Research On Technique Of Transcoding From HDTV To SDTV

Digital TV techniques have already entered practical stage. Applications of HighDefinition TV (HDTV) and Standard Definition TV (SDTV) will existent together fora long time. In order to share the DTV program resource, utilize the transmittingchannel efficiently and adopt the program data to all kinds of terminals, the DTV bitstreams are often converted from one format to another, which include bit-rate spatialand temporal resolution conversion. This technology is called video transcoding. MPEG-2 standard is mainly use in DTV application. In order to satisfy thedifferent requirements such as high quality interlace DTV broadcasting, digital mediastorage and scalable video coding, MPEG-2 video coding supports different bit-rate,spatial and temporal resolution, video quality and service type. Because of theflexibility of MPEG-2 coding, Transcoding of MPEG-2 video data encounters manyissues and difficulties. This thesis is focused on transcoding from HDTV to SDTV. Algorithms ofmacro-blocks (MB) coding type reuse, motion vectors composition and optimizationof interlaced video data have been deeply studied. An HDTV to SDTV transcodingplatform has been constructed. Based on the research and comparison result ofdifferent algorithm, we acquired many methods which can complete HDTV to SDTVtranscoding with good performance. During the HDTV to SDTV transcoding procedure, some issues should beconsidered. The spatial resolution, image aspect rate (IAR) and pixel aspect rate (PAR)are different in HDTV and SDTV. Transcoder should meet the requirements ofkeeping the image integrity and avoiding geometry distortion. Another issue is how tomaintain or enhance the image definition during transcoding. Base on the Subsampling/Interpolation theory which can recover the picturedefinition and combined some existed Subsampling/Interpolation algorithm, thispaper introduces a 3/4 self-adaptive Subsampling/Interpolation algorithm. Accordingto our theory analyses and experimental results, the proposed Subsampling/Interpolation algorithm can recover good image horizontal definition. Based on the study of Subsampling/Interpolation algorithm, four transcodingschemes from HDTV (1920×1080i) to SDTV (720×576i, 4:3 or 16:9) have beendesigned according the DTV standard in China. By analyzing these transformstructure and comparing experimental result, this paper recommends two tanscodingschemes from HDTV to SDTV, and this offer a way to realize share and transition.Software simulation and experiment by DVB-C system indicate the twotranscoding scheme can serve for the terminal with 4:3 IAR and the terminal with16:9 IAR respectively, and good picture quality can be acquired.The transcoding scheme which is used for the 16:9 displays of SDTV can utilizeoriginal SDTV channel. Through the spatial resolution downscaling in the front endand the simple spatial resolution upscaling in the terminals, we can rebuild integratepicture without geometry distortion, and horizontal definition can reach theoreticalupper limit (540 line) in theory of SDTV system. This scheme meets the request ofwide vision sense, it is not only compatible with the current display products, but alsocan support future products with 16:9 IAR. With the increasing 16:9 LCD and PDPdisplayer, the displayer may be unified into 16:9. To realize this is favorable to thecompatibility of HDTV, SDTV equipment in broadcasting studio, help SDTV to shareprogram resources of HDTV, reduce the memory carrier needed to store two programsto consume.To realize transcoding HDTV (1920*1080i) to SDTV (720*576i 4:3 or 16:9), aseries of problems need to be studied and solved, especially, the motion vectorscomposition of the spatial resolution transcoding with non-integer factor. For thisreason, this paper provides the composition algorithms of motion vectors based onfield prediction and dual prime prediction. Considering the selection of MB codingtype (prediction mode and direction), this paper recommend a motion estimatescheme. This scheme can achieve better tanscoding result. It is of universalsignificance to take the wide technological domain of trancoding.Among the thesis study, some other projects have been finished. The conversioncircuit for parallel data interface of SPI to the serial data interface of ASI had beendesigned for the MPEG-2 TS transmit card;Having studied the broadcasting studioSDI signal form, the coding and decoding software is realized;Have designed,produced many kinds of digital TVs test signal;Work out many kind standard,different various kinds of parameter test signal video stream. These tasks are realizedbased on research results, cooperated with laboratory teachers and students, havesubstantiate the digital TV software and hardware experimental system, has facilitatedthis subject and other research projects, and I have got the cultivation and training ofthe ability of the software and hardware among them.