693 results about "Dct coefficient" patented technology

A watermarking method involves mostly invisible artifacts and is sensitive to any modification of the picture at the level of precision rendered by the compressed version of the image. The image is compressed according to a known compression standard, such as the JPEG standard, and with a fixed quality setting. Using the JPEG standard, the original image is cut into blocks to which the Discrete Cosine Transform (DCT) is applied and the DCT coefficients quantized. The watermark according to the invention is applied to the quantized DCT coefficients. This is done using an encryption function, such as a secret key / public key algorithm. The JPEG compression is then completed using a lossless compression scheme, such as Huffman coding, to produce the compressed and watermarked image. Authentication of the compressed and watermarked image begins with a lossless decompression scheme to obtain the set of quantized DCT coefficients. The coefficients are authenticated, and the DCT output of each block is dequantized. If necessary, an inverse DCT is applied to each block to output the decompressed watermarked image.

To reduce bandwidth of non-scalable MPEG-2 coded video, certain non-zero AC DCT coefficients for the 8x8 blocks are removed from the MPEG-2 coded video. In one implementation, high-frequency AC DCT coefficients are removed at the end of the coefficient scan order. This method requires the least computation and is most desirable if the reduced-bandwidth video is to be spatially sub-sampled. In another implementation, the smallest-magnitude AC DCT coefficients are removed. This method may produce an undesirable increase in the frequency of occurrence of escape sequences in the (run, level) coding. This frequency can be reduced by retaining certain non-zero AC DCT coefficients that are not the largest magnitude coefficients, and by increasing a quantization scale to reduce the coefficient levels. The reduced-bandwidth video can be used for a variety of applications, such as browsing for search and play-list generation, bit stream scaling for splicing, and bit-rate adjustment for services with limited resources and for multiplexing of transport streams.

Transform coefficients for blocks of pixels in an original picture are quantized to produce respective sets of quantization indices for the blocks of pixels. The quantization indices for at least some of the blocks are produced by using a quantization step size that is not uniform within each block. Largest magnitude quantization indices are selected from the respective sets of quantization indices for (run, level) encoding to produce the (run, level) encoded picture. For example, MPEG-2 coded video includes a set of non-zero AC discrete cosine transform (DCT) coefficients for 8x8 blocks of pixels. For scaling the MPEG-2 coded video, non-zero AC DCT coefficients are removed from the MPEG-2 coded video to produce reduced-quality MPEG-2 coded video that includes no more than a selected number of largest magnitude quantization indices for the non-zero AC DCT coefficients for each 8x8 block.

Original-quality MPEG coded video is processed to produce reduced-quality MPEG coded video for trick mode operation by removing non-zero AC DCT coefficients from the 8×8 blocks of I-frames of the MPEG coded video to produce I-frames of reduced-quality MPEG coded video, and inserting freeze frames in the reduced-quality MPEG coded video. Preferably, the coded video is stored in a main file, a fast-forward file and a fast-reverse file. The fast forward file and the fast reverse files contain reduced-quality I frames corresponding to original-quality I frames in the main file. A reading of the main file produces an MPEG transport stream for an audio-visual presentation at a normal rate, a reading of the fast-forward file produces an MPEG transport stream of the audio-visual presentation in a forward direction at a fast rate, and a reading of the fast-reverse file produces an MPEG transport stream of the audio-visual presentation in a reverse direction at a fast rate. Preferably, the files share a volume that includes at least one GOP index associating the corresponding I frames of the files.

Disclosed is a multi-dimensional selectivity estimation method using compressed histogram information which the database query optimizer in a database management system uses to find the most efficient execution plan among all possible plans. The method includes the several steps to generate a large number of small-sized multi-dimensional histogram buckets, sampling DCT coefficients which have high values with high probability, compressing information from the multi-dimensional histogram buckets using a multi-dimensional discrete cosine transform(DCT) and storing compressed information, and estimating the query selectivity by using compressed and stored histogram information as the statistics.

3D video can be transmitted in a legacy 2D video format by conveying 3rd dimension parameters within a steganographic channel of the perceptual video signal, e.g., DCT coefficients, video samples (luminance, chrominance values), etc. The 3rd dimension parameters can be coded as depth values, disparity, displacement, difference, or parallax values, including depth that is converted into X-Y shifts for adjustment to motion vectors in coded video sequence. To limit the amount of information for the steganographic channel, the 3rd dimension information can be quantized relative to the depth from viewer and other prioritization parameters that limit the need for 3rd dimension information to only aspects of the scene that are deemed important to create a desired 3D effect.

A transform is applied to a region of a current video frame to generate transform signals corresponding to the region. An activity measure is generated using the transform signals. The activity measure is then used to determine whether to encode the region as a skipped region. The region is encoded in accordance with that determination to generate an encoded bit stream for the region. In a preferred embodiment, the transform signals are DCT coefficients and the activity measure is a weighted sum of the DCT coefficients, where the weighting of the low-frequency DCT coefficients is greater than the weighting of the high-frequency DCT coefficients. The region is encoded as a skipped region if the activity measure is less than a threshold value; otherwise, the region is encoded as either an inter encoded region or an intra encoded region.

The present invention discloses a system and method for rate control of MPEG video streams to achieve a target bit rate in a transcoder at the best visual quality possible. The invention monitors video buffer fullness for selecting the amount of rate reduction necessary to achieve a target bit rate. The invention also utilizes a method for selective requantization of DCT coefficients to assure visual quality.

A method and systems are disclosed for removing artifacts, such as blocking noise and contouring effects, from a block-encoded video signal. One method for removing blocking artifacts comprises decoding the block-encoded signal to obtain a decoded sequence of video frames and one or more associated motion vectors. By using the motion vector, the location of one or more blocking artifacts may be identified within at least one of the frames. The location identified by the motion vector is filtered to remove at least some of the blocking artifacts. Another method for removing contouring effects comprises decoding the block-encoded signal to obtain a decoded sequence of video frames, detecting a contouring effect by evaluating the macroblock mode and DCT coefficient information from the decoded signal, and filtering one or more blocks correlating to the detected contouring effect.

The present invention relates to a method and system for evaluating the quality of encoded video data without gaining access to the source data or the compressed video bitstream. The system is configured to decode compressed video data using an MPEG decoder to produce decompressed video data. The decoded data is analyzed to determine whether the decompressed video data is intra-coded. If so, a discrete cosine transform (DCT) is performed to produce a set of DCT coefficients for at least one AC frequency band in the decompressed video data. At the same time, quantization matrix data of a frame of the decompressed video data as well as a quantizer scale for each block of the decompressed video data are extracted. Thereafter, the variance of the converted DCT coefficients is obtained, and then an average quantization error for each set of said DCT coefficients is determined based on the variance, the quantization matrix, and the quantizer scale. Lastly, a peak signal to noise ratio (PSNR) is calculated based on the resultant average quantization error.

A method of encoding a video stream in a video encoder is provided that includes computing an offset into a transform matrix based on a transform block size, wherein a size of the transform matrix is larger than the transform block size, and wherein the transform matrix is one selected from a group consisting of a DCT transform matrix and an IDCT transform matrix, and transforming a residual block to generate a DCT coefficient block, wherein the offset is used to select elements of rows and columns of a DCT submatrix of the transform block size from the transform matrix.

Transform coefficients for blocks of pixels in an original picture are quantized to produce respective sets of quantization indices for the blocks of pixels. The quantization indices for at least some of the blocks are produced by using a quantization step size that is not uniform within each block. Largest magnitude quantization indices are selected from the respective sets of quantization indices for (run, level) encoding to produce the (run, level) encoded picture. For example, MPEG-2 coded video includes a set of non-zero AC discrete cosine transform (DCT) coefficients for 8×8 blocks of pixels. For scaling the MPEG-2 coded video, non-zero AC DCT coefficients are removed from the MPEG-2 coded video to produce reduced-quality MPEG-2 coded video that includes no more than a selected number of largest magnitude quantization indices for the non-zero AC DCT coefficients for each 8×8 block.

A system of estimating and reducing image blur in digital images stored in a digital file as a sequence of DCT coefficients arranged in a plurality of blocks. The disclosed system may preferably calculate one or more blur indicators from selected ones of the sequence of DCT coefficients and selectively filter a digital image based upon the calculated one or more blur indicators.

A video coding method enabling implementation of resolution scalability while improving the coding efficiency. In the method, a band dividing section 104 performs band division on a high-resolution original image to generate a middle-resolution image, horizontal component, vertical component and diagonal component. The horizontal component is subjected to the DCT processing in horizontal layer DCT section 124, and then subjected to the bit-plane VLC processing in horizontal layer bit-plane VLC section 126. The vertical component is subjected to the DCT processing in vertical layer DCT section 130, and then subjected to the bit-plane VLC processing in vertical layer bit-plane VLC section 132. The diagonal component is subjected to the DCT processing in diagonal layer DCT section 136, and then subjected to the bit-plane VLC processing in diagonal layer bit-plane VLC section 138. In scanning, a scanning order is determined in consideration of bias in the distribution of DCT coefficients for each band component.

A power-scalable hybrid technique to reduce blocking and ringing artifacts in low bit-rate block-based video coding is employed in connection with a modified decoder structure. Fast inverse motion compensation is applied directly in the compressed domain, so that the transform (e.g., DCT) coefficients of the current frame can be reconstructed from those of the previous frame. The spatial characteristics of each block is calculated from the DCT coefficients, and each block is classified as either low-activity or high-activity. For each low-activity block, its DC coefficient value and the DC coefficient values of the surrounding eight neighbor blocks are exploited to predict low frequency AC coefficients which reflect the original coefficients before quantization in the encoding stage. The predicted AC coefficients are inserted into the low activity blocks where blocking artifacts are most noticeable. Subject to available resources, this may be followed by spatial domain post-processing, in which two kinds of low-pass filters are adaptively applied, on a block-by-block basis, according to the classification of the particular 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. 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 2- or 3-tap filters, applied horizontally and / or vertically, which makes the architecture simple.

An efficient digital video (DV) decoder process that utilizes a specially constructed quantization matrix allowing an inverse quantization subprocess to perform parallel computations, e.g., using SIMD processing, to efficiently produce a matrix of DCT coefficients. The present invention utilizes a first look-up table (for 8x8 DCT) which produces a 15-valued quantization scale based on class number information and a QNO number for an 8x8 data block ("data matrix") from an input encoded digital bit stream to be decoded. The 8x8 data block is produced from a deframing and variable length decoding subprocess. An individual 8-valued segment of the 15-value output array is multiplied by an individual 8-valued segment, e.g., "a row," of the 8x8 data matrix to produce an individual row of the 8x8 matrix of DCT coefficients ("DCT matrix"). The above eight multiplications can be performed in parallel using a SIMD architecture to simultaneously generate a row of eight DCT coefficients. In this way, eight passes through the 8x8 block are used to produce the entire 8x8 DCT matrix, in one embodiment consuming only 33 instructions per 8x8 block. After each pass, the 15-valued output array is shifted by one value position for proper alignment with its associated row of the data matrix. The DCT matrix is then processed by an inverse discrete cosine transform subprocess that generates decoded display data. A second lookup table can be used for 2x4x8 DCT processing.

A system and method are disclosed that provide a simple and efficient layered video coding technique using a backward adaptive rate-distortion optimized data partitioning (RD-DP) of DCT coefficients. The video coding system may include an rate-distortion optimized data partitioning encoder and decoder. The RD-DP encoder adapts the partition point block-by-block which greatly improves the coding efficiency of the base layer bit stream without explicit transmission thereby saving the bandwidth significantly. The RD-DP decoder can also find the partition location in backward-fashion from the decoded data.

The present invention provides an apparatus and a method for error concealment. The control core receives an input signal and identifies an error macro-block in a column of slice of a frame and a frame type of the frame. The parameter computation module receives a plurality of DCT coefficients and temporal data to derive at least a coefficient for the weighting in an adaptive computation for the frame. The temporal compensation module computes the temporal data to obtain a result of the temporal compensation. The spatial processing module computes spatial data to obtain a result of the spatial processing. The adaptive processing module proceeds the adaptive computation with the coefficient for the weighting derived by the parameter computation module, the result of the temporal compensation and the result of the spatial processing, and generates a result of the adaptive processing. The spatial processing may be a bilinear interpolation or a spatial interpolation.

A method is provided for transcoding between video signals in two standards, DV and MPEG-2, each standard including discrete cosine transform (DCT) compressed signals. The each of the signals have macroblocks containing a plurality of DCT blocks. The DCT blocks are quantized according to respective quantization methods defined by the standards. The coefficients in each block are zigzag scanned, run-length coded and variable-length coded. The process variable-length decodes the coefficients and translates the quantized coefficients in the DV standard into quantized coefficients in the MPEG standard without fully dequantizing at least some of the DV coefficients and without performing an inverse DCT operation on any of the DCT coefficients. DV blocks that are encoded in a 248 format are translated into an 88 format before they are converted to MPEG-2 blocks. A method for transcoding from MPEG-2 to DV is also described. The MPEG-2 signals are intra-frame encoded, have a 4:2:2 chrominance format and an 88 frame-encoded block format. According to this method, converted 88 DV blocks that represent significant intra-field motion are converted from the 88 format to a 248 format. The method also controls which overflow coefficients in the DV signal are transcoded into corresponding coefficients in the MPEG-2 signal to control the data rate of the MPEG-2 signal.

The method includes following steps: scanning DCT coefficient blocks according to sequence so as to obtain last one nonzero coefficient (NC) and the coefficient in front of the last one NC in coefficient block, and number value of NC; based on the number value of NC to calculate difference value between number value of NC in this block and number value of NC in adjacent block, and constructing context model for number value of NC; calculating flag bit of NC for last one NC and coefficients before the last one NC; selecting context model to encode flag bit of NC; subtracting 1 from absolute value of NC according to scanning sequence or scanning inverted sequence; and selecting context model to encode number value of NC, and its position in the scan etc; encoding sign bit. The invention also discloses corresponding decoding method.

A system providing methods for improved compression of images that have been compressed using Discrete Cosine Transform (DCT) based compression is described. A digital image that has been compressed using DCT based compression, such as an image compressed using the Joint Photographic Experts Group (JPEG) compression scheme, is received and partially decompressed to generate DCT coefficients of the image. The decoded coefficients of the image are then rearranged to aggregate like frequencies together. After rearrangement, the image is recompressed using a wavelet-based compression scheme.

A color conversion module 42 carries out color conversion of original color image data Grgb from the RGB color system into the CMYK color system to obtain color-converted original color image data Gcmyk (step S104). A DCT module 44 applies DCT (discrete cosine transform) over the whole color-converted original color image data Gcmyk to generate DCT coefficients Dcmyk (step S106). An embedding module 46 embeds the watermark information s into the components C, M, Y, and K of the DCT coefficients Dcmyk (step S108). An IDCT module 48 applies IDCT (inverse discrete cosine transform) onto DCT coefficients D'cmyk with the watermark information s embedded therein to generate embedding-processed color image data G'cmyk (step S110). The color conversion module 42 carries out color conversion of the embedding-processed color image data G'cmyk from the CMYK color system into the RGB color system to obtain embedding-processed color image data G'rgb (step S112). This arrangement does not require any correction of the position or the shape of image blocks in the process of extracting the embedded watermark information.

A method is disclosed for decoding multiple-coded symbols from a coded input symbol stream in a single clock cycle. The method constructs an original Huffman look-up table by extending the associated Huffman tree to decode multiple symbols in one clock cycle in a first embodiment and decodes multiple DCT coefficient symbols in an alternate embodiment. An advantage of the method is that the depth of the new Huffman tree is adjustable thereby making the method easily adaptable to various hardware architectures. A further advantage of the present invention is that the decoding process speed is significantly increased while the size of the lookup table is nominally increased.

An implementation efficient method of distinguishing between foreground and background regions of a digital image of a scene includes capturing two images of nominally the same scene and storing the captured images in DCT-coded format. The first image is taken with the foreground more in focus than the background and the second image is taken with the background more in focus than the foreground. Regions of the first image are assigned as foreground or background according to whether the sum of selected higher order DCT coefficients decreases or increases for the equivalent regions of the second image.

A first bit string extracting unit extracts a first bit string. A first bit length judging unit detects a first codeword from the first bit string. A first decoding unit generates a first run-level pair from the first codeword. A second bit string extracting unit extracts a second bit string. A second bit length judging unit detects a second codeword from the second bit string. A second decoding unit generates a second run-level pair from the second codeword. A first inverse quantizing unit inverse quantizes the first level to obtain a DCT coefficient. A second inverse quantizing unit inverse quantizes the second level to obtain a DCT coefficient. A second buffer controller writes the DCT coefficients and their first buffer addresses into a second buffer. A first buffer controller reads the DCT coefficients and the first buffer addresses from the second buffer and writes the DCT coefficients into a first buffer at the respective first buffer addresses.

Digital watermarks are embedded in image data (102)in order to enable authentication of the image data and / or replacement of rejected portions of the image data. Authentication codes are derived by comparing selected discrete cosine transform (DCT) (104) coefficients within DCT data (106) derived from the original, spatial-domain image data. The authentication codes thus generated are embedded in DCT coefficients (612) other than the ones which were used to derive the authentication codes. The resulting, watermarked data can be sent or made available to one or more recipients who can compress or otherwise use the watermarked data. Image data derived from the watermarked data—e.g, compressed versions of the watermarked data—can be authenticated by: extracting the embedded authentication codes, comparing DCT coefficients derived from the coefficients from which the original authentication codes were generated; and determining whether the compared DCT coefficients are consistent with the extracted authentication codes.

A method for automatically classifying a printed image, includes scanning the printed image; selecting an n by n block of pixels from the scanned image; calculating an array of DCT coefficients of the pixel block, wherein the array of calculated DCT coefficients are representative of spatial frequency and spatial orientation of the pixel block; comparing the DCT coefficients with an array of predetermined values, wherein the array of predetermined values are indicative of different image marking processes used to produce printed images; and determining an image marking process used to create the printed image based on the comparison of the DCT coefficients with the array of predetermined values. The array of DCT coefficients may be sampled into a feature set and the feature set provided to a neural network to output the determined image marking process.

A method and arrangement are disclosed for embedding a watermark in an MPEG compressed video stream. The watermark (a spatial noise pattern) is embedded by selectively discarding the smallest quantized DCT coefficients. The discarded coefficients are subsequently merged in the runs of the remaining coefficients. The decision whether a coefficient is discarded or not is made on the basis of a pre-calculated watermark buffer and the number of already discarded coefficients per 8x8 DCT block. The advantages of this method are (i) a very simple bit rate control system and (ii) no need for drift compensation. The algorithm can be implemented in a very efficient manner with respect to memory requirements and computational complexity.