DPCM Coding Research Articles

An Ingenious Design of a High Performance-Low Complexity Image Compressor for Wireless Capsule Endoscopy.

Wireless Capsule Endoscopy is a state-of-the-art technology for medical diagnoses of gastrointestinal diseases. The amount of data produced by an endoscopic capsule camera is huge. These vast amounts of data are not practical to be saved internally due to power consumption and the available size. So, this data must be transmitted wirelessly outside the human body for further processing. The data should be compressed and transmitted efficiently in the domain of power consumption. In this paper, a new approach in the design and implementation of a low complexity, multiplier-less compression algorithm is proposed. Statistical analysis of capsule endoscopy images improved the performance of traditional lossless techniques, like Huffman coding and DPCM coding. Furthermore the Huffman implementation based on simple logic gates and without the use of memory tables increases more the speed and reduce the power consumption of the proposed system. Further analysis and comparison with existing state-of-the-art methods proved that the proposed method has better performance.

Performance of Predictive Coders for Wireless Capsule Endoscopy Image Compression

Wireless capsule endoscopy is a medical diagnostic technique developed for the endoscopic examination of the small bowel. The encoder module is the core of the wireless capsule endoscopic system impacting on power and area requirement for the hardware implementation of the capsule. One of the remarkable features of the endoscopic image is that the neighboring pixels are highly correlated. Two predictive coding techniques are considered in this work exploiting the above fact. The first predictive coder i.e., DPCM coder is based on previous horizontal neighboring pixel, whereas the second predictive coder is based on adjacent horizontal and diagonal neighbors. The performance of the predictive coders is tested with 41 small bowel type endoscopic images available in the Gastrolab dataset. The results show that the average compression rate and peak signal to noise ratio attained by DPCM coder and newly tested predictive coder are 66.37 % & 73.03 % and 32.17 dB & 35.55 dB, respectively.

Hybrid DWT-DCT compression algorithm & a new flipping block with an adaptive RLE method for high medical image compression ratio

Huge number of medical images are generated and needs for more storage capacity and bandwidth for transferring over the networks. Hybrid DWT-DCT compression algorithm is applied to compress the medical images by exploiting the features of both techniques. Discrete Wavelet Transform (DWT) coding is applied to image YCbCr color model which decompose image bands into four subbands (LL, HL, LH and HH). The LL subband is transformed into low and high frequency components using Discrete Cosine Transform (DCT) to be quantize by scalar quantization that was applied on all image bands, the quantization parameters where reduced by half for the luminance band while it is the same for the chrominance bands to preserve the image quality, the zigzag scan is applied on the quantized coefficients and the output are encoded using DPCM, shift optimizer and shift coding for DC while adaptive RLE, shift optimizer then shift coding applied for AC, the other subbands; LH, HL and HH are compressed using the scalar quantization, Quadtree and shift optimizer then shift coding. In this paper, a new flipping block with an adaptive RLE is proposed and applied for image enhancement. After applying DCT system and scalar quantization, huge number of zeros produced with less number of other values, so an adaptive RLE is used to encode this RUN of zeros which results with more compression.Standard medical images are selected to be used as testing image materials such as CT-Scan, X-Ray, MRI these images are specially used for researches as a testing samples. The results showed high compression ratio with high quality reconstructed images

An object-based lossless compression approach for medical images using DPCM

In this paper, an object-based coding technique for the lossless compression of medical images has been introduced. Since the region of interest in medical images is generally the object in the centre of the image, it is extracted and encoded using a lossless DPCM coder. The non-image region is split into sub-regions and concatenated after pre-processing, and encoded using the same DPCM method. For performance analysis, the proposed method is applied to various medical images. Bits per pixel values are calculated and compared with those of the object based wavelet transform coder and the direct coders. The results show that the proposed coder yields improved bits per pixel value than the rest of the coders.

Pyramid Vector Quantization of Video Subband With Dithering

This paper describes the development of a low complexity and fixed–rate video compression scheme based on three–dimensional subband coding of video signals. The video codec first performs three–dimensional subband decomposition on a group of video frames, and then encode high frequency subbands with pyramid vector quantization and lowest tempo–spatial band with a DPCM coding in time and space. To improve the visual quality of reconstructed video, different types of subtractive and non–subtractive dithering of pyramid vector quantizers were experimented and its effectiveness was proved by a standard pair comparison subjective test. Coder complexity was reduced by using longer filters in the first level of spatial decomposition for better selectivity and coding gain and shorter filter in the second level of decomposition for lower complexity. Results at different low bit–rate (64, 128 and 384 Kbps) for several standard video sequences are reported and compared with ITU standard H.263.

On the Operational Rate-Distortion Performance of Uniform Scalar Quantization-Based Wyner–Ziv Coding of Laplace–Markov Sources

Wyner-Ziv (WZ) coding has recently been proposed as a low encoding complexity alternative to traditional DPCM coding for compression of sources with memory, in particular, in applications like multimedia compression. The viability of this alternative approach clearly depends on the compression performance of WZ coding compared to that of DPCM coding. In an attempt to understand the performance gap between WZ coding and DPCM coding, this paper studies the operational rate-distortion performance of WZ coding, using uniform scalar quantization followed by perfect Slepian-Wolf coding, for compression of a Laplace-Markov (LM) source. It is shown that at low rates or for weakly correlated LM sources, WZ coding is indeed a competitive alternative to DPCM coding. However, at high rates the performance gap becomes non-negligible for strongly correlated LM sources. In order to reduce the gap at high rates, a hybrid approach that combines DPCM coding and WZ coding is further investigated. It is shown that the hybrid approach is indeed competitive to DPCM coding at all rates even for strongly correlated LM sources.

Motion-compensated video compression with reduced complexity encoding for remote transmission

Abstract Efficient operation at very low bit-rates necessitates a complex encoder that can exploit both spatial and temporal redundancy in a video sequence. To reduce the complexity of such an encoder, we introduce here a new form of motion compensation similar to the conventional hybrid DPCM-transform method but where the compensation is performed outside the feedback loop. In addition to reducing encoder complexity, the proposed out-of-loop (OOL) compensation scheme also supports resolution and frame-rate scalability. While the basic idea is conceptually similar to the pan compensation proposed by Taubman and Zakhor, our method continually tracks and updates the image in the feedback loop in the same way as the conventional DPCM coder. Using OOL compensation, we have observed an average encoder speed increase of 33% on a typical CIF-size video sequence compared to the conventional approach with no significant decrease in decoder speed. Furthermore, we have also found that OOL pan compensation significantly improves the rate-distortion performance of the system relative to conventional pan compensation – taken over five different video sequences, the average bit-rate reduction is 9.2% and the average mean-squared error reduction is 29.6%.

Analysis of linear prediction, coding, and spectral estimation from subbands

Linear prediction schemes make a prediction x/spl circ//sub i/ of a data sample x/sub i/ using p previous samples. It has been shown by Woods and O'Neil (1986) as well as Pearlman (1991) that as the order of prediction p/spl rarr//spl infin/, there is no gain to be obtained by coding subband samples. This paper deals with the less well understood theory of finite-order prediction and optimal coding from subbands which are generated by ideal (brickwall) filtering of a stationary Gaussian source. We first prove that pth-order prediction from subbands is superior to pth-order prediction in the fullband, when p is finite. This fact adduces that optimal vector p-tuple coding in the subbands is shown to offer quantifiable gains over optimal fullband p-tuple coding, again when p is finite. The properties of subband spectra are analyzed using the spectral flatness measure. These results are used to prove that subband DPCM provides a coding gain over fullband DPCM, for finite orders of prediction. In addition, the proofs provide means of quantifying the subband advantages in linear prediction, optimal coding, and DPCM coding in the form of gain formulas. Subband decomposition of a source is shown to result in a whitening of the composite subband spectrum. This implies that, for any stationary source, a pth-order prediction error filter (PEF) can be found that is better than the pth-order PEF obtained by solving the Yule-Walker equations resulting from the fullband data. We demonstrate the existence of such a super-optimal PEF and provide algorithmic approaches to obtaining this PEF. The equivalence of linear prediction and AR spectral estimation is then exploited to show theoretically, and with simulations, that AR spectral estimation from subbands offers a gain over fullband AR spectral estimation.

Weighted median filters: a tutorial

Weighted Median (WM) filters have the robustness and edge preserving capability of the classical median filter and resemble linear FIR filters in certain properties. Furthermore, WM filters belong to the broad class of nonlinear filters called stack filters. This enables the use of the tools developed for the latter class in characterizing and analyzing the behavior and properties of WM filters, e.g. noise attenuation capability. The fact that WM filters are threshold functions allows the use of neural network training methods to obtain adaptive WM filters. In this tutorial paper we trace the development of the theory of WM filtering from its beginnings in the median filter to the recently developed theory of optimal weighted median filtering. Applications discussed include: idempotent weighted median filters for speech processing, adaptive weighted median and optimal weighted median filters for image and image sequence restoration, weighted medians as robust predictors in DPCM coding and Quincunx coding, and weighted median filters in scan rate conversion in normal TV and HDTV systems.

New Image/Video Media and It's Application. A Lossless Hybrid Coding Scheme for Computer Cartoon Images.

This paper presents a lossless hybrid coding scheme for compressing computer cartoon images, such as those used in TV cartoon programs and computer games. Such images are usually composed of simple multi-color characters/graphs and complicated full-color backgrounds. The hybrid coding scheme is based on the basic principle of Structure Runlength Coding (SRC) and is combined with prediction coding. It solves two main problems in the conventional methods : that SRC cannot cope with the complicated full-color regions and that predictive DPCM coding cannot efficiently compress the simple multi-color regions. Through an evaluation of entropy, we prove that our hybrid coding scheme is superior to the conventional methods at compressing these computer cartoon images. Compared with an adaptive DPCM coding, our hybrid coding can decrease the entropy by about 1 bit per pixel on average. Compared with SRC, it can decrease the entropy up to 5 bits per pixel in the case of complicated backgrounds. An experimental result shows high compression ratios.

Composite source model of DPCM coders

A new model regarding the difference values of a DPCM coder as a composite source is presented. It can provide a decrease in the entropy of prediction errors and is especially useful in lossless coding and distortion limited compression. Application to image coding demonstrates its effectiveness.

Digital image coding using legendre transform

Image coding can be implemented through DPCM, transform, hybrid, or segmentation coding techniques. Some transform coding techniques, such as cosine and Hadamard, have been exhaustively analyzed and evaluated, while others, such as Legendre, have not. This paper introduces the use of Legendre transform in image coding. The transform matrix for different block sizes is calculated, the fast algorithm is derived, and the performance is evaluated through both mean square error and subjective quality. The results obtained have indicated that the system performance is comparable with that of optimum KLT and cosine transforms; moreover, it is simpler in implementation.

Digital filters implementation using DPCM video signal processing

A new realisation of DPCM video signal/image processing is introduced to increase the throughput rate and reduce the hardware cost of the 2D systolic digital filters. This achieved by using a DPCM coding system with a 2D predictor and a 27-level symmetric nonuniform quantiser prior to processing. The advantage of the symmetric nonuniform quantiser is that the size of memory required for multiplication is reduced by a factor of 16 compared to 4 in the existing DPCM implementations. It is shown that the new realisation results in a 64% increase in the throughput rate and a significant reduction in the hardware cost. From the objective and subjective tests carried out, it is shown that the new realisation results in images with visual quality similar to those obtained using conventional processing. Also, the effect of the choice of the 2D predictor is discussed, where it is shown that a 2D predictor with integer coefficients is the most appropriate for DPCM processing.

On the statistics of the error in predictive coding for stationary Ornstein-Uhlenbeck processes

Explicit expression are derived for the conditional expectation and variance of the encoder in a predictive DPCM coder with an N-level quantizer, when a stationary Ornstein-Uhlenbeck process is a source. A representation of the encoder in terms of a stochastic integral is presented. These expressions yield a nonlinear stochastic difference equation for the decoding error process and a stochastic differential equation (SDE) as a weak limit for the error process. The statistical properties of the error obtained as a solution of the limiting SDE are interpreted in terms of the slope overload error. >

Design of a perfect reconstructive subband image coding scheme

The Broadband Integrated Services Digital Network (B-ISDN) is being designed to support multimedia signals. Nationwide image-signal transmission systems will be constructed to offer high-quality and reliable services to customers. The largest users of image transmission systems will be broadcasting stations. The transmission of image signals within and between studios or broadcasting stations requires the ability to multiply encode/decode signals without visible degradation. The ideal system would be free of quantization noise. A subband coding scheme is presented which can achieve distortion-free encoding. It is provided that the required entropy can be reduced by using two-tap filters for subband splitting; the original picture quality is maintained. A new short-kernel subband filter architecture is proposed which can further reduce the entropy of subband signals. Experimental results show that four-band splitting with adaptive DPCM coding is the most promising of the various subband configurations. This subband DPCM coding scheme has higher performance than full-band DPCM coding.

Source Coding

This article presents different source coding techniques like PCM, DPCM and DM and discusses various stages of analog to digital conversion, like sampling, quantising and coding. It also discusses about the effects of undersampling like aliasing and the advantages of oversampling. It highlights the various companding techniques like A-law companding and μ-law companding and concludes with the discussion on comparative performance of PCM, DPCM and DM coding techniques.

Adaptive sub-band DCT coding for HDTV signal transmission

This paper presents an adaptive sub-band DCT coding for high-quality HDTV signal transmission. In the coder, the first stage quadrature mirror filters (QMFs) decompose the input signal into two bands in the horizontal direction, while the second stage filters decompose the two bands into four bands in the vertical direction. An adaptive DCT is adopted for horizontal-low and vertical-low (LL) signal coding. To maximize bit-rate reduction efficiency, this paper proposed adaptive selection of the input signal mode to the DCT coding from the intra-field signal as well as the inter-field and motion compensated inter-frame signals. One-dimensional DPCM coding is applied to the signals on the same horizontal line of the LH band. The other-band signals are coded by PCM having a dead zone. To further reduce information bit-rates, variable length coding and run-length coding are applied to the quantized signal in each band. Computer simulation results are presented in terms of bit-per-pel and SNR of the reconstructed picture. This paper also presents codec characteristics when it is connected in tandem. It focuses mainly on causes of quantization-noise accumulation in digital tandem connections which are essential to coding algorithms. A coder configuration that reduces noise accumulation to less than 1 dB after three tandem links is proposed.

Six-bit DPCM video signal processing and implementation using systolic arrays

A novel approach to increase the speed and reduce the hardware requirement of 2-D systolic convolvers for real-time video signal/image processing is proposed. This is achieved by coding video signals/images more efficiently using six-bit I-D DPCM coding. It is shown that using six-bit differential pulse-code modulation processing results in a 57% improvement in speed and a significant saving in the cost of 2-D systolic convolvers. The effect of quantisation errors on DPCM image convolution is also presented.

Effects of error propagation on the performance of coding schemes for still pictures

AbstractThis paper investigates the effects of noise‐induced transmission errors on the performance of compression coding methods for still pictures. The following four coding methods are considered: (1) adaptive cosine transform coding; (2) DPCM coding; (3) adaptive block coding; and (4) vector quantization coding. First, the relations among the bit error rate, signal‐to‐noise ratio (SNR), and code lengths by these coding methods are compared in the case of transmission without error control. Adaptive cosine transform coding and adaptive block coding require control information for adaptivity; therefore, they are investigated with and without transmission errors in the coding control information. Further, transmission with error control is studied for sending control information. Considering the error control methods, both automatic repeat request and forward error correction are considered. In these cases SNR deterioration by transmission noise beyond error correction capability and the amount of additional data required for error detection/correction or retransmission are examined. BCH codes are used for error detection and correction.

Combining fast DPCM compression of pictures with tree encoding

This contribution presents a fast DPCM coder built around a ROM of feasible size, in which an elementary form of tree encoding is integrated, to improve the quality of the decodedpicture. Simulations illustrate the improvements of this technique in comparison with normal DPCM encoding.