Showing papers on "Quantization (image processing) published in 1980"

Digital processing techniques for encoding of graphics

Abstract: This paper deals with two classes of preprocessing techniques for documents which are essentially black and white These are bilevel quantization and preprocessing techniques for noisy input documents The effect of such techniques on the compression ratio and the subjective quality of the output copy are studied It is shown that for noisy documents, certain preprocessing techniques considerably improve the compression ratio The improvement is substantially more for two-dimensional coding algorithm such as relative address coding (RAC) Simulation results of the effect of preprocessing techniques for noise reduction for both multilevel and bilevel signals are described The results of a subjective experiment to determine the effect of certain preprocessing techniques on the quality of clean and noisy documents are reported

Reduction Of Quantization Noise In Pulse Code Modulation Image Coding

Abstract: A new technique to reduce the effect of quantization in pulse code modulation image coding is presented. The technique consists of Roberts's pseudonoise technique followed by a noise reduction system. The technique by Roberts effectively transforms the signal dependent quantization noise to a signal independent additive random noise. The noise reduction system that follows reduces the additive random noise. Some examples are given to illustrate the performance of the quantization noise reduction system.

Artifacts in Digital Images

Abstract: Three kinds of artifacts unique to digital images are illustrated, namely aliasing caused by undersampling, interference phenomena caused by improper display of images, and harmonic overtones caused by quantization of amplitudes. Special attention is given to undersampling when the sample size and interval are the same. It is noted that this situation is important because it is typical of solid-state cameras. Quantization of image data of necessity introduces energy at harmonic overtones of the image spectrum. This energy is aliased if the frequency of the overtones is greater than 0.5 cycle/pixel. It cannot be selectively removed from the image through filtering, and the best way to suppress it is to maximize the amplification of the sensor before digital encoding.

Empirical Determination Of Processing Parameters For A Real Time Two-Dimensional Discrete Cosine Transform (2D-DCT) Video Bandwidth Compression System

Abstract: An interactive process is described for fine tuning a specific algorithm for use in a real time video bandwidth compression system. Parameters for the algorithm are initially optimized using computer simulation, then implemented in hardware to observe performance. The next step is the modification of the parameters to improve the real time performance of the system. This paper describes some of the algorithm parameter choices that were made in the implementation of a two-dimensional discrete cosine transform processor for the Air Force Wright Aeronautical Laboratory. Examples are shown of alternate choices for DCT scaling strategies, filter functions, and bit assignment procedures. The impact of these parameter selections on the resulting imagery is included using both simulation and hardware outputs.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Image Compression With Approximate Transform Implementation

Abstract: In this paper we examine the effects of using an imperfect transform encoder to compress an image. The forward transform is noisy to reflect imperfections in a possible hardware implementation. We find that these imperfections cause unacceptable image degradations unless they are very carefully calibrated out. Particular attention must be paid to the bias of each vector in the transform. To illustrate the concept we present a computer simulation of a hybrid encoder that uses a Hadamard transform on the rows and DPCM on the columns. In a series of images and error pictures we show the effects of different encoder and decoder strategies which use various degrees of uncertainty about the encoder.© (1980) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.