Study On Image Chromaticity Sensor

Chromaticity measurement is widely used in textile dyeing, printing, lighting engineering, food inspection, military camouflage and recognition. Typical chromaticity measurement used photoelectric sensor such as silicon photocell, photo-electric multiplier. Measurement result is the mean value of the area within the visual angle. In the applications such as monitor screen quality appraisal, roadway luminance detection, building luminance appraisal and city light pollution control, which needs exquisite chromaticity information and large area chromaticity distribution, typical measurement is hard to meet the demand. Image chromaticity sensor can get chromaticity of every bit in the visual angle, which accord with the demand of modern chromaticity sensing. So the image chromaticity sensor has broad application prospect and good development potential. The main contents of this paper can be generalized into several aspects as below:1. The present situation of CCD image detection and image chromaticity measurement is introduced and the feasibility of CCD image chromaticity measurement is analyzed. On that we designed the specific scheme with industrial area CCD. It adopts DSP as controller, CCD analog front end chip as the driver and analog signal processor. According to the situation of complex CCD driving sequences and multiple driving signals, the CCD driving period division and signal synchronization are brought forward. According to the rigid time limit, big flow data acquisition and store is completed by combining with the DSP internal architecture.2. To meet the demand of big payload and generality, the USB2.0is chosen for data transmission. According to current low utilization of USB bandwidth, we bring forward the Large Buffer Multiple Pipes method in USB transmission, whose speed is close to the theoretical highest transferring speed. According to the busy data processing, large data flow and high real-time requirements, we designed corresponding PC program. For the close information interaction and huge data transfer among multiple subsystems, we designed the synchronization protocol for subsystems.3. The noise source in CCD image chromaticity sensor is analyzed in this paper. Noise suppressing methods, including correlated double sampling, calibration of dark current, high-order passive band-pass filter design, power noise and ground current noise suppressing, accurate exposure time control, clock jitter control, signal integrity and digital image filter, were adopted in the noise reduction. The final system noise statistical result is given in this paper.4. To fit the standard chromaticity function, we designed three groups of optical filter to calibrate the CCD’s spectrum response. The tri-stimulus data of the CCD image chromaticity sensor is tested in this paper.Finally, we put forward some research and development which remains to be improved in future.