Scan Conversion Technology Research

Employing the interlaced scanning,current TV system can compress the frequency band of TV signal effectively and facilitate transmission. But this method reduces the scanning lines of pictures and the frequency of the field. It leads the pictures displayed on TV to have such disadvantages as large area flicker,edge flicker,interlace flicker,raster visibility and creeping line etc. To satisfy people' s vision feeling better,the big-screen,multi-function and high quality TV-set have been made great progress. However,the application of the advanced transmission needs a long process because of its complicated technique and high expense. Instead of it,the scanning converting technique is an effective way to improve the quality of the picture in current TV transmission.Current TV system has two types:one is the 60Hz based system,the other is the 50Hz. The phenomenon of large area flicker is not obvious in the 60Hz based system,so the scanning converter uses the way of converting the 60Hz and 50Hz based interlaced scanning signal to 60Hz based progressive scanning signal. Employing this way the converter can not only reduce the large area flicker and interline twitter,but erase the raster and display finer and smoother pictures .The scanning converter comprises five parts :video signal decoding,data reconstruction,progressive video signal encoding,control signal producing and communication. In order to solve the phenomenon of splitting picture which is caused by dismatching of writing and reading speed during converting 50Hz based interlaced signal to 60Hz based progressive signal,the two-frame memory which can effectively prevent it emerging is used. The scanning converter supplies two communicative ways:RS-422 and RS-232. Through these ways the main controlling system controls the brightness,contrast,saturation of output pictures. At the same time CPLD technology is adopted to produce all kinds of controlling signals and reduce the volume and the power consumption.Finally the paper analyses the ways of picture interpolation detailedly and presents the methods of field and line interpolation.