William F. Schreiber

Advanced television systems for terrestrial broadcasting: Some problems and some proposed solutions

The first part of this paper discusses the requirements that must be met by a new television broadcasting system to maximize its acceptability to the various stakeholders, including broadcasters, equipment manufacturers, program producers, regulatory authorities, and viewers. The most important performance factors are efficient use of over-the-air spectrum, coverage versus quality, cost, interoperability, and the existence of a practical transition scenario. It is concluded that all receivers need not have the same peformance, and that low-cost receivers must be available for noncritical locations in the home. If this variation in price and performance is made possible by appropriate system design, then interoperability is facilitated and nondisruptive improvement over time is made possible, as desired by the Federal Communications Commission. In the second part of the paper, techniques that may permit meeting these requirements are discussed. These include joint multiresolution source and channel coding, multicarrier modulation, and hybrid analog/digital coding and transmission. The analog transform coefficients are subjected to spread-spectrum processing, and coded orthogonal frequency-division multiplex (COFDM) is applied to the complex hybrid symbols to be transmitted through the channel. Various methods of equalization and of improving noise, interference, and multipath rejection are compared. Finally, an example is given of a system that meets the various requirements by making use of a number of the techniques discussed. The system provides extended coverage, albeit at lower quality than currently proposed all-digital systems, and equal or higher quality than such systems in much of their service area. It also features self-optimization at each receiver depending on signal quality and receiver characteristics, and facilitates the design of receivers of lower cost and performance for less-critical applications. >

Wirephoto quality improvement by unsharp masking

Abstract We present a simple technique for improving, in real time, the quality of wirephoto pictures. This technique can be incorporated in conventional wirephoto transmitters with very little cost.

Image processing for quality improvement

In order to encourage the development of computer-based methods which produce better quality pictures, the long and successful history of image processing in photography and graphic arts is called to the attention of the computer fraternity. Studies of contrast sensitivity and of the relationships among illumination, object reflectance, and image luminance are presented. Homomorphic filtering is analyzed in this light. Adaptive filtering methods which exploit perceptual phenomena as well as the physical properties of imaging systems are given. These methods attempt to permit the attainment, of a very high degree of sharpening, equally visible throughout the tone scale as well as in image areas of quite different character, without the concomitant appearance of quality-destroying artifacts such as haloes or overshoots. Results are compared with linear and homomorphic nonadaptive sharpening.

Improvements to NTSC by Multidimensional Filtering

This article presents, in a tutorial fashion, the basic elements required for understanding compatible improvement techniques for NTSC color multiplexing using multidimensional filtering at the transmitter and receiver. It discusses the multidimensional spectrum of moving pictures and relates the form of this spectrum to different types of image material. It also presents the basics of multidimensional filtering that are key to the techniques we discuss for improving NTSC. Finally, systems for NTSC encoding and decoding using multidimensional processing are described.

A Two-Channel Picture Coding System: II--Adaptive Companding and Color Coding

The two-channel picture coding system previously reported is improved by adaptive companding and extended to component color coding. The basic system divides the spectrum into lowand high-frequency spatial components. The former are coarsely sampled and finely quantized, while the latter are finely sampled and coarsely quantized using a companded, randomized quantizer. The adaptive version uses a companding factor, larger than one, which multiplies the highs before coding and divides the result after decoding. This substantially raises the signal-to-noise ratio, which is calculated for both the adaptive and nonadaptive cases and confirmed by computer simulation. The color version uses an achromatic highs channel as in the basic monochrome system, plus a three-color lows channel coded in a perceptually uniform color space. With 3.5-4.3 bits/pel for 512 × 512 monochrome and color still images, the nonstatistical version produces images free of visible defects under normal viewing conditions. Projections are made for system parameters capable of achieving the very high quality now being proposed for production component coding systems, but with substantial reduction in channel capacity.

Transmission of signals through analog channels using adaptive frequency modulation

Improved effifiency of frequency-modulated (FM) transmission of signals through analog channels, i.e., achievement of a higher bandwidth and/or signal-to-noise ratio (SNR) in the received signal for a given channel bandwidth and channel carrier-to-noise ratio (CNR), is accomplished by adaptive adjustment of the modulation index in such a manner that the spectrum of the channel signal more nearly occupies the entire channel more of the time than it would otherwise. Data is transmitted, along with the signal, to enable the receiver to calculate the modulation index at each instant so that the signal can be properly demodulated. The invention has application to FM transmission of signals representing visual image or other information, such as sound, for which human perception of noise is greatest in areas of low amplitude and/or frequency and reduced in and immediately adjacent to areas of high amplitude and/or frequency.

Hybrid channel coding for multiresolution HDTV terrestrial broadcasting

This paper describes a new HDTV system that applies joint multiresolution (MR) source and channel coding to efficiently use the available radio spectrum. Hybrid analog/digital MR channel modulation provides the benefits of digital source coding and the more efficient spectrum usage of analog transmission. Nonuniform spacing of the digital signaling levels provides MR delivery of the digital components while spread-spectrum processing permits MR delivery of the analog components. Error correction coding and OFDM channel modulation deliver the MR service in widely varying channel conditions. Simulation results demonstrate performance in various regions of the service area. >

A Two-Channel Picture Coding System: I--Real-Time Implementation

The two-channel system previously reported has been implemented in hardware using system parameters appropriate to consumer television. The basic system divides the spectrum into lowand high-frequency spatial components. The lows are coarsely sampled and finely quantized and the highs finely sampled and coarsely quantized using a companded, randomized quantizer. The purpose of this experiment was to demonstrate the potential of the system for low-cost practical application, to study the effect of the character of the randomizing noise, and to ascertain that there were no deleterious effects due to interlace, motion, or input noise. Theoretical noise calculations were qualitatively confirmed.

Automated Engraving of Gravure Cylinders

A computer-based system for automated engraving of gravure cylinders has been developed and is now used in a normal production environment. Either fully composed pages or individual page components are scanned and stored on a large disk. In the case of fully composed pages, an operator uses a TV display to segment the page image into line and tone areas. The image is then coded by a software process and is ready for subsequent engraving. Prior to the scanning of page components, the operator uses a tablet in order to demark both cropping locations and to specify the location of the components on the final page image. The scanned components are then assembled and coded by a single software process. The encoding process reduces the data storage requirement by a factor of two without any apparent loss of quality. Data are retrieved from disk storage, buffered, decoded, transmitted to a special formatter, and used to drive a Helio Klischograph,® which engraves the cylinder in approximately one hour. Completely arbitrary imposition (the arrangement of pages on the gravure cylinder) is accomplished at the time of engraving. Provision is made for the arbitrary intermixture of computer-processed pages and conventional engraving by means of Cronapaquesgi mounted on the companion scanning machine. The motivation for this development was to reduce the cost and time required for the production of gravure cylinders.

Image enhancement/coding systems using pseudorandom noise processing

A new technique for image compression and/or enhancement is presented. The method comprises dividing the two-dimensional spectrum into low- and high-frequency components and digitizing the latter with a tapered, randomized quantizer. A version of the system in which the highs component is adaptively adjusted gives improved picture quality.