121 results about "Ac coefficient" patented technology

A technique to reduce blocking and ringing artifacts in low bit-rate block-based video coding is applied to each reconstructed frame output from the decoder. For each pixel block of a reconstructed frame, its DC value and DC values of the surrounding eight neighbor blocks are exploited to predict AC coefficients which might be lost in the quantization stage in the encoding process. The predicted AC coefficients are used to classify each reconstructed block as either a low-activity or a high-activity block. Low-pass filtering is then adaptively applied according to the classification of the block. Strong low-pass filtering is applied in low-activity blocks where the blocking artifacts are most noticeable, whereas weak low-pass filtering is applied in high-activity blocks where ringing noise as well as blocking artifacts may exist. The adaptive filtering reduces ringing noise as well as blocking artifacts without introducing undesired blur. In low activity blocks, the blocking artifacts are reduced by one dimensional horizontal and vertical low-pass filters which are selectively applied in either the horizontal and / or vertical direction depending on the locations and absolute values of the predicted AC coefficients. In high activity blocks, de-blocking and de-ringing is conducted by a single filter, applied horizontally and / or vertically, which makes the architecture simple.

A trick play information stream is generated from a normal play information stream, so that they can be recorded together as a composite information stream on the record carrier, such that upon reproduction in a trick play reproduction mode, an information signal of sufficient quality, e.g., as regards visibility, can be obtained. GOPs are generated, each GOP including an I-frame retrieved from the original normal play information stream, and one or more so-called "empty P frames'. Another aspect is the requirement of generating GOPs for the trick play information stream that have a constant bitcost per GOP. Again, another aspect lies in the retrieval of the I-frame for the trick play information stream from the normal play information. More specifically, an I-frame is generated by retrieving, from an I-frame included in the normal play information, the DC coefficient of the I-frame and a number of AC coefficients from that I frame, and generating the I-frame for the trick play information stream therefrom. More specifically, the number of AC coefficients for an I-frame of the trick play information signal depends on the difference between the DC coefficients of two subsequent I-frames in the normal play information from which the I-frame to be generated and the just previously generated I-frame for the trick play information signal have been derived.

The invention provides method and apparatus of video bit stream encoding. In non-intra type encoding, block pixel differences between a target block and the corresponding best match block is compared to other blocks' to determine whether a bit stream of a previously compressed block can be used to represent a target block. In Intra-coding, a target block is compared to other blocks to determine whether a bit stream of a previously compressed block can represent the target block. Should variance range of a block pixel of an intra-coded frame or block pixel differences of a non-intra coding frame is less than predetermined thresholds, the DC coefficient is represented by a predetermined value, or a certain amount of AC coefficients are calculated.

Tools and techniques for applying scan patterns during encoding and decoding of progressive video are described. For example, a video decoder entropy decodes transform coefficients in a one-dimensional array and scans the transform coefficients into a block according to a scan pattern. The block is 8×4, and the scan pattern biases the vertical direction for at least the lowest frequency AC coefficients in the horizontal and vertical directions. Or, the block is 4×8, and the scan pattern biases the horizontal direction for at least the lowest frequency AC coefficients in the horizontal and vertical directions. A corresponding video encoder applies the scan patterns to scan transform coefficients from blocks to one-dimensional arrays.

The invention discloses a digital image compressing, encrypting and encoding combined method, and belongs to the technical field of image encrypting. The method is achieved on the basis of the JPEG compressing and encoding standard which is most widely applied at present, and the encrypting algorithm based on chaos is integrated with the encoding process; according to the characteristic that DC coefficients and AC coefficients are separately encoded on the basis of the JPEG standard, the DC coefficients and the AC coefficients of an image are separately encrypted; in order to give consideration to both security and compressing efficiency, all the DC coefficients and part of the AC coefficients are encrypted through the method, coefficients at the same positions in all DCT blocks are divided into different groups and are scrambled and diffused within the groups, and damage to differential encoding and run length encoding in the encrypting process is reduced as much as possible; scrambling and diffusing are achieved on the basis of logistic chaotic mapping and Chebyshev chaotic mapping respectively. The experiments prove that the method has high data compressing capacity while providing effective image data security protection.

The invention relates to a video watermark treatment method, in particular to a DCT domain video watermark treatment method based on texture features, which belongs to technologies of information safety. The method comprises the steps of scrambling a watermark; calculating the brightness sum of a video image according to the color value of RGB of the video image, sequencing the brightness sum, selecting a frame for embedding, determining the middle position and the lower position of AC coefficients for embedding the watermark after the scrambling into the video image according to the texture distribution of the video image, carrying out distortion compensation on the video image with the embedded watermark by introducing motion compensation, reducing the video distortion caused during thewatermark embedding, and extracting and detecting the video image with the embedded watermark by utilizing the correlation of the watermark. The method has the advantages of good invisibility, stronganti-attack ability, good safety and real-time property and large capacity of embedded information.

The present invention relates to a method and system for foreground segmentation in which frames of a video sequence are analyzed in the transform domain to determine one or more features. The features are used to model the background. The background can be modeled as a single Gaussian model with a mean and variance of the features. A current frame is segmented by determining if one or more features of the current frame analyzed in the foreground domain satisfy a threshold between the background model. The threshold value can be based on the mean and / or variance of features. During the segmentation, the mean and variance can be updated based on previous corresponding values and current features to adaptively update the background model. In one embodiment, the frames are divided into a plurality of blocks. A transform is used to analyze the blocks in the transform domain. For example, the transform can be a discrete cosine transform (DCT). The features can be a DC feature comprising the DC coefficient and an AC feature comprising a weighted sum of the AC coefficients. The weighted sum is determined with weights which are varied to emphasize different aspects of the present invention. Additional processing steps can be used to remove false positives, handle sudden global illumination changes, handle sudden local illumination changes and remove false negatives.

Modify H.263-type quantization with an adaptive quantization parameter floor; this limits clipping of quantized DCT coefficients and consequent artifacts. The maximum absolute level of AC coefficients of a DCT transformed macroblock provides a minimum quantization parameter from integer division by 256 when the quantized levels are clipped to a range such as −127 to +127.

Methods and systems for JPEG encoding and decoding are disclosed. In the encoding method, an image is split into 8×8 pixel blocks and the 8×8 pixel blocks are grouped into a number of minimum coded units (MCU's), such that each MCU consists of a constant number of 8×8 pixel blocks. The MCU's are then scanned to forward discrete cosine transform, quantization, zigzag scanning and entropy encoding processes and are subsequently converted into bitstreams according to entropy encoding coding tables. In the entropy encoding process, AC coefficients are run-length encoded, while DC coefficients are not subjected to differential pulse-code modulation. The bitstreams are byte-aligned by stuffing zeroes and compression data for a special JPEG file are generated from the byte-aligned bitstreams. A position table is established, recording positions of the bitstreams in the compression data. The method enables fast positioning of bitstreams corresponding to an image region of interest.

The invention relates to an intra-class coefficient scrambling-based JPEG image encryption method. The method comprises the following steps: firstly reading in a JPEG image file, acquiring a Huffman coding table and image data which undergoes JPEG coding compression, carrying out decoding to acquire all the non-zero quantized DCT coefficient numerical values and positions and carrying out classification; selecting a password, carrying out chaotic iteration by utilizing the password, so as to generate a chaotic sequence, and scrambling the non-zero coefficients and 8*8 block of each class by utilizing the chaotic sequence; and carrying out entropy coding on a scrambled quantized DCT coefficient matrix, and writing the coded data into the JPEG image file so as to complete intra-class coefficient scrambling-based JPEG image encryption. According to the method disclosed in the invention, scrambling is carried out on different classes of quantized DCT coefficients through the chaotic sequence, and the quantized DC coefficients and the non-zero AC coefficients are processed by directly using one encryption scheme, so that the safety and the high efficiency are both considered; and the encrypted images are similar to clear text image files in the aspect of size, and have high compression ratios.

The invention provides a detection method for secondary compression of a JPEG image. By using the characteristic that an AC coefficient histogram in a DCT coefficient of primary JPEG compression accords with Laplace distribution, a Laplace distribution function of the AC coefficient of the primary JPEG compression of an image to be detected is estimated in a fit mode according to the AC coefficient distribution of the JPEG image to be detected; the statistic is detected through a difference structure of normalized histogram distribution of the fit distribution function and an actual AC coefficient; and whether the JPEG image is subjected to the secondary compression is judged by using SVM classification. The method has high detection accuracy and wide applicability.

The invention discloses a method for extracting compressed video key frames. The method includes: firstly, extracting color characteristics of a video from a DC coefficient, then extracting characteristics of edges, textures and the like of an AC coefficient and normalizing different values by means of a Gaussian model to obtain fusion characteristics, so that complete characteristic similarities are obtained to improve representativeness and increase the accuracy rate of the key frames; and then establishing a curve by the aid of the complete characteristic similarities, and performing curvature detection for the curve for twice so as to extract the key frames. By the method, the key frames capable of reflecting main contents of the video can be accurately extracted, and the defect of incomplete video content descriptions by using DC coefficient characteristic information only is made up. Moreover, automatic extraction of the key frames is realized by means of two-time curve detection, and artificial determination of the amount of the key frames is avoided.

The invention discloses a method and a device for controlling bit rate of compressed images. Data quantity in data cache is first obtained; if the number of the AC coefficient preserved presently is the maximum number of the AC coefficient and the data cache is judged to over run, the number of the AC coefficient preserved presently is set as the minimum number of the AC coefficient and a target compression ratio is set as initial valve of the target compression ratio; if the data cache is judged not to over run, the maximum valve of the data quantity during data caches is counted when the record is interrupted for N times and the present target compression ratio is reduced if the maximum valve is less than the low threshold of the data cache; the present target compression ratio is increased if the maximum valve is more than the high threshold of the data cache. The invention realizes dynamic target compression ratio adjustment and is combined with the number adjustment of the AC coefficient at the same time, and therefore the over-run is avoided to the utmost extend when image of comparatively good quality is guaranteed, thereby improving the quality of the compressed image.

A method for decoding a stream of coded data representative of a sequence of images is disclosed. The decoding method comprisesdetermining a prediction block,calculating the average of said prediction block,reconstructing, from said stream, a DC coefficient and AC coefficients relating to said current block,calculating an average of said current block from said average of said prediction block and said DC coefficient,calculating a weighted prediction parameter as being the ratio of the average of said current block and the average of said prediction block,transforming a block of coefficients comprising a null value as DC coefficient and said reconstructed AC coefficients into a residual block,reconstructing the current block by merging said residual block and said prediction block weighted by said weighted prediction parameter.A method for coding is further disclosed.

A method of image / video compression with intra-coding blocks analyzed for sum of absolute magnitudes of AC coefficients of DCT of block to determine whether to approximate the block with 0 AC coefficients, and with inter-coding blocks analyzed for sum of absolute differences of block and predicted block to determine whether to approximate the block with a 0 block.

The invention discloses an encryption method based on H.264 video streaming. During the H.264 coding, a frame of images is divided into m slices (m is more than or equal to 1), each slice contains n macro blocks (n is more than or equal to 1), each macro block is divided into 16 sub-blocks based on 4*4 as a basic unit: that is, Zm,n,0, Zm,n,1, Zm,n,15, and each sub-block contains 16 DCT coefficients, that is, Zm,n,i ={Cm,n,i, 0, Cm,n,i, 1, Cm,n,i,15} (m is more than or equal to 1, n is more than or equal to 1, i is more than or equal to 0 but less than or equal to 15); a DCT coefficient hierarchical model is established in correspondence to the macro block and then divided into a DC coefficient layer and other 15 AC coefficient layers; sequentially, each frame of image data is distributed with a key, that is, each layer is distributed with a key, if necessary, a plurality of layers share one key; each frame of image data is encrypted and the key sequence pointer resets to scramble layer after layer until the frame is completed. The invention has good safety and high compression ratio.

A technique for eliminating the division in decoding a predicted AC coefficient includes calculating and storing the values of I / / AC_stepsize in a table. This allows one to convert a division into a multiplication.

The invention provides a method for encrypting MPEG (moving picture experts group) video streaming information based on a hyper-chaotic sequence, which is characterized in that a streaming encryption technology is combined with a block encryption technology so as to encrypt I frames and P frames of MPEG video streaming; in an algorithm, an initial value of a four-dimensional hyper-chaotic system is taken as an external secret key, the hyper-chaotic sequence generated by the four-dimensional hyper-chaotic system is utilized, and AC (alternating current) coefficients of video images are utilized to generate an inner secret key; and an XOR operation is carried out on DC (direct current) and AC coefficients of the I frames respectively, position scrambling is carried out on luminance information of the I frames by taking a 8*8 block as a unit, the XOR operation is carried out on motion vectors of F macro blocks in the P frames, and original video information is disturbed sufficiently. In the method, the space of the secret keys is huge, and the capacity to resist brute force attacks is strong; because an encryption process is embedded into an MPEG coding process, the method is good in instantaneity; and due to the introduction of the inner secrete key, the capacity of the encryption algorithm to resist plain text attacks is strengthened.

The present invention provides a JPEG image encryption method compatible in format and invariant in size, and belongs to the technical field of multimedia information safety. The method of the presentinvention includes three encryption steps: 1) classifying and scrambling AC coefficient-encoded zero runs; 2) grouping and scrambling DC coefficient-differentially encoded adjacent same symbols; 3) grouping and iteratively encrypting DC coefficient differential codes. According to the invention, the method can be used for protecting the safety and the privacy of military images, commercial images, medical images or personal images when the images are transmitted through a public channel or stored in the public cloud. The method aims to improve the ubiquitous defect that the size of a ciphertext image increases and the format compatibility of the image is not ideal based on existing JPEG image encryption methods. The above method can resist the known-plaintext attack, and substantially maintain the size of the ciphertext image to be unchanged. Meanwhile, the format compatibility is better and the encryption strength is adjustable.

Modify H.263-type quantization with an adaptive quantization parameter floor; this limits clipping of quantized DCT coefficients and consequent artifacts. The maximum absolute level of AC coefficients of a DCT transformed macroblock provides a minimum quantization parameter from integer division by 256 when the quantized levels are clipped to a range such as −127 to +127.

Methods and systems are disclosed for a video system. In a first exemplary embodiment, the video system comprises a video processing circuit that receives a picture and provides video compression by using an optimal macroblock mode of operation, the optimal macroblock mode of operation being identified by processing at least one macroblock of the picture, the processing being performed independent of other macroblocks contained in the picture. Additionally, the video processing circuit comprises a mode selection circuit that identifies the optimal macroblock mode of operation by using a rate-distortion model. The rate-distortion model incorporates an overall macroblock mode distortion D that is defined as the sum of DAC a distortion due to AC coefficients, and DDC a distortion due to DC coefficients.

A method and arrangement are disclosed for embedding a watermark (W) in a media signal (MP) comprising signal samples (x(n)) being encoded as variable-length code words (VLC). The variable-length coded DCT coefficients of an MPEG2 video signal constitute such a media signal. The watermark is embedded by inverting the signs of the AC coefficients as far as such an inversion indeed causes the coefficients to be increased or decreased as prescribed (s(n)) by the watermark to be embedded. The invention is simple to implement, does not require re-encoding of the signal and does not affect the bit rate of the bit stream.

The invention provides a method for classifying pixel blocks of JPEG images and image falsification detecting and falsified area positioning methods based on the same. The method comprises the following steps of: dividing to-be-detected JPEG images into continuous and non-overlapped 8*8 pixel blocks; taking one pixel block as the center and selecting a square area combined by (2n+1)*(2n+1) pixel blocks as a sub-image; utilizing a first number distribution probability feature of AC coefficients in the front i AC coefficient regions of the sub-image to divide the central pixel block into singlecompression or double compression; and confirming a classifying result as the double compression and a connected region with an area more than M 8*8 pixel blocks as a falsified area. According to themethod provided by the invention, the falsified area can be accurately detected and positioned; the falsified areas of three different falsifying technologies can be detected according to the method;the method is wide in application scope; the method is an automatic blind detecting method for JPEG falsified images and does not require any priori knowledge; and the detection coverage rate is higher and the error detection rate is low.

Presented herein are system(s), method(s), and apparatus for AC coefficient prediction. In one embodiment, there is presented a method for predicting AC coefficients for a macroblock. The method comprises determining whether a particular block is predicted from a top neighboring block or a left neighboring block; retrieving from a buffer, data from the top neighboring block or left neighboring block from which the particular block is predicted; and writing data from the particular block to the buffer.

Provided are a method and apparatus for predicting frequency transform coefficients in a video codec, a video encoder and decoder having the apparatus, and an encoding and decoding method using the method. The method of predicting the frequency transform coefficients in a frequency transform domain includes: calculating a cost between a DC coefficient of a current frequency transformed block that is to be predicted and DC coefficients of frequency transformed blocks adjacent in horizontal, vertical, and diagonal directions with respect to the current frequency transformed block; and selecting an adjacent block with the smallest calculated cost, and predicting DC and AC coefficients of the current frequency transformed block using coefficients of the selected adjacent block. Accordingly, compression efficiency can be improved, and video data can be effectively encoded reflecting the characteristics of various patterns by calculating prediction values of numerous patterns.

The invention relates to hyperspectral image compressing and restructuring device and method. The method includes steps of firstly, subjecting each spectrum range of a hyperspectral image to three-level two-dimensional 9 / 7 integer discrete and lifting wavelet transformation; organizing wavelet coefficients to sections and blocks through CCDSD-IDC, encoding section header information and DC (direct current) coefficient initializing and AC (alternating current) coefficient depth of each block, extracting AC coefficient and residual DC coefficient bit plane simultaneously, and finally subjecting the AC coefficient and residual DC coefficient bit plane to distributed signal source encoding by a Slepian-Wolf encoder based on LDPC (low density parity check). The hyperspectral image compressing and restructuring device and method have the advantages that by adopting distributed signal source encoding strategy, complexity of the integral encoder is lowered, and the method is easy to implement through processors such as FPGA (field programmable gate array) and DSP (digital signal processor).