unsatisfactory structural light, we propose a calibration algorithm. To verify the phase compensation algorithm, we had built an endoscope system using the arranged fiber bundles. On the wedge objects with different tilt angles, the measurement error of the phase is improved more than 30% after using phase compensation algorithm. Then, the plaster model with complex surface was used in the experiment. The result indicated that the measured shape of the model is more precise after phase compensation. It is shown that the proposed phase compensation algorithm can effectively correct the error of phase measurement caused by non-sinusoidal structured light in the endoscope system.
Spectroscopy has a long history. The theory of is difficult for students to understand. So we want to improve the traditional teaching to some way of interesting experience combined with historical knowledge, practical application and development frontiers. We make use of all kinds of resources to get vivid information of big events of spectroscopy development in order to show students the specific process of some phenomenon. Meanwhile, students will be suggested to read all kinds of latest papers relevantly to obtain much more information about this discipline. Both in class and in lab, we lead students to do some very useful experiments and give them guidance. Through this practice, they will understand the theory much more deeply, especially they will know how to solve the problems in research.
This paper studies the realization of image processing algorithm of multispectral endoscope. The research contents include: local brightness enhancement and adaptive contrast enhancement. Firstly, this paper transforms the image from the RGB space to the HSV space, and then carries on the image enhancement processing to the V space, finally transforms to the RGB space. Local brightness enhancement algorithm divides V space image into smaller windows, and then calculates the nonlinear transfer function of each window, which enhances the pixels in the window, and finally the contrast of brightness enhanced image is restored. The adaptive contrast enhancement adopts the unsharp mask technique based on the guided filter. First of all, this paper uses guided filter to the RGB channel of the original image and gets the unsharp mask of each channel, then plus a scaled image which is the result of the original image subtracts the unsharp mask. So the enhancement of the image is achieved. This paper uses subjective evaluation criteria and enhance factor α to evaluate the effect of enhancement.
And this paper compares the enhancement effect of the proposed image enhancement algorithm and the traditional algorithm. The results show that the α of histogram equalization is smallest and AINDANE method is better than histogram equalization. The proposed method has the best α. The subjective evaluation also shows that the effect of HE is not satisfactory and the proposed method enhances the detail information tremendously. The subjective and objective criteria shows that the proposed method produces better enhancement effect.
One method for three-dimensional (3D) measurement based on structured light is proposed for the medical electric endoscope in the present study. The structured light of black and white strips is generated by that the point sources illuminate the grating mask plate. Four point sources are aligned linearly by a certain space and they are lighted sequentially. Then four images of modulated fringes by the height of object with different phase shifts can be obtained. The algorithm proposed by Wang Z is employed to extract the accurate phase shift from the fringe images since the phase shift cannot be exactly set as π/2 by hardware. An experimental prototype endoscope was built according to the proposed method. One high-definition CMOS camera module developed by ourselves was used to acquire the endoscopic images and the structured light was generated by four fiber LEDs and a transmission grating with a pitch of 0.1 mm. one C# program was designed to light up LEDs in turn, acquire the phase shifted images and calculate the 3D information. The experimental results indicate that its precise of depth measurement at the working distance of 40 mm is better than 0.5 mm and its consuming time of 3D depth calculation is less than 0.5 s.
A new encoding method for absolute angular encoder based on optical diffraction was proposed in the present study. In this method, an encoder disc is specially designed that a series of elements are uniformly spaced in one circle and each element is consisted of four diffraction gratings, which are tilted in the directions of 30°, 60°, -60° and -30°, respectively. The disc is illuminated by a coherent light and the diffractive signals are received. The positions of diffractive spots are used for absolute encoding and their intensities are for subdivision, which is different from the traditional optical encoder based on transparent/opaque binary principle. Since the track's width in the disc is not limited in the diffraction pattern, it provides a new way to solve the contradiction between the size and resolution, which is good for minimization of encoder. According to the proposed principle, the diffraction pattern disc with a diameter of 40 mm was made by lithography in the glass substrate. A prototype of absolute angular encoder with a resolution of 20" was built up. Its maximum error was tested as 78" by comparing with a small angle measuring system based on laser beam deflection.
Nowadays, binocular stereo matching technology has achieved a great progress in theory, but most of the algorithms have good results only for standard image pairs. In the actual binocular systems, the image pair will be different in color, intensity and sharpness because of the inconsistence of illumination, optical defocus, color response of image sensors and so on, which will significantly reduce the stereo matching accuracy or even totally get wrong matching result. To acquire a good disparity map, a new stereo matching method was proposed for actual binocular system in this paper. After acquiring image pair, an automatic method based on Log-space is used to rectify left and right images in order that they are consistent in color, intensity and sharpness. Then the disparity map is obtained from the rectified images by Census algorithm. Experimental results show that our proposed method is more robust to illumination changes and can improve disparity map largely.
Designing of a novel depth camera is presented, which targets close-range (20-60cm) natural human-computer interaction especially for mobile terminals. In order to achieve high precision through the working range, a two-stepping method is employed to match the near infrared intensity image to absolute depth in real-time. First, we use structured light achieved by an 808nm laser diode and a Dammann grating to coarsely quantize the output space of depth values into discrete bins. Then use a learning-based classification forest algorithm to predict the depth distribution over these bins for each pixel in the image. The quantitative experimental results show that this depth camera has 1% precision over range of 20-60cm, which show that the camera suit resource-limited and low-cost application.
A real-time matching method, which is used to locate an object in the binocular stereo vision system and measure the
distance from the object to camera, was proposed in this paper. The 3D image is composited of one left-image and one
right-image captured by the binocular cameras and is displayed in a 3D liquid crystal TV. The target is chosen by
user-controlled cursor constrained in the left-image. Then, the matched point in the right-image with the current position
of mouse in the left-image is detected by an effective point matching algorithm, and the right-cursor is generated on this
matched point. Meanwhile the distance is calculated by the parallax between the pair points. The above algorithm was
realized using the own program compiled by C sharp language. The results show that our method can match selected
pixel accurately and the real-time distance measurement is realized. Moreover, our method is low-cost with little
requirements for hardware.
Although CMOS cameras with USB interface are popular, their sizes are not small enough and working lengths are not
that long enough when used as industrial endoscope. Here we present a small-sized image acquisition system for
high-definition industrial electronic endoscope based on USB2.0 high-speed controller, which is composed of a 1/6 inch
CMOS image sensor with resolution of 1 Megapixels. Signals from the CMOS image sensor are put into computer
through the USB interface using the slave FIFO mode for processing, storage and display. LVDS technology is used for
image data stream transmission between the sensor and USB controller to realize a long working distance, high signal
integrity and low noise system. The maximum pixel clock runs at 48MHz to support for 30 fps for QSXGA mode or15
fps for SXGA mode and the data transmission rate can reach 36 megabytes per second. The imaging system is simple in
structure, low-power, low-cost and easy to control. Based on multi-thread technology, the software system which realizes
the function of automatic exposure, automatic gain, and AVI video recording is also designed.
The resolution of a new subdivision technique proposed in our previous studies, directly subdividing grating stripes by using the combination of CMOS microscopic imaging and image processing, was theoretically discussed and experimentally tested. The relations of resolution to the parameters, such as subdivision number, grating period, magnifying power, included angle, etc., were discussed in theory on the basis of resolution equations derived from subdivision principle and the object - image relation. And it was concluded that the resolution is higher as the subdivision number is more, the grating period is shorter, the magnifying power is higher or the tilt angle is smaller. Five subdivision systems with various resolutions were constructed with two kinds of metrological gratings and CMOS arrays and their performances were tested on an Abbe comparator with a minimum scale mark of 1 μm in the distance range of one grating period. The conclusion that subdivision system performs better under the higher resolution can be drawn from experimental results. At present, the maximum displacement error is 0.2 μm for the subdivision system with a resolution of 0.04 μm.
A new method which bases on the attenuated total reflection (ATR) technique is developed to determine the electro-optic coefficient of a poled-polymer film. The proposed ATR arrangement consists of a coupling prism, and four film layers deposited directly onto the base of the prism in sequence. The four film layers are metal film (which serves as a top electrode), poled polymer film, buffer and base electrode, respectively. A convergent light beam covering a suitable angular range is incident onto the prism base to excite a guided wave mode and the reflected light beam is imaged by a CCD array. Then resonance angle of the guided wave mode can be determined from the position of the reflectance minimum. It is demonstrated that the applying electrical field will cause a minute change in the refractive index of a poled- polymer film, due to the Pockles effect, which will result in a shift of the resonance angle. In order to make the measurement more successful, computer image processing method and optical image spatial filter technology are used in our measurement.
A novel method with single-wavelength light is developed to determine the optical constants and the thickness of a thin metal film. It bases on a new geometry which consists of a coupling prism, a transparent coating layer directly deposited onto the prism base, a thin metal film (most often gold or silver), and air. The attenuated total reflection technique is employed in our configuration to excite two different kind of surface plasma waves simultaneously. One is the conventional surface plasma wave which propagates along the metal-air interface. The other is a modified long-range surface plasma wave which propagates along the nonsymmetrical structure (coating layer-metal and metal-air interfaces). The reflectivity shows to obvious surface plasmon resonance dips in a single-scan measurement. Every dip can be characterized by three main parameters: the position of the minimum, the peak height at the minimum, and the width of the resonance dip. These parameters provide enough information to determine the thickness, real and imaginary part of the optical constant of the thin metal film. Compared to conventional double- wavelength method and the double-medium technique, the present single-scan method not only avoids of the ambiguity of different conditions caused by two-scan technique, but also the dispersion problem with different light wavelength.
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