Motion vector detecting method and system for motion compensating predictive coder

In a method of detecting motion vector data indicative of motion of a partial area in an input picture from any area on a reference picture, a first distortion between a partial area constructed by fields of the input picture and a partial area constructed by fields of the reference picture is calculated as a first evaluation value; a position of the partial area constructed by the fields of the reference picture at which the first evaluation value becomes the minimum value is detected; a search window on a frame of the reference picture is set on the basis of a detected position of the partial area constructed by the fields of the reference picture previously detected; and a second distortion between a partial area constructed by a frame in the set search window and a partial area constructed by a frame of the input picture is calculated as a second evaluation value, and a position of the partial area constructed by the frame of the reference picture at which the second evaluation value becomes the minimum value is detected. Therefore, the frame vectors can be detected on the basis of the field vector detection positions, so that the amount of calculations required to retrieve frame vectors can be reduced markedly, without degrading the detection precision of the frame vectors.

BACKGROUND OF THE INVENTION 
The present invention relates to a coder of moving picture signals used for 
recording, communications, transmissions, broadcasting, etc., and in 
particular to a motion vector detecting method and a motion vector 
detecting system for motion compensating predictive coders which can code 
differences between motion vector data (representative of an area from 
which motion vectors move on a coded picture) and areas indicated by the 
motion vector data. 
In video signals of multi-gradation such as television (TV) or photograph, 
since the quantity of video data is huge, when the digital video signals 
are processed (e.g., transmitted, recorded, etc.) in an unencoded format, 
a transmission path of wide frequency band and a recording medium of large 
capacity are inevitably required. Therefore in a video signal processing 
apparatus handling TV (visual) telephone, TV (visual) conference, cable 
television service (CATV), picture filing apparatus, etc., a coding 
technique for compressing the huge video signals down to a small quantity 
of data is required. As one of the moving picture coding methods, steps 
are performed as follows: a highest correlation area relative to a partial 
area of an input picture is detected on a coded reference picture; motion 
vector data indicative of from which area the partial area of the input 
picture moved on the coded reference picture is determined; and a 
difference between the partial area of the input picture and the detected 
partial area indicated by the motion vector data is coded. 
On the other hand, as a scanning method for pictures, there exist methods 
of non-interlaced scanning (scanned one by one in sequence) and interlaced 
scanning (scanned every other line or alternately). An imperfect picture 
obtained by interlaced scanning (ore line is omitted between scanning 
lines) is referred to as a field, and a perfect picture obtained by one 
non-interlaced scanning or two interlace scannings is referred to as a 
frame. 
In the case where no motion exists between two fields of the same frame, as 
with the case of the interlaced scanning picture, it is often effective to 
adopt the motion compensating predictive method using motion vector data 
detected on the basis of frame construction. 
In contrast with this, in the case of the interlaced scanning picture, 
since some motion exists between the two fields in the same frame, it is 
often effective to adopt the motion compensating predictive method using 
motion vector data detected on the basis of the field construction. 
Therefore, in the conventional method, in order to cope with both the cases 
where motion exists between two fields of the same frame and where no 
motion exists, the motion vector has been so far detected separately for 
both the partial area formed by the input picture frame and the partial 
area formed by a field separated according to the field phase. Further, 
the predictive distortion (obtained when one motion vector detected for 
the partial area formed by the frame is used) is compared with the 
addition of the predictive distortions (obtained when two motion vectors 
detected for two partial areas of two fields for constituting the same 
frame are used), and the motion vector is compensated for so that these 
distortions can be minimized in the conventional predictive coding method. 
In the conventional motion vector detecting method, however, motion vector 
detection at a partial area of the frame of the input picture and the 
motion vector detection at a partial area of the field are executed 
separately. In other words, in order to obtain the motion vector for a 
partial area of the input picture, the calculation for detecting one frame 
motion vector and the calculation for detecting two field motion vectors 
are executed independently at a wide search window. There is thus a 
problem in that a huge quantity of calculations is required. 
SUMMARY OF THE INVENTION 
With these problems in mind, therefore, it is the object of the present 
invention to provide a motion vector detecting method and system, which 
can markedly reduce the total retrieval calculations required to detect 
motion vectors, without degrading the detection precision of the motion 
vectors, in spite of the fact that the search window of the motion vectors 
is fairly narrow. In this method, the motion vector is detected with 
respect to a partial area formed by an input picture field; and the 
position on the reference picture indicated by the detected field vector 
is determined as the basic point of the frame vector search window. 
To achieve the above-mentioned object, the present invention provides a 
method of detecting motion vector data representative of motion of a 
partial area in an input picture from any area on a reference picture, 
comprising: a first step of determining a first distortion between a 
partial area constructed by fields of the input picture and a partial area 
constructed by fields of the reference picture as a first evaluation 
value, and detecting a position of the partial area constructed by the 
fields of the reference picture at which the first evaluation value 
becomes the minimum value; a second step of setting a search window on a 
frame of the reference picture on the basis of a detected position of the 
partial area constructed by the fields of the reference picture previously 
detected; and a third step of determining a second distortion between a 
partial area constructed by a frame in the set search window and a partial 
area constructed by a frame of the input picture as a second evaluation 
value, and detecting a position of the partial area constructed by the 
frame of the reference picture at which the second evaluation value 
becomes the minimum value. 
Further, the present invention provides a system for detecting motion 
vector data representative of motion of a partial area in an input picture 
from any area on a reference picture, comprising: means for calculating a 
first distortion between a partial area constructed by fields of the input 
picture and a partial area constructed by fields of the reference picture 
an a first evaluation value; means for detecting a position of the partial 
area constructed by the fields of the reference picture at which the first 
evaluation value becomes the minimum value; means for setting a search 
window on a frame of the reference picture on the basis of a detected 
position of the partial area constructed by the fields of the reference 
picture previously detected; means for calculating a second distortion 
between a partial area constructed by a frame in the set search window and 
a partial area constructed by a frame of the input picture as a second 
evaluation value; and means for detecting a position of the partial area 
constructed by the frame of the reference picture at which the second 
evaluation value becomes the minimum value. 
Further, the present invention provides a method of detecting motion vector 
data indicative of from which area on a reference picture a partial area 
on an input picture moves, comprising the steps of: obtaining a first 
distortion between a partial area formed by an input picture field and a 
partial area formed by reference picture field, as a first evaluation 
rate, a plurality of the first distortions being obtained by shifting the 
partial area in a search window for each field; detecting a position of a 
partial area formed by a reference picture field, at which the obtained 
first evaluation rates are minimized, to detect a motion vector for each 
field; setting a search window on a reference picture frame on the basis 
of the detected position of the partial area formed by the reference 
picture field; obtaining a second distortion between a partial area formed 
by a frame within the set search window and a partial area formed by a 
frame of the input picture, as a second evaluation rate, a plurality of 
the second distortions being obtained by shifting the partial area in the 
set search window for each frame; and detecting a position of a partial 
area formed by a reference picture frame, at which the obtained second 
evaluation rates are minimized, to detect an motion vector for each frame. 
Further, the present invention provides a system for detecting motion 
vector data indicative of from which area on a reference picture a partial 
area on an input picture moves, which comprises: means for calculating a 
first distortion between a partial area formed by an input picture field 
and a partial area formed by a reference picture field, as a first 
evaluation rate, a plurality of the first distortions being calculated by 
shifting the partial area in a search window for each field; means for 
detecting a position of a partial area formed by a reference picture 
field, at which the calculated first evaluation rates are minimized, to 
detect a notion vector for each field; means for setting a search window 
on a reference picture frame on the basis of the detected position of the 
partial area formed by the reference picture field; means for calculating 
a second distortion between a partial area formed by a frame within the 
set search window and a partial area formed by a frame of the input 
picture, as a second evaluation rate, a plurality of the second 
distortions being calculated by shifting the partial area in the set 
search window for each frame; and means for detecting a position of a 
partial area formed by a reference picture frame, at which the calculated 
second evaluation rates are minimized, to detect a motion vector for each 
frame. 
In the motion vector detecting method according to the present invention, 
in the first step, a correlation degree between the partial area 
constructed by the fields of the input picture and the partial area 
constructed by the fields of the reference picture is calculated be 
calculating the distortion between the partial area constructed by the 
fields of the input picture and the partial area constructed by the fields 
of the reference picture. Further, a position of the partial area 
constructed by the fields of the reference picture at which the calculated 
first distortion becomes the minimum value is determined to detect a 
motion vector for each field. Further, in the second step, a narrow search 
window for detecting the frame vector on the frame of the reference 
picture is determined on the basis of the position indicated by the 
detected field vector on the reference picture detected by the first step. 
Further, in the third step, a correlation degree between the partial area 
constructed by the frame of the input picture and the partial area 
constructed by the frame of the reference picture frame is calculated, by 
calculating a second distortion between the partial area within the search 
window constructed by the frame of the referential picture set in the 
second step and the partial area formed by the frame of the input picture. 
Further, a position of the partial area formed by the frame of the 
reference picture at which the calculated second distortion becomes the 
minimum value is determined to detect a motion vector for each frame. 
Further, in the motion vector detecting system according to the present 
invention, in the first means, a correlation degree between the partial 
area constructed by the fields of the input picture and the partial area 
constructed by the fields of the reference picture is calculated by 
calculating the distortion between the partial area constructed by the 
fields of the input picture and the partial area constructed by the fields 
of the reference picture. Further, in the second means, a field vector is 
detected by detecting a position of the partial area constructed by the 
fields of the reference picture at which the calculated first distortion 
becomes the minimum value. Further, on the basis of the position of the 
reference picture indicated by the field vector detected by the second 
means, a search window for detecting the frame vector on the frame of the 
reference picture is determined narrow. Further, in the fourth means, a 
correlation degree between the partial area constructed the frame of the 
input picture and the partial area constructed by the frame of the 
reference picture frame is calculated, by calculating a second distortion 
between the partial area within the search window constructed by the frame 
of the referential picture set in the second step and the partial area 
formed by the frame of the input picture. Further, in the fifth means, a 
position of the partial area constructed by the frame of the reference 
picture at which the calculated second distortion becomes the minimum 
value is determined to detect a motion vector for each frame. 
Here, the frame vector is used for motion compensation, when the distortion 
between the partial area of the reference picture frame and the partial 
area of the input picture frame is calculated without separating the 
partial area of the input picture by phase and farther the calculated 
distortion is small relative to the other motion compensation. In other 
words, this corresponds to the case where the direction and the magnitude 
of the motion vector are both roughly equal to each other in both the 
field lines of the partial area of the input picture frame. Further, when 
the field vector is detected, the partial area of the input picture is 
detected by detecting the partial area of the reference picture field 
having a small distortion relative to the respective partial areas 
separated by the field phase. In other words, in the case where the frame 
vector is selected for motion compensation, as far as the picture motion 
can be detected firmly on the basis of the field vector detection, it is 
natural that the position indicated by the field vector roughly matches 
the position indicated by the frame vector on the picture. Therefore, when 
the detection result of the field vector is used to determine the basic 
retrieval position, even if the search window or the frame vector is 
limited narrow, it is possible to reduce the amount of calculations 
required to detect the frame vector, without raising any problem with 
respect to frame vector detection. 
As described above, in the present invention, since the motion vector is 
detected for the partial area formed by the input picture field and since 
the position indicated by the obtained field vector on the reference 
picture is determined as a basic retrieval point, the frame vector search 
window is narrowed, and it is possible to markedly reduce the total 
quantity of the retrieval and calculation required to detect the motion 
vectors, without degrading the detection precision of the frame vectors.

DETAILED DESCRIPTION OF THE EMBODIMENTS 
With reference to the attached drawings, the motion vector detecting method 
and system according to the present invention will be explained 
hereinbelow on the basis of some preferred embodiments. 
FIG. 1 is a flowchart showing the basic concept of the motion vector 
detecting method according to the present invention. The control procedure 
is executed by the control system provided with a controller (CPU) and 
other necessary memory units (ROM, RAM, etc.) in accordance with software 
as shown in the attached flowcharts. Therefore, in explaining the control 
procedure with reference to the attached flowcharts, the controller is 
referred to simply as control. 
First, in first step ST1, control sets an input picture and a reference 
picture, respectively. In this case, two reference field pictures are set 
for each input frame picture. In succeeding step ST2, a search window is 
set on the two reference field picture, respectively. 
In the following steps from ST3 to ST7 control detects a position of the 
reference partial area, at which the error between the input partial area 
and the reference partial area in each field car be minimized In other 
words, in step ST3, an distortion between the partial areas at each 
reference field is calculated. In step ST4, control uses the distortion 
between the partial areas as an evaluation rate. When the current 
distortion is equal to or smaller than the preceding distortion, control 
updates both the motion vector and the distortion to detect the motion 
vector for each field. In step ST5, control detects whether the retrieval 
ends at ace search window. If it does not end, in step ST6, control 
updates the reference partial area, and repeats the procedure from step 
ST3 to step ST5 above. 
On the other hand, in step ST5, control discriminates whether the retrieval 
at the search window ends. If it ends, control proceeds to step ST7 to 
complete the field vector detection. Accordingly, in a series of a group 
from step ST3 to step ST7, control sets the distortion between the partial 
area formed by the input picture field and the partial area formed by the 
reference picture field to an evaluation rate, and detects the partial 
area position formed by the fields of the reference picture at which the 
evaluation rate can be minimized. 
Successively, in step ST8, control sets the search window on the reference 
picture frame on the basis of the detection position of the partial area 
formed by the reference picture field and detected through the step groups 
from step ST3 to step ST7. 
After that, in a step group including from step ST9 to step ST13, control 
detects the position of the reference partial area at which the error 
between the partial area of the input frame and the partial area of the 
reference frame can be minimized. 
In other words, in step ST9, control calculates the distortion between the 
partial area formed by the frame in the above-mentioned search window and 
the partial area formed by the frame of the input picture. Further, in 
step ST10, control updates both the motion vector and the distortion 
according to the difference between the preceding distortion and the 
current distortion (evaluation rate). In step ST11, control checks whether 
the frame search ends in the search window. If it does not end, control 
updates the reference partial area again in step ST12, repeating the 
procedure from step ST9 to step ST11, again. 
On the other hand, in step ST11, control discriminates whether the 
retrieval in the search window ends. If it ends, control proceeds to step 
ST13, to complete the frame vector detection. Therefore, a series of 
groups from ST9 to ST13 detects the position of the partial area formed by 
the frame of the reference picture, at which the distortion (the 
evaluation rate) between the partial area formed by the frame in the 
search window and the partial area formed by the frame of the input 
picture can be minimized. 
The motion vector detecting method of the first embodiment according to the 
present invention will be described hereinbelow with reference to the 
flowchart shown in FIGS. 2 to 4. 
Prior to the description of the flowcharts shown in FIGS. 2 to 4, the 
motion vector detecting method will be explained with reference to FIGS. 
5A to 5C and FIGS. 6A to 6C. In FIG. 5A, a partial area 203 in an input 
field 103 is shown. In FIG. 5B, a partial area 204 in the input field 104 
is shown. In FIG. 5C, a partial area 201 in the input frame is shown. 
Further, in FIG. 6A, a search window 301 in a reference field 105 is 
shown, and in FIG. 6B, a search window 302 in the reference field 106 is 
shown, In FIG. 6C, a partial area 202 in the reference frame is shown. 
The motion vector detection method from the reference fields 105 and 106 as 
shown in FIGS. 6A end 6B are explained hereinbelow. 
In step S01 in FIG. 2, control reads the reference field 105 and the 
reference field 106 as the reference picture, and further reads the input 
field 103 as the coded picture. Further, in step S02, control reads the 
partial area 203 on the input field 103. 
In step S03, control sets the motion vector search window 301 at a 
predetermined position on the reference field 105 (shown in FIG. 6A) and 
the motion vector search window 302 at a predetermined position on the 
reference field 106 (shown in FIG. 6B). Further, control stores 
temporarily the default motion vector candidate for the preceding input 
partial area 203 (shown in FIG. 5A) and the distortion for each reference 
field. 
In step S04, control cats away the reference partial area from the 
retrieval ranges 301 and 302, respectively to calculate the distortion 
between the reference partial area and the input partial area, 
respectively. 
In steps S05 and S06, control compares the distortion obtained in step S04 
with the temporarily stored motion vector candidate distortion for each 
reference partial area 301 or 302. Here, if the distortion obtained in 
step S04 is equal to or less than the distortion of the temporarily stored 
distortion of the motion vector candidate, control updates the temporarily 
stored motion vector candidate and the distortion with the motion vector 
indicative of the position in the reference field of the reference partial 
area and the distortion corresponding thereto. Further, if the distortion 
obtained in step S04 is larger, control does not update both the 
temporarily stored motion vector candidate and the distortion, proceeding 
to step S07. 
In step S07, control checks whether the reference partial area is the final 
reference partial area of the search window 301 or the 302. If it is not 
the final reference partial range, control returns to step S04 via step 
S04. If it is the final reference partial range, control proceeds to step 
S09. 
In step S08, control updates the reference partial area of the search 
window 301 or 302 by shifting the position of the reference partial range 
in the search window pixel by pixel, respectively. 
In step S09, control outputs two one-pixel precision field vectors detected 
at the search window 301 or 302 of the reference fields 105 and 106 with 
respect to the partial area 203 of the input field 103, through the 
processing from step S03 to step S08. For instance, the motion vector 501 
on the reference field 105 as shown in FIG. 6A and the motion vector 502 
on the reference field 106 as shown in FIG. 6B are outputted as the 
one-pixel precision field vectors from the reference field 105 and the 
reference field 106 for the partial area 203 on the input field 103 shown 
in FIG. 5A. 
In step S10, control selects the motion vector having a smaller distortion 
between the reference partial area and the input partial area, as a 
one-pixel precision field vector, from the two motion vectors detected by 
the two reference fields as described above. For instance, in FIGS. 6A and 
6B, if the distortion between the partial area on the input field 103 
(shown in FIG. 5A) and the partial area 402 on the reference field 106 
(shown in FIG. 6B) is smaller than the distortion between the partial area 
on the input field 103 (shown in FIG. 5A) and the partial area 401 on the 
reference field 105 (shown in FIG. 6A), the motion vector 502 is selected 
as the field vector of one-pixel precision. 
In FIG. 3, in step S11, in order to detect a half-pixel precision field 
vector, control sets a small search window 306 by determining the 
reference partial area 402 as its center. In addition, control stores 
temporarily the default motion vector candidate with respect to the 
preceding input partial area 203 and the distortion. 
In step S12, control cuts off the reference partial area from the search 
window 306, and further calculates the distortion between the reference 
partial area and the input partial area 203. 
In step S13 and step S14, control compares the distortion obtained in step 
S12 with the distortion of the motion vector candidate previously stared 
temporarily for each reference partial area. If the distortion obtained in 
step S12 is equal to or less than the distortion of the motion vector 
candidate temporarily stored, control updates the temporarily stored 
motion vector candidate and the distortion with the motion vector 
indicative of the position in the reference field of the reference partial 
area and its distortion. Further, if the distortion obtained in step 12 is 
larger than the distortion of the motion vector candidate temporarily 
stored, control does not update the temporarily stored motion vector 
candidate and the distortion, proceeding to step S15. 
In step S15, control checks whether the reference partial area is the final 
reference partial area in the search window 306. If it is not the final 
reference partial area, control returns to step S12 via step S16. If it is 
the final reference partial area, control proceeds to step S17. 
In step S16, control updates the reference partial area by shifting the 
position of the reference partial area in the search window 306 half pixel 
by half pixel. 
In step S17, control outputs the half pixel precision field vector detected 
from the search window 306 for the partial area 203 of the input field 103 
through the processing from step S11 to step S16. For instance, the motion 
vector 503 on the reference field 106 shown in FIG. 6B is outputted as the 
half pixel precision field vector from the reference field 106 shown in 
FIG. 6B with respect to the partial area 203 on the input field 103 shown 
in FIG. 5A. 
In step S18, control checks whether the partial area 203 of the input field 
103 at which the field vector is now being detected is the final input 
partial area of the input field. If it is not the final input partial 
area, control updates the partial area of the input field 103 in step S19, 
and returns to step S03 shown in FIG. 2. If it is the final input partial 
area of the input field, control proceeds to step S20. 
In step S20, control checks whether the field vectors have all been 
detected for a predetermined number of the input fields constituting one 
frame. If all are not yet detected, control proceeds to step S21 to reads 
the succeeding input field, and returns to step S01 shown in FIG. 2. If 
the field vectors have been all detected for a predetermined number of the 
input field constituting one frame, control proceeds to step S22. For 
instance, after the field vector as been detected for the input field 103 
shown in FIG. 5A, control reads the succeeding input field 104 shown in 
FIG. 5B in step S21, and further reads the partial area 204 on the input 
field 104. The field vector for the partial area 204 on the input field 
104 is executed in the same procedure as when the field vector for the 
partial area 203 is detected on the input field 103. 
In step S03, on both the pictures of the reference field 105 and the 
reference field 106, shown in FIGS. 6A and 6B, control sets motion vector 
retrieval ranges 303 and 304 on the reference fields 105 and 106, 
respectively, on the basis of the motion vector 502 indicative of the 
position of the partial area having a smaller distortion between the 
reference and input partial areas in the one-pixel precision field vector 
obtained for the partial area 203 on the preceding input field 103. At the 
same time, control stores temporarily the default motion vector candidate 
and the distortion with respect to the input partial area 204 in the 
respective search windows. 
Further, through the procedure from step S04 to step S08, control detects 
one-pixel precision field vectors from the search window 203 and the 
search window 304, respectively. The obtained two one-pixel precision 
field vectors (e.g., the motion vector 504 on the reference field 105 and 
the motion vector 505 on the reference field 504) are outputted in step 
S09. 
In step S10, control selects one motion vector having a smaller distortion 
relative to the partial area 204 on the input field 104 from the two 
one-pixel precision field vectors as the one-pixel precision field vector. 
For instance, in FIG. 6A, the motion vector 504 indicative of the partial 
area 404 on the reference field 105 is selected as the one-pixel precision 
field vector. 
In step S11 shown in FIG. 3, in order to detect the half-pixel precision 
field vector, control sets a small motion vector search window 305 by 
setting the reference partial area 404 as its center, and further stores 
temporarily the default motion vector candidate and the distortion of the 
preceding input partial area 204. 
Further, through the procedure from step S12 to S16, control detects the 
half-pixel precision field vector from the search window 305. 
In step S17, control outputs the obtained half-pixel precision field vector 
506. 
In step S18, control checks whether the partial area 204 of the input field 
104 whose field vector is now being detected is the final input partial 
area of the same input field. If it is not the final input partial area, 
in stop S19, control updates the partial area of the input field 104, 
returning to step S03. If it is the final input partial area of the input 
field, control proceeds to step S20. 
In step S20, through the above-mentioned procedure from step S03 to step 
S19, control checks whether the field vector detection is complete for a 
predetermined number of input fields for constituting one frame (e.g., the 
input fields 103 and 104 shown in FIGS. 5A and 5B. If it is not complete, 
control proceeds to step S21 to read the succeeding input field (e.g., the 
input field 104 slogan in FIG. 5B), returning to step S02 to execute the 
field vector detection processing for the succeeding input field. If it is 
complete, control proceeds to step S22. 
Here, the motion vector detecting method of the partial area 201 on the 
input frame 101 as shown in FIG. 5C on the basis of the reference frame 
102 as shown in FIG. 6C will be described hereinbelow. 
First, in step S22, control constructs one input frame and one reference 
frame on the basis of one set of input fields and one set of reference 
fields all read in the above-mentioned steps S02 and S21, respectively. 
For instance, the input frame 101 as shown in FIG. 5C can be constructed 
by the two input fields 103 and 104 as shown in FIGS. 5A and 5B, and the 
reference frame 102 as shown in FIG. 6A can be constructed by the two 
input fields 105 and 106 as shown in FIGS. 6A and 6B. 
In step S23 shown in FIG. 4, control reads the partial area of the input 
frame. The partial area 201 on the frame 101 now read is constructed by 
two field portions located at roughly the same positions on the two field 
pictures. For instance, the partial area 201 on the input frame 101 as 
shown in FIG. 5C is constructed by the partial area 203 on the input field 
103 and the partial area 204 on the input field 104. 
In step S24, control selects a one-pixel precision field vector having a 
smaller distortion between the reference partial area and the input 
partial area, as the retrieval standard of the half-pixel precision frame 
vector, from the two one-pixel precision field vectors detected for the 
two partial areas of the two input fields constituting one partial area of 
the one input frame. For instance when the distortion between the input 
partial area and the partial area on the reference field 105 as shown in 
FIG. 6A is indicated by the one-pixel precision motion vector 504 detected 
for the partial area 204 on the input field 104 as shown in FIG. 5B is 
smaller than the distortion between the input partial area and the partial 
area on the reference field 106 as shown in FIG. 6B indicated by the 
one-pixel precision motion vector 502 detected for the partial area 203 on 
the input field 103 as shown in FIG. 5A, the motion vector 504 s selected 
as the search basis of the half-pixel precision frame vector. 
In step S25, in order to detect the half-pixel precision frame vector, 
control converts the position on the reference field 105 indicated by the 
motion vector 504 into the position on the reference frame 102, and sets a 
small motion vector search window 307 for determining the reference 
partial area 405 on the reference frame (existing on this position) as its 
center. In addition, control stores temporarily the motion vector 
candidate and the distortion at the input partial area 201. 
In step S26, control cuts off the reference partial area from the search 
window 307 and calculates a distortion between the reference partial area 
and the input partial area 201. 
In steps S27 and S28, control compares the distortion obtained in step S26 
with the motion vector candidate previously stored temporarily for each 
reference partial area. If the distortion obtained in step S26 is equal to 
or less than the distortion of the temporarily stored motion vector 
candidate, control updates the temporarily stored motion vector candidate 
and the distortion with the motion vector indicative of the position of 
the reference partial area in the reference frame and the distortion. If 
the distortion obtained in step S26 is larger than the temporarily stored 
motion vector candidate and the distortion, control proceeds to step S29 
without updating the temporarily stored motion vector candidate and the 
distortion. 
In step S29, control checks whether the reference partial area is the final 
reference partial area of the search window 307. If it is not the final 
reference partial area, control returns to step S26 via step S30. If it is 
the final reference partial area, control proceeds to step S31. 
In the above-mentioned step S30, control updates the reference partial area 
in the search window 307 by shifting the reference partial area in the 
search window half pixel by half pixel 
In step S31, control outputs the half-pixel precision frame vector (e.g., 
the motion vector 507 on the reference frame 102 as shown in FIG. 6C) 
detected from the search window 307 with respect to the partial area 201 
of the input frame 101 as shown in FIG. 5C through the above-mentioned 
procedure from step S25 to step S30. 
In step S32, control checks whether the partial area 201 of the input frame 
101 whose frame vector is now being detected is the final input partial 
area of the same input frame. If it is not the final input partial area, 
in step S33, control updates the partial area of the input frame 101, 
returning to step S24. If it is the final input partial area of the input 
frame, control proceeds to step S34. 
In step S34, control checks whether the motion vectors have been detected 
for a predetermined number of input fields. If the motion vectors of a 
predetermined number of input fields have not yet been detected, control 
resets the previous input fields in step S35 and reads the succeeding 
input field, returning to step S02 shown in FIG. 2. If the motion vectors 
of a predetermined number of input fields have been detected, control ends 
the motion vector detection processing for the same reference picture. 
A second embodiment of the motion vector detecting method according to the 
present invention will be described hereinbelow with reference to the 
flowcharts shown in FIGS. 7 to 10. In this second embodiment, the reduced 
partial areas 207 and 208 on the reduced input fields 107 and 108 as shown 
in FIGS. 11A and 11B can be obtained by sampling the input fields 103 and 
104 as shown in FIGS. 11C and 11D, respectively. Further, the reduced 
reference fields 109 and 110 as shown in FIGS. 12A and 12B can be obtained 
by sampling the reference fields 105 and 106 as shown in FIGS. 12C and 
12D, respectively. In this embodiment, the motion vectors are detected 
from the reduced reference fields 109 and 110 with respect to the reduced 
partial areas 207 and 208 on the reduced input fields 107 and 108, 
respectively. 
In step S01 shown in FIG. 7, control reads two reference fields 105 and 106 
as shown in FIGS. 12C and 12D as the reference pictures, and further reads 
an input field 103 (as shown in FIG. 11C) to be coded. Further, control 
samples the read reference fields 105 and 106 to form reduced reference 
fields 109 and 110 as shown in FIGS. 12A and 12B. Further, in step S02, 
control reads the partial area 203 on the input field 103. 
In step S36, control forms the reduced input fields. In the example as 
shown in FIGS. 11A to 11E, the reduced input field 107 is formed by 
sampling the input field 103 as shown in FIG. 11C. In this case, the input 
partial area 203 on the input field 103 corresponds to the reduced input 
partial area 207 on the reduced input field 107. 
In step S37, control sets the motion vector search windows 311 and 312 on 
the pictures of the reduced reference fields 109 and 110, as shown in 
FIGS. 12A and 12B, respectively, and further temporarily stores the 
default motion vector candidate and the distortion of the preceding 
reduced input portion areas 207 for each reduced reference field. 
In step S36, control cuts off the reduced reference partial areas from the 
search windows 311 and 312, respectively to calculate the distortion 
between the reduced reference partial area and the reduced input partial 
area 207, respectively. 
In steps S39 and S40, control compare its the distortion obtained in step 
S38 with the distortion of the previously and temporarily stored motion 
vector candidate for each reduced reference partial area of both the 
search windows 311 and 312. If the distortion obtained in step S38 is 
equal to or less then the distortion of the temporarily stored notion 
vector candidate, the temporarily stored motion vector candidate and the 
distortion are updated with the motion vector indicative of the position 
at the reduced reference partial area in the reduced reference field, and 
the distortion. If the distortion obtained in step S38 is more than the 
distortion of the temporarily stored motion vector candidate, control 
proceeds to step S41, without updating the temporarily stored motion 
vector candidate and the distortion. 
In step S41, control checks whether the reduced reference partial area is 
the final reference partial area of each of the search windows 311 and 
312. If it is not the final reduced reference partial area, control 
returns to step S38 via step S42. If it is the final reduced reference 
partial area, control proceeds to step S43. 
In the above-mentioned step S42, control updates the reduced reference 
partial area of each of the search windows 311 and 312 by shifting the 
position of the reduced reference partial area of each of the search 
windows 311 and 312 for each node (one pixel by one pixel). 
In step S43, through the processing from the above-mentioned steps S37 to 
S42, control outputs the two one-node precision field vectors detected 
from the search windows 311 and 312 with respect to the reduced partial 
area 207 of the reduced input field 107. For instance, the motion vectors 
511 on the reduced reference field 109 as shown in FIG. 12A and the motion 
vectors 514 on the reduced reference field 110 as shown in FIG. 12B are 
outputted as the one-node precision field vectors from the reduced 
reference fields 109 and 110, respectively with respect to the reduced 
partial area 207 on the reduced input field 107 as shown in FIG. 11A. 
The method of detecting the motion vectors for the partial area 203 on the 
input field 103 and the partial area 204 on the input field 104 as shown 
in FIGS. 11C and 11D on the basis of the reference fields 105 and 106 as 
shown in FIGS. 12C and 12D, respectively will be described hereinbelow. 
In step S44, control projects the one-node precision motion vectors 511 and 
512 outputted in step S43 upon the non-reduced reference fields 105 end 
106 as shown in FIGS. 12C and 12D, respectively. 
In step S45 shown in FIG. 8, control sets two search windows 315 and 317 
(each of whose sizes corresponds to a sampling ratio) by determining the 
partial areas 414 and 417 existing at a position on the reference fields 
105 and 106 and further indicated by the projected motion vectors 511 and 
512 as their centers, respectively. Further, control stores temporarily 
the default motion vector candidate and the distortion for the input 
partial area 203 corresponding to the preceding reduced input partial area 
207. 
In step S04, control cuts off the reference partial area from the search 
windows 315 and 317, respectively, to calculate the distortion between the 
reference partial area and the input partial area 203, respectively. 
In steps S05 and S06, control compares the distortion obtained in step S04 
with the distortion of the temporarily stored motion vector candidate, for 
each of the two search windows 315 and 317. If the distortion obtained in 
step S04 is equal to or less than the distortion of the temporarily stored 
motion vector candidate, control updates the temporarily stored motion 
vector candidate and the distortion with the motion vector indicative of 
the position of the reference partial area on the reference field and the 
distortion. If the distortion obtained in step S04 is larger than the 
distortion of the temporarily stored motion vector candidate, control 
proceeds to step S07, without updating the temporarily stored motion 
vector candidate and the distortion, proceeding to step S07. 
In step S07, control checks whether each of the reference partial areas are 
the final reference partial areas. If they are not the final reference 
partial areas, control returns to step S04 via the step S08. If they are 
the final reference partial areas, control proceeds to step S09. 
In step S08, control updates the reference partial areas of each of the 
search windows 315 and 317 by shifting the position of the reference 
partial area in the search window pixel by pixel, respectively. 
In step S09, control outputs two one-pixel precision field vectors detected 
at search window 315 or 317 with respect to the partial area 203 of the 
input field 103 through the processing from step S45 to step S08. For 
instance, the motion vectors 515 and 517 or the reference fields 105 and 
106 as shown in FIGS. 12C and 12D are outputted as the one-pixel precision 
field vectors from the reference fields 105 and 106 for the partial area 
203 on the input field 103 as shown in FIG. 11C. 
In step S10, control selects the motion vector (whose distortion between 
the reference partial area and the input partial area is smaller) from the 
two motion vectors detected from the two reference fields as described 
above, as the one-pixel precision field vector. For instance, in FIG. 12C, 
the motion vector 515 on the reference field 105 is selected as the 
one-pixel precision field vector. 
In step S11, in order to detect the half-pixel precision field vector, 
control sets a small search window 319 by setting the reference partial 
area 418 (existing on the reference field 105 indicated by the one-pixel 
precision field vector 515) as its center. Further, control temporarily 
stores the default motion vector candidate and the distortion of the 
preceding input partial area 208. 
In step S12 shown in FIG. 9, control cuts away the reference partial area 
from the search window 319 to calculate the distortion between the 
reference partial area and the input partial area 203. 
In steps S13 and 14, control compares the distortion obtained in step S12 
with the distortion of the temporarily stored motion vector for each 
reference partial area. If the distortion obtained in step S12 is equal to 
or less than the distortion of the temporarily stored motion vector 
candidate, control updates the temporarily stored motion vector candidate 
and the distortion with the motion vector indicative of the position of 
the reference partial area in the reference field and the distortion. If 
the distortion obtained in step S12 larger than the distortion of the 
temporarily stored motion vector candidate, control proceeds to step S15, 
without updating the temporarily stored motion vector candidate and the 
distortion. 
In step S15, control checks whether the reference partial area is the final 
reference partial area in the search window 319. If it is the final 
reference partial area, control returns to step S12 via step S16. If it is 
not the final reference partial area, control proceeds to step S17. 
In step S16, control updates the reference partial area by shifting the 
reference partial area in the search window 319 half pixel by half pixel. 
In step S17, control outputs the half-pixel precision field vector detected 
from the search window 319 for the partial area 203 of the input field 103 
through the processing from step S11 to step S16. For instance, the motion 
vector 519 on the reference field 105 shown in FIG. 12C is outputted as 
the half-pixel precision field vector from the reference field 105 for the 
partial area 203 on the input field as shown in FIG. 11C. 
In step S18, control checks whether the partial area 203 of the input field 
103 at which the field vector is now being detected is the final input 
partial area in the input field. If it is not the final input partial 
area, control updates the partial reads of the input field 103 in step 
S19, returning to step S36 shown in FIG. If it is the final input partial 
area, control proceeds to step S20. 
In step S20, control checks whether the field vector detection ends for a 
predetermined number of input fields constituting one frame. If does not 
end, control reads the succeeding input field in step S21, returning to 
step S02 shown in FIG. 7. If the field vectors of a predetermined number 
of input fields constituting ore frame have been detected, control 
proceeds to step S22. For instance, after the field vector of the partial 
area or the input field has been detected, control reads the succeeding 
input field 104 in step S21, and further reads the partial area 204 or the 
input field 104 (as shown in FIG. 11D) in step S02 shown in FIG. 7. For 
the partial area 204 on the input field 104, in the same way as with the 
case of the field vector detecting procedure for the partial area 203 on 
the input field 103, the field vectors are detected as follows: 
In step S36 shown in FIG. 7, control forms a reduced input field. In the 
example shown in FIG. 11B, the reduce input field 108 is formed by 
sampling the input field 104. In this case, the input partial area 204 on 
the input field 104 corresponds to the reduced input partial area 208 on 
the reduced input field 103. Further, the reduced reference field is used 
in the same way as with the case of the motion vector detection for the 
input field 103. Therefore, when the same reduced reference field is being 
used, the reduced reference fields 109 and 110 can be kept stored in a 
memory; or whenever the input field is updated, the reduced reference 
field can be formed again. 
In step S37, control sets the motion vector search windows 313 and 314 on 
the pictures of the reduced reference fields 109 and 110 as shown in FIGS. 
12A and 12B, respectively, on the basis of the motion vector 511 
indicative of the position of the reduced partial area and having the 
smaller distortion (between the reduced reference partial area and the 
reduced input partial area) in the two one-node precision field vectors 
previously obtained for the reduced partial area 207 on the reduced input 
field 107. Further, control stores the default motion vector candidate and 
the distortion for the reduced input partial area 208 temporarily for each 
search window. 
Further, through step S38 to step S42 control detects one-node precision 
field vectors from the retrieval ranges 313 and 314, respectively. 
Further, in step S43, control outputs the two detected one-node precision 
field vectors (e.g., the motion vectors 513 and 514 on the reduced 
reference fields 109 and 110 in FIGS. 12A and 12B, respectively). 
In step S44, control projects the one-node precision motion vectors 513 and 
514 outputted in step S43 upon the non-reduced reference fields 105 and 
106 as shown in FIGS. 12B and 12C, respectively. 
In step S45 shown in FIG. 6, control sets the retrieval ranges 316 and 318 
(each of whose sizes corresponds to the sampling ratio) by determining the 
partial areas 415 and 416 existing on the reference fields 105 and 106 
indicated by the projected motion vectors 513 end 514 as their centers, 
respectively. Further, control stores temporarily the default motion 
vector candidates and the distortions for the preceding reduced input 
partial area 208 end the corresponding input partial area 204 for each 
reference field. 
Further, in step S04 to step S08, control detects the one-pixel precision 
field vector from the search windows 316 and 316, respectively. 
Further, in step S09, control outputs the obtained two one-node precision 
field vectors (e.g., the motion vectors 516 and 518 on the reference 
fields 105 and 106 in FIGS. 12C and 12D), respectively. 
In step S10, control selects the motion vector having a smaller distortion 
between the partial area on the reference field and the partial area or 
the input field from the two one-pixel precision field vectors as the 
one-pixel precision field vector. In the example shown in FIG. 12, the 
motion vector 518 indicative of the partial area 419 on the reference 
field 106 is selected as the one-pixel precision field vector. 
In step S11, in order to detect the half-pixel precision field vector, 
control sets the small vector search windows 320 by setting the reference 
partial area 419 as its center, and further stores temporarily the default 
vector candidate and the distortion for the input partial area 204. 
Further, in FIG. 9, control executes the processing from step S12 to step 
S16 to detect the half-pixel precision field vector from the search window 
320. 
In step S17, control outputs the half-pixel precision field vector 520 
obtained as the result of the above-mentioned search processing. 
In step S18, control discriminates whether the partial area 204 of the 
input field (in which the field vector is now being detected) is the final 
input partial area of the input field. If it is not the final input 
partial area, in step S19, control updates the partial area of the input 
field 104, returning to the step S36 shown in FIG. 7. If it is the final 
input partial area of the input field, control proceeds to step S20. 
In step S20, through the processing from step S36 to step S19, control 
checks whether the field vector detections have been completed for a 
predetermined number of input fields for constituting one frame (e.g., two 
input fields 103 and 104 as shown in FIGS. 11C and 11D). If not yet 
completed, in step S21, control reads the succeeding field (the input 
field 104 as shown in FIG. 11D), returning to step S02 for executing the 
processing of detecting field vectors for the succeeding input field. If 
completed, control proceeds to step S22. 
The method of detecting a motion vector for the partial area 201 on the 
input frame as shown in FIG. 11E on the basis of the reference frame 102 
as shown in FIG. 12E will be described hereinbelow. 
First, in step S22 in FIG. 9, control forms a single input frame and a 
signal reference frame on the basis of one set of the input fields and one 
set of reference fields read in steps S02 and S21. For instance the input 
frame 101 as shown in FIG. 11E can be formed by the two input fields 103 
and 104 as shown in FIGS. 11C and 11D. Further, the reference frame 102 as 
shown in FIG. 12E can be formed by the two reference fields 105 and 106 as 
shown in FIGS. 11C and 11D. 
In step S23 in FIG. 10, control reads the partial area 201 on the input 
frame 101. The partial area on the frame picture read in this step is 
formed by two partial areas located at roughly the same positions on the 
two field pictures. For instance, the partial areas 201 on the input frame 
101 as shown in FIG. 11E is formed by the two partial areas 203 and 204 on 
the two input fields 103 and 104 as shown in FIGS. 11C and 11D, 
respectively. 
In step S24, control selects in one-pixel precision the field vector with a 
smaller distortion between the reference partial area and the input 
partial area, from the two one-pixel precision field vectors detected for 
the partial areas of two input fields for forming thee partial area on one 
input frame, as the search standard of the half-pixel precision frame 
vector. For instance, when the distortion between the reference partial 
area and the input partial area at the partial area on the reference field 
105 (as shown in FIG. 12C) indicated by the one-pixel precision motion 
vector 515 detected for the partial area 203 on the input field 103 as 
shown in FIG. 11C is smaller than the distortion between both at the 
partial area on the reference field 106 (as shown in FIG. 12D) indicated 
by the one-pixel precision motion vector 518 detected for the partial area 
204 on the input field 104 as shown in FIG. 11D, the motion vector 515 is 
selected as the search standard of the half-pixel precision frame vector. 
In step S25, in order to detect the half-pixel precision frame vector, 
control converts the position on the reference field 105 indicated by the 
motion vector 515 into the position on the reference frame 102, and 
further sets a small motion vector search window 321 by setting the 
reference partial area 420 on the reference frame existing on the position 
as its center. In addition, control stores temporarily the motion vector 
candidate and the distortion for the input partial area 201. 
In step S26, control cuts away the reference partial area from the search 
window 321, and calculates distortion between the reference partial area 
and the input partial area 201. 
In steps S27 and S28, control compares the distortion obtained in step S26 
with the distortion of the motion vector candidate previously stored for 
each reference partial area. If the distortion obtained in step S26 is 
equal to or less than the distortion or the temporarily stored motion 
vector candidate, the temporarily stored motion vector candidate and the 
distortion are updated with the motion vector indicative of the position 
of the reference partial area in the reference frame and the distortion. 
If the distortion obtained in step S26 is larger than the distortion of 
the temporarily stored motion vector candidate, control proceeds to step 
S29, without updating the temporarily stored motion vector candidate and 
the distortion. 
In step S29, control checks whether the reference partial area is the final 
reference partial area of the search window 321. If it is not the final 
reference partial area, control returns to step S26 via step S30. If it is 
the final reference partial area, control proceeds to step S31. 
In the above-mentioned step S30, control updates the reference partial area 
of the search window 321 by shifting the reference partial area in the 
search window half pixel by half pixel. 
In step S31, control outputs the half-pixel precision frame vector (e.g.. 
the motion vector 521 on the reference frame 102 as shown in FIG. 12E) 
detected from the search window 321 for the partial area 201 of than input 
frame 101 through the above-mentioned procedure from step S25 to step S30. 
In step S32, control checks whether the partial area 201 of the input frame 
201 whose frame vector is now being detected is the final input partial 
area of the same input frame. If not the final input partial area, in step 
S33, control updates the partial area of the input frame 101, returning to 
step S24. If the final input partial area of the input frame, control 
proceeds to step S34. 
In step S34, control checks whether the motion vectors have been detected 
for a predetermined number of input fields. If the motion vectors of a 
predetermined number of input fields have not yet been detected, control 
resets the previous input field in step S35 and reads the succeeding input 
field, returning to step S02 shown in FIG. 7. If the motion vectors of a 
predetermines number of input fields have all been detected, control ends 
the motion vector detecting processing for the same reference picture. 
A third embodiment of the motion vector detecting system according to the 
present invention will be described hereinbelow with reference to a block 
diagram shown in FIG. 13. 
First, the reference field 21 is inputted to a first field vector detector 
1, and the reference field 23 is inputted to a second field vector 
detector 2. Further, the input field 21 to be coded is inputted to both 
the first field vector detector 1 and the second field vector detector 2. 
Separately, the one-pixel precision field vector 24 already detected to 
determine the search window is inputted through a delay circuit 4 to the 
first field vector detector 1 and the second field vector detector 2, 
respectively. 
The first and second field vector detectors 1 and 2 operate in the same 
way, to search the inducted one-pixel precision field vectors on the 
reference fields, respectively. The circuit construction of each of these 
field vector detectors 1 and 2 is shown in detail in FIG. 14. 
With reference to FIG. 14, the operation of the first field vector detector 
1 will be described hereinbelow by way of example. 
In FIG. 14, a search window setter 141 sets a search window for detecting 
the one-pixel precision field vector on the bases of the already detected 
field vector 24. The set search window data 43 is outputted to a reference 
field memory 143. Further, when the already-detected motion vector is not 
used to set the retrieval range, the search window setter 141 sets a 
search window for detecting a motion vector to a predetermined position on 
the reference field. The set search window data 43 is outputted to the 
reference field memory 143. 
The reference field memory 143 stores the reference field 22, outputs the 
reference partial area data 45 in the search window indicated by the 
search window data 43 (inputted from the search window setter 141), and 
outputs the one-pixel precision position date 46 in the reference partial 
area on the picture to a minimum distortion detector 145. 
On the other hand, an input field 21 is inputted to an input partial area 
memory 142. The input partial area memory 142 outputs the input partial 
area data 44 to a distortion calculator 144. 
The distortion calculator 144 calculates distortion 47 between the inputted 
input partial area data 44 and the inputted reference partial area data 
45, and outputs the calculated distortion 47 to the minimum distortion 
detector 145. 
The minimum distortion detector 145 detects the position data 46 in the 
reference partial area which can minimize the distortion 47 in the search 
window, and outputs a motion vector 26 indicative of the position on the 
reference partial area on the picture and the minimum distortion 25. 
As described above, the first field vector detector 1 obtains the one-pixel 
precision field vector 26 retrieved on the reference field 22, and the 
minimum distortion 25 at that time. These obtained data are inputted to 
the first motion vector discriminator 3 shown FIG. 13. In the same way, 
the field vector detector 2 obtains the one-pixel precision field vector 
28 retrieved on the reference field 23, and the minimum distortion 27 at 
that time. These obtained data are also Inputted to the first motion 
vector discriminator 3. 
The first motion vector discriminator 3 compares the inputted minimum 
distortion 25 with the minimum distortion 27, and selects the motion 
vector which can minimize the distortion between the input and reference 
partial areas from the two inputted one-pixel precision field vectors 26 
and 28. The selected motion vector is outputted as the field vector 30. 
Further, at the same time, the minimum distortion 29 is outputted as the 
distortion 29. In addition, the select data 31 indicative of the reference 
field having a smaller distortion between the input and reference partial 
areas is also outputted. Further, the one-pixel precision field vector 30 
is inputted as it is to a second motion vector discriminator 10 and the 
third field motion vector discriminator 9, and further delayed through a 
delay circuit 4 by a time required to detect one field motion vector as an 
already-detected motion vector 24. The delayed motion vector 24 is 
inputted to the first and second field vector detectors 1 and 2, 
respectively so as to be used to set the motion vector search windows for 
the succeeding input fields. 
The select data 31 indicative of the reference field having a smaller 
distortion is inputted to a reference field selector 8. Further, the 
reference field data 22 is delayed by a delay circuit 5 by a time required 
to detect the one-pixel precision field vector in a single search window. 
The reference field data 32 delayed by this delay circuit 5 is also 
inputted to the reference field selector 8. In the same way, the reference 
field data 23 is also delayed by a delay circuit 6 by a time (the same as 
the delay time of the delay circuit 5), and the delayed reference data is 
also inputted to the reference field selector 8. 
The reference field selector 8 selects one of the inputted reference field 
data 32 and the reference field data 33 on the basis of the inputted 
reference field select data 31, and outputs the selected reference field 
data as the reference field 35. 
The reference field 35 is inputted to a third field vector detector 9. 
Further, the input field 21 is delayed by a delay circuit 7 by a time the 
same as that of the delay circuit 5. The delayed input field 34 is also 
inputted to the third field vector detector 9. Further, the one-pixel 
precision field vector 30 outputted from the first motion vector 
discriminator 3 is also inputted to the third field vector detector 9. 
The third field vector detector 9 retrieves the half-pixel precision field 
vectors for the input partial area on the inputted input field 3, within a 
small search window determined by setting the position indicated by the 
inputted one-pixel precision field vector 30 to its center on the inputted 
reference field 35, and outputs the detected half-pixel precision field 
vectors 36. 
The above-mentioned one-pixel precision field vector 30 and the minimum 
distortion 29 are both inputted to the second motion vector discriminator 
10. The second motion vector discriminator 10 accumulates the one-pixel 
precision field vector 30 and the minimum distortion 29 for only one 
field, respectively, selects the one-pixel precision field vector having a 
smallest distortion between the input and reference partial areas from a 
plurality of one-pixel precision field vectors obtained for a plurality of 
respective input partial areas located at the same position on the 
picture, and outputs the selected one as the one-pixel precision field 
vector 37. 
The outputted one-pixel precision field vector 37 is delayed by a delay 
circuit 13 by a time obtained to detect one field motion vector. The 
delayed one-pixel precision field vector 40 is inputted to a frame vector 
detector 15. 
The input field 34 obtained by delaying the input field 21 through a delay 
circuit 7 by a time required to retrieve a one-pixel precision field 
vector in one search window is inputted to a frame memory 11. The frame 
memory 11 has a capacity for storing two fields. Therefore, an input frame 
39 can be formed by writing a predetermined number (e.g., two in this 
case) of the input fields for constituting one frame. The input frame 39 
is inputted to the frame vector detector 15. 
Further, the reference fields 32 and 33 delayed through the delay circuits 
5 and 7 (the same delay time by the delay circuit 7) by the same time, 
respectively are inputted to a frame memory 12. The frame memory 12 has a 
capacity for storing two fields. Therefore, a reference frame 38 can be 
formed by writing a predetermined number (e.g., two in this case) of the 
reference fields constituting one frame. The reference frame 38 is delayed 
through a delay circuit 14 by a time required to detect a field motion 
vector. The delayed reference frame 41 is inputted to the frame vector 
detector 15. 
The half-pixel precision frame vector can be searched on the reference 
frame 41 by use of the frame vector detector 15. 
FIG. 15 shows the frame vector detector 13. Here, the construction and the 
operation of the frame vector detector 15 will be described hereinbelow. 
Here, a first position converter 151 converts the position on the reference 
field indicated by the already-inputted and detected one-pixel precision 
field vector 40 into the position on the reference frame, and outputs the 
converted position on the reference frame to a search window setter 152 as 
the frame vector 48. 
The search window setter 152 sets the small search window for detecting the 
half-pixel precision frame vector on the basis of the inputted frame 
vector 48, and inputs the search window date 49 to a reference frame 
memory 154. 
The reference frame memory 154 stores the reference frame 41, and outputs 
the reference partial area date 51 in the small search window indicated by 
the search window data 49 (inputted by the search window setter 152) to a 
distortion calculator 155. In addition, the reference frame memory 154 
outputs the half-pixel precision position data 52 to a minimum distortion 
detector 156. 
On the other hand, the input frame 39 is inputted to an input partial area 
memory 153. The input partial area memory 153 outputs the input partial 
area data 50 to a distortion calculator 155. 
The distortion calculator 155 calculates the distortion between the 
inputted input partial area data 50 and the inputted reference partial 
area data 51 and outputs the calculated distortion 53 to the minimum 
distortion detector 156. 
The minimum distortion calculator 156 detects the position data 52 which 
can minimize the distortion 58 in the search window, and outputs the 
half-pixel precision frame vector 42 indicative of the reference partial 
area position on the picture. 
The fourth embodiment of the vector detector according to the present 
invention will be described hereinbelow with reference to FIG. 16. 
The reference field 22 is inputted to a fourth field vector detector 161, 
and the reference field 23 is inputted to a fifth field vector detector 
162. 
Further, the input field 21 to be coded is inputted to the fourth and fifth 
field vector detectors 161 and 162, respectively. 
Separately, the already-detected one-node precision field vector 55 
required to set the search window is inputted to the fourth and fifth 
field vector detectors 161 and 162, respectively. 
Operating in the same way, the fourth and fifth field vector detectors 161 
and 162 retrieve the one-node precision field vectors on the inputted 
reference fields, respectively, which are constructed as shown in FIG. 17, 
respectively. 
With reference to FIG. 17, the construction and the operation of the fourth 
field vector detector 161 will be explained hereinbelow by way of example. 
Here, the already-detected field vector 55 is converted by a second 
position converter 171 into the motion vector 65 on the reduced reference 
field. Further, on the basis of the converted field vector 65, a search 
window setter 172 sets the search window for detecting the one-node 
precision field vector, and outputs the search window date 66 to a reduced 
reference field memory 175. Further, when the already-obtained motion 
vector is not used to set the retrieval range, the search window setter 
172 sets a search window to a predetermined position on the reduced 
reference field to detect the motion vector. The search window data 66 is 
outputted to a reduced reference field memory 175. 
The reduced reference field memory 175 stores the reduced reference field 
68 (obtained by sampling the reference field 22 by a sub-sampler 176), and 
outputs the reduced reference partial area data 70 in the search window 
indicated by the search window data 66 (inputted from the search window 
setter 172) to a distortion calculator 177. Further, the reduced reference 
field memory 175 outputs the one-node precision position data 71 on the 
reduced picture of the reduced reference partial area to a minimum 
distortion detector 178. 
On the other hand, the input field 21 is sampled by a sub-sampler 173, and 
the sampled input field 67 is inputted to a reduced input partial area 
memory 174. The reduced input partial area memory 174 outputs the reduced 
input partial area data 69 to the distortion calculator 177. 
The distortion calculator 177 calculates a distortion between the inputted 
reduced input partial area data 69 and the reduced reference partial area 
date 70, and outputs the calculated distortion 72 to the minimum 
distortion detector 178. 
The minimum distortion detector 178 detects the position date 71 in the 
reduced reference partial area having a minimum distortion 72 in the 
search window, and outputs the motion vector 74 indicative of the position 
in the reduced reference partial area on the reduced reference field and 
the minimum distortion 56. Further, the motion vector 74 indicative of the 
position on the reduced reference field is converted into a motion vector 
57 on the non-reduced reference field by a third position converter 179. 
As described above, the one-node precision field vector 57 (obtained by 
sampling the reference field 22 and searched on the reduced reference 
field) and the minimum distortion 56 at that time both obtained by the 
fourth field vector detector 161 are inputted to a third motion vector 
discriminator 163 shown in FIG. 16. In the same way, the one-node 
precision field vector 59 (obtained by sampling the reference field 23 and 
searched on the reduced reference field in the same way as with the case 
of the fourth field vector detector 151) and the minimum distortion 59 at 
that time both obtained by the fifth field vector detector 162 are 
inputted to the third motion vector discriminator 163. In addition, the 
one-node precision field vector 57 is also inputted to the first field 
vector detector 1, and the one-node precision field vector 59 is inputted 
to the second field vector detector 2. 
The third motion vector discriminator 163 compares the inputted minimum, 
distortion 56 with the minimum distortion 58 to select the motion vector 
having a smaller distortion between the reduced input partial area and 
reduced reference partial area from the inputted one-node precision field 
vectors 57 and 59, and outputs the selected motion vector as the field 
vector 54. The one-node precision field vector 54 is delayed through a 
delay circuit 165 by a time required to detect the motion vector on one 
reduced field, and outputted as the already-detected motion vector 55 to 
the fourth and fifth field vector detectors 161 and 162, respectively. The 
motion vector 55 is used when the motion vector search window on the 
reduced field is set for the succeeding input field. 
The one-node precision field vector 57 is inputted to the first field 
vector detector 1, and the one-node precision field vector 59 is inputted 
to the second field vector detector 2. Further, the input field 21 is 
delayed through a delay circuit 164 by a time required to detect the 
motion vector on one reduced field. The delayed input field 60 is inputted 
to the first and second field vector detectors 1 and 2, respectively. 
Further, the reference field 22 is delayed through a delay circuit 166 by 
a delay time the same as that of the delay circuit 164, and the delayed 
reference field 62 is inputted to the first field vector detector 1. 
Further, the reference field 23 is delayed through a delay circuit 167 by 
a delay time the same as that of the delay circuit 164, and the delayed 
reference field 63 is inputted to the second field vector detector 2. 
The first field vector detector 1 searches, on the delayed reference field 
62, the one-pixel precision field vector in the search window of a size 
determined according to the sub-sampling ratio and by setting the position 
indicated by the one-node precision field vector 57 on the picture as its 
center. In the same way, the second field vector detector 2 retrieves, on 
the delayed reference field 63, the one-pixel precision field vector in 
the search window of a size determined according to the sub-sampling ratio 
and by setting the position indicated by the one-node precision field 
vector 59 on the picture as its center. 
The one-pixel precision field vector 26 obtained by the first field vector 
detector 1 and the minimum distortion 25 at that time are inputted to the 
first motion vector discriminator 3. Further, in the same way, the 
one-pixel precision field vector 28 obtained by the second field vector 
detector 2 and the minimum distortion 25 at that time are inputted to the 
first motion vector discriminator 3. 
The first motion vector discriminator 3 compares the inputted minimum 
distortion 25 with the minimum distortion 27 to select the motion vector 
having a smaller distortion between the input partial area and reference 
partial area from the inputted one-pixel precision field vectors 26 and 
28, and outputs the selected one as the field vector 30. Further, the 
minimum distortion at that time is outputted as the distortion 29. 
Further, the select data 31 indicative of the reference field of smaller 
distortion between the input and reference partial areas is also 
outputted. Further, the one-pixel precision field vector 30 is inputted as 
it is to the second motion vector discriminator 10 and the third field 
vector detector 9 as it is. 
The select data 21 indicative of the reference field having a smaller 
distortion is inputted to a reference field selector 8. Further, the 
reference field data 62 already delayed through the delay circuit 166 by 
the time required to detect the motion vector on the reduced field is 
further delayed through a delay circuit 5 by a time required to search the 
one-pixel precision yield vector in one search window. The reference field 
data 32 delayed through this delay circuit 5 is also inputted to the 
reference field selector 8. In the same say, the reference field data 63 
already delayed through the delay circuit 167 is further delayed through a 
delay circuit 6 (the same delay time as that of the delay circuit 5). The 
reference field data 33 delayed through this delay circuit 6 is also 
inputted to the reference field selector 8. 
The reference field selector 8 selects one of the inputted reference field 
data 32 and the reference field data 33 on the basis of the inputted 
reference field select data 31, and outputs the selected one as the 
reference field 35. 
The reference field 35 is inputted to the third field vector detector 9. 
Further, the input field date 60 already delayed through a delay circuit 
164 by a time required to detect the motion vector on the reduced field is 
further delayed through a delay circuit 7 by the time same as that of the 
delay circuit 5. This delayed input field 34 is also inputted to the third 
field vector detector 9. Further, the one-pixel precision field vector 30 
outputted by the first motion vector discriminator 3 is also inputted to 
the third field vector detector 9. 
The third field vector detector 3 searches the half-pixel precision field 
vector for the input partial area on the inputted input wield 34, in the 
small search window determined by setting the position indicated by the 
inputted one-node precision field vector 30 on the inputted reference 
field 35 as its center. The detected half-pixel precision field vector 36 
is outputted. 
The above-mentioned one-pixel precision field vector 30 and the minimum, 
distortion 29 are both inputted to the second motion vector discriminator 
10. The second motion vector discriminator 10 accumulates the one-pixel 
precision field vector 30 and the minimum distortion 29 for only one 
field, respectively, selects one-pixel precision field vector having a 
smallest distortion between the input and reference partial areas from a 
plurality of one-pixel precision field vectors obtained for a plurality of 
respective input partial areas located at the same position on the 
picture, and outputs the selected one as the one-pixel precision field 
vector 37. 
The outputted one-pixel precision field vector 37 is delayed through the 
delay circuit 13 by a time required to detect one field motion vector. The 
delayed one-pixel precision field vector 40 is outputted to the frame 
vector detector 15. 
The input field 34 delayed by a time required to retrieve a one-pixel 
precision field vector in one search window through the delay circuit 7 is 
inputted to a frame memory 11. The frame memory 11 has a capacity for 
storing two fields. Therefore, an input frame 39 can be formed by writing 
a predetermined number (e.g., two in this case) or the input fields of 
constituting one frame. The input frame 39 is inputted to the frame vector 
detector 15. 
Further, the reference fields 32 and 33 delayed through the delay circuits 
5 and 7, respectively by the same delay time as that of the delay circuit 
7 are inputted to a frame memory 12. The frame memory 12 has a capacity 
for storing two fields. Therefore, a reference frame 38 can be formed by 
writing a predetermined number (e.g., two in this case) of the reference 
fields for constituting one frame. The reference frame 38 is delayed 
through a delay circuit 14 by a time required to detect a one field motion 
vector. The delayed reference frame 41 is inputted to the frame vector 
detector 15. 
The frame vector detector 15 searches the half-pixel precision field vector 
on the reference frame 41, and outputs the detected half-pixel precision 
frame vector 42. 
The method and system of detection motion vectors according to the present 
invention have been described as above. Without being limited only 
thereto, however, the present invention can be modified in various ways as 
far as: the motion vector is detected for the partial area formed by the 
input picture field; and the frame vector is obtained by detecting notion 
vectors for the partial area formed by the input picture frame within a 
search window determined on the basis of a position indicated by the 
obtained field vector on the reference picture. For instance, the motion 
vector for the partial area formed by the field is detected for each 
partial area formed by the frame, and the frame vector is obtained by 
detecting motion vectors for the partial area formed by the input picture 
frame within a search window determined on the basis of a position 
indicated by the obtained field vector on the reference picture. 
Further, the present invention can be applied to fields and frames sampled 
in the horizontal direction as with the case of MUSE (multiple sub-Nyquist 
sampling encoding), for instance in the same way as the above-mentioned 
embodiments in which the non-sampled fields and framers are used. 
Further, without being limited only to the embodiments described above, the 
present invention can be modified with respect to the processing procedure 
and the processing block arrangement, within the scope not departing from 
the gist of the present invention. For instance, in the fourth embodiment, 
it is possible to construct the fourth field vector detector 161 (the same 
as the fifth field vector detector 162) in such a way that the input field 
21 can be directly inputted to the input partial area memory 174; the 
sub-sampler 173 is arranged so that the input partial area data 69 
outputted by the input partial area memory 174 can be inputted thereto; 
and the input partial area memory 174 is used in common with the input 
partial area memory 142 used in the third embodiment. Further, it is also 
possible to arrange the system in such a way that the reference field 22 
can be directly inputted to the reference field memory 175; the 
sub-sampler 176 is arranged so that the reference partial area data 70 
outputted by the reference partial area memory 175 can be inputted 
thereto; and the reference field memory 175 is used in common with the 
reference field memory 143 used in the third embodiment. 
Further, in the first to fourth embodiments, fine precision field and frame 
vector retrieval methods and systems have been described, in which the 
motion vectors are detected on the basis of a field vector having the 
minimum distortion detected in relatively coarse precision. Without being 
limited only thereto, however, it is also possible to construct the 
invention in such a way that fine precision field and frame vector 
searches can be executed on the basis of a plurality of field vectors 
detected in a coarse precision.