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.

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.

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 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.

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.