Low-delay encoding methods of moving pictures

A method and apparatus for low-delay-encoding digital video data for moving pictures. For removing artifacts appearing on a screen, where there is a large amount of motion in a vertical direction, a modified intra-slice method is used. Similarly, for removing artifacts appearing on a screen, where there is a large amount of motion in a horizontal direction, a modified intra-column method is used. For both the modified intra-slice method and the modified intra-column method, first and second rows of hatched rectangles, called intra-segments, are used to determine where in a given frame intra-frame-encoding is to be performed. Regions outside of these intra-segments are inter-frame encoded. However, while the intra-segments are disposed in a horizontal direction for the intra-slice method, they are disposed in a vertical direction for the intra-column method. Both of these methods can be performed simultaneously, as well.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a moving pictures encoding technology, and 
particularly to a low-delay encoding method capable of reducing a time 
delay generated in encoding and decoding operations into a boundary needed 
in an actual application. 
2. Description of Related Art 
Recently, systems such as a high-definition television (HD-TV), a high 
definition video cassette recorder (HD-VCR), a digital camcorder, a 
multimedia videophone, a video conference unit, chiefly use a method for 
digitally encoding and decoding moving pictures and associated audio. The 
MPEG (Moving Pictures Experts Group) for international standardization of 
the encoded representation of moving pictures and associated audio, 
classifies patterns of the pictures into an intra-coded (I) picture, a 
predictive-coded (P) picture and a bidirectionally predictive-coded (B) 
picture according to three different encoding methods, and proposes a COP 
(Group of Pictures) layer for encoding video data having a picture 
sequence of "IBBPBBPBBI . . . ." The schemes for encoding and decoding the 
video data using the GOP structure proposed by the MPEG is described in 
"ISO/IEC 13818-2." A special playback function such as random access 
function can be accomplished with respect to the video data encoded using 
the GOP structure in the decoding end. However, since the decoding end 
cannot perform a normal decoding operation with respect to the GOP until 
all the video data of one GOP has been received, of a decoding delay 
phenomenon occurs. Such a decoding delay phenomonen occurs when the 
decoding end starts to decode a video bitstream which is newly applied due 
to a channel change, power-on or reset operation. 
To reduce a decoding delay time due to the above-described GOP structure, a 
low-delay encoding technology for encoding video data having a picture 
sequence of "IPPP . . . " is being researched and developed. Since the 
structure of "IPPP . . . " does not adopt a concept of the GOP, the random 
access function is not possible. However, there are merits that a decoding 
delay time is shorter than that of the GOP structure and complexity of 
hardware is reduced, because of absence of the B-picture. The low-delay 
encoding method in intra-codes only a portion of the data in each frame, 
unlike the GOP structure which adopts a forced intra-frame encoding method 
with respect to a total of one picture. There are an intra-slice method 
and an intra -column method as encoding methods used in a low-delay 
encoding technology. The intra-slice method intra-codes a predetermined 
number of slices or one slice per picture from the uppermost end to the 
lowermost end with respect to all P-pictures. FIGS. 1A and 1B show 
movement of the slice intra-coded by the intra-slice method. On the other 
hand, the intra-column method intra-codes a column composed of a unit of a 
predetermined number of bits per picture from the leftmost end to the 
rightmost end with respect to all P-pictures. FIGS, 2A and 2B show 
movement of the column intra-coded by the intra-column method. 
However, it is know that the intra-slice method is not proper in case of a 
large amount of vertical movement, and intra-column method is not proper 
in case of a large amount of horizontal movement. Thus, using only one 
method cannot completely reconstruct the picture. Problems will be 
described below, which occur when the video data encoded by the 
intra-column is applied to a receiver. If a channel change or power-on 
operation is performed, a decoder in the receiver stores video data in the 
intra-coded image region and video data in an intra-coded image region as 
a reference frame picture, and performs motion compensation to restore the 
picture of the current frame. In this case, however, the reference frame 
data used for the motion compensation to restore the current frame picture 
includes the predictive-coded P-picture data. Accordingly, in case of a 
large amount of the horizontal movement, artifacts are not completely 
removed from the restored picture even after the intra-coded columns 
corresponding to one entire screen have been inputted. Such a problem 
occurs in the same manner when the data encoded by he intra-slice method 
is restored and in case of a large amount of motion in the vertical 
direction, as well. 
SUMMARY OF THE INVENTION 
Therefore, to solve the above problems, it is an object of the present 
invention to provide a method of removing artifacts effectively even in 
case of a large amount of motion in the vertical direction, by improving a 
low-delay encoding method which uses a existing intra-slice. 
Another object of the present invention is to provide a method for 
effectively removing artifacts even in case of a large amount of motion in 
the horizontal direction, by improving a low-delay encoding method which 
uses an existing intra-column. 
Still another object of the present invention is to provide a method of 
effectively removing artifacts by combining the improved intra-slice 
encoding method and the improved intra-column encoding method. 
To accomplish the above object of the present invention, there is provided 
a method of low-delay-encoding digital video data for moving pictures, the 
method comprising the steps of: 
a) determining a first row position of first in intra-segments in an image 
frame and a second row position of second intra-segments therein, with 
respect to odd-numbered first intra-segments and even-numbered second 
intra-segments having a respectively predetermined size which are 
interposed between each other when the first and second intra-segments are 
disposed in the row direction on a screen and are placed in the same row 
axis; 
b) intra-frame-encoding video data contained in the first and second 
intra-segments among the video data in the image frame, and 
intra-frame-encoding video data which exits outside of the first and 
second intra-segments; and 
c) re-determining row positions of the first and second intra-segments with 
respect to the image frame to be used for encoding, by shifting the first 
row position of the first intra-segments from the upper end of the scree 
the lower end thereof by a predetermined interval, and the second row 
position of the second intra-segments from the lower end of the screen to 
the upper end thereof by the predetermined interval, whenever the image 
frame is changed. 
To accomplish the other object of the present invention, there is provided 
a method low-delay-encoding digital video data for motion images, the 
method comprising the steps of: 
a) determining a first column position of first intra-segments in an image 
frame and a second column position of second intra-segments therein, with 
respect to odd-numbered first intra-segments and even-numbered second 
intra-segments having a respectively predetermined size which are 
interposed between each other when the first and second intra-segments are 
disposed in the column direction on a screen and are placed in the same 
column axis; 
b) intra-frame-encoding video data contained in the first and second 
intra-segments among the video data in the image frame, and 
inter-frame-encoding video data which exists outside of the first and 
second intra-segments; and 
c) re-determining column position of the first and second intra-segments 
with respect to the image frame to be used for encoding, by shifting the 
first column position the first intra-segments from the end of the screen 
to the right end thereof by a predetermined interval, and the second 
column position of the second intra-segments from the right end of the 
screen to the left end thereof by the predetermined interval, whenever the 
image frame is changed. 
To accomplish the above still another object of the present invention, 
there is provided a method of low-delay-encoding digital video data for 
motion images, the method comprising the steps of: 
a) determining a first row position of first intra-segments in an image 
frame and a second row position of second intra-segments therein, with 
respect to odd-numbered first intra-segments and even-numbered second 
intra-segments having a respectively predetermined size which are 
interposed between each other when the first and second intra-segments are 
disposed in the row direction on a screen and are placed in the same row 
axis; 
b) determining a first column position of third intra-segments in the image 
frame and at second column position of fourth intra-segments therein, with 
respect to odd-numbered third intra-segments and even-numbered fourth 
intra-segments having a respectively predetermined size which are 
interposed between each other when the third and fourth intra-segments are 
disposed in the column direction of the screen and are placed in the same 
column axis; 
c) intra-frame-encoding video data contained in the first through fourth 
intra-segments among fine video data in the image frame, and 
inter-frame-encoding video data which exists outside of time first through 
fourth intra-segments; and 
d) re-determining first and second row positions and first and second 
column positions of the first through fourth intra-segments with respect 
to the image frame to be used for encoding, by shifting the first row 
position of the first intra-segments from the upper end of the screen to 
the lower end thereof by a predetermined interval, the second row position 
of the second intra-segments from the lower end of the screen to the upper 
end thereof by the predetermined interval, the first column position of 
the third intra-segments from the left end of the screen to the right end 
thereof by the predetermined interval, and the second column position of 
the fourth intra-segments from the right end of the screen to the left end 
thereof by the predetermined interval, whenever the image frame is changed 
.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Preferred embodiments of the present intention will be described below in 
more detail with reference to the accompanying FIGS. 3 through 6B. 
FIG. 3 is a block diagram showing a moving pictures encoding apparatus 
which operates according to one of the improved low-delay encoding methods 
of the present invention. The FIG. 3 apparatus encodes video data whose 
order is determined in units of a block having a predetermined size, which 
has the same structure as the motion image encoding apparatus proposed by 
the MPEG, except for a refresher portion 12. In other words, low-delay 
encoding methods according to the present invention are embodied on the 
basis of an on- or off-operation of switches 13 and 14 by refresher 
portion 12. 
A low-delay encoding method using a modified intra-slice concept among the 
encoding methods according to the present invention will be described 
below with reference to FIGS. 4A and 4B. 
In FIGS. 4A and 4B, intra-segments represented in the form of hatched 
rectangles includes odd-numbered first intra-segments and even-numbered 
second intra-segments respectively placed along the horizontal axis. 
Whenever an image frame is changed, the first intra-segments are shifted 
to the lower direction of the image frame by a predetermined interval, and 
the second intra-segments are shifted to the upper direction of the image 
frame by a predetermined interval. Here, the shift intervals of the first 
and second intra-segments are the same as the number of pixels the 
vertical direction of the intra-segments. The shifting of the first and 
second intra-segments is shown in FIG. 4A, showing an ith image frame, and 
in FIG. 4B, showing an (i+1)th image frame. When the first and second 
intra-segments are placed in the same horizontal axis by the shift of 
position, the first and second intra-segments are interposed therebetween 
and become the same pattern as that of the existing intra-slices. When the 
first intra-segments are placed in the uppermost end of the image frame, 
the second intra-segments are placed in the lowermost end of the image 
frame. When refresher portion 12 uses the first and second intra-segments 
to encode the video data of the image frame, artifacts appearing in a 
screen can be effectively removed even in case of a large amount of motion 
in the vertical direction. 
Another low-delay encoding method using a modified intra-column concept 
among the encoding methods according to the present invention will be 
described below with reference to FIGS. 5A and 5B. 
In FIGS. 5A and 5B, intra-segments represented in the form of hatched 
rectangles include odd-numbered third intra-segments and even-numbered 
fourth intra-segments respectively placed along the vertical axis. 
Whenever an image frame is changed, the third intra-segments are shifted 
to the right of the image frame by a predetermined interval, and the 
fourth intra-segments are shifted to the left of the image frame by a 
predetermined interval. Here, the shift intervals of the third and fourth 
intra-segments are the same as the number in pixels of the horizontal 
direction of the intra-segments. The shifting of the third and fourth 
intra-segments is shown in FIG. 5A, showing an ith image frame, and in 
FIG. 5B, showing an (i+1)th image frame, When the third and fourth 
intra-segments are placed in the same vertical axis by the shift of the 
position, the third and fourth intra-segments are interposed therebetween 
and become the same pattern as that of the existing intra-column. When the 
third intra-segments are placed in the leftmost end of the image frame, the 
fourth intra-segments are placed in the rightmost end of the image frame. 
When refresher portion 12 uses the third and fourth intra-segments to 
encode the video data of the image frame, artifacts appearing on the 
screen can be effectively removed even in case of a large amount of motion 
in the horizontal direction. 
In FIGS. 6A and 6B showing still another low-delay encoding method 
according to the present invention, first through fourth intra-segments 
are all used. Thus, the first and second intra-segments shown in FIGS. 6A 
and 6B are shifted according to the method described referring to FIGS. 4A 
and 4B and the third and fourth intra-segments shown in FIGS. 6A and 6B are 
shifted according to the method described referring to FIGS. 5A and 5B. The 
low-delay encoding method described in connection with FIGS. 6A and 6B can 
effectively remove artifacts appearing on the screen even in case of a 
large amount of motion with respect to both the horizontal and vertical 
directions. 
When the number of the pixels with respect to a picture according to the 
CCIR (International Radio Consultative Committee) is 720 (horizontal 22 
pixels).times.480 (vertical pixels), with each of the first through fourth 
intra-segments comprising 48.times.32 pixels, respectively. Each 
intra-segment includes six macroblocks with each macroblock composed of 
16.times.16 pixels as shown in FIGS. 4A through 6B. This intra-segment 
size can refresh an overall screen in a period of fifteen image frames. 
Also, in the case of the video signal of which the thirty frames per 
second are transmitted, each intra-segment becomes placed in the same 
position twice every second. Although the size of each of the first 
through fourth intra-segments can be randomly determined by the system to 
be adapted thereto, it is desirable to choose a size will allow the 
overall screen to be refreshed at least several times per a second. 
The operation of the FIG. 3 apparatus will be described according to one 
among the above-described low-delay encoding methods. 
When the FIG. 3 apparatus performs an inter-frame encoding operation, that 
is, if video data is applied to a subtractor from an external video data 
source (not shown) outside of the above-described intra-segments, 
refresher portion 12 turns on first and second switches 13 and 14. 
Subtractor 1 subtracts data supplied from a motion compensator 11 from the 
input data, and outputs the differential data resulting from the 
subtraction to a transformer 2. Transformer 2 transforms this differential 
data of a spatial domain into transformation coefficients of a frequency 
domain. The transformation coefficients are input to a quantizer 3 which 
quantizes the transformation coefficients according to quantization level 
signal Q fedback from a buffer 5. The data output from quantizer 3 is 
processed by a variable-length coder 4 and then stored in buffer 5. Buffer 
5 generates quantization level signal Q for transmitting the input data at 
a constant transmission rate. Quantization level signal Q is applied to 
quantizer 3, and is used for preventing buffer 5 from overflowing or 
underflowing. The data output from quantizer 3 and the quantization level 
signal Q output from buffer 5 are also applied to an inverse quantizer 6. 
Inverse quandtizer 6 inversely quantizes the input data. The data output 
from inverse quantizer 6 is transformed into data of a spatial domain by 
an inverse transformer 7. An adder 8 adds the differential data supplied 
from motion compensator 11 to the data supplied from inverse transformer 
7, and outputs the added result to a frame memory 9. Frame memory 9 stores 
the data output from adder 8 in units of a frame and reconstructs the 
image. A motion estimator 10 uses the video data supplied from the 
external video data source and the data stored in frame memory 9 and 
performs a well-known motion estimation operation, with a result that a 
motion vector is outputs to motion compensator 11. Motion compensator 11 
outputs the data in frame memory 9 and designated by the motion vector to 
subtractor 1. 
On the other hand, the FIG. 3 apparatus also performs an intra-frame 
encoding operation, if the video data applied to subtractor 1 from the 
external video data source exists will in the above-described 
intra-segments, refresher 12 turns off first and second switches 13 and 
14. In this case, adder 8 outputs the intra-frame-encoded data output from 
inverse transformer 7 to frame memory 9. 
On the other hand, when the FIG. 3 apparatus performs a low-delay encoding 
operation relating to FIGS. 6A and 6B, a first intra-segment can be 
overlapped with a third intra-segment as can be seen from FIGS. 6B ("A" of 
FIG. 6B). Even in such a case, since one overlapped intra-segment is 
obtained by overlapping a first intra-segment with a third intra-segment, 
refresher 12 turns off switch 13 and 14 with respect to the video data 
contained in the overlapped intra-segment in order to perform intra-frame 
encoding therein. 
As described above, the low-delay encoding methods for encoding moving 
pictures according present invention can remarkably improve problems that 
the artifacts show up on the screen by a conventional low-delay encoding 
method using an intra-slice concept or an intra-column concept, when there 
is a large amount of motion between moving pictures in a horizontal 
direction or a vertical direction. 
While only certain embodiments of the invention have been specifically 
described herein, it will apparent that numerous modifications may be made 
thereto without departing from the spirit and scope of the invention.