Direct encoding system of composite video signal using inter-frame motion compensation

Direct encoding of composite video signal which includes both luminance signal (Y) and chrominance signal (C) is carried out without separating luminance signal from chrominance signal. A motion of a block in a frame (8) which provides a motion vector (MV.sub.x, MV.sub.y), and a from a preceding frame is detected in a motion detector reference block is defined in said preceding frame which is locally decoded according to said motion vector. A block to be encoded in a current frame is converted through Hadamard conversion H (1). A composite motion compensation (7) provides a prediction block according to said reference block, which is subject to phase compensation of color sub-carrier, according to remainder of the value MV.sub.x +MV.sub.y when said value is divided by 4assuming that sampling frequency of video signal is four times as high as color sub-carrier frequency. The difference (9) of each element between output matrix of said Hadamard conversion (1) and matrix of said prediction block is quantized (2) and encloded (3). The encoded output is transmitted together with said motion vector. Thus, composite video signal is encoded directly signal, and excellent signal quality with high compression ratio is obtained.

BACKGROUND OF THE INVENTION 
The present invention relates to a direct encoding system for composite 
video signal, in particular, relates to such a system which uses Hadmard 
conversion and inter-frame motion compensation for high quality 
transmission of video signal. 
Conventionally, composite video signal including luminance signal and 
chrominance signal is converted to component video signal which has 
separated luminance signal and chrominance signal so that each component 
signals (luminance signal and chrominance signal) are separately 
compressed and reproduced. Then, those component signals are combined to 
composite signal in a reproducing side. 
FIG. 9 shows a block diagram of a conventional converter between composite 
video signal and component video signal. 
FIG. 9A shows the case that composite video signal is converted to 
component video signal. In FIG. 9A, the numeral 100 is an input terminal 
of composite video signal E.sub.M which includes both luminance signal 
E.sub.Y and chrominance signal. The numeral 102 is a hybrid circuit for 
separating luminance signal E.sub.Y and chrominance signals (E.sub.R-Y, 
E.sub.B-Y). The separated luminance signal E.sub.Y is output to the output 
terminal 120. The chrominance signals are applied to the modulators 104 
and 106 which modulates the chrominance signals with the sub-carrier 
signals cos(2 f.sub.sc +.phi.) and sin(2 f.sub.sc +.phi.) where f.sub.sc 
is color sub-carrier frequency and is equal to 3.58 MHz. The first 
chrominance signal (E.sub.R-Y) thus modulated is applied to the output 
terminal 122 through the low pass filter 108, the multiplier 112 which 
multiplies the constant b.sub.1 =2.28 and the 2:1 sub-sampling circuit 
116. Similarly, the second chrominance signal (E.sub.B-Y) is applied to 
the output terminal 124 through the low pass filter 110, the multiplier 
114 which multiplies the constant b.sub.2 =4.06 and the 2:1 sub-sampling 
circuit 118. 
FIG. 9B shows a converter from component video signal to composite video 
signal. The component signals E.sub.Y, E.sub.R-Y and E.sub.B-Y are applied 
to the input terminals 130, 132 and 134, respectively. The luminance 
signal E.sub.Y is applied to the adder 152. The chrominance signals are 
applied to the 1:2 up-sampling circuits 136 and 138, respectively. The 
first chrominance signal is applied to the demodulator 148 through the 
multiplier 140 which multiplies the constant a.sub.1 =1/1.14, and the low 
pass filter 144. The second chrominance signal is applied to the 
demodulator 150 through the multiplier 142 which multiplies the constant 
a.sub.2 =1/2.03 and the low pass filter 146. The demodulators 148 and 150 
which are supplied with the color sub-carrier signals cos(2 f.sub.sc 
+.phi.), and sin(2 f.sub.sc +.phi.), respectively, demodulate the 
chrominance signals, and provide the outputs to the adder 152, which 
provide the composite video signal E.sub.M to the output terminal 154. 
If composite video signal is directly encoded without converting it to 
component signals, a direct encoding system has the advantages that an 
encoding system is simple in structure, and no signal deterioration due to 
decrease of resolving power because of the use of filters, leakage between 
luminance signal and chrominance signal, and the round error in sampling 
process occurs. 
Therefore, a direct encoding system which encodes a composite video signal 
directly is preferable for high picture quality transmission. 
However, conventional information compression system takes inter-frame 
motion compensated DCT (discrete cosine transform) system which handles 
component signal with prediction encoding system because of high 
compression ratio. 
When a composite video signal is separated or converted to component video 
signal, some filters are used for separating luminance signal and 
chrominance signal, and therefore, deterioration of picture quality is 
unavoidable. 
Therefore, if we try to use component video signal, deterioration of 
picture quality because of composite to component conversion process is 
unavoidable. Further, although inter-frame encoding system is useful for 
high compression ratio, it is not useful for composite video signal, since 
composite video signal has chrominance signal modulated with sub-carrier 
signal multiplexed with luminance signal, and therefore, even if a 
composite video signal is encoded through inter-frame encoding system on 
time region axis, high compression ratio is not obtained because of phase 
error of sub-carrier signal. 
SUMMARY OF THE INVENTION 
It is an object, therefore, of the present invention to overcome the 
disadvantages and limitations of a prior video signal encoding system by 
providing a new and improved video signal encoding system. 
It is also an object of the present invention to provide a video signal 
encoding system which encodes directly composite video signal which 
includes both luminance signal and chrominance signal without separating 
those signals. 
The above objects are attained by a direct encoding system of composite 
video signal using inter-frame motion compensation comprising; an input 
terminal for receiving a block of input composite video signal which 
includes both luminance signal (Y) and chrominance signal (C) modulated 
with color sub-carrier signal, said block being a part of video frame, and 
having a plurality of pels; a first Hadamard converter coupled with said 
input terminal for effecting Hadamard conversion for each block in said 
input composite video signal; a subtractor for providing difference 
between each element of matrix of output of said first Hadamard converter 
and each related element of matrix of a prediction block; a quantizer for 
quantizing output of said subtractor; a first encoder for encoding output 
of said quantizer; an inverse quantizer coupled with output of said 
quantizer; an adder coupled with output of said inverse quantizer for 
providing sum of said output and said prediction block; a second Hadamard 
converter coupled with output of said adder for providing inverse Hadamard 
conversion; a frame memory coupled with output of said second Hadamard 
converter to store a frame of locally decoded video signal; a motion 
detector coupled with said input terminal through a luminance separation 
circuit, and output of said frame memory through a luminance separation 
circuit to provide motion vector (MV.sub.x, MV.sub.y) of each block 
between a current frame and a preceding frame; a composite motion 
compensator having at least a third Hadamard conversion unit, and a phase 
compensation circuit, coupled with output of said motion detector, and 
output of said frame memory, to determine a reference block in a preceding 
frame according to said motion vector (MV.sub.x, MV.sub.y), to carry out 
Hadamard conversion to said reference block, to effect phase compensation 
of color sub-carrier of said Hadamard converted reference block, so that 
the phase compensated reference block is applied to said subtractor as 
said prediction block; a second encoder for encoding said motion vector; a 
multiplexer for multiplexing outputs of said first encoder and said second 
encoder; and an output terminal coupled with output of said multiplexer to 
provide encoded video signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The basic concepts of the present invention have three steps. The first 
step may be carried out solely. The combination of the steps (1) and (2), 
and/or the combination of the steps (1), (2) and (3) may be carried out so 
that the further improved effect is obtained as compared with the case 
with only the step (1). 
The step (1) is to effect Hadamard conversion to composite video signal so 
that color sub-carrier component is packed to small number of coefficients 
or elements of the matrix of Hadamard converted signal, and differential 
quantization (DPCM) is carried out by using a reference block which is 
obtained through motion detection for each block between a current frame 
and a preceding frame. The step (2) is the phase compensation of color 
sub-carrier component according to sum of elements of motion vector. The 
step (3) is the motion compensation for a reference block with half pel 
spacing through interpolation for matrix of Hadamard converted block which 
is locally decoded so that high picture quality is obtained in spite of 
high compression ratio. 
The embodiment is assumed that composite video signal is NTSC composite 
signal, but it should be appreciated of course that the concepts of the 
present invention are applicable to other video standards. 
(1) Step (1) 
First, direct encoding using inter-frame compression through Hadamard 
conversion is described. 
FIG. 1 shows a block diagram of an encoder according to the present 
invention. In the figure, the numerals 1 and 5 are an Hadamard conversion 
unit, 2 is a quantizer, is a first encoder for encoding output of the 
quantizer 2, 3a is a second encoder for encoding elements of motion 
vector, 4 is an inverse quantizer, 6 is a frame memory having the capacity 
of one frame of picture, 7 is a composite motion compensation, 8 is a 
motion detector, 9 is a digital subtractor, 10 is a digital adder, 11a and 
11b are a separator of luminance signal, SW1 and SW2 are a switch, and 15 
is a multiplexer for multiplexing outputs of the first encoder 3 and the 
second encoder 3a. 
It is assumed that an input composite video signal is interlace signal, 
which is field-merged at the input portion so that a frame signal is input 
to the system. 
In the present invention, a frame is divided into a plurality of blocks, 
each of which has a plurality of pels. In a preferred embodiment, each 
block has 8.times.8 (=64) pels. So, a block is expressed by a vector or 
matrix X which has 8.times.8 (=64) elements X.sub.i,j (i,j=1-8). When a 
block has 8.times.8 pels, an Hadamard conversion unit is 8 order Hadamard 
conversion unit. The 8 order Hadamard matrix is expressed as follows. 
##STR1## 
The Hadamard conversion unit 1 carries out the Hadamard conversion to an 
input block and provides the Hadamard converted block Y as follows. 
EQU Y=H.times.X.times.H 
The converted block Y has also 8.times.8 elements Y.sub.i,j (i,j=1-8). 
All the blocks in a picture frame are carried out the above Hadamard 
conversion for each block. Therefore, an inter-frame DPCM loop is carried 
out for elements of Hadamard converted block signal. 
The quantizer 2 quantizes the difference between an output Y of the 
Hadamard conversion 1 and a prediction block P, and the inverse quantizer 
4 carries out the inverse quantization to provide reproduced picture 
signal, which is applied to the Hadamard conversion 5 through an adder 10 
which adds the prediction block P to the output of the inverse quantizer 4 
for inverse Hadamard conversion so that the video signal of time region is 
locally reproduced and is stored in the frame memory 6. 
The motion detector 8 takes luminance signal (intensity signal) of an 
output of the frame memory 6, which stores a preceding frame, through a 
luminance signal separator 11b, and a block of luminance signal from an 
input signal through a luminance signal separator 11a. The structure of 
the separators 11a and 11b are similar to the hybrid circuit 102 in FIG. 
9A. 
The motion detector 8 determines a motion vector (MV.sub.x,MV.sub.y) of the 
current block, through block matching operation between a current block 
and each block in a preceding frame. In other words, (see FIG. 2B), the 
block B.sub.11 in the current frame having 8.times.8 (=64) pels is 
considered that it moves from a reference block B.sub.01 in the preceding 
frame with the motion vector (MV.sub.x, MV.sub.y). 
The motion vector has precision with one pel spacing in horizontal 
direction, and two lines precision spacing in vertical direction 
considering interlace. 
FIG. 2A shows a block diagram of the composite motion compensation 7. In 
FIG. 2A, the numeral 11 is an Hadamard conversion, 12 is a phase 
compensator, 13 is an interpolator, and 14 is a prediction block decision 
unit. 
The composite motion compensation 7 takes a reference block from the frame 
memory 6, according to the motion vector. The reference block thus taken 
is applied to the Hadamard conversion unit 11. Preferably, a plurality of 
reference blocks (B.sub.01, B.sub.02, B.sub.03 et al) are taken for each 
current block, and a plurality of Hadamard conversion units 9 are provided 
for each reference blocks, for providing excellent picture quality. When a 
plurality of reference blocks are taken, those blocks are adjacent blocks 
with one another determined by the motion vector. Preferably, a number of 
reference blocks is nine (9), so that three continuous blocks in 
horizontal direction, and three continuous blocks in vertical direction 
are taken. 
Each of the Hadamard conversion units 11 effects the 8.times.8 Hadamard 
conversion for each reference block. 
The phase compensator 12 carries out the phase compensation of color 
sub-carrier in each block according to the motion vector, since color 
sub-carrier in each block may have phase error of 0.degree., 90.degree., 
180.degree. or 270.degree. between a current frame and a preceding frame, 
due to the fact that the sampling frequency of video signal is four times 
as high as the frequency of color sub-carrier. 
It should be noted that a plurality of phase compensators 12 are provided 
when a plurality of reference blocks are taken. 
After the phase compensation for color sub-carrier, the interpolator 13 
provides the interpolated blocks I.sub.m (m=1-15) so that an interpolated 
block has coordinates with fraction although a reference block read out of 
the frame memory has coordinates with integer. Preferably, the 
interpolator provides 15 interpolated blocks with fraction precision from 
9 reference blocks with integer precision. 
The prediction block decision unit 14 selects a prediction block P 
(P.sub.i,j, i,j=1-8) from said interpolated blocks I.sub.m (I.sub.m(i,j), 
i,j=1-8, m=1-15) so that the selected prediction block P has the minimum 
sum of absolute value of difference of Hadamard converted elements of the 
same coordinate between a candidate block I.sub.m (interpolated block) and 
a block Y (Y.sub.i,j, i,j=1-8) to be encoded. In other words, one of the 
interpolated blocks I.sub.m is selected as the prediction block so that 
the value of 
##EQU1## 
is the minimum for each value of m. 
The prediction block P thus selected is applied to the subtractor 9, which 
provides the difference (Y-P) of each element between a matrix of a block 
to be encoded and a matrix of a prediction block, for the purpose of DPCM 
(differential pulse code modulation). The prediction block is also applied 
to the adder 10 through switch SW2 when it is inter mode. 
Then, the sum of the absolute value of Hadamard converted elements Y 
(=Y.sub.i,j) of the output of the Hadamard converter 1, and the output 
(Y-P) of the subtractor 9 are compared, except for the DC component 
(Y.sub.1,1 and (Y-P).sub.1,1) on the Hadamard converted elements. When the 
former is the smaller, an intra mode is selected, and when the latter is 
the smaller, an inter mode is selected. The switches SW1 and SW2 in FIG. 1 
are switched whether it is intra mode or inter mode. 
Similarly, the succeeding blocks B.sub.12, B.sub.13 et al (see FIG. 2B) are 
encoded. 
(2) Step 2 
Next, phase compensation of color sub-carrier is described. 
Chrominance signal C in NTSC signal is expressed as follows. 
EQU C=(1/1.14)(E.sub.R -E.sub.Y)cos(W.sub.sc t)+(1/2.03)(E.sub.B 
-E.sub.y)sin(W.sub.sc t) (1) 
where W.sub.sc is angular frequency of color sub-carrier component. The 
equation (1) is converted as follows. 
##EQU2## 
Therefore, if the color video signal is sampled with the sampling frequency 
which is four times as high as the color sub-carrier frequency, the coded 
block S.sub.frame in a frame (which is field merged) is shown as follows. 
##STR2## 
where x.sub.ij =A.sub.ij cos(.phi..sub.ij +.THETA.), Y.sub.ij =A.sub.ij 
sin(.phi..sub.ij +.THETA.), .THETA. is constant, 
When it is assumed that the motion detection is carried out with one pel 
precision in horizontal direction, and two lines precision in vertical 
direction considering interlace, the phase error of color sub-carrier 
signal between a coded block and a reference block may be one of 
0.degree., 90.degree., 180.degree. and 270.degree. . That phase error 
occurs because of the sampling frequency which is four times as high as 
the color sub-carrier frequency. 
When the motion vector (MV.sub.x, MV.sub.y) is defined so that MV.sub.x is 
positive (+) in right direction, and MV.sub.y is positive (+) in downward 
direction, watching a preceding frame (reference frame) from a current 
frame (coded frame), the relations between the motion vector (MV.sub.x, 
MV.sub.y) and the phase error of color sub-carrier are shown in the 
expression (4) and FIG. 3, where n is an integer, depending upon a 
remainder (0, 1, 2 or 3) when MV.sub.x +MV.sub.y is divided by 4. In FIG. 
3, a number (0, 1, 2 or 3) in a circle shows the code of the phase error 
in the equation (4). 
##EQU3## 
Therefore, if we shift the phase of color sub-carrier on S.sub.frame by 
0.degree., 90.degree., 180.degree. or 270.degree. the following equation 
(5) is obtained. 
##EQU4## 
S.sub.frame (90.degree.), S.sub.frame (180.degree.) and S.sub.frame 
(270.degree.) relate to the cases that S.sub.frame (0.degree.) shifts by 1 
pel length, 2 pels length, and 3 pels length, respectively, in horizontal 
direction. 
It is assumed in chrominance signal that the correlation between pels is 
strong, and two adjacent pels in horizontal direction are the same as each 
other, so that the following equation is satisfied. 
##EQU5## 
Accordingly, the following equation (7) and the table 1 are obtained. 
##EQU6## 
The Hadamard conversion in horizontal direction is carried out by 
multiplying 8.times.8 Hadamard matrix H to S.sub.frame from right, where 
it is assumed that the matrix H is arranged in sequence. The Hadamard 
conversion of multiplying H only from right is enough in considering phase 
error, although the Hadamard conversion in the converters 1 and 5 are 
carried out in both directions, since phase error occurs only in 
horizontal direction. 
Table 1 shows the conversion result showing for each line vector for four 
kinds of S.sub.frame. It should be appreciated in table 1 that S.sub.frame 
(90.degree.)H, S.sub.frame (180.degree.)H and S.sub.frame (270.degree.)H 
may become equal to S.sub.frame(0.degree.)H by exchanging lines, and/or 
inversing polarity, so that the phase error of color sub-carrier is 
compensated, and the correlation between frames for chrominance signal is 
improved. 
FIG. 4 shows shematically the phase compensation shown in the table 1. 
In the table 1 and FIG. 4, when MV.sub.x MV.sub.y =4n+3 (the remainder is 4 
when MV.sub.x +MV.sub.y is divided by 4, and the phase error is 
90.degree.), the phase error is compensated to 0.degree. by inserting the 
line 8 into the line 1 with the sign conversion, inserting the line 7 into 
the line 1 with the sign conversion, inserting the line 6 into the line 3 
with the sign conversion, inserting the line 5 into the line 4 with the 
sign conversion, inserting the line 4 into the line 5 with no sign 
conversion, inserting the line 3 into the line 6 with no sign conversion, 
inserting the line 2 into the line 7 with no sign conversion, and 
inserting the line 1 into the line 8 with no sign conversion. 
When the phase error is 0.degree., no exchange nor sign conversion is 
necessary. 
when the phase error is 180.degree.,it is compensated to the phase error 
0.degree. by converting the sign. 
When the phase error is 270.degree., it is compensated to the phase error 
90.degree. by inverting the sign, and the phase error 90.degree. is 
compensated to the phase error 0.degree. as mentioned above. 
As mentioned above, some elements or coefficients of the result of the 
Hadamard conversion of a reference block are exchanged and/or the polarity 
or the sign is inversed between the lines of the Hadamard converted 
matrix, so that the phase error of color sub-carrier which is specific to 
composite video signal is compensated between a coded block and a 
reference block. Therefore, the four patterns of the phase error of the 
color sub-carrier are changed only to one pattern, and the information 
compression ratio is improved. 
TABLE 1 
______________________________________ 
Horizontal elements of each line for each phase error 
of color sub-carrier 
Matrix line element 
______________________________________ 
S.sub.frame (0.degree.) H 
1 X.sub.1 +Y.sub.1 -X.sub.3 -Y.sub.3 +X.sub.5 +Y.sub.5 
-X.sub.7 -Y.sub.7 
2 X.sub.1 +Y.sub.1 -X.sub.3 -Y.sub.3 -X.sub.5 -Y.sub.5 
+X.sub.7 +Y.sub.7 
3 X.sub.1 +Y.sub.1 +X.sub.3 +Y.sub.3 -X.sub.5 -Y.sub.5 
-X.sub.7 -Y.sub.7 
4 X.sub.1 +Y.sub.1 +X.sub.3 +Y.sub.3 +X.sub.5 +Y.sub.5 
+X.sub.7 +Y.sub.7 
5 X.sub.1 -Y.sub.1 +X.sub.3 -Y.sub.3 +X.sub.5 -Y.sub.5 
+X.sub.7 -Y.sub.7 
6 X.sub.1 -Y.sub.1 +X.sub.3 -Y.sub.3 -X.sub.5 +Y.sub.5 
+X.sub.7 -Y.sub.7 
7 X.sub.1 -Y.sub.1 -X.sub.3 +Y.sub.3 -X.sub.5 +Y.sub. 5 
+X.sub.7 -Y.sub.7 
8 X.sub.1 -Y.sub.1 -X.sub.3 +Y.sub.3 +X.sub.5 -Y.sub.5 
-X.sub.7 +Y.sub.7 
S.sub.frame (90.degree.) H 
1 -Y.sub.1 +X.sub.1 +Y.sub.3 -X.sub.3 -Y.sub.5 +X.sub.5 
-Y.sub.7 -X.sub.7 
2 -Y.sub.1 +X.sub.1 -Y.sub.3 -X.sub.3 +Y.sub.5 -X.sub.5 
-Y.sub.8 +X.sub.7 
3 -Y.sub.1 +X.sub.1 -Y.sub.3 +X.sub.3 +Y.sub.5 -X.sub.5 
+Y.sub.7 -X.sub.7 
4 -Y.sub.1 +X.sub.1 -Y.sub.3 +X.sub.3 -Y.sub.5 +X.sub.5 
-Y.sub.7 +X.sub.7 
5 -Y.sub.1 -X.sub.1 -Y.sub.3 -X.sub.3 -Y.sub.5 -X.sub.5 
-Y.sub.7 -X.sub.7 
6 -Y.sub.1 -X.sub.1 -Y.sub.3 -X.sub.3 +Y.sub.5 +X.sub.5 
+Y.sub.7 +X.sub.7 
7 -Y.sub.1 -X.sub. 1 +Y.sub.3 +X.sub.3 +Y.sub.5 +X.sub.5 
-Y.sub.7 -X.sub.7 
8 -Y.sub.1 -X.sub.1 +Y.sub.3 +X.sub.3 -Y.sub.5 -X.sub.5 
+Y.sub.7 +X.sub.7 
S.sub.frame (180.degree.) H 
-S.sub.frame (0.degree.) H 
S.sub.frame (270.degree.) H 
-S.sub.frame (90.degree.) H 
______________________________________ 
(3) Step 3 
Next, the motion compensation with fraction precision is described. 
The motion compensation with integer precision is improved by interpolation 
to fraction precision so that interpolated pels are generated by using 
pels in a reference block and adjacent pels. 
In the present invention, an interpolation is carried out for generating a 
plurality of interpolated blocks with fraction precision by using original 
blocks with integer precision after the phase compensation of color 
sub-carrier on Hadamard conversion matrix region is carried out. The 
interpolation is carried out for each element of Hadamard converted 
matrix. 
Assuming that X is a matrix on time region, Y=HXH is a matrix on Hadamard 
conversion region, the following equation is obtained. 
##EQU7## 
where p, q=1/2 or 1/4 or a or b 
FIG. 5 shows an interpolation with half pel length and half line precision 
based upon a motion vector with integer precision. It is assumed in FIG. 5 
that length between two adjacent pels in horizontal direction is the same 
as length between two adjacent lines in vertical direction. 
In FIG. 5, the symbols A1 through A9 show reference position of blocks with 
integer precision obtained by using a motion vector. The A5 shows the 
block obtained by the motion vector, and A1 through A4, and A6 through A8 
are the blocks adjacent the block A5. 
The symbols B1 through B15 show reference position of blocks with fracion 
integer obtained through interpolation. 
The value at a pel in the block B1 is interpolated by using the values at 
the pels A1, A2, A4 and A5 with the weight of 1/4 each. The value at a pel 
in the block B2 is interpolated by using the values at the pels A2 and A5 
with the weight of 1/2 each. The value at a pel in the block B3 is 
interpolated by using the values at the pels A2, A3, A5 and A6 with the 
weight of 1/4 each. The value at a pel in the block B7 is interpolated by 
using the values at the pels A4 and A5 with the weight of 1/2 each. The 
value at a pel in the block B13 is interpolated by using the values at the 
pels A4, A5, A7 and A8 with the weight a for A4 and A5, and the weight b 
for A7 and A8, where a and b are shown in FIG. 5. The value of a pel in 
the block B11 is interpolated by using the values at the pels A5 and A8 
with the weight 3/4 for A5 and 1/4 for A8. The value at B8 is the same as 
the value at A5. 
Thus, 15 interpolated reference blocks with fraction precision are obtained 
by using 9 blocks with interger precision. Those interpolated reference 
blocks are output by the interpolator 13 (FIG. 2) to the prediction block 
decision circuit 14. 
The prediction block decision circuit 14 selects one of the 15 interpolated 
reference blocks as a prediction block so that the sum of the absolute 
value of the difference of an element between each reference block and a 
block to be encoded is the minimum. The selected reference block is 
forwarded to the subtractor 9, and the adder 10 through the switch SW2 as 
a prediction block. 
As mentioned above, the compression ratio in the encoding is improved by 
using a prediction reference block with fraction precision obtained 
through interpolation for the coefficients of Hadamard converted matrix 
between candidate blocks obtained by using a motion vector. 
Said interpolation is carried out after said step (2) for phase error 
compensation. 
(4) The experimental test result of the present invention is described 
below. 
First, the effect for the steps (1), (2) and (3) is shown, and then, the 
effect of the present invention carrying out all the steps (1), (2) and 
(3) is shown, with the conventional motion compensation DCT system for 
NTSC composit video signal. 
The parameters for the test are shown in table 2. 
TABLE 2 
__________________________________________________________________________ 
Experimental parameters 
__________________________________________________________________________ 
Test data 
Flower garden, Mobile and calendar 
converted from digital component VTR to 
digital composite VTR by using a commercial 
digital data converter 
Range of horizontal; .+-.15 pel, vertical; .+-.14 lines 
motion detection 
(1 pel and 2 lines precision) 
(Motion 465 (=(15.times.2+1).times.(7.times.2+1)) vectors, full search 
Estimation ME) 
(all the 465 vectors are searched for 
finding the best vector having the minimum 
prediction error) 
Unit of ME 
16 pel .times. 16 line (macro block) 
Quantization 
linear quantization with fixed step size for 
all the elements of matrix 
Variable conversion coefficient; 2 dimensional 
runlength 
length code 
motion vector;B2 code, 
X;1/2 pel precision 
Y;1/2 line precision 
Refresh 15 frames interval 
__________________________________________________________________________ 
FIG. 4 shows the general solution of phase compensation when frequency band 
of chrominance signal is not restricted. However, since frequency band of 
chrominance signal of a real image is usually restricted, the power of 
chrominance signal is concentrated to a small number of coefficients of 
Hadamard conversion. 
FIG. 6 shows the ratio R=20log(C/Y), where Y is luminance signal separated 
from composite video signal, and C is chrominance signal separated from 
composite video signal, where a test pattern is CCIR standard test pattern 
(flower garden, and mobile and calendar). When the value R is large, the 
chrominance signal is significant. The eight coefficients (shaded 
coefficients in FIG. 6) which are not negative in both the patterns are 
taken as an object for phase compensation of chrominance signal. So, it 
should be appreciated that phase compensation for only a part of elements 
of matrix is enough. 
FIG. 7 shows the scanning sequence in Hadamard coefficients, considering 
composite signal. 
FIG. 8 shows curves of the result of SN(S=255.times.0.7) versus bit-rate in 
the simulation with the parameters of table 2. In those curves, (a) shows 
the case that only intra Hadamard conversion is carried out, (b) shows the 
case that only the step (1) is carried out so that inter-frame difference 
on Hadamard conversion is taken, (c) shows the case that the steps (1) and 
(2) are carried out, and (d) shows the case that all the steps (1), (2) 
and (3) are carried out. 
As shown in those curves, as compared with curve (a) for simple intra frame 
Hadamard conversion, it is improved by using the step (1) curve (b) by 1-2 
dB for the test pattern Mobile and Calendar, and by 2-5 dB for the test 
pattern Flower Garden, in particular, is should be noted that it is much 
improved for high bit rate. 
When the steps (1) and (2) are carried out in the curve (c), it is further 
improved by 0.5-1.0 dB for Mobile and Calendar, and the 1-2 dB for Flower 
Garden. 
When the steps (1), (2) and (3) are carried out, it is further improved by 
approximate 2 db for both the test patterns. 
Therefore, the improvement when all the steps (1), (2) and (3) are carried 
out is 3-5 dB for Mobile and Calendar, and 5-9 dB for Flower Garden as 
compared with a simple intra frame system (curve (a)). In other words, the 
bit rate may be half for providing the same S/N ratio. 
Next, the present invention is compared with conventional motion 
compensation DCT (discrete cosine transform) system. It is assumed that 
the parameters for conventional motion compensation DCT system (range of 
motion detection, unit, refresh, et al) are the same as those in table 2. 
It is also assumed that the quantization step size is the same for both 
luminance signal and chrominance signal, irrespective of coefficients, and 
the scanning sequence of DCT coefficients is shown in FIG. 7 for both 
luminance signal and chrominance signal. The conversion from composite 
signal to component signal in conventional system is shown in FIG. 9, and 
the parameters of the filters for the conversion in FIG. 9 are shown 
below. 
##EQU8## 
FIG. 10 shows the test result, where (A) shows the result for the test 
pattern Flower Garden, and (B) shows the result for the test pattern 
Mobile and calendar. In those figures, the curve (a) shows the case of 
conventional system (component signal), and the curve (b) shows the case 
of the present invention (steps (1), (2) and (3)). 
As shown in those figures, according to the present invention, the slope of 
the velocity-distortion curve is almost constant in the range shown in the 
figure (SNR=20-40 dB), and no saturation is observed. However, in the 
conventional system, the curves are tend to saturate less than 40 dB. 
The value of SNR according to the present invention is improved by 2-3 dB 
in low bit rate lower than 10 Mbps, and even 5-10 dB in high bit rate 
higher than 20 Mbps, as compared with that of the conventional system. The 
main reason of the improvement by the present invention is that no 
conversion between composite signal and component signal is used. 
As described above in detail, the present invention provides the direct 
encoding system for composite video signal by using Hadamard conversion, 
without separating luminance signal and chrominance signal. 
From the foregoing it will now be apparent that a new and improved direct 
encoding system for composite video signal has been found. It should be 
understood of course that the embodiments disclosed are merely 
illustrative and are not intended to limit the scope of the invention. 
Reference should be made to the appended claims, therefore, rather than 
the specification as indicating the scope of the invention.