Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2001-02-16
2004-11-09
Vo, Tung T. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06816550
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image signal coding apparatus and particularly, to a coding apparatus for encoding and outputting a moving image data in real time according to MPEG (Moving Picture Experts Group) standards.
2. Description of the Background Art
In general, compression processing according to MPEG 1 and MPEG 2 standards has been employed in order to encode a moving image data including a great amount of information efficiently. In the MPEG standards, processing is performed as follows: A picture of a field or a frame is divided into compression units called macroblocks. A macroblock of a reference picture having the highest correlationship with a macroblock of interest of a current picture is detected, difference values between corresponding pixels of the macroblocks having the highest correlationship are obtained and the difference values are encoded. In the MPEG standards, redundancy of moving image information and characteristics of a human visual organ are exploited, and redundant information and information unimportant in terms of a human visual characteristics are removed to compress moving image information. An amount of codes of digital information (a bit stream) obtained as a result of the compression varies to a great extent depending on characteristics of an input image, such as correlation degree between pictures (frames or fields) and an amount of high spatial frequency components, even under the same compression conditions. Therefore, an amount of codes resulting from the compression fluctuates even in one picture period. A target of an amount of codes is generally set for each picture (image), a compression parameter is controlled such that an amount of codes coincides with the target amount.
Coded image information have to be transmitted to a decoder through a transmission line. A bit stream buffer is used for transmitting a bit stream through a transmission line with a constant data transfer rate. In a period in which an amount of codes is great, a transmission amount is lowered by storing codes in excess of a transmission capacity in a bit stream buffer, while in a period in which an amount of codes is small, codes are read out from the bit stream buffer and transferred at a predetermined data transfer rate. Transmission of coded data at a constant transfer rate can be realized by smoothing of a data transfer rate through exploitation of a bit stream buffer.
FIG. 14
shows a configuration of an output section of a conventional moving image signal processing apparatus schematically. In
FIG. 14
, the moving image signal processing apparatus includes: a quantization circuit
901
receiving DCT (Discrete Cosine Transformation) coefficient data of a picture of a field or a frame in macroblock units and performing quantization thereof; a scanning sequence conversion circuit
902
converting a scanning order of DCT coefficient data quantized by the quantization circuit
901
according to a zigzag scanning method, for example; a variable-length coding circuit
903
performing variable-length coding of quantized data having the scanning order converted by the scanning sequence conversion circuit
902
; a bit stream buffer
904
for storing variable-length codes from the variable-length coding circuit
903
; and an output control circuit
905
reading out sequentially data stored in the bit stream buffer
904
and outputting the data at a constant data transfer rate. In the variable-length coding circuit
903
, quantized DCT coefficient data from the scanning sequence conversion circuit
902
are subjected to variable-length coding, thus effecting compression of an information volume.
This image signal coding apparatus further includes: a code amount sum circuit
906
summing up an amount of codes, in macroblock units, generated by the variable-length coding circuit
903
; and a rate control circuit
907
controlling an amount of generated codes by adjusting a quantizing scale of the quantization circuit
901
according to the sum from the code amount sum circuit
906
. The rate control circuit
907
generally sets a target amount of codes to be generated in a following picture according to the sum of the code amount sum circuit
906
and adjusts a quantizing scale of the quantization circuit
901
such that an amount of codes generated actually in the following picture coincides with the target. The rate control circuit
907
adjusts an amount of generated codes in macroblock units such that an average of an amount of codes outputted from the variable-length coding circuit
903
coincides with a transmission rate on a transmission line through which a bit stream outputted from the output control circuit
905
is transmitted. This coding of one picture of a frame in macroblock units is carried out sequentially in one picture period of input images.
In coding of a picture (an image of a field or a frame), when an amount of codes does not reach a target, a byte data of “0” called as a stuff byte is generated and the stuff byte is added to a coded data such that an amount of generated codes of a picture coincides with a target. The term “stuffing” indicates an operation of inserting a stuff byte into a bit stream. The stuff bytes are discarded in decoding. A shortage of an amount of codes from a target can be filled up with stuff bytes with no adverse influence on a reproduced image.
This stuffing, in the MPEG 2 standard, can be performed in GOP (group of pictures) units, picture units or slice units and, in the MPEG 1 standard, can be performed in GOP units, picture units, slice units or macroblock units. Generally, stuffing is performed in picture units or sequence units in most cases. When stuffing is performed in macroblock units, a picture quality is degraded due to limitation of an amount of codes in each macroblock. For example, if stuffing is performed in picture units, an amount of codes can be allotted to individual macroblocks according to complexity thereof.
In a case of stuffing in picture units, the stuffing is performed after coding of one picture is completed and the sum of codes of the one picture is calculated.
FIGS. 15A and 15B
are illustrations showing distributions in amount of stuff bytes and generated codes of macroblocks when an amount of coded data of one picture is close to a target schematically. As shown in
FIG. 15A
, stuff bytes are inserted after a region for placing coded data of one picture. When an amount of coded data of one picture is close to a target, amounts of codes in respective macroblocks, as shown in
FIG. 15B
, are large, but an amount of stuff bytes is small. When stuff bytes are inserted after a coded data store region for one picture, an amount of codes is summed in the code amount sum circuit
906
shown in FIG.
14
and stuff bytes are generated according to a result of the summing and stuff bytes generated are multiplexed with coded data to be written into the bit stream buffer
904
. In this case, since a generation amount of stuff bytes is small, necessary stuff bytes can be generated and written in the bit stream buffer
904
with a sufficient margin.
FIGS. 16A and 16B
are illustrations showing distributions of codes and stuff bytes when an amount of coded data of one picture is extremely small schematically. In
FIG. 16
, coded data of one picture are extremely small in amount. This phenomenon arises when a motion of a picture is extremely low in speed or amount in a prediction coding scheme. Since amounts of generated codes of macroblocks are small as shown in
FIG. 16B
, stuff byte tens of times as large as an amount of coded data of one picture are required to be generated.
Generation of the stuff bytes and a write operation thereof into the bit stream buffer
904
are executed in a period between pictures, for example in a vertical blanking period. In a case where a transmission rate of a bit stream is as high as several tens Mbps (bit/sec), an extremely large amount of stuff bytes are necessary to be inserted in order to transfer coded da
McDermott Will & Emery LLP
Vo Tung T.
LandOfFree
Image signal coding apparatus with bit stream buffer of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Image signal coding apparatus with bit stream buffer of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Image signal coding apparatus with bit stream buffer of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3342510