DTV 테스트용 고화질 정지화 스트림의 생성 및 이음매 없는 스위칭
Generation of high quality test and its seamless switching in DTV
텔레비전 DTV 테스트용 고화질;
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The basic structure of present TV is newly created by digital technology, delivering high quality video, audio, and data. As the service using the digital TV increases, how to measure a picture quality in digital TV becomes the main problem. When an original image for a test has been encoded and decoded, there will be differences between the original and decoded images. So, generating the reference test stream to guarantee the high picture quality is need for the test of DTV receiver. For the reference test stream, various static test patterns have been mainly used. They have been played by user's selection during development and manufacturing test after compressing and storing at hard-disk drive of PC. In that case, the method of repeating each transport stream infinitely has been used for considering the storing space and compression time. Recently, the method of repeating seamlessly has been also developed to distinguish the discontinuity phenomenon that can occur at repeated visual point and malfunction occurred by receiver itself. With the above method, the seamless and repeated playing is possible, however, when user selects the various test transport streams such as colorbar, multiburst and 5-step there is some possibility that discontinuity phenomenon can be observed as before. Therefore, besides the bit rate control which is proper to the static test pattern and is able to guarantee the stable and high picture quality, the seamless swithing of test streams is indispensable for reliable and robust test of the DTV receiver. Moreover, in order to be used widely in manufacturing site of commercial DTV receiver, the steam player should be implemented at low cost by maximally using the characteristics of static video. We developed a method to generate the bit stream of static video test patterns in high quality for testing the picture quality in DTV receiver without any overflow of video buffer. And we also developed the seamless switching method for changing the test transport stream by user during testing the picture quality of the DTV receiver. To perform the high quality video compression for static test patterns such as color bar, pulse & bar, and multiburst, we propose a new target bit allocation method using normalized complexities, which are updated or maintained by means of GOP picture qualities. In our method, we use the fact that the generated bits and average quantization value have almost identical distribution per each GOP and we propose new target bit allocation method suitable to compression of the static test pattern while the target bit allocation method in MPEG-2 TM5 is suitable to moving picture. And, by using a minimum zero stuffing which prevents video buffer overflow due to static image compression, the stable and high-quality video stream was achieved. Finally, we eliminated discontinuity phenomena at switching point when changing one test transport to another one, by guaranteeing the PCR, PTS, and DTS to be continuous at switching point without any indicators at header of the transport stream. Further this algorithm includes an easy implementation method. Experiments are carried out on static test patterns such as multiburst, crosshatch, and KNU video pattern at various bit rates. Experimental results showed that average PSNRs of the proposed method is about 5 dB higher than those of the conventional case. For testing the seamless switching of the transport stream, we captured the frame image at the moment of switching from one transport stream to another. As a result, we could see that the discontinuity of switching point was perfectly eliminated by proposed methods. We have tested the generated test stream in experimental DTV broadcasting system, and confirmed that the proposed algorithm has a stable bit rate and good video quality and it is suitable for evaluating a DTV receiver.