U.S. patent application number 14/796413 was filed with the patent office on 2015-10-29 for image decoding device and method thereof using inter-coded predictive encoding code.
This patent application is currently assigned to HITACHI MAXELL, LTD.. The applicant listed for this patent is HITACHI MAXELL, LTD.. Invention is credited to Tomokazu MURAKAMI, Yoshinori SUZUKI.
Application Number | 20150312586 14/796413 |
Document ID | / |
Family ID | 35187086 |
Filed Date | 2015-10-29 |
United States Patent
Application |
20150312586 |
Kind Code |
A1 |
MURAKAMI; Tomokazu ; et
al. |
October 29, 2015 |
IMAGE DECODING DEVICE AND METHOD THEREOF USING INTER-CODED
PREDICTIVE ENCODING CODE
Abstract
An image encoding device and corresponding decoding device are
disclosed for achieving a high rate of compression. The encoding
device includes an image conversion module that converts the
direction of the images using right-left symmetry mode convention
or up-down symmetry mode conversion. Encoding modules are used to
encode both the unconverted and converted images. A mode selector
module compares the quantity of codes in the encoded unconverted
images and the quantity of codes in the encoded converted images,
and selects codes that are smaller in the quantity of codes for
output.
Inventors: |
MURAKAMI; Tomokazu;
(Kokubunji, JP) ; SUZUKI; Yoshinori; (Saitama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
HITACHI MAXELL, LTD. |
OSAKA |
|
JP |
|
|
Assignee: |
HITACHI MAXELL, LTD.
OSAKA
JP
|
Family ID: |
35187086 |
Appl. No.: |
14/796413 |
Filed: |
July 10, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14624889 |
Feb 18, 2015 |
9118924 |
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14796413 |
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14551114 |
Nov 24, 2014 |
8971403 |
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14624889 |
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14295525 |
Jun 4, 2014 |
8923387 |
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14551114 |
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11066169 |
Feb 28, 2005 |
8787456 |
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14295525 |
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Current U.S.
Class: |
375/240.02 |
Current CPC
Class: |
H04N 19/176 20141101;
H04N 19/521 20141101; H04N 5/145 20130101; H04N 19/139 20141101;
H04N 19/85 20141101; H04N 19/11 20141101; H04N 19/172 20141101;
H04N 19/105 20141101; H04N 19/46 20141101; H04N 19/167 20141101;
H04N 19/103 20141101; H04N 19/593 20141101; H04N 19/61 20141101;
H04N 19/146 20141101; H04N 19/44 20141101; H04N 19/513
20141101 |
International
Class: |
H04N 19/513 20060101
H04N019/513; H04N 19/139 20060101 H04N019/139; H04N 19/176 20060101
H04N019/176; H04N 19/105 20060101 H04N019/105 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2004 |
JP |
PCT/JP2004/006169 |
Claims
1. A decoding method for decoding a signal of an intra-coded image,
the decoding method comprising: a determination step of determining
whether an partial area of the image has been converted in an
up-down symmetry conversion mode to flip the partial area of the
image vertically or in a right-left symmetry conversion mode to
flip the partial area of the image horizontally with reference to
information sent together with the signal of the image; and a
decoded image creation step of creating a decoded image with
executing conversion associated with a conversion mode determined
in the determination step after intra-coded predicting, wherein the
information includes information indicating a direction of the flip
of the partial area of the image and information indicating a
position of the flipped partial area, and wherein the options of
the direction of the flip include horizontal flipping.
Description
CLAIM OF PRIORITY
[0001] This application is a continuation of application Ser. No.
14/624,889, filed Feb. 18, 2015, which is a continuation of
application Ser. No. 14/551,114, filed Nov. 24, 2014, now U.S. Pat.
No. 8,971,403, which is a continuation of application Ser. No.
14/295,525, filed Jun. 4, 2014, now U.S. Pat. No. 8,923,387, which
is a continuation of application Ser. No. 11/066,169, filed Feb.
28, 2005, now U.S. Pat. No. 8,787,456, which claims benefit of
priority to Japanese application PCT/JP2004/006169 filed on Apr.
28, 2004, the disclosures of which are incorporated herein by
reference.
BACKGROUND
[0002] This invention relates to an image encoding device, an image
encoding program and an image encoding method for encoding images,
an image decoding device, a decoding program, and a decoding method
for decoding encoded images, a medium recording an encoded image
encoding stream, and a method of transmitting encoded image
data.
[0003] As methods of recording large quantities of visual and audio
information as compressed digital data and transmitting them,
encoding systems including the Moving Picture Experts Group (MPEG)
system have been formulated, and established as encoding systems of
international standards, such as MPEG-1, MPEG-2 and MPEG-4
standards. Systems prescribed for enhancing the rate of compression
include the H.264/Advanced Video Coding (AVC) standard (see Joint
Video Team (JVT) of ISO/IEC MPEG ITU-T VCEG: "Text of International
Standard of Joint Video Specification", ITU-T Rec. H264|ISO/IEC
14496-10 Advanced Video Coding (December, 2003)). These systems
have been adopted as encoding systems for use in digital satellite
broadcasting, DVDs, cellular telephones and digital cameras among
others, and are now finding even more extensive and familiar
use.
[0004] Of these encoding systems, the H.264/AVC systems uses, in
addition to arithmetic transform encoding techniques using motion
compensative prediction and discrete cosine transform (DCT), a
technique known as intra-coded predictive encoding. This technique
permits prediction of the signal level from an encoded adjoining
block in an intra-frame without having to use any other picture
information.
[0005] FIG. 3 illustrates the intra-coded predictive encoding. The
description here will refer, by way of example, to block-by-block
prediction, the size of each block being 4.times.4 pixels, in a
raster scanning system of sequentially scanning a frame rightward
and downward from the top left. The signal level of a pixel 304 in
a prediction block 303 (the block to be predicted) is predicted
from the signal level of the boundary pixel 302 of an already
encoded adjoining block 301 (the pixels adjoining the prediction
block, out of the pixels of the adjoining block 301, except that a
pixel on the lowest line where the block adjoining the prediction
block to the upper right is concerned), and the difference between
the predicted value and the actual value (residual component) is
subjected to arithmetic transform encoding by DCT or otherwise. At
this step, a pixel 305 of an adjoining block not yet encoded cannot
be used for prediction. There are a plurality of directions of
prediction (i.e. encoding modes) 306. Residual components resulting
from prediction in all the directions are compared, the direction
giving the smallest residual component is selected, and that
residual component is subjected to arithmetic transform encoding.
The direction "O:DC" here is the mode in which the average signal
level of all the boundary pixels is used as the predictive
value.
[0006] Incidentally, in block-by-block prediction in which the size
of each block is 16.times.16 pixels, intra-coded predictive
encoding can also be accomplished though the directions of
prediction are limited.
[0007] Inter-coded predictive encoding, though similar to the
conventional MPEG systems, the motion vector of each block is
encoded as the difference from the upper and left side motion
vectors, which are already encoded.
SUMMARY
[0008] As stated above, intra-coded predictive encoding cannot be
applied to pixels of any adjoining block which is not yet encoded.
For this reason, a difference in the accuracy of prediction may
occur depending on the direction of prediction 306. For instance,
where blocks are scanned by a raster scanning system of
sequentially scanning a frame rightward and downward from the top
left, the accuracy of predicting rightward and downward from the
top left is high, but that of predicting leftward and downward from
the top right is low. Thus, in an image in which pixels similar in
signal level consecutively appear rightward and downward from the
top left (left-to-right sloping image), prediction is easier and
accordingly a high rate of compression can be achieved. However,
prediction is more difficult for an image in which pixels similar
in signal level consecutively appear leftward and downward from the
top right (right-to-left sloping image), and accordingly the rate
of compression is lower.
[0009] Similarly in inter-coded predictive encoding, there is
directional dependence of characteristics of images subjected to
raster scanning. Since the motion vector of each block is encoded
as the length of difference from the motion vectors of the
adjoining blocks on the left and upper sides, the closer the
sequence in correlation to the motion in the rightward and downward
direction, the higher the accuracy of prediction and the higher the
efficiency of encoding. Further, as the selection of a context
model in entropy encoding also uses information on the adjoining
blocks on the left and upper sides, a similar trend is found of the
accuracy of prediction.
[0010] Moreover, as only boundary pixels are used in conventional
intra-coded predictive encoding, there is a problem that
consecutive variations in signal level within a block cannot be
predicted with a sufficiently high accuracy. Usually, the signal
level of pixels varies in a gentle slope. However, in conventional
intra-coded predictive encoding, boundary pixels on a block
boundary are extended in prediction (i.e. the pixels to be
predicted are assumed to be the same as the boundary pixels). As a
result, the farther a given pixel from the boundary pixels, the
greater the residual component and the greater the quantity of
codes after arithmetic transform.
[0011] An object of this invention, attempted in view of the
problems, is to provide an image encoding device capable of
intra-coded prediction always in the direction of higher accuracy
of prediction without having to alter the scanning direction by
inverting the input image in the vertical or horizontal direction
or rotating it at any desired angle before performing intra-coded
prediction, and an image decoding device matching this encoding
device.
[0012] Another object of the invention is to provide an image
encoding device capable of inter-coded prediction always in the
direction of higher accuracy of prediction without having to alter
the scanning direction by inverting the input image in the vertical
or horizontal direction or rotating it at any desired angle before
performing inter-coded prediction, and an image decoding device
matching this encoding device.
[0013] Still another object of the invention is to provide an image
encoding device capable of realizing intra-coded prediction at high
accuracy using not only boundary pixels but also pixels inside the
block according to a prescribed interpolation formula when
performing intra-coded prediction, and an image decoding device
matching this encoding device.
[0014] According to the invention, there is provided an encoding
device for encoding signals of images, comprising an image
conversion module for converting the direction of the images,
encoding modules for encoding the images and images converted in
the direction, and a mode selector module for comparing the
quantity of codes in the encoded images and the quantity of codes
in the encoded images converted in the direction, selecting codes
smaller in the quantity of codes, and outputting the selected codes
and a flag for identifying the selected codes.
[0015] Also according to the invention, there is provided an
encoding device for encoding signals of images, comprising an
encoding module for calculating a first difference between
information on a first pixel of a prediction area for second pixel
which is in a predictive direction from the first pixel, encoding
the first difference of the prediction area, calculating a
predicted value calculated by applying a forward interpolation
formula to information on a plurality of third pixels which are in
a predictive direction from the first pixel, calculating a second
difference from the predicted value and encoding the second
difference of the prediction area; and a mode selector module for
comparing the quantities of codes in the quantities of codes in the
first and second differences of the prediction areas calculated for
a plurality of the predictive directions, selecting codes smallest
in the quantity of codes, and outputting the selected codes and a
flag indicating which of the predictive directions the first or
second difference has been calculated for the selected codes.
[0016] Therefore according to the invention, it is possible to
provide an image encoding device enhanced in the rate of
compression by performing intra-coded prediction and inter-coded
prediction always in the direction of higher accuracy of prediction
without having to alter the scanning direction, and an image
decoding device matching this encoding device.
[0017] Also according to the invention, it is possible to provide
an image encoding device enhanced in the rate of compression by
performing highly accurate intra-coded prediction using pixels
inside the block, and an image decoding device matching this
encoding device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a block diagram of the hardware configuration of
an image encoding device, which is a first preferred embodiment of
this invention;
[0019] FIG. 2 is a block diagram of the functions of the image
encoding device, which is the first preferred embodiment of the
invention;
[0020] FIG. 3 illustrates intra-coded predictive encoding;
[0021] FIG. 4 illustrates the procedure of image encoding by the
first preferred embodiment of the invention;
[0022] FIG. 5 is a block diagram of the hardware configuration of
an image decoding device, which is a second preferred embodiment of
the invention;
[0023] FIG. 6 is a block diagram of the functions of the image
decoding device, which is the second preferred embodiment of the
invention;
[0024] FIG. 7 illustrates the procedure of image decoding by the
second preferred embodiment of the invention;
[0025] FIG. 8 illustrates an intra-coded predicting method in a
third preferred embodiment of the invention;
[0026] FIG. 9 is a block diagram of the functions of the
intra-coded predicting module to which the intra-coded predicting
method is applied in the third preferred embodiment of the
invention;
[0027] FIG. 10 illustrates the procedure of intra-coded prediction
in the third preferred embodiment of the invention;
[0028] FIG. 11 illustrates a data recording medium in a fourth
preferred embodiment of the invention;
[0029] FIG. 12 illustrates a packet in a fifth preferred embodiment
of the invention;
[0030] FIG. 13 is a block diagram of the functions of an image
encoding device, which is a sixth preferred embodiment of the
invention;
[0031] FIG. 14 illustrates the procedure of image encoding by the
sixth preferred embodiment of the invention;
[0032] FIG. 15 is a block diagram of the functions of an image
decoding device, which is a seventh preferred embodiment of the
invention; and
[0033] FIG. 16 illustrates the procedure of image decoding by the
seventh preferred embodiment of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0034] The embodiments and advantages of this invention will be
described in detail with the accompanying drawings.
[0035] FIG. 1 is a block diagram of the hardware configuration of
an image encoding device, which is a first preferred embodiment of
this invention.
[0036] An image encoding device 101, which is the first embodiment
of the invention, comprises a processor 102, a memory 103, an input
interface (input 1/F) 104 and an output interface (output I/ F) 106
connected to permit communication among one another. The input I/F
104 is connected to an input device 105, and the output I/F 106 is
connected to an output device 107.
[0037] The processor 102, intended to process image encoding
according to the invention, codes data received from the input I/F
104 by executing a program stored in the memory 103, and delivers
the encoded data to the output I/F 106.
[0038] Programs to be executed by the processor 102 are stored in
the memory 103. Also, data to be processed by the processor 102 are
temporarily stored therein.
[0039] The image encoding device 101 may be provided with a
plurality each of processors 102 and memories 103. For instance,
there may be a processor dedicated to execution of only a part of
the processing of image encoding according to the invention. Also,
a plurality of processors for performing the same processing may be
provided.
[0040] The processor 102 and the memory 103 may be mounted on a
single chip.
[0041] The input I/F 104 is an interface for receiving from the
input device 105 image data to be processed by the processor
102.
[0042] The input device 105 is a device for entering into the input
I/F 104 image signals to be processed by the image encoding device
101, and may be a video camera or a TV tuner, for instance. In this
case, the input I/F 104 may be a video capture card, for example.
Further, the input device 105 may be a storage device in which
image data not encoded are to be stored. In this case, the input
I/F 104 may be an SCSI interface, for instance.
[0043] The output I/F 106 is an interface for transmitting to the
output device 107 data encoded by the processor 102.
[0044] The output device 107 is the destination to which data
encoded by the image encoding device 101 are to be supplied, for
instance a storage device in which encoded image data are to be
stored. In this case, the output I/F 106 may be an SCSI interface,
for instance. Further, the output device 107 may be a computer
system connected to the output I/F 106 via a LAN, IP network or the
like (not shown). In this case, the output I/F 106 is a network
interface. The output device 107 may as well be an image receiver
device connected to the output I/F 106 via a telephone
communication network (not shown). In this case, the output I/F 106
is a transmitter of telephone signals. Or the output device 107 may
be a digital TV receiver. In this case, the output I/F 106 is a
transmitter of digital TV signals.
[0045] The image encoding device 101 may as well be provided with a
plurality each of input I/Fs 104 and output I/Fs 106, with an input
device and an output device each of a different type being
connected to each input I/F 104 and output I/F 106. For instance,
the image encoding device 101 may have two output I/Fs 106, a hard
disk device being connected to one of them, and a magneto-optical
disk device being connected to the other. Or a hard disk device may
be connected to one of them, and a computer system may be connected
to the other via a LAN or the like.
[0046] FIG. 2 is a block diagram of the functions of the image
encoding device 101, which is the first preferred embodiment of the
invention.
[0047] The image encoding device 101 comprises an original image
memory 201, an image converting module 202, an encoding module 203,
a mode control module 213 and a mode selector module 214. The
original image memory 201 here is a partial area of the memory 103,
and the image converting module 202, the mode control module 213
and the mode selector module 214 are programs stored in the memory
103 and to be executed by the processor 102. The encoding module
203 comprises a motion predicting module 204, an intra-coded
predicting module 205, an arithmetic transform module 206, a
quantizing module 207, a coefficient encoding module 208, an
inverse quantizing module 209 and an inverse arithmetic transform
module 210, which are programs to be executed by the processor 102,
and a decoded image memory 211 and a predictive image memory 212,
which are a partial area of the memory 103.
[0048] Next will be described the functions of the individual
modules of the image encoding device 101 along the procedure of
encoding an image.
[0049] The original image memory 201 temporarily buffers the
original image to be encoded. Next, the image converting module 202
processes conversion of the whole or part of the frame of the image
acquired from the original image memory 201. Part of the frame in
this context may be one of macro-blocks or blocks of a prescribed
size into which the frame is divided or a prescribed rectangular
area. Usually, the unit of encoding is a macro-block.
[0050] The image converting module 202 may divide the data having
undergone conversion processing of the whole frame into
macro-blocks and transmit those macro-blocks to the encoding module
203, or subject the macro-blocks into which the frame has been
divided to conversion processing. Information regarding whether or
not conversion processing has been done is transmitted to the mode
control module 213.
[0051] The conversion processing performed by the image converting
module 202 is processing to convert the direction of images.
Processing to convert the direction of images is, for instance,
axial symmetry conversion or point symmetry conversion. Axial
symmetry conversion means, for instance, right-left symmetry
conversion by which the frame is inverted laterally or up-down
symmetry conversion by which the frame is inverted vertically.
Point symmetry conversion means, for instance, rotational
conversion by which the frame is rotated. The image converting
module 202 may combine these modes of conversion. The following
description will refer to, by way of example, a case in which
subjecting the whole images to right-left symmetry conversion and
not subjecting it to such conversion is compared and what involves
a smaller quantity of codes is selected.
[0052] The encoding module 203 acquires from the image converting
module 202 images subjected to right-left symmetry conversion and
images not subjected to such conversion, and sequentially codes
each image. Or a plurality of encoding modules 203 may be provided,
and each image may be encoded by two encoding modules 203 in
parallel. Where a plurality of encoding modules 203 are provided,
the image encoding device 101 is provided with a plurality of
processors 102 dedicated to the execution of programs of the
encoding modules 203.
[0053] The motion predicting module 204 subjects the images
acquired from the image converting module 202 to inter-frame
prediction by using images from the predictive image memory 212 and
the decoded image memory 211, transmits information on motion
vectors and the like to the mode control module 213, and transmits
to the arithmetic transform module 206 the residual component of
the encoded block obtained by prediction.
[0054] The intra-coded predicting module 205 subjects the images
acquired from the image converting module 202 to intra-coded
prediction by using images from the decoded image memory 211,
transmits information on modes and the like to the mode control
module 213, and transmits to the arithmetic transform module 206
the residual component of the encoded block obtained by
prediction.
[0055] The arithmetic transform module 206, the quantizing module
207 and the coefficient encoding module 208 are the same as their
respective counterparts in conventional encoding devices, and
respectively perform DCT operation, quantization of conversion
coefficients and conversion of coefficients into codes. The inverse
quantizing module 209 and the inverse arithmetic transform module
210, which also are the same as their respective counterparts in
conventional encoding devices, return encoded data into image
information by inverse conversion, and store the resultant
information into the decoded image memory 211 and the predictive
image memory 212.
[0056] The mode control module 213 manages the encoding mode in the
whole image (frame) and macro-blocks on the way of encoding.
Regarding the whole image, it holds an encoding process for images
having undergone conversion processing and one for images not
having undergone conversion processing. Thus it holds items of
information referenced for motion prediction (including motion
vectors and information on the reference frame) and information on
the intra-coding mode (direction on the intra-coded prediction
side) among others with respect to each of the case in which
conversion processing has been performed and that in which no
conversion processing has been performed. Regarding macro-blocks,
it holds information as to whether the current macro-block is to
undergo intra-coding or inter-frame prediction encoding and
information related to them concerning the intra-coding mode,
motion vectors and reference frames among others. The mode control
module 213 transmits these items of information to the mode
selector module 214.
[0057] The mode selector module 214 composes encoded data of images
from information on encoded data and encoding modes regarding the
whole image and macro-blocks on the way of encoding, and outputs
the data so composed. It compares the overall quantity of codes in
the case of encoding through conversion processing by the image
converting module 202 with the quantity of codes in the case of
encoding without conversion processing, and outputs codes of the
smaller quantity as a stream. Further a flag indicating whether or
not conversion processing has been performed and, where a partial
area of an image has been converted, positional information on that
area, are added to the stream as data.
[0058] It is sufficient for the flag indicating whether or not
conversion processing has been performed to have one bit each for
right-left symmetry conversion and up-down symmetry conversion. In
the case of rotational conversion, if the number is to be increased
by 1 for every 90-degree rotation, two bits will be sufficient for
expressing a 360-degree rotation.
[0059] FIG. 4 illustrates the procedure of image encoding by the
first preferred embodiment of the invention.
[0060] First, the image converting module 202 decides on the
encoding system (step 401). Thus, it decides on whether to apply
conversion processing to the whole frame or macro-block by
macro-block. The following description will refer to a case in
which the whole frame is to be converted by way of example. The
process of performing conversion processing goes advances to step
402 while that of not performing conversion processing goes to step
404.
[0061] At step 402, the image converting module 202 converts the
input image. Thus the image is subjected frame by frame to
right-left symmetry conversion, up-down symmetry conversion,
rotational conversion and so forth. Then the sequence advances to
step 403.
[0062] At step 403 and step 404, the encoding module 203 codes the
image. This encoding was already described with reference to FIG.
2.
[0063] Next, the mode selector module 214 compares the quantities
of codes and decides on the mode (step 405). Thus, as described
with reference to FIG. 2, it compares the quantities of codes
obtained by encoding between process of having performed conversion
processing and that of not having performed conversion processing,
and decides to output data of the smaller quantity of codes.
[0064] Then, the mode selector module 214 outputs a code and a flag
(step 406). As described with reference to FIG. 2, it outputs as a
stream the flag indicating whether or not conversion processing has
been performed, positional information on the partial area of an
image has been converted if any, and the selected encoded data. The
processing of encoding is thereby completed.
[0065] FIG. 5 is a block diagram of the hardware configuration of
an image decoding device, which is a second preferred embodiment of
the invention.
[0066] An image decoding device 501, which is the second preferred
embodiment of the invention, comprises a processor 502, a memory
503, an input interface (input I/F) 504 and an output interface
(output I/F) 506, connected to permit communication among one
another. The input I/F 504 is connected to an input device 505, and
the output I/F 506 is connected to an output device 507.
[0067] The processor 502, intended to process image decoding
according to the invention, decodes data received from the input
I/F 504 by executing a program stored in the memory 503, and
delivers the decoded data to the output I/F 506.
[0068] Programs to be executed by the processor 502 are stored in
the memory 503. Also, data to be processed by the processor 502 are
temporarily stored therein.
[0069] The image encoding device 501 may be provided with a
plurality each of processors 502 and memories 503. For instance,
there may be a processor dedicated to execution of only a part of
the processing of image decoding according to the invention.
[0070] The processor 502 and the memory 503 may be mounted on a
single chip.
[0071] The input I/F 504 is an interface for receiving from the
input device 505 image data to be processed by the processor
502.
[0072] The input device 505 is a device for entering into the input
I/F 504 encoded data to be processed by the image decoding device
501, and may be a storage device in which encoded image data are to
be stored. In this case, the input I/F 504 may be an SCSI
interface, for instance. Further, the input device 505 may be a
computer system connected to the input I/F 504 via a LAN, IP
network or the like (not shown). In this case, the input I/F 504 is
a network interface. The input device 505 may as well be an image
data transmitter device connected to the input I/F 504 via a
telephone communication network (not shown). In this case, the
input I/F 504 is a receiver of telephone signals. Or the input
device 505 may be a digital TV broadcast station. In this case, the
input I/F 504 is a digital TV tuner.
[0073] The output I/F 506 is an interface for transmitting to the
output device 507 data decoded by the processor 502.
[0074] The output device 507 is the destination to which data
decoded by the image decoding device 501 are to be supplied, for
instance a display on which images are to be displayed. In this
case, the output I/F 506 may be a video card, for instance.
Further, the output device 507 may be a storage device in which
decoded data are to be stored in a stream. In this case, the output
I/F 506 is a SCSI interface.
[0075] The image decoding device 501 may as well be provided with a
plurality each of input I/Fs 504 and output I/Fs 506, with an input
device and an output device each of a different type being
connected to each input I/F 504 and output I/F 506. For instance,
the image encoding device 501 may have two output I/Fs 506, a hard
disk device being connected to one of them, and an optical disk
device being connected to the other. Or a hard disk device may be
connected to one of them, and a computer system may be connected to
the other via a LAN or the like.
[0076] FIG. 6 is a block diagram of the functions of the image
decoding device 501, which is the second preferred embodiment of
the invention.
[0077] The image decoding device 501 comprises a stream analyzing
module 601, a mode decision module 602, a decoding module 603, an
image converting module 610 and a decoded image memory 611. The
stream analyzing module 601, the mode decision module 602, the
decoding module 603 and the image converting module 610 here are
programs stored in the memory 503 and to be executed by the
processor 502, and the decoded image memory 611 is a partial area
of the memory 103. Further, the decoding module 603 comprises a
motion predicting module 604, an intra-coded predicting module 605,
a coefficient analyzing module 606, an inverse quantizing module
607 and an inverse arithmetic transform module 608, which are
programs to be executed by the processor 502, and a predictive
image memory 609, which is a partial area of the memory 503.
[0078] The decoding device 501, which is the second embodiment of
the invention, can decode a stream encoded by the image encoding
device 101, which is the first embodiment. Next, the functions of
the different modules of the image decoding device 501 will be
described along the procedure of decoding the encoded stream.
[0079] The stream analyzing module 601 analyzes the data of the
inputted encoded stream, and transmits to the mode decision module
602 information on flags and data. The stream analyzing module 601
analyzes the data of the stream and flags created by the encoding
device 101.
[0080] Then, the mode decision module 602 controls modes regarding
motion prediction, intra-coded prediction and image conversion on
the basis of the information analyzed by the stream analyzing
module 601. If a flag indicating that the image was subjected at
the time of encoding to conversion processing such as inversion,
rotation or the like is attached to the stream, information on the
type of conversion processing performed (for instance, information
on whether or not right-left symmetry conversion has been
performed) is transmitted to the image converting module 610.
[0081] The motion predicting module 604 performs inter-frame
prediction by using information including motion vectors
transmitted from the mode decision module 602 and images from the
predictive image memory 609 and the decoded image memory 611, and
transmits predictive information to the coefficient analyzing
module 606.
[0082] The intra-coded predicting module 605 performs intra-coded
prediction by using information including the intra-coding mode
transmitted from the mode decision module 602 and images from the
decoded image memory 611, and transmits predictive information to
the coefficient analyzing module 606.
[0083] The coefficient analyzing module 606, the inverse quantizing
module 607 and the inverse arithmetic transform module 608 are the
same as their respective counterparts in conventional decoding
devices, and respectively perform synthesis of predictive
information and coefficient information, inverse quantization of
conversion coefficients and DCT operation.
[0084] The image converting module 610 subjects to conversion
processing the whole frame or part of the decoded image in
accordance with information transmitted from the mode decision
module 602. Thus it performs processing to undo the conversion
processing performed by the image converting module 202 of the
encoding device 101 shown in FIG. 1 and FIG. 2 above.
[0085] The decoded image memory 611 stores decoded images having
gone through conversion processing by the image converting module
610, and transmits those images to the output device 507 to have
the decoded images displayed on a screen or supplied to a
stream.
[0086] FIG. 7 illustrates the procedure of image decoding by the
second preferred embodiment of the invention.
[0087] First, the stream analyzing module 601 and the mode decision
module 602 analyze the stream and the flag (step 701). Then, the
decoding module 603 decodes the image (step 702). Next, the image
converting module 610 converts the decoded image, and stores it
into the decoded image memory 611 (step 703). Finally, images
stored in the decoded image memory 611 are outputted for displaying
or stream recording (step 704). The processing of decoding is
thereby completed. Incidentally, since particulars of the
processing by the above-described modules were already stated with
reference to FIG. 6, their detailed description will be dispensed
with here.
[0088] The image encoding device 101 of the first embodiment of the
invention and the image decoding device 501 of the second
embodiment described above may be packaged as the same hardware
unit. In this case, the programs described with reference to FIG. 2
and FIG. 6 are stored in the memory 103 (or the memory 503),
wherein the areas described with reference to FIG. 2 and FIG. 6 are
secured.
[0089] Thus, the first and second embodiments of the invention can
respectively provide an image encoding device capable of reducing
the quantities of codes after encoding (i.e. achieving a higher
rate of compression) by performing intra-coded prediction always in
the direction of higher accuracy of prediction without having to
alter the scanning direction, and an image decoding device matching
this encoding device. As a result, the quantity of codes can be
reduced by about 10% at the maximum compared with conventional
intra-coded prediction. The quantity of codes, however, is not
reduced always at a constant rate because it varies with the
particulars of the original image.
[0090] FIG. 8 illustrates an intra-coded predicting method in a
third preferred embodiment of the invention.
[0091] This embodiment provides a method which uses, in predicting
the signal level of the pixels of a prediction block 802 not only
the signal level of the boundary pixel but also the signal level of
pixels of the whole of the already encoded adjoining block 801, and
is used by the intra-coded predicting modules 205 and 605 of FIG. 2
and FIG. 6, respectively. The "prediction block" here means a block
which is the object of encoding but not yet encoded yet, and the
"adjoining block" means an encoded block adjoining the prediction
block.
[0092] The directions of prediction are shown in 306 in FIG. 3.
Although the description of this embodiment will limit itself to
prediction in only some of these directions for the sake of
brevity, actual prediction is performed in all the directions of
prediction 306 and the direction in which the residual component is
the smallest is selected. Prediction in this context means a
procedure, where it refers to encoding, of encoding the difference
(residual component) between the actual signal level of pixels in
the prediction block 802 and a predicted value calculated from the
signal level of pixels in the adjoining block used for prediction.
On the other hand, where it refers to decoding, prediction means a
procedure of obtaining a decoded image by adding a decoded residual
component to a predicted value calculated in the same way. The
procedure of encoding will be described below.
[0093] Any conventional intra-coded predicting method uses boundary
pixels alone. Where, for instance, prediction is to be done in the
vertical direction, prediction is done in the downward direction by
using the boundary pixels (pixels of the lowest line) of the
adjoining block 801 right above the prediction block 802. Thus, the
prediction block 802 is divided into four rows and, from the value
of the signal level of each pixel, the value of the signal level of
the boundary pixels bordering above the row including that pixel is
subtracted. Where prediction is to be done in the horizontal
direction, similarly prediction is done in the rightward direction
by using the boundary pixels (pixels of the rightmost line) of the
adjoining block bordering the prediction block on the left. Thus,
the prediction block 802 is divided into four rows and, from the
signal level of each pixel, the value of the signal level of the
boundary pixels bordering the row including that pixel on the left
is subtracted. Thus in prediction in either of the directions
mentioned above, the signal level of the pixels of the prediction
block is predicted to be the same as the signal level of the
boundary pixels, and the difference (residual component) between
the predicted value and the actual value is calculated.
[0094] On the other hand, the intra-coded predicting method
provided by the third preferred embodiment of the invention, is a
predicting method using composite pixels including not only
boundary pixels but also pixels inside adjoining blocks. The
composite pixels here mean pixels in a plurality of blocks used in
the prediction of pixels in the prediction block. Where prediction
is to be done in the horizontal direction for instance, composite
pixels constitute one line (803) of the block adjoining the line to
be predicted. In this case, the predicted value is calculated from
the value of the composite pixels 803 by an interpolation formula,
and the values of the pixels of one of the adjoining prediction
block are predicted. This prediction uses, for instance, Newton's
forward interpolation formula. By way of example, a case in which
the composite pixels of the adjoining block and the pixels to be
predicted of the prediction block are assigned numbers n of 0 to 7,
the signal level of a pixel n is supposed to be yn, and n=4, 5, 6,
7 (uncoded) is to be figured out from n=0, 1, 2, 3 (coded). In this
calculation, the predicted signal level value yn of the pixel n is
obtained by Equation (1).
[0095] The residual component is figured by subtracting the
predicted value, calculated by Equation (1), from the value of the
pixel of the prediction block. If n=7 for instance, the residual
component of pixel 7 is the remainder of the subtraction of y7 from
the actual value of pixel 7. Where prediction is to be done
diagonally, similarly numbers n (n=0 to 7) are assigned to the
pixels to be predicted of the prediction block and the pixels of
the adjoining block, which constitute the basis of prediction, and
the predicted value is calculated by Equation (1) (805). If the
pixels to be predicted are less than four, the calculation should
be done in a more narrowly limited range of n. For instance, if
there are three pixels to be predicted, the range of n should be
reduced to 0 to 6 (806).
y n = y 0 + n D 0 + n ( n - 1 ) D 1 + n ( n - 1 ) ( n - 2 ) D 2 D 0
= y 1 - y 0 D 1 = 1 2 ( y 2 - 2 y 1 + y 0 ) D 2 = 1 6 ( y 3 - 3 y 2
+ 3 y 1 - y 0 ) ( 1 ) ##EQU00001##
[0096] Whereas Equation (1) is a formula applicable to a block size
of 4.times.4 pixels, the predicting method provided by this
embodiment can also be applied to other block sizes (e.g.
16.times.16 pixels). Generally regarding pixels numbered from 0 to
n, where the values of signal levels of pixels m+1 to n are to be
predicted from the values of known signals of pixels 0 to m, the
predicted value y can be obtained by Equation 2, wherein nCj is a
two-term coefficient.
y n = y 0 + j = 1 m C j n i = 0 j C i j ( - 1 ) j - i y i C i j = n
! j ! ( n - j ) ! ( 2 ) ##EQU00002##
[0097] Next, the residual from the conventional predicting method
will be compared with that from the predicting method provided by
this embodiment. A signal level 808 according to the conventional
predicting method is the same as the signal level of pixel 3
(boundary pixel). On the other hand, a signal level 809 according
to the predicting method provided by this embodiment is a value
calculated by Equation (1).
[0098] For instance, when the signal level of pixels 0 to 3 varies
at a certain rate, often the actual signal level 810 of pixels 4 to
7 also varies at a rate close to that level. Thus, the actual
signal level 810 is often close to the signal level 809 according
to the predicting method provided by this embodiment than to the
signal level 808 according to the conventional predicting method.
As a result, a residual 812 according to the predicting method
provided by this embodiment becomes smaller than a residual 811
according to the conventional predicting method, and therefore a
smaller quantity of codes for this embodiment. Incidentally, though
Equations (1) and (2) use the signal level of all the known pixels
for prediction, prediction is also possible by using the signal
level of only some of the pixels.
[0099] To add, the method of least squares can as well be used for
this embodiment of the invention. In this case, a linear equation
inferred from a known signal level by the method of least squares
is used. For instance, when the signal level yn of pixel n at n=4,
5, 6, 7 is to be obtained on the basis of the known signal level yn
of pixel n at n=0, 1, 2, 3 as in the above-described case, Equation
(3) is used. Here, m represents the number of pixels which is the
basis of prediction, and m=4 holds in this example.
y n = a n + b a = i = 0 m - 1 ( y i - y _ ) ( i - n _ ) i = 0 m - 1
( i - n _ ) 2 b = y _ - a n _ , y _ = 1 m i = 0 m - 1 y i n _ = 1 m
i = 0 m - 1 i ( 3 ) ##EQU00003##
[0100] FIG. 9 is a block diagram of the functions of the
intra-coded predicting module 205 to which the intra-coded
predicting method is applied in the third preferred embodiment of
the invention.
[0101] The intra-coded predicting module 205 in this embodiment
determines the intra-coding mode of the prediction block (i.e. the
direction of prediction 306 of FIG. 3 above) on the basis of
information 907 on the signal level of the already encoded
adjoining block, performs prediction processing, and transmits the
encoding mode and information 906 on the residual component to the
mode control module 213 and the arithmetic transform module
206.
[0102] The intra-coded predicting module 205 comprises an
intra-coded prediction control module 901 and a plurality of
predicting modules each matching one or another of the encoding
modes. This plurality of predicting modules are classified into
what performs conventional prediction using boundary pixels and
what predicts by this embodiment using composite pixels, each
including what predicts in each of the directions of prediction 306
shown in FIG. 3.
[0103] For the sake of brevity of description, FIG. 9 shows only a
vertical direction boundary pixel mode predicting module 902 which
predicts in the vertical direction ("0:Vertical" in FIG. 2) using
boundary pixels, a horizontal direction boundary pixel mode
predicting module 903 which predicts in the horizontal direction
("1:Horizontal" in FIG. 2) using boundary pixels, a vertical
direction composite pixel mode predicting module 904 which predicts
in the vertical direction using composite pixels, and a horizontal
direction composite pixel mode predicting module 905 which predicts
in the horizontal direction using composite pixels, but actually a
predicting module using boundary pixels and a predicting module
using composite pixels are provided for each of the other
directions of prediction 306 in FIG. 2.
[0104] The intra-coded prediction control module 901 manages the
intra-coded predicting method. Thus it checks whether or not blocks
adjoining the prediction block can be used, and controls
information for intra-coded prediction.
[0105] Each of the mode predicting modules 902 to 905 predicts the
signal level of pixels of the prediction block from the signal
level of pixels of adjoining blocks, and calculates residual
components relative to the signal level of actual pixels. Next,
information on the mode in which the calculated residual component
is the smallest is transmitted to the mode control module 213, and
the residual component calculated in that mode is transmitted to
the arithmetic transform module 206.
[0106] The vertical direction boundary pixel mode predicting module
902 predicts in the downward direction by using the boundary pixels
of the adjoining block above the prediction block. The horizontal
direction boundary pixel mode predicting module 903 predicts
rightward by using the boundary pixels of the adjoining block to
the left of the prediction block.
[0107] The vertical direction composite pixel mode predicting
module 904 and the horizontal direction composite pixel mode
predicting module 905 perform intra-coded prediction by using
composite pixels of this embodiment. The vertical direction
composite pixel mode predicting module 904 calculates the predicted
value of the signal level by Equation (1) or Equation (2) by using
composite pixels of the adjoining block above the prediction block
(i.e. boundary pixels and inside pixels) to figure out residual
components relative to the actual signal level. The horizontal
direction composite pixel mode predicting module 905 calculates the
predicted value of the signal level by Equation (1) or Equation (2)
by using composite pixels of the adjoining block to the left of the
prediction block to figure out residual components relative to the
actual signal level.
[0108] FIG. 10 illustrates the procedure of intra-coded prediction
in the third preferred embodiment of the invention.
[0109] First, the intra-coded prediction control module 901 checks
the intra-coded prediction mode (step 1001). Thus, it decides
whether or not the pixels of the adjoining blocks can be used and,
on the basis of the result of that decision, specifies pixels to be
used for prediction in the applicable directions of prediction 306
and each of the directions of prediction 306.
[0110] Next, intra-coded prediction is performed regarding the
directions of prediction 306 to which the mode predicting modules
902 to 905 are applicable. In the procedure of FIG. 10, prediction
using conventional boundary pixels and prediction using the
composite pixels of this embodiment are performed both in the
vertical direction and in the horizontal direction (steps 1002 to
1005).
[0111] Then, the optimal intra-coded prediction mode is selected on
the basis of prediction results from steps 1002 to 1005 (step
1006). The total of residual components relative to different
pixels in each mode is calculated as a result of prediction at
steps 1002 to 1005. As the smaller this total, the smaller the
quantity of codes after encoding, the mode which gives the smallest
total of residual components is selected as the optimal mode. Next,
the selected residual components are transmitted to the arithmetic
transform module 206, and information on the selected mode is
transmitted to the mode control module 213. For even more accurate
decision, the mode selector module 214 may selected as the optimal
mode the mode which gives the smallest total of residual components
after arithmetic transform by the arithmetic transform module 206.
Processing of intra-coded prediction is completed hereupon.
[0112] The mode selector module 214 adds to the stream of codes to
be outputted a flag indicating the selected optimal mode.
[0113] To add, though prediction in only the vertical direction and
the horizontal direction is included in the procedure illustrated
in FIG. 10 for the sake of brevity of description, actually
prediction is performed in every direction of prediction which the
intra-coded prediction control module 901 has determined to be
applicable, and the optimal mode is selected from the result.
[0114] While the image encoding device 101 was described with
reference to FIG. 9 and FIG. 10, the intra-coded predicting method
provided by this embodiment can be similarly applied to the image
decoding device 501. In this case, the intra-coded predicting
module 605 is provided with, in addition to the conventional
boundary pixel mode predicting module, a composite pixel mode
predicting module for each of the directions of prediction 306. By
performing intra-coded prediction in the predicting mode for the
inputted encoded data, an image decoding device 501 matching the
intra-coded predicting method provided by this embodiment can be
realized.
[0115] Thus, the mode decision module 602 references the flag
attached to the image stream to be decoded, and determines the
intra-coded prediction mode selected at the time of encoding the
image. Next, the intra-coded predicting module 605 performs
prediction in the determined intra-coded prediction mode and
decodes the image. For instance, if the image to be decoded is
encoded in the boundary pixel mode in the rightward direction, the
signal level of pixels of the prediction block will be predicted to
be the same as that of the boundary pixels of the adjoining block
to the left of the prediction block, and decoding will be performed
on that basis. Or if the image to be decoded is encoded in the
composite pixel mode in the rightward direction for instance, the
predicted value of the signal level of the pixels of the prediction
block is calculated by applying Equation (1) to the composite
pixels of the adjoining block to the left of the prediction block,
and decoding will be performed on that basis.
[0116] The third embodiment of the invention so far described can
provide an image encoding device can reduce the quantity of codes
after encoding (i.e. raise the rate of compression) by performing
highly accurate intra-coded prediction by using composite pixels
(pixels inside the block), and an image decoding device matching
this encoding device.
[0117] FIG. 11 illustrates a data recording medium in a fourth
preferred embodiment of the invention.
[0118] A data recording medium 1101 is a recording medium for use
where the output device 107 or the input device 505 is a storage
device, and may be a magnetic disk for instance. Encoded data
created by the image encoding device 101 of the first embodiment of
the invention are recorded on the data recording medium 1101 as a
data stream 1102. The data stream 1102 is recorded as an encoded
stream conforming to a certain grammar. An example of the H.264/AVC
standard will be described below.
[0119] According to H.264/AVC, a stream comprises a sequence
parameter set 1103, a picture parameter set 1104 and slices 1105,
1106 and 1107. The following description will refer, by way of
example, to a case in which one image (frame) is stored in each
slice.
[0120] In a stream where the whole frame has been subjected to
conversion processing including right-left symmetry conversion,
up-down symmetry conversion or rotational conversion, a slice
header 1108 is recorded at the leading edge of the slice 1105, and
information 1109 on a flag and the like related to conversion
processing is stored within the slice header 1108. The contents of
this information include a flag indicating whether or not
conversion processing has been performed and, where a partial area
of the image has been converted, positional information and the
like on that partial area. For the flag indicating whether or not
conversion processing has been performed, one bit will be
sufficient for each of right-left symmetry conversion and up-down
symmetry conversion. In rotational conversion, if the number is to
be increased by 1 for every 90-degree rotation clockwise, two bits
will be sufficient for expressing a 360-degree rotation. The
positional information concerning the area in which conversion
processing has taken place includes such items as abscissas and
ordinates in the image, its width and height. Where conversion
processing is to be performed macro-block by macro-block, these
items of information can be stored in the part where the flag of
each macro-block is to be recorded in place of a slice header.
[0121] Regarding the flag indicating whether or not conversion
processing has been performed, flags for indicating such
information as conversion processing performed only on the
intra-coded prediction frame together with that, conversion
processing performed also on the inter-coded prediction frame, or
conversion processing performed in group-of-pictures (GOP) units
may also be stored. To add, an embodiment in which conversion is
processed on the inter-coded prediction frame will be described
afterwards. Further, where the intra-coded predicting method
provided by the third embodiment of the invention is to be applied,
a new mode in which composite pixels are used in the encoded stream
of the H.264/AVC standard is added. In this case, numerical values
representing the new mode are added to the information 1109 on the
conventional flags and the like, and stored. Regarding the form of
expressing the new mode may be the addition of bits indicating the
use of composite pixels or the allocation of numerical values where
mode prediction using composite pixels is performed.
[0122] FIG. 12 illustrates a packet in a fifth preferred embodiment
of the invention.
[0123] FIG. 12 shows, by way of example, the procedure of
generating from the data stream 1102 of FIG. 11 an IP packet to be
transmitted by the output I/F 106 of the image encoding device 101
to an IP network.
[0124] First, the data stream 1102 is divided into TCP segments
1201 to 1203 of a prescribed size, to which TOP headers 1204 to
1206 are respectively assigned. FIG. 12 shows an example in which
one segment is generated from one slice. In this case, the slice
header 1108 contained in each slice is also included in a segment.
As described with reference to FIG. 11, the information 1109 on the
flags and the like related to conversion processing is stored
inside the slice header 1108. Though description with reference to
FIG. 12 is dispensed with, segments are also generated similarly in
the slices 1107 onward.
[0125] Then, each segment is divided into IP packets of a
prescribed size, each with an IP header. For instance, the segment
1202 is divided into IP packets 1207 and 1208 of a prescribed size,
to which IP headers 1209 and 1210 are respectively assigned. Though
only the IP packets 1207 and 1208 generated from part of the
segment 1202 are shown here, IP packets are similarly generated
from the whole segment 1202 as well. Further, though description
with reference to FIG. 12 is dispensed with, other segments 1201
onward are similarly divided to generate IP packets.
[0126] The IP packets 1209 and so forth are generated by the output
I/F 106 of the image encoding device 101 for instance, and
transmitted to the output device 107 via the IP network (not
shown).
[0127] Also, the IP packets 1209 and so forth may as well be
transmitted from a packet transmitter device (not shown) which is
equipped with a storage device, wherein the data stream 1102 is
stored and an output interface for generating the IP packets 1209
and so forth from the data stream 1102 and transmitting them, but
has no image encoding function.
[0128] In the same way as illustrated in FIG. 12, the image
encoding device 101 or the packet transmitter device may as well
wireless packets from the data stream 1102, and transmit them to
the output device 107 via a wireless packet communication
network.
[0129] FIG. 13 is a block diagram of the functions of the image
encoding device 101, which is a sixth preferred embodiment of the
invention. This shows, regarding the image encoding device of the
first embodiment of the invention illustrated in FIG. 2, a case in
which conversion processing is also performed in inter-coded
prediction.
[0130] The image encoding device 101 comprises an original image
memory 201, an image converting module 202, an encoding module
1302, a mode control module 213 and a mode selector module 214. The
original image memory 201, the image converting module 202, the
mode control module 213 and the mode selector module 214 here are
the same as their respective counterparts in the image encoding
device of the first embodiment. A distinct feature of the image
encoding device of the sixth embodiment is that it has in the
encoding module 1302 an image conversion module 1301 for inversely
converting a predictive image controlled by the mode control module
213.
[0131] The conversion processing performed by the image conversion
module 1301, though similar to the processing done by the image
converting module 202, has as its object a reference frame. Thus,
the image conversion module 1301 executes, for instance, axial
symmetry conversion or point symmetry conversion of the reference
frame. The axial symmetry conversion means, for instance,
right-left symmetry conversion by which the reference frame is
inverted laterally or up-down symmetry conversion by which the
reference frame is inverted vertically. Point symmetry conversion
means, for instance, rotational conversion by which the reference
frame is rotated. The image converting module 1301 may combine
these modes of conversion.
[0132] To add, the image encoding device 101 of this embodiment is
provided with two image converting modules 202 and 1301 as shown in
FIG. 13. However, they may be physically a single image conversion
module. Thus, the image encoding device 101 may be provided with a
single image conversion module, which is enabled to serve as either
the image converting module 202 or the image conversion module 1301
by switching its input/output.
[0133] FIG. 14 illustrates the procedure of image encoding by the
sixth preferred embodiment of the invention. This shows, regarding
the image encoding procedure of the first embodiment of the
invention illustrated in FIG. 4, a case in which conversion
processing is also performed in inter-coded prediction.
[0134] This procedure differs from image encoding by the first
embodiment in that, before encoding the image having undergone
right-left symmetry conversion at step 403, the image conversion
module 1301 performs conversion of the reference image already at
step 1401 in accordance with information transmitted to the mode
control module 213 as to whether or not conversion processing has
been performed. The method of image conversion is the same as the
method of conversion at step 402, and the particulars of processing
are the same as those shown in FIG. 13.
[0135] In this way, the image converting modules 202 and 1301
perform conversion processing to code in the same direction the
frame to be encoded and stored into the original image memory 201
and the reference frame to be stored into the predictive image
memory 212. Processing including motion prediction in the
inter-coded prediction can be the same as in the conventional
system. In this embodiment as well, a case in which the whole image
is subjected to right-left symmetry conversion and a case in which
it is not are compared and what involves a smaller quantity of
codes for picture quality of about the same level is selected, data
of higher encoding efficiency can be used.
[0136] FIG. 15 is a block diagram of the functions of an image
decoding device 501, which is a seventh preferred embodiment of the
invention. This shows, regarding the image decoding device of the
second embodiment of the invention illustrated in FIG. 6, a case in
which conversion processing is also performed in inter-coded
prediction.
[0137] The image decoding device 501 comprises a stream analyzing
module 601, a mode decision module 602, a decoding module 1502, an
image converting module 610 and an decoded image memory 611. The
stream analyzing module 601, the mode decision module 602, the
image converting module 610 and the decoded image memory 611 are
the same as their respective counterparts in the image decoding
device of the second embodiment. A distinct feature of the image
decoding device of the seventh embodiment is that the decoding
module 1502 has within it an image conversion module 1501 for
inversely converting a predictive image (reference frame)
controlled by the mode decision module 602. Conversion processing
performed by the image conversion module 1501 is the same as that
by the image converting module 610 described above.
[0138] In the decoding of inter-coded prediction according to the
invention, when the mode decision module 602 detects an inversion
flag, the image converting module 610 and the image conversion
module 1501 within the decoding module are instructed to perform
conversion processing and, after the reference frame is processed
for inversion, the current frame is subjected to inter-coded
prediction and decoding, followed by the inversion of the finished
image and its outputting.
[0139] To add, the image decoding device 501 of this embodiment is
provided with two image converting modules 610 and 1501 as shown in
FIG. 15. However, they may be physically a single image conversion
module. Thus, the image decoding device 501 may be provided with a
single image conversion module, which is enabled to serve as either
the image converting module 610 or the image conversion module 1501
by switching its input/output.
[0140] FIG. 16 illustrates the procedure of image decoding by the
seventh preferred embodiment of the invention. This shows,
regarding the image decoding procedure of the second embodiment of
the invention illustrated in FIG. 7, a case in which conversion
processing is also performed in inter-coded prediction.
[0141] This procedure differs from image decoding by the second
embodiment in that, before decoding the image at step 702, the
reference frame is converted at step 1601. The method of image
conversion is the same as the method of conversion at step 703, and
the particulars of processing are the same as those shown in FIG.
15.
[0142] Thus, the sixth and seventh embodiments of the invention can
respectively provide an image encoding device capable of reducing
the quantities of codes after encoding (i.e. achieving a higher
rate of compression) by performing inter-coded prediction always in
the direction of higher accuracy of prediction without having to
alter the scanning direction, and an image decoding device matching
this encoding device. As a result, the quantity of codes can be
reduced by about 10% compared with conventional intra-coded
prediction.
[0143] To add, this invention is applicable to image encoding
devices, image decoding devices and the like conforming to not only
H.264/AVC but also various other standards.
[0144] This invention can be utilized in the recording and
transmission of image data, and contributes to reducing the
recording capacity requirement and enhancing the transmission speed
by improving the rate of compression and curtailing the quantity of
data. For instance, the invention can be used in video recorders
and video players using a hard disk or a DVD. The invention can
also be utilized in image distribution services using a wired or
wireless communication network, including cellular telephones and
television broadcasting. Furthermore, the invention can be used in
TV telephone and TV conference systems.
* * * * *