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Showing papers on "Quantization (image processing) published in 2003"


Proceedings ArticleDOI
TL;DR: A new dataset, UCID (pronounced "use it") - an Uncompressed Colour Image Dataset which tries to bridge the gap between standardised image databases and objective evaluation of image retrieval algorithms that operate in the compressed domain.
Abstract: Standardised image databases or rather the lack of them are one of the main weaknesses in the field of content based image retrieval (CBIR). Authors often use their own images or do not specify the source of their datasets. Naturally this makes comparison of results somewhat difficult. While a first approach towards a common colour image set has been taken by the MPEG 7 committee 1 their database does not cater for all strands of research in the CBIR community. In particular as the MPEG-7 images only exist in compressed form it does not allow for an objective evaluation of image retrieval algorithms that operate in the compressed domain or to judge the influence image compression has on the performance of CBIR algorithms. In this paper we introduce a new dataset, UCID (pronounced ”use it”) - an Uncompressed Colour Image Dataset which tries to bridge this gap. The UCID dataset currently consists of 1338 uncompressed images together with a ground truth of a series of query images with corresponding models that an ideal CBIR algorithm would retrieve. While its initial intention was to provide a dataset for the evaluation of compressed domain algorithms, the UCID database also represents a good benchmark set for the evaluation of any kind of CBIR method as well as an image set that can be used to evaluate image compression and colour quantisation algorithms.

1,117 citations


Journal Article
TL;DR: A steganalytic method that can reliably detect messages (and estimate their size) hidden in JPEG images using the steganographic algorithm F5 is presented.
Abstract: In this paper, we present a steganalytic method that can reliably detect messages (and estimate their size) hidden in JPEG images using the steganographic algorithm F5. The key element of the method is estimation of the cover-image histogram from the stego-image. This is done by decompressing the stego-image, cropping it by four pixels in both directions to remove the quantization in the frequency domain, and recompressing it using the same quality factor as the stego-image. The number of relative changes introduced by F5 is determined using the least square fit by comparing the estimated histograms of selected DCT coefficients with those of the stego-image. Experimental results indicate that relative modifications as small as 10% of the usable DCT coefficients can be reliably detected. The method is tested on a diverse set of test images that include both raw and processed images in the JPEG and BMP formats.

433 citations


Journal ArticleDOI
Zhigang Fan1, R.L. de Queiroz1
TL;DR: A fast and efficient method is provided to determine whether an image has been previously JPEG compressed, and a method for the maximum likelihood estimation of JPEG quantization steps is developed.
Abstract: Sometimes image processing units inherit images in raster bitmap format only, so that processing is to be carried without knowledge of past operations that may compromise image quality (e.g., compression). To carry further processing, it is useful to not only know whether the image has been previously JPEG compressed, but to learn what quantization table was used. This is the case, for example, if one wants to remove JPEG artifacts or for JPEG re-compression. In this paper, a fast and efficient method is provided to determine whether an image has been previously JPEG compressed. After detecting a compression signature, we estimate compression parameters. Specifically, we developed a method for the maximum likelihood estimation of JPEG quantization steps. The quantizer estimation method is very robust so that only sporadically an estimated quantizer step size is off, and when so, it is by one value.

373 citations


Jan Lukás1
01 Jan 2003
TL;DR: It is explained in this paper, how double compression detection techniques and primary quantization matrix estimators can be used in steganalysis of JPEG files and in digital forensic analysis for detection of digital forgeries.
Abstract: In this report, we present a method for estimation of primary quantization matrix from a double compressed JPEG image. We first identify characteristic features that occur in DCT histograms of individual coefficients due to double compression. Then, we present 3 different approaches that estimate the original quantization matrix from double compressed images. Finally, most successful of them Neural Network classifier is discussed and its performance and reliability is evaluated in a series of experiments on various databases of double compressed images. It is also explained in this paper, how double compression detection techniques and primary quantization matrix estimators can be used in steganalysis of JPEG files and in digital forensic analysis for detection of digital forgeries.

353 citations


Journal ArticleDOI
TL;DR: An image enhancement algorithm for images compressed using the JPEG standard is presented, based on a contrast measure defined within the discrete cosine transform (DCT) domain that does not affect the compressibility of the original image.
Abstract: An image enhancement algorithm for images compressed using the JPEG standard is presented. The algorithm is based on a contrast measure defined within the discrete cosine transform (DCT) domain. The advantages of the psychophysically motivated algorithm are 1) the algorithm does not affect the compressibility of the original image because it enhances the images in the decompression stage and 2) the approach is characterized by low computational complexity. The proposed algorithm is applicable to any DCT-based image compression standard, such as JPEG, MPEG 2, and H. 261.

317 citations


Journal ArticleDOI
TL;DR: The results show that the proposed watermark scheme is robust to common signal distortions, including geometric manipulations, and robustness against scaling was achieved when the watermarked image size is scaled down to 0.4% of its original size.
Abstract: In recent years, digital watermarking techniques have been proposed to protect the copyright of multimedia data. Different watermarking schemes have been suggested for images. The goal of this paper is to develop a watermarking algorithm based on the discrete cosine transform (DCT) and image segmentation. The image is first segmented in different portions based on the Voronoi diagram and features extraction points. Then, a pseudorandom sequence of real numbers is embedded in the DCT domain of each image segment. Different experiments are conducted to show the performance of the scheme under different types of attacks. The results show that our proposed watermark scheme is robust to common signal distortions, including geometric manipulations. The robustness against Joint Photographic Experts Group (JPEG) compression is achieved for a compression ratio of up to 45, and robustness against average, median, and Wiener filters is shown for the 3/spl times/3 up to 9/spl times/9 pixel neighborhood. It is observed that robustness against scaling was achieved when the watermarked image size is scaled down to 0.4% of its original size.

179 citations


Journal ArticleDOI
TL;DR: Two new techniques that implement the contrast sensitivity function at significantly higher precision are presented, adapting even to local variations of the spatial frequencies within a decomposition subband, and are compared to conventional CSF-schemes.
Abstract: The visual efficiency of an image compression technique depends directly on the amount of visually significant information it retains. By "visually significant" we mean information to which a human observer is most sensitive. The overall sensitivity depends on aspects such as contrast, color, spatial frequency, and so forth. One important aspect is the inverse relationship between contrast sensitivity and spatial frequency. This is described by the contrast sensitivity function (CSF). In compression algorithms the CSF can be exploited to regulate the quantization step-size to minimize the visibility of compression artifacts. Existing CSF implementations for wavelet-based image compression use the same quantization step-size for a large range of spatial frequencies. This is a coarse approximation of the CSF. This paper presents two new techniques that implement the CSF at significantly higher precision, adapting even to local variations of the spatial frequencies within a decomposition subband. The approaches can be used for luminance as well as color images. For color perception three different CSFs describe the sensitivity. The implementation technique is the same for each color band. Implemented into the JPEG2000 compression standard, the new techniques are compared to conventional CSF-schemes. The proposed techniques turn out to be visually more efficient than previously published methods. However, the emphasis of this paper is on how the CSF can be implemented in a precise and locally adaptive way, and not on the superior performance of these techniques.

174 citations


Journal ArticleDOI
TL;DR: This work proposes an adaptive approach which performs blockiness reduction in both the DCT and spatial domains to reduce the block-to-block discontinuities and takes advantage of the fact that the original pixel levels in the same block provide continuity.
Abstract: One of the major drawbacks of the block-based DCT compression methods is that they may result in visible artifacts at block boundaries due to coarse quantization of the coefficients. We propose an adaptive approach which performs blockiness reduction in both the DCT and spatial domains to reduce the block-to-block discontinuities. For smooth regions, our method takes advantage of the fact that the original pixel levels in the same block provide continuity and we use this property and the correlation between the neighboring blocks to reduce the discontinuity of the pixels across the boundaries. For texture and edge regions, we apply an edge-preserving smoothing filter. Simulation results show that the proposed algorithm significantly reduces the blocking artifacts of still and video images as judged by both objective and subjective measures.

171 citations


Journal ArticleDOI
TL;DR: It is shown how down-sampling an image to a low resolution, then using JPEG at the lower resolution, and subsequently interpolating the result to the original resolution can improve the overall PSNR performance of the compression process.
Abstract: The most popular lossy image compression method used on the Internet is the JPEG standard. JPEG's good compression performance and low computational and memory complexity make it an attractive method for natural image compression. Nevertheless, as we go to low bit rates that imply lower quality, JPEG introduces disturbing artifacts. It is known that, at low bit rates, a down-sampled image, when JPEG compressed, visually beats the high resolution image compressed via JPEG to be represented by the same number of bits. Motivated by this idea, we show how down-sampling an image to a low resolution, then using JPEG at the lower resolution, and subsequently interpolating the result to the original resolution can improve the overall PSNR performance of the compression process. We give an analytical model and a numerical analysis of the down-sampling, compression and up-sampling process, that makes explicit the possible quality/compression trade-offs. We show that the image auto-correlation can provide a good estimate for establishing the down-sampling factor that achieves optimal performance. Given a specific budget of bits, we determine the down-sampling factor necessary to get the best possible recovered image in terms of PSNR.

168 citations


Proceedings ArticleDOI
06 Apr 2003
TL;DR: The paper presents a digital color image watermarking scheme using a hypercomplex numbers representation and the quaternion Fourier transform (QFT) and the fact that perceptive QFT embedding can offer robustness to luminance filtering techniques is outlined.
Abstract: The paper presents a digital color image watermarking scheme using a hypercomplex numbers representation and the quaternion Fourier transform (QFT). Previous color image watermarking methods are first presented and the quaternion representation is then described. In this framework, RGB pixel values are associated with a unique quaternion number having three imaginary parts. The QFT is presented; this transform depends on an arbitrary unit pure quaternion, /spl mu/. The value of /spl mu/ is selected to provide embedding spaces having robustness and/or perceptual properties. In our approach, /spl mu/ is a function of the mean color value of a block and a perceptual component. A watermarking scheme based on the QFT and the quantization index modulation scheme is then presented. This scheme is evaluated for different color image filtering processes (JPEG, blur). The fact that perceptive QFT embedding can offer robustness to luminance filtering techniques is outlined.

135 citations


Patent
10 Nov 2003
TL;DR: In this article, a method and apparatus are provided for identifying differences between a stored pattern and a matching image subset, where variations in pattern position, orientation, and size do not give rise to false differences.
Abstract: A method and apparatus are provided for identifying differences between a stored pattern and a matching image subset, where variations in pattern position, orientation, and size do not give rise to false differences. The invention is also a system for analyzing an object image with respect to a model pattern so as to detect flaws in the object image. The system includes extracting pattern features from the model pattern; generating a vector-valued function using the pattern features to provide a pattern field; extracting image features from the object image; evaluating each image feature, using the pattern field and an n-dimensional transformation that associates image features with pattern features, so as to determine at least one associated feature characteristic; and using at least one feature characteristic to identify at least one flaw in the object image. The invention can find at least two distinct kinds of flaws: missing features, and extra features. The invention provides pattern inspection that is faster and more accurate than any known prior art method by using a stored pattern that represents an ideal example of the object to be found and inspected, and that can be translated, rotated, and scaled to arbitrary precision much faster than digital image re-sampling, and without pixel grid quantization errors. Furthermore, since the invention does not use digital image re-sampling, there are no pixel quantization errors to cause false differences between the pattern and image that can limit inspection performance.

01 Jan 2003
TL;DR: Dynapack as discussed by the authors exploits space-time coherence to compress the consecutive frames of the 3D animations of triangle meshes of constant connectivity, and predicts the position of each vertex v of frame f from three of its neighbors in frame f and from the positions of v and of these neighbors in the previous frame.
Abstract: Dynapack exploits space-time coherence to compress the consecutive frames of the 3D animations of triangle meshes of constant connectivity. Instead of compressing each frame independently (space-only compression) or compressing the trajectory of each vertex independently (time-only compression), we predict the position of each vertex v of frame f from three of its neighbors in frame f and from the positions of v and of these neighbors in the previous frame (space-time compression). We introduce here two extrapolating spacetime predictors: the ELP extension of the Lorenzo predictor, developed originally for compressing regularly sampled 4D data sets, and the Replica predictor. ELP may be computed using only additions and subtractions of points and is a perfect predictor for portions of the animation undergoing pure translations. The Replica predictor is slightly more expensive to compute, but is a perfect predictor for arbitrary combinations of translations, rotations, and uniform scaling. For the typical 3D animations that we have compressed, the corrections between the actual and predicted value of the vertex coordinates may be compressed using entropy coding down to an average ranging between 1.37 and 2.91 bits, when the quantization used ranges between 7 and 13 bits. In comparison, space-only compression yields a range of 1.90 to 7.19 bits per coordinate and time-only compressions yields a range of 1.77 to 6.91 bits per coordinate. The implementation of the Dynapack compression and decompression is trivial and extremely fast. It perform a sweep through the animation, only accessing two consecutive frames at a time. Therefore, it is particularly well suited for realtime and out-of-core compression, and for streaming decompression.

Journal ArticleDOI
TL;DR: The results show how model observers can be successfully used to perform automated evaluation and optimization of diagnostic performance in clinically relevant visual tasks using real anatomic backgrounds.
Abstract: We compared the ability of three model observers (nonprewhitening matched filter with an eye filter, Hotelling and channelized Hotelling) in predicting the effect of JPEG and wavelet-Crewcode image compression on human visual detection of a simulated lesion in single frame digital x-ray coronary angiograms. All three model observers predicted the JPEG superiority present in human performance, although the nonprewhitening matched filter with an eye filter (NPWE) and the channelized Hotelling models were better predictors than the Hotelling model. The commonly used root mean square error and related peak signal to noise ratio metrics incorrectly predicted a JPEG inferiority. A particular image discrimination/perceptual difference model correctly predicted a JPEG advantage at low compression ratios but incorrectly predicted a JPEG inferiority at high compression ratios. In the second part of the paper, the NPWE model was used to perform automated simulated annealing optimization of the quantization matrix of the JPEG algorithm at 25:1 compression ratio. A subsequent psychophysical study resulted in improved human detection performance for images compressed with the NPWE optimized quantization matrix over the JPEG default quantization matrix. Together, our results show how model observers can be successfully used to perform automated evaluation and optimization of diagnostic performance in clinically relevant visual tasks using real anatomic backgrounds.

Journal ArticleDOI
TL;DR: An algorithm for the application of support vector machine (SVM) learning to image compression that combines SVMs with the discrete cosine transform (DCT) and demonstrates that even though there is an extra lossy step compared with the baseline JPEG algorithm, the new algorithm dramatically increases compression for a given image quality.
Abstract: We present an algorithm for the application of support vector machine (SVM) learning to image compression. The algorithm combines SVMs with the discrete cosine transform (DCT). Unlike a classic radial basis function networks or multilayer perceptrons that require the topology of the network to be defined before training, an SVM selects the minimum number of training points, called support vectors, that ensure modeling of the data within the given level of accuracy (a.k.a. insensitivity zone /spl epsi/). It is this property that is exploited as the basis for an image compression algorithm. Here, the SVMs learning algorithm performs the compression in a spectral domain of DCT coefficients, i.e., the SVM approximates the DCT coefficients. The parameters of the SVM are stored in order to recover the image. Results demonstrate that even though there is an extra lossy step compared with the baseline JPEG algorithm, the new algorithm dramatically increases compression for a given image quality; conversely it increases image quality for a given compression ratio. The approach presented can be readily applied for other modeling schemes that are in a form of a sum of weighted basis functions.

Journal ArticleDOI
TL;DR: A novel watermarking scheme to ensure the authenticity of digital images using characteristics of the human visual system to maximize the embedding weights while keeping good perceptual transparency and an image-dependent method to evaluate the optimal quantization step allowing the tamper proofing of the image.

Journal ArticleDOI
TL;DR: A novel heuristic for requantizing JPEG images which incorporates the well-known Laplacian distribution of the AC discrete cosine transform coefficients with an analysis of the error introduced by requantization is reported.
Abstract: We report a novel heuristic for requantizing JPEG images. The resulting images are generally smaller and often have improved perceptual image quality over a "blind" requantization approach, that is, one that does not consider the properties of the quantization matrices. The heuristic is supported by a detailed mathematical treatment which incorporates the well-known Laplacian distribution of the AC discrete cosine transform (DCT) coefficients with an analysis of the error introduced by requantization. We note that the technique is applicable to any image compression method which employs discrete cosine transforms and quantization.

Patent
11 Jun 2003
TL;DR: In this article, an encoder and a re-encoder are used to encode an image while continuously inputting the image with a relatively simple configuration, where the encoder discards the data in the first memory and instructs the encoded data to increase the quantization step and continue encoding.
Abstract: This invention reliably encodes an image while continuously inputting the image with a relatively simple configuration. For this purpose, in this invention, input image data is encoded by an encoder ( 102 ) and stored in first and second memories. An encoding sequence controller ( 108 ) monitors the code amount. Upon determining that the code amount has reached a set value, the encoding sequence controller discards the data in the first memory and instructs the encoder ( 102 ) to increase the quantization step and continue encoding. Preceding encoded data is stored in the second memory. The encoded data is re-encoded by a re-encoder ( 109 ) using the same quantization step as that of the encoder ( 102 ) after the parameter is changed. The re-encoded data is stored in the first and second memories. The quantization steps set in the encoder ( 102 ) and re-encoder ( 109 ) at this time have such values that re-encoding by the re-encoder ( 109 ) is ended before time when the code amount reaches the set value again.

Proceedings ArticleDOI
06 Jul 2003
TL;DR: A novel content-based image authentication framework which embeds the authentication information into the host image using a lossless data hiding approach and can tolerate JPEG compression to a certain extent while rejecting common tampering to the image.
Abstract: In this paper, we present a novel content-based image authentication framework which embeds the authentication information into the host image using a lossless data hiding approach. In this framework the features of a target image are first extracted and signed using the digital signature algorithm (DSA). The authentication information is generated from the signature and the features are then inserted into the target image using a lossless data hiding algorithm. In this way, the unperturbed version of the original image can be obtained after the embedded data are extracted. An important advantage of our approach is that it can tolerate JPEG compression to a certain extent while rejecting common tampering to the image. The experimental results show that our framework works well with JPEG quality factors greater than or equal to 80 which are acceptable for most authentication applications.

Journal ArticleDOI
TL;DR: The design, implementation, and testing of a more efficient algorithm to perform this task are presented, known as the grey level co-occurrence integrated algorithm (GLCIA), which is a dramatic improvement on earlier implementations.

Journal ArticleDOI
TL;DR: Experimental results show that the proposed watermarking scheme is robust to a wide range of image distortions and is superior to the conventional quantization based technique.

Proceedings ArticleDOI
24 Nov 2003
TL;DR: A new JPEG2000-compliant encoding approach is proposed to control the JPEG2000 encoding in order to achieve a desired perceptual quality, based on a vision model that incorporates various masking effects of the human visual perception and on a perceptual distortion metric.
Abstract: In this paper, a new JPEG2000-compliant encoding approach is proposed to control the JPEG2000 encoding in order to achieve a desired perceptual quality. Our method is based on a vision model that incorporates various masking effects of the human visual perception and on a perceptual distortion metric that takes spatial and spectral summation of individual quantization errors into account. Compared with the conventional JPEG2000 rate-based distortion minimization encoding, our method provides a way to generate consistent quality images with lower bit rate.

Patent
14 Nov 2003
TL;DR: In this paper, a system and method for variable bit rate encoding using a complexity ratio is provided, where complex pictures are allocated a larger bit budget relative to simple pictures and the quality of complex pictures can be maintained while reducing the overall size of the encoded video stream.
Abstract: A system and method is provided for variable bit rate encoding using a complexity ratio. Quantization parameter is calculated using a complexity ratio, which is equal to a local complexity divided by a global complexity. Complex pictures are allocated a larger bit budget relative to simple pictures. With the larger bit budget the quality of complex pictures can be maintained while reducing the overall size of the encoded video stream.

Journal ArticleDOI
TL;DR: A novel approach to secret image sharing based on a (k,n)-threshold scheme with the additional capability of share data re- duction is proposed, which is suitable for certain application environments, such as the uses of mobile or handheld devices, where only a small amount of network traffic and space for data storage are allowed.
Abstract: A novel approach to secret image sharing based on a (k,n)-threshold scheme with the additional capability of share data re- duction is proposed. A secret image is first transformed into the fre- quency domain using the discrete cosine transform (DCT), which is ap- plied in most compression schemes. Then all the DCT coefficients except the first 10 lower frequency ones are discarded. And the values of the 2nd through the 10th coefficients are disarranged in such a way that they cannot be recovered without the first coefficient and that the inverse DCT of them cannot reveal the details of the original image. Finally, the first coefficient is encoded into a number of shares for a group of secret- sharing participants and the remaining nine manipulated coefficients are allowed to be accessible to the public. The overall effect of this scheme is achievement of effective secret sharing with good reduction of share data. The scheme is thus suitable for certain application environments, such as the uses of mobile or handheld devices, where only a small amount of network traffic for shared transmission and a small amount of space for data storage are allowed. Good experimental results proving the feasibility of the proposed approach are also included. © 2003 Society

Journal ArticleDOI
G. Lakhani1
TL;DR: A minor modification to the Huffman coding of the JPEG baseline compression algorithm is presented, which all move the end-of-block marker up in the middle of DCT block and use it to indicate the band boundaries.
Abstract: It is a well observed characteristic that when a DCT block is traversed in the zigzag order, the AC coefficients generally decrease in size and the run-length of zero coefficients increase in number This article presents a minor modification to the Huffman coding of the JPEG baseline compression algorithm to exploit this redundancy For this purpose, DCT blocks are divided into bands so that each band can be coded using a separate code table Three implementations are presented, which all move the end-of-block marker up in the middle of DCT block and use it to indicate the band boundaries Experimental results are presented to compare reduction in the code size obtained by our methods with the JPEG sequential-mode Huffman coding and arithmetic coding methods The average code reduction to the total image code size of one of our methods is 4% Our methods can also be used for progressive image transmission and hence, experimental results are also given to compare them with two-, three-, and four-band implementations of the JPEG spectral selection method

Journal ArticleDOI
TL;DR: The human visual system (HVS) model is used to estimate the J2J data hiding capacity of JPEG images, or the maximum number of bits that can be embedded in JPEG-compressed images.
Abstract: In JPEG-to-JPEG image watermarking (J2J), the input is a JPEG image file. After watermark embedding, the image is JPEG-compressed such that the output file is also a JPEG file. We use the human visual system (HVS) model to estimate the J2J data hiding capacity of JPEG images, or the maximum number of bits that can be embedded in JPEG-compressed images. A.B. Watson's HVS model (Proc. SPIE Human Vision, Visual Process., and Digital Display IV, p.202-16, 1993) is modified to estimate the just noticeable difference (JND) for DCT coefficients. The number of modifications to DCT coefficients is limited by JND in order to guarantee the invisibility of the watermark. Our capacity estimation method does not assume any specific watermarking method and thus would apply to any watermarking method in the J2J framework.

Patent
15 Jan 2003
TL;DR: In this article, a system and method for printer control and color balance calibration is proposed to address the image quality problems of print engine instability, low quality of color balance and contouring from the calibration.
Abstract: A system and method for printer control and color balance calibration. The system and method address the image quality problems of print engine instability, low quality of color balance and contouring from the calibration. The method includes defining combinations of colorants, such as inks or toners that will be used to print images, defining a desired response for the combinations that are to be used and, in real time, iteratively printing CMY halftone color patches, measuring the printed patches via an in situ sensor and iteratively performing color-balance calibration based on the measurements, accumulating corrections until the measurements are within a predetermined proximity of the desired response. The calibration is performed on the halftones while they are in a high quantization resolution form.

Patent
Wenjun Zeng1, Lei Shawmin
02 Oct 2003
TL;DR: In this paper, a method of quantizing image data including the step of varying the magnitude of a quantization step as a function of the distortion of an image is disclosed for further visually optimizing image quantization.
Abstract: The ability of the visual system to detect contrast in an image is a function of the frequency of the contrasting pattern and the distortion of the image. The visual system is more sensitive to contrasting patterns of lower frequency. When the image is significantly distorted, the visual system is even more sensitive to lower frequencies than higher frequencies. An image encoder employs lossy data compression processes producing a distorted reconstructed image. A method of quantizing image data including the step of varying the magnitude of a quantization step as a function of the distortion of an image is disclosed for further visually optimizing image quantization. Another method utilizes distortion adaptive weighting to vary the limit of code block truncation during embedded bitstream coding to visually optimize image compression by increasing relative lossiness of compression at higher frequencies.

Patent
Hartmut Wiesenthal1
18 Dec 2003
TL;DR: In this article, an adaptive encoding of digital multimedia information is performed by measuring link parameters, such as a received signal strength, a bit error rate, or a rate of received acknowledgement signals, in order to determine an available transmission rate.
Abstract: Adaptive encoding of digital multimedia information may be performed by measuring link parameters, such as a received signal strength, a bit error rate, or a rate of received acknowledgement signals, in order to determine an available transmission rate. A maximum encoding rate may then be determined based on the available transmission rate by, for example, dividing the available transmission rate by an overhead factor. If the encoding rate of the digital multimedia information exceeds the calculated maximum encoding rate, adaptive encoding of the digital multimedia information may be performed in order to conform the encoding rate of the digital multimedia information to the calculated maximum encoding rate. This process may involve compressing selected frames within a frame sequence, deleting high frequency components within selected frames, deleting I-frame components within selected frames, or mapping values within selected frames to corresponding values having coarser quantization.

Patent
Taku Kodama1
14 Mar 2003
TL;DR: In this paper, an image compression device comprising an image division unit dividing an image into a plurality of regions, a region designation unit designating a region of interest in the image, a quantization rate determination unit determining quantization rates with respect to each region divided by the image division, and a compression control unit controlling compression based on each region based on the quantisation rate determined by the Quantization Rate determination unit is disclosed.
Abstract: An image compression device comprising an image division unit dividing an image into a plurality of regions, a region designation unit designating a region of interest in the image, a quantization rate determination unit determining quantization rate with respect to each region divided by the image division unit, and a compression control unit controlling compression with respect to each region based on the quantization rate determined by the quantization rate determination unit is disclosed. In the image compression device, the quantization rate determination unit can determine quantization rate for the region of interest different from the quantization rate for the regions other than the region of interest.

Journal ArticleDOI
TL;DR: A novel postprocessing technique based on the theory of the projection onto convex sets (POCS) in order to reduce the blocking artifacts in digital high definition television (HDTV) images by detecting and eliminating the undesired high-frequency components.
Abstract: In this paper, we present a novel postprocessing technique based on the theory of the projection onto convex sets (POCS) in order to reduce the blocking artifacts in digital high definition television (HDTV) images. By detecting and eliminating the undesired high-frequency components, mainly caused by blocking artifacts, we propose a new smoothness constraint set (SCS) and its projection operator in the DCT domain. In addition, we propose an improved quantization constraint set (QCS) using the correlation of DCT coefficients between adjacent blocks. In the proposed technique, the range of the QCS is efficiently reduced as close to the original DCT coefficient as possible to yield better performance of the projection onto the QCS. Computer simulation results indicate that the proposed schemes perform better than conventional algorithms. Furthermore, we introduce a fast implementation method of the proposed algorithm. The conventional POCS-based postprocessing techniques require the forward/inverse discrete cosine transform (DCT/IDCT) operations with a heavy computational burden. To reduce the computational complexity we introduce a fast implementation method of the proposed algorithm that does not perform DCT/IDCT operations. Estimates of computation savings vary between 41% and 64% depending on the task.