A set of international standards is becoming effective in late 1990 to early 1992 for coding of bi-level pictures, natural still pictures and moving pictures. This paper presents an overview of collaborative standardization activities carried out in CCITT, ISO/IEC and their sub-committees, and summarizes technical features of respective standards.

The R & D of EDTV (Extended Definition TV, or Enhance D TV) in Japan is reviewed. The EDTV is a television system with higher quality video and audio, and at the same time remains compatible with existing standards. First, IDTV (Improve D TV) is reviewed; it achieves better picture quality by sophisticated signal processing at TV receivers within existing standards. The main issue is the reduction of deficiencies caused by the current standards. Then, the EDTV is reviewed. This concept achieves much better picture quality by sending more information through the more efficient utilization of the transmission channel. Since originally proposed, it has been studied nation-wide in Japan under the direction of MPT (Ministry of Post and Telecommunications) with two stages: EDTV- and EDTV-. EDTV- broadcasting began in 1989, under the nickname "Clear-Vision", with IDTV techniques as the key technology for receivers. Proposed ideas and the historical process are reviewed. EDTV- is now under study for higher-resolution and wide-aspect TV with digital audio. The proposed techniques and related technical issues are summarized.

Fiber loss fluctuations due to manual handling are sometimes inevitable when it comes to touching cable connection points during maintenance and operational activities. These fluctuations cause momentary input optical power changes and give raise to bit errors in receivers. This phenomenon is a serious problem for fiber optic subscriber systems in which cable construction and maintenance frequently take place. Measures to counter this degradation have to be considered to realize stable transmission characteristics. As a result of this consideration, the loss fluctuation tolerance of digital optical receivers has been investigated for fiber optic subscriber transmission systems. From the viewpoint of design and adjustment, the most effective method to solve the fluctuation problem is to adopt d.c. balanced transmission line coding. A receiver having an optimum low cutoff frequency for this type of coding performs well against fiber loss fluctuations without adjustment for special operational conditions.