Image matching is an important topic in the field of computer vision, in view of high robustness and accuracy, SIFT or the improved methods based on SIFT is generally used for image matching algorithms. The traditional SIFT method is implemented on grayscale images without regard to the color information of images, which may cause decreasing of the matching points and reduction of the matching accuracy. Prevailing color descriptors can effectively add color information into SIFT, however dramatically increase the complexity of algorithm. In this paper, a novel approach is proposed to take advantage of the color information for image matching based on SIFT. The proposed algorithm uses the gradient information of color channel as the compensation of luminance channel, which can effectively enhance the color information with SIFT. Experimental results show that the number of feature points and matching accuracy can be significantly promoted, while the complexity and performance of image matching algorithm are well trade-off.
The dark current noise existing in the CCD of the astronomical observation camera has a serious influence on its working performance, reducing the working temperature of CCD can suppress the influence of dark current effectively. By analyzing the relationship between the CCD chip and the dark current noise, the optimum working temperature of the red band CCD focal plane is identified as -75℃. According to the refrigeration temperature, a cooling control system for focal plane based on a thermoelectric cooler (TEC) was designed. It is required that the system can achieve high precision temperature control for the target. In the cooling control system, the 80C32 microcontroller was used as its systematic core processor. The advanced PID control algorithm is adopted to control the temperature of the top end of TEC. The bottom end of the TEC setting a constant value according to the target temperature used to assist the upper TEC to control the temperature. The experimental results show that the cooling system satisfies the requirements of the focal plane for the astronomical observation camera, it can reach the working temperature of -75℃ and the accuracy of ±2℃.
Because of larger measurement ability of wave-front deviation and no need of reference plat, the lateral shearing interferometry based on four step phase shifting has been widely used for wave-front measurement. After installation shearing interferograms are captured by CCD camera, and the actual phase data of wave-front can be calculated by four step phase shift algorithm and phase unwrapping. In this processing, the pixel resolution and gray scale of CCD camera is the vital factor for the measurement precision. In this paper, Based on the structure of lateral shearing surface interferometer with phase shifting, pixel resolution more or less for measurement precision is discussed. Also, the gray scale is 8 bit, 12 bit or 16 bit for measurement precision is illustrated by simulation.
The accurate calibration for a 3D profile measurement system based on structured light projection is important to the precision measurement system; however, system calibration is always complicated and time-consuming. An improved fast method is proposed to calibrate the measurement system. First, LCD monitor, as a calibration plate, displays chessboard pattern designed by computer programming, and camera captures 1 image. Then LCD monitor displays white pattern, projector projects horizontal and vertical color-encoded fringes to the LCD monitor, and camera collects 2 images respectively. A Phase-shifting algorithm is used to establish a highly accurate correspondent relationship between camera pixels and projector pixels, and projector images are generated. Next, move the LCD monitor to other 8 places, get camera and projector images which are set for camera and projector calibration respectively using Zhang’s calibration method. Compared with ordinary techniques which use expensive equipments such as two or three orthogonal plates, LCD monitor is easy-to-use and flexible, and experiments show that calibration accuracy is improved by 5 times. In comparison with traditional projector calibration method, this method decreases the number of captured images from 8 to 2 in each place and increases the processing speed. Combining camera calibration and projector calibration, the complex calculation process of integrating traditional camera calibration and projector calibration can be simplified. Experiments have been performed based on the proposed technique and good results have been obtained.