Statistical Dependence Between Components of a Differentially Quantized Color Signal

The statistical dependence (redundancy) between three differentially coded color components of a video-telephone signal are explored by means of an entropy study. We measure the entropy of the differentially coded color baseband signals both jointly and as three separate signals. The source material consisted of a number of portraittype pictures. The color signal is treated in a format containing a baseband luminance channel and two baseband chrominance channels. Various orthogonal and nonorthogonal transformations, including the Karhunen-Loève transform, are applied to the chrominance signals to study the effect on the entropy. With a well-chosen format for the color signal, our results show that the redundancy resulting from using a separate encoding of the signals rather than a joint encoding ranges between 0.2 and 0.5 bits. The possible savings accruing from considering the relationship between coded color differential components was only about 1 percent of the total bit rate for most pictures and increased to a maximum of 4 percent for one particular picture.     

An experimental real-time color-TV display with a DC gas-discharge panel

An experimental color-TV picture display is presented on a dc gas-discharge panel which is based on the Burroughs' "self-scan" panel. An array of 127 × 160 dots of three color phosphors were formed on the inner surface of the front glass plate to reproduce color pictures. A thinner center sheet of soda glass with a thickness of 0.25 mm was used so that the phosphors might be excited effectively by the UV radiation generated from the negative glow of the discharge. Based on our vacuum-spectroscopic measurements on various phosphors, Y2SiO5:Ce (blue), Zn2SiO4:Mn (green), and Y2O3:Eu (red) were selected. An excellent color picture was reproduced with a contrast ratio of greater than 30:1 with continuous gray scale.     

An experimental time-compression system for satellite television transmission

We describe an experimental system for demonstrating time-compression multiplexing (TCM) of two NTSC color television signals in a satellite channel of 36 MHz. The system employs digital processing to derive line or field differentials from each picture. The television signals are then converted into interleaved lines (or fields) of unimpaired baseband video and companded line (or field) differentials. These signal components are finally time compressed and multiplexed into a combined signal for single-carrier FM transmission. With 4.5-m earth stations, the field-differential technique offers extremely good transmission quality suitable for TV distribution to cable head-ends (weighted signal-to-noise ratio, WSNR ≈ 51.5 dB), while the line-differential method provides a slightly lower WSNR ( ≈ 49 dB). We recommend the field-differential approach because of its superior overall picture quality. For larger receive stations (7m), higher picture quality (WSNR ≈ 56 dB) could be obtained. If 10-m earth stations are employed, the received video performance is practically indistinguishable from the corresponding one in the one-television-per-transponder case, and we infer that three pictures can indeed be sent with a graceful degradation as previously suggested. By choosing the parameters properly, the current TCM system can be optimized for a wide variety of applications with higher channel capacity.     

Design of Quantizers for DPCM Coding of Picture Signals

Visual thresholds play an important role in the process of incorporating properties of the human visual system in encoding picture signals. They tell us how much the picture signal can be perturbed without the perturbations being visible to human observers. We describe psychovisual experiments to determine the amplitude thresholds at a single edge having a given slope and then present methods to incorporate the visual threshold data directly into the design of quantizers for use in Differential Pulse Code Modulation (DPCM) systems. In the first class of methods, quantizer characteristics are obtained such that the quantization error is kept below the visual threshold as determined by the slope at a picture element and either (a) the number of quantizer levels, or (b) the entropy of the quantized output is minimized. In the second class of methods, different measures of the suprathreshold quantization error are minimized for a fixed number of levels, or for a given constraint on the entropy of the quantized signal. We present empirical relationships between the various distortion measures and the subjective quality of the pictures rated on a five point impairment scale. We then discuss the structure of the quantizers obtained by the above mentioned optimization methods, evaluate their performance on real pictures, and compare them with the ones described in the literature.     

Area properties of television pictures

Area size distributions are measured for four different still pictures formed of510 times 512elements linearly quantized to eight amplitude levels (3bits). The initial results of this continuing measurement program indicate that for the measured pictures: 1) First-order brightness distributions tend to be uniform. 2) The largest number of areas occur for the intermediate grey levels, with considerably fewer areas encountered at either black or white. 3) The average size of black or white areas is larger than for the intermediate greys. 4) Black and white areas appear to be more simply connected than intermediate grey areas. 5) The frequency of occurrence of areas of sizen-elements falls off withna little slower than1/n^{2}. 6) The area size distributions for each picture appear quite similar; the greatest difference between them is in the area size range20-200elements, and in the presence or absence of one or two very large areas. 7) Areas of size smaller than3elements constitute up to50percent of the total number of areas and cover from five to ten percent of the total picture. These areas probably are of doubtful visual significance in the sense that their brightness values could be highly distorted without materially degrading the subjective appearance of the picture.     

Orthogonal Transform Coding System for NTSC Color Television Signals

A two-dimensional, 32nd-order orthogonal transform coding system which performs three types of transformations in realtime for NTSC color television signals has been developed. This paper reports on a hardware realization of this system, the optimum bitassignments for 32 and 22 Mbit/s transmission rates and the effects of bit errors during transmission. Through the evaluation of picture quality, the system gave a fine quality of pictures after compressing an 8-bit digitized television signal into 3 bits/pel corresponding to 32 Mbit/s transmission, and a passable quality of pictures by 2.25 bits/ pel corresponding to 22 Mbit/s transmission.     

Efficient Encoding of Colored Pictures in R, G, B Components

The encoding of colored pictures in components has attracted a lot of attention. In this paper, for their efficient transmission in the 2-3 bit/pel range, the direct encoding of the red (R), green (G), and blue (B) primaries is investigated. Differential PCM with vector quantization is used and the encoding efficiencies are compared to the similar result obtained using the properly converted luminance (Y) and chrominance (I,Q) component signals. A new quantization scheme is proposed forRGBencoding to improve the picture quality. As a result, it is shown thatRGBencoding can attain a comparable or slightly higher encoding efficiency as compared toYIQencoding, and a higher resolution can be obtained for strong color edges defined by the primary colors, but the resulting picture quality is much noisier; thus, it is better suited for such applications in which the edges of primary colors play important roles, such as in graphics materials. An adaptive vector quantization is introduced in order to apply the proposedRGBencoding scheme to a wider range of pictures. The quantity called activity is introduced, considering the form of the predictor used. The optimum adaptive scheme is derived and its effectiveness is verified through simulations.     

Combined Blockiness,Blurriness and White Noise Distortion Meter

Due to discrete cosine transform (DCT) based compression, the loss appears in the form of blocky and blurry distortions in coded pictures. One of the degradation is white noise which corrupts nearly all pixels in the picture. In image transmission system, to assess the image quality at receiver end, lesser image features are sent, instead of the whole reference original picture to accommodate the available bandwidth. The purpose of this research is to propose a procedure which quantifies or estimates the objective picture quality automatically. The presented combined white noise image quality assessment meter (CWNIQAM) functions in the frequency domain for computation of three artefacts blockiness, blurriness and white noise in the corrupted coded images. The designed quality meter at first converts RGB pictures into YC_bC_r, gray scaled pictures and then edge detection method is applied. Afterward the picture is divided into blocks of 32 × 32 pixels to get local level blockiness, blurriness and white noise value. Next the picture is transformed from spatial to frequency domain and different features called reduced reference parameters are estimated. The composite magnitudes strength through horizontal and vertical harmonics is obtained for estimation of blocky and blurry artefacts in the coded images, while the strength of all ac coefficients and dc component is obtained for computation of white noise. The reduced reference features are computed and compared for reference and coded picture for estimating the particular type of distortion. The uniqueness of the proposed CWNIQAM meter is that, it can estimate the quality of corrupted images by estimating the combination of blockiness, blurriness and white noise through this single meter. The LIVE database2 having 174 different white noise (wn) corrupted images are used for measuring combined objective value of the three artefacts using the designed reduced reference image quality assessment meter algorithm. The objective results are correlated with subjective wn, DMOS LIVE scores. The correlation of about 98% is attained which indicate that much better picture quality index is achieved by the offered reduced reference combined white noise image quality evaluation meter in the frequency domain.     

Design of DPCM Quantizers for Video Signals Using Subjective Tests

The application of differential pulse code modulation (DPCM) for broadcast color television signals requires a design which produces no visible impairments under normal viewing conditions. This paper describes a quantizer design which is based on measured visibility thresholds of the various kinds of DPCM impairments such as granular noise, edge busyness, and slope overload. The visibility thresholds are determined by subjective tests based on comparisons of DPCM and PCM encoded pictures. Constructions of quantizers are carried out such that the number of levels is minimized without exceeding the measured visibility thresholds. Besides nonadaptive quantizers, adaptive quantizers are also constructed which are controlled by the signal changes of surrounding picture elements. These investigations show that for component coding of color video signals with two-dimensional prediction, a transmission rate of 31.7 Mbits/s is possible for natural types of test pictures without visible impairments using constant word length coding.     

Gray scale pictures via Group 3 facsimile

The CCITT has developed a recommendation for Group 3 facsimile that is based on the transmission of binary picture elements (pels) having a brightness value that is either black or white. By introducing a minor modification into the basically bilevel facsimile system, dither coding delivers an output image that conveys gray-scale information. An analysis is made of three dither coding techniques: random dither, clumped dither and distributed dither. The comparison of random and clumped dither was also studied by simulation. The random dither simulation runs having the intermediate random number range (RNR=192) exhibited the best combination of maximum image quality and minimum number of transmitted bits, relative to the other random dither runs. The clumped dither images are superior to the best random dither image when both image quality and transmitted bits are considered. For clumped dither, the average compression ratio for the three images is only 1.39, which is significantly poorer than for the same images without dither coding. This compression ratio corresponds to a transmission time of 4.5 min over the public switched telephone network. Although this time is significantly longer than the 1 min typical for nondithered pictures, this performance may be most satisfactory for many requirements and applications     

Telemedicine: New Application of Communications Technology

Telemedicine may be defined as the practice of medicine at long distance by means of telecommunications, in particular, closed-circuit television and telemetry. Two-way television enables physicians to establish a nominal doctor-patient relationship with patients at a remote location, while providing the means for visual examination of patients. Biomedical telemetry transmits patients' vital signs, detected by standard medical bioelectric sensors and physiological function transducers. In a telemedicine simulation experiment, a test group of physicians deemed black-and-white television adequate for most diagnostic purposes, but expressed a preference for color. The group evidenced little interest in picture resolution greater than that provided by the standard U.S. 525-line system. The Plumbicon camera was said to provide better pictures for medical purposes than the vidicon. In either color or black-and-white television, lighting is a critical factor in the proper rendition of flesh tones as well as in providing the necessary illusion of depth for the observation of detail. Commercial television lighting practices are directly applicable. The inclusion of certain colored items in the televised scene aid in the interpretation of color television pictures. Designing the biomedical portion of a telemedicine system requires knowledge of the various electrical characteristics of the vital signs to be transmitted. These cover a wide range of frequencies and amplitudes. Most bioelectric potentials are so small that special care must be taken to avoid artifacts produced by electrical interference.     

Predictive ordering technique and feedback transform coding fordata compression of still pictures

A picture data compression method consisting of a hybrid cascade having four processing stages is presented. The processing stages are: predictive ordering technique (POT), feedback transform coding (FTC), vertical subtraction of quantized coefficients (VSQC), and predictive coding refinements in the signal space consisting of either overshoot suppression (OS) as a first variant or hybrid block truncation coding (HBTC) as a second one. Each of these stages is described, and reconstructed pictures are presented with their coding fidelity performances (mean square quantization error, mean absolute error and signal-to-noise ratio), using as test pictures a portrait and a LANDSAT image. It is shown that good quality images at low bit rates (0.55 to 1.1 bits/pixel) have been obtained     

Flicker effect and television compression

The perception of flicker by the human eye depends upon the picture content, and this paper describes a relation between the critical flicker frequencyf_cand the spatial frequencyf_x. Provided that the visual picture is presented in such a way that each spatial component, presented at a frequencyf_p, obeys the inequalityf_p geq f_c = f(f_x) = f_0 exp (-k f_x), no flicker effect is perceived. The constantsf_0andkare weakly dependent upon the brightness and picture area; they are a little more strongly dependent upon the contrast ratio and the type of picture. The effect can be exploited in motion pictures or television by presenting high-quality pictures interleaved with low-quality ones. In the latter, some high spatial frequencies would be omitted. For television, band reduction of a face by 9:1 is possible. Practical consideration may reduce this compression ratio to a little short of 2:1.     

不良文字图片识别技术研究

5G消息服务的开展为不良图片信息的传播提供了便利条件.不良文字图片作为一种特殊的不良图片信息给通信网络的内容安全带来了挑战.为了能够对不良文字图片进行有效治理,运营商需要借助人工智能技术对图片中的文字信息进行识别和提取.本文详细介绍了不良文字图片治理整个技术过程需要引入的3个处理步骤,并对3个处理步骤涉及到的深度学习模...     

基于机器学习的文字判别算法

复杂背景下的文字处理一直是OCR领域中的难题。基于SIFT、K-means和SVM三种算法相结合,提出了一种全新的复杂背景下的文字判断方案。在学习阶段利用SIFT进行特征点提取和描述,并用K-means进行聚类,最后用SVM进行学习。在测试阶段对图片进行了SIFT特征点提取,并用学习阶段得到的聚类中心和SVM判决函数进行最终的判断,得出图片中是否含有文字的结果。     

A Picture Browsing System

We describe a system for storing pictures in a database and retrieving them from a remote location over a low bit-rate channel. Even with compression techniques, it takes a long time to transmit a picture, making search for a picture of desired attributes time-consuming. Our system improves the human interaction with the picture database by constructing an auxiliary text database containing a list of attributes of each picture, a hierarchical encoder-decoder, and a light pen to select the areas of picture buildup. Picture searching (or browsing) takes place in two stages: in the first stage, knowing the required picture attributes, a user selects a subset of pictures by matching attributes to the text database; in the second stage, these selected pictures are displayed hierarchically so that a low resolution picture is reproduced first and made sharper gradually. A light pen allows the user to give priority to upgrade selected areas or reject a picture. Our techniques of hierarchical coding are simple to implement. Informal tests indicate that it is much easier to browse through a picture database using this system and that the time to retrieve a picture of given attributes decreases considerably compared to sequential picture presentation.     

Variable bit-rate coding of video signals for ATM networks

Statistical characteristics of video signals for video packet coding, are clarified and a variable-bit-rate coding method for asynchronous transfer mode (ATM) networks is described that is capable of compensating for packet loss. ATM capabilities are shown to be greatly affected by delay, delay jitter, and packet loss probability. Packet loss has the greatest influence on picture quality. Packets may be lost either due to random bit error in a cell header or to network control when traffic is congested. A layered coding technique using discrete-cosine transform (DCT) coding is presented which is suitable for packet loss compensation. The influence of packet loss on picture quality is discussed, and decoded pictures with packet loss are shown. The proposed algorithm was verified by computer simulations     

RF Pulse Measurement Techniques and Picture Quality

One of the most critical performance characteristics of the TV antenna system is its ability to transmit "ghost-free" pictures. It has been shown that the amount of reflection from the antenna can be correlated to picture quality. How the vestigial sideband RF pulse technique, developed by RCA, more closely simulates TV operation than any other method is discussed. The selection of optimal RE pulse-widths to best reflect correlation with picture quality is discussed. Two RP pulsewidths, one of long duration (up to 2,?s) and the other of shorter duration (0.25, ?s), are recommended for use in antenna test measurements. The RF pulse testing procedure can also be used for measuring the color performance of antenna systems.     

全数字HDTV的图像质量

本文从图像压缩编码的角度，讨论不同全数字ＨＤＴＶ方案的图像质量，从讨论结果中可以看出：经过编码／解码后全数字ＨＤＴＶ的重建图像质量，将接近或非常接近ＣＣＩＲ７０９建议的演播室图像质量。