Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1997-11-07
2002-04-30
Nguyen, Chau (Department: 2663)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C375S240030
Reexamination Certificate
active
06381254
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to moving image encoding device/method for encoding a plurality of moving images in such a manner that the quality of moving images reproduced by a decoding device is enhanced after the process of compressing/encoding the plurality of moving images and multiplexing the encoded signals to generate moving image encoded signals at a constant bit rate.
The present invention also relates to moving image multiplexing device/method for multiplexing moving image encoded signals obtained after the process of compressing/encoding a plurality of moving images or moving image segments obtained by dividing a high-precision moving image.
The present invention further relates to an image transmission device which compresses/encodes a plurality of moving images and transmits the resultant moving image encoded signals at a limited bit rate, used in the moving image transmission for satellite communications or network communications such as a LAN, for example.
2. Description of the Related Art
In one of the methods for compressing/encoding and multiplexing a plurality of moving images to transmit the resultant moving images as a bit stream at a constant bit rate, a predetermined fixed bit rate is allocated for each of the moving images so that the sum of the bit amounts representing the plurality of moving images after the compression/encoding constitutes a constant bit rate. In such a method, when moving images with high complexity are input, the allocated bit rate is insufficient, resulting in great degradation in the image quality. Conversely, when moving images with low complexity are input, stuffing increases, resulting in wasteful use of the bit rate. As a result, two opposite problems arise. That is, when an effective use of the bit rate is attempted, the image quality lowers. Conversely, when high image quality is attempted, the bit rate is not effectively used, decreasing the number of moving images which can be multiplexed.
In order to solve the above problems, Japanese Laid-Open Publication No. 8-23540 discloses an encoding control device in which the bit rate at the encoding of respective moving image signals is made variable to improve the quality of moving images reproduced by a decoding device. In this encoding control device, the moving images reproduced from moving image encoded signals are compared with the original moving images. The bit rate is increased when a reproduced moving image is largely distorted from the original one, while it is decreased when a reproduced moving image is little distorted, so that the quality of the moving images is made uniform and thus the entire image quality improves.
According to the above method, however, the bit rate is changed after the amount of distortion is determined. Therefore, in the case where the moving images become complicated suddenly due to a scene change and the like, the quality of the moving image immediately after the scene change is low.
Moreover, in this conventional device in which the bit rate at the encoding of the moving images is variable, when a simple multiplexing operation is conducted such as changing the bit rate in proportion to the bit amount generated during a predetermined time period, an input buffer of a decoding device may cause overflow or underflow.
An encoding device which encodes moving images with different resolutions is disclosed in Japanese Laid-Open Publication No. 6-6777, for example.
FIG. 37
shows the configuration of such an encoding device, where high-quality HDTV moving images are divided into a plurality of blocks by a frame synthesization blocking section
1101
, and the resultant blocks are sent to a block distribution section
1102
. When a signal switch
1107
which operates in response to an operation mode signal is switched to one terminal connecting with the block distribution section
1102
, the block distribution section
1102
distributes the respective blocks received from the frame synthesization blocking section
1101
to moving image encoding sections
1103
to
1106
. The moving image encoding sections
1103
to
1106
encode the respective blocks and output resultant encoded signals. When the signal switch
1107
is switched to the other terminal, TV moving images with a normal quality are supplied to the moving image encoding section
1103
via the signal switch
1107
. The moving image encoding section
1103
encodes the TV moving images and outputs resultant encoded signals.
Thus, in this conventional device, both low-resolution moving image signals and high-resolution moving image signals can be encoded by switching the signal switch
1107
.
However, the conventional device with the above configuration provides no conception of encoding and multiplexing moving images with different resolutions simultaneously. This device is therefore not applicable to the simultaneous transmission of moving images with different resolutions which is employed in broadcasting and the like.
In one conventional technique of multiplexing a plurality of moving images for transmission, a fixed bit rate is allocated for each encoding device, so that moving images are encoded by each encoding device at the allocated bit rate and resultant moving image encoded signals are multiplexed. However, this technique has the following problem. The complexity of moving images changes with time. Accordingly, in order to encode and transmit the moving images so that the degradation in the image quality is always inconspicuous, the respective bit rates are required to be set so that the degradation in the image quality of the reproduced moving image is inconspicuous even when a moving image with highest complexity is encoded. This lowers the transmission efficiency.
In order to solve the above problem, a method in which the bit rate is changed depending on the complexity of the encoding of moving images has been attempted. According to this method, the bit rate is lowered for simple moving images to realize efficient transmission, and multi-channel communication using more channels is possible f or the same transmission bit rate. This method is described in WO 95/32565, for example.
FIG. 38
shows a device implementing the above method. Referring to
FIG. 38
, moving image encoding sections
2101
,
2102
, and
2103
encode input moving images in accordance with respective target rates specified by a multiplexing section
2104
, and output resultant encoded signals to the multiplexing section
2104
. The multiplexing section
2104
multiplexes the received encoded signals and outputs multiplexed signals to a transmission route. The multiplexing section
2104
also adjusts the target rates based on a transmission rate for the encoded signals and supplies the new target rates to the moving image encoding sections
2101
to
2103
.
The target rates are set so that a total of the target rates is equal to the transmission rate. More specifically, each of the moving image encoding sections
2101
to
2103
sends the amount of encoding distortion at the encoding to the multiplexing section
2104
every fixed period. The multiplexing section
2104
adjusts the target rate depending on the amount of encoding distortion sent from each of the moving image encoding sections
2101
to
2103
while the total of the target rates is kept equal to the transmission rate. That is, the target rate is increased for the moving image encoding section which has sent a large distortion amount, while it is lowered for the moving image encoding section which has sent a small distortion amount. In this way, moving images encoded by the moving image encoding sections
2101
to
2103
are provided with bit rates allocated depending on the complexity of the encoding.
In the above conventional method, however, the target rates are corrected so as to reduce the amount of distortion after the distortion is generated. Accordingly, the image quality tends to be low at an instance immediately after the scene change to a scene of which encoding is difficult, for
Katta Noboru
Kurosaki Toshihiko
Mori Toshiaki
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