Television – Image signal processing circuitry specific to television – Motion dependent key signal generation or scene change...
Reexamination Certificate
2000-09-01
2003-04-08
Kostak, Victor R. (Department: 2614)
Television
Image signal processing circuitry specific to television
Motion dependent key signal generation or scene change...
C375S240260
Reexamination Certificate
active
06545727
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to digital decoders of sequences of video images, and, more particularly, to a method for recognizing the progressive or interlaced content of an image to improve the effectiveness of the video coding for low cost applications. Due to the importance of the MPEG standard in treating digitized video sequences, reference will be made to an MPEG2 system to illustrate the present invention. The present invention is also applicable to systems that transfer video sequences based on different standards.
BACKGROUND OF THE INVENTION
The MPEG (Moving Pictures Experts Group) standard defines a set of algorithms dedicated to the compression of sequences of digitized pictures. These techniques are based on the reduction of the spatial and temporal redundance of the sequence. Reduction of spatial redundance is achieved by compressing independently the single images via quantization, discrete cosine transform (DCT) and Huffman coding.
The reduction of temporal redundance is obtained using the correlation that exist between successive pictures of a sequence. Each image can be expressed locally as a translation of a preceding and/or successive image of the sequence. To this end, the MPEG standard uses three kinds of pictures; I (Intra Coded Frame), P (Predicted Frame) and B (Bidirectionally Predicted Frame). The I pictures are coded in a fully independent mode. The P pictures are coded with respect to a preceding I or P picture in the sequence. The B pictures are coded with respect to two pictures of the I or P kind, which are the preceding one and the following one in the video sequence (see FIG.
1
).
A typical sequence of pictures can be I B B P B B P B B I B . . . , for example. This is the order in which they will be viewed. Given that any P is coded with respect to the preceding I or P, and any B is coded with respect to the preceding and following I or P, it is necessary that the decoder receive the P pictures before the B pictures, and the I pictures before the P pictures. Therefore, the order of transmission of the pictures will be I P B B P B B I B B . . .
Pictures are processed by the coder sequentially, in the indicated order, and are successively sent to a decoder which decodes and reorders them, thus allowing their successive displaying. To code a B picture it is necessary for the coder to keep in a dedicated memory buffer, called frame memory, the I and P pictures, coded and thereafter decoded, to which current B picture refers, thus requiring an appropriate memory capacity.
One of the most important functions in coding is motion estimation. Motion estimation is based on the following consideration. A set of pixels of a frame of a picture may be placed in a position of the successive picture obtained by translating the preceding one. These transpositions of objects may expose parts that were not visible before as well as changes of their shape, such as during a zooming, for example.
The family of algorithms suitable to identify and associate these portions of pictures is generally referred to as motion estimation. Such an association of pixels is instrumental to calculate a difference picture removing redundant temporal information, thus making more effective the successive processes of DCT compression, quantization and entropic coding.
A typical example of a system using this method may be illustrated based upon the MPEG-2 standard. A typical block diagram of a video MPEG-2 coder is depicted in FIG.
1
. Such a system is made of the following functional blocks:
1) Chroma filter block from 4:2:2 to 4:2:0. In this block there is a low pass filter operating on the chrominance component, which allows the substitution of any pixel with the weighed sum of neighboring pixels placed on the same column and multiplied by appropriate coefficients. This allows a successive subsampling by two, thus obtaining a halved vertical definition of the chrominance.
2) Frame ordinator. This blocks is composed of one or several frame memories outputting the frames in the coding order required by the MPEG standard. For example, if the input sequence is I B B P B B P etc., the output order will be I P B B P B B . . .
The Intra coded picture I is a frame or a semi-frame containing temporal redundance. The Predicted-picture P is a frame or semi-frame from which the temporal redundance with respect to the preceding I or P (precedingly co/decoded) has been removed. The Biredictionally predicted-picture B is a frame or a semi-frame whose temporal redundance with respect to the preceding I and successive P (or preceding P and successive P) has been removed. In both cases the I and P pictures must be considered as already co/decoded.
Each frame buffer in the format 4:2:0 occupies the following memory space:
Standard PAL
720 × 576 × 8 for the luminance
(Y) =
3,317,760 bits
360 × 288 × 8 for the chrominance
(U) =
829,440 bits
360 × 288 × 8 for the chrominance
(V) =
829,440 bits
total
Y + U + V =
4,976,640 bits
Standard NTSC
720 × 480 × 8 for the luminance
(Y) =
2,764,800 bits
360 × 240 × 8 for the chrominance
(U) =
691,200 bits
360 × 240 × 8 for the chrominance
(V) =
691,200 bits
total
Y + U + V =
4,147,200 bits
3) Estimator. This is the block that removes the temporal redundance from the P and B pictures. This functional block operates only on the most energetic component, and, therefore, the richest of information of the pictures which compose the sequence to code, such as the luminance component.
4) DCT. This is the block that implements the discrete cosine transform according to the MPEG-2 standard. The I picture and the error pictures P and B are divided in blocks of 8*8 pixels Y, U, and V on which the DCT transform is performed.
5) Quantizer Q. An 8*8 block resulting from the DCT transform is then divided by a quantizing matrix to reduce the magnitude of the DCT coefficients. In such a case, the information associated to the highest frequencies, less visible to human sight, tends to be removed. The result is reordered and sent to the successive block.
6) Variable Length Coding (VLC). The codification words output from the quantizer tend to contain a large number of null coefficients followed by nonnull values. The null values preceding the first nonnull value are counted and the count figure forms the first portion of a codification word, the second portion of which represents the nonnull coefficient.
These pairs tend to assume values more probable than others. The most probable ones are coded with relatively short words composed of 2, 3 or 4 bits while the least probable are coded with longer words. Statistically, the number of output bits is less than in the case such a criteria is not implemented.
7) Multiplexer and buffer. Data generated by the variable length coder, the quantizing matrices, the motion vectors and other syntactic elements are assembled for constructing the final syntax contemplated by the MPEG-2 standard. The resulting bitstream is stored in a memory buffer, the limit size of which is defined by the MPEG-2 standard requirement that the buffer cannot be overfiled. The quantizer block Q attends to such a limit by making the division of the DCT 8*8 blocks dependent upon how far the system is from the filling limit of such a memory buffer and on the energy of the 8*8 source block taken upstream of the motion estimation and DCT transform steps.
8) Inverse Variable Length Coding (I-VLC). The variable length coding functions specified above are executed in an inverse order.
9) Inverse Quantization (IQ). The words output by the I-VLC block are reordered in the 8*8 block structure, which is multiplied by the same quantizing matrix that was used for its preceding coding.
10) Inverse DCT (I-DCT). The DCT transform function is inverted and applied to the 8*8 block output by the inverse quantization process. This permits passing from the domain o
Pau Danilo
Pezzoni Luca
Rovati Fabrizio
Sirtori Daniele
Allen Dyer Doppelt Milbrath & Gilchrist, P.A.
Kostak Victor R.
STMicroelectronics S.r.l.
LandOfFree
Method for recognizing a progressive or an interlaced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for recognizing a progressive or an interlaced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for recognizing a progressive or an interlaced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3103512