Television – Basic receiver with additional function – Multimode
Reexamination Certificate
1998-09-02
2002-10-22
Miller, John (Department: 2614)
Television
Basic receiver with additional function
Multimode
C348S443000, C348S452000, C348S459000, C348S526000, C348S666000
Reexamination Certificate
active
06469745
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image signal processor for detecting and removing duplicate fields of an image signal such as an NTSC television signal of 30 Hz produced from a movie film of 24 Hz by means of a 3-2 pull-down system or the like.
2. Description of Related Art
While a movie is made of a film of 24 Hz, the NTSC(National Television System Committee) signaling system which is the television system presently adopted in Japan, the U.S. and other countries is an interlace signaling system having a frame rate of 30 Hz. Each NTSC signal frame is composed of two fields (hereinafter referred to respectively as a first field and a second field). Therefore, the 3-2 pull-down operation is implemented in order to convert a movie film signal into the NTSC image signal.
This point will be explained below with reference to FIG.
13
. In
FIG. 13
, a movie film signal is shown in the upper stage and an NTSC image signal is shown in the lower stage. Fields
501
and
503
are generated as signals of the first field of the NTSC signal from one frame
401
of the movie film signal and Field
502
is generated as a signal of the second field. Regarding the array of like fields, the same signal is repeated in Fields
501
and
503
of the first field of the NTSC signal and the same signal is repeated in Fields
506
and
508
of the second field as shown in the figure. Thus, the odd frame of the movie film signal is displayed for a period of three fields and the even frame is displayed for a period of two fields on the converted NTSC signal. The signal of 24 Hz is converted into the signal of 30 Hz by making five frames of the NTSC signal from four frames of the movie film signal. The converted signal is called a telecinema signal.
Here, when an amount of information of the image signal is to be compressed by using an image coding system such as MPEG-2(Moving Picture Experts Group) standardized by the International Standardization Organization for example, there is a possibility that the coding efficiency cannot be enhanced when the telecinema signal is coded because redundant duplicate fields are also coded. Thus, there has been implemented a process of implementing the coding process after removing the duplicate fields and converting the 30 Hz signal into a signal of 24 Hz which corresponds to the movie film signal. Then, the 3:2 pull-down operation is implemented after decoding the converted 24 Hz signal to form an NTSC signal of 30 Hz again.
FIG. 14
is a diagram showing a structure of a prior art television signal converter disclosed in Japanese Patent Laid-Open No. Hei. 9-55879 for example. The converter comprises VF generating means
1
for generating a VF signal indicative of whether an input signal belongs to the first field or the second field, a duplicate field detecting means
2
for detecting a duplicate field, and a duplicate field removing means
3
.
FIG. 15
is a diagram showing a structure of the duplicate field detecting means
2
in detail. The duplicate field detecting means
2
comprises field memories
10
and
11
, a subtracter
12
, absolutizing means
13
, one-field cumulative adder means
14
, duplicate field determining means
15
, comparator means
16
, a memory
17
for storing a cumulative addition signal for a period of one field, and threshold value determining means
18
.
The operation of the converter will now be explained. In
FIG. 14
, the VF generating means
1
decides whether an input image signal
100
is a signal belonging to the first field or the second field and outputs the VF signal
102
. Then, the duplicate field detecting means
2
detects a duplicate field and outputs a duplicate field discriminating signal
103
. The duplicate field removing means
3
removes the duplicate field of an image signal
101
which has been delayed for a period of two fields by the duplicate field detecting means
2
in correspondence to the duplicate field discriminating signal
103
and outputs a television signal
104
of 24 Hz.
Here, the operation of the duplicate field detecting means
2
will be explained in detail with reference to FIG.
15
. The image signal
100
is input to the field memory
10
and to the subtracter
12
. The subtracter
12
takes a difference between the image signal
101
which has been delayed by a period of two fields by the two field memories and the input image signal
100
and outputs a difference signal
201
.
The absolutizing means
13
finds an absolute value of the difference signal
201
and outputs an absolute difference signal
202
. The one-field cumulative adder means
14
cumulatively adds the absolute difference signals
202
of only one field and outputs a cumulative addition signal
203
. The cumulative addition signals
203
corresponding to the first and second fields are output alternately. The memory
17
holds the cumulative addition signals
203
sequentially and outputs a result of the cumulative addition of the first field and a result of the cumulative addition of the second field in correspondence to the VF signal
102
so that cumulative addition signals of the first and second fields can be compared by the comparator means
16
. The comparator means
16
decides whether the image signal
100
is a duplicate field or not by comparing the cumulative addition signal of the first field with the cumulative addition signal of the second field and outputs a duplicate field discriminating signal
205
and a threshold value decision signal
206
.
The decision is made as follows. The result of the cumulative addition of the first field is multiplied with a coefficient greater than 1 and compared with the result of the cumulative addition of the second field. When the result of comparison is smaller than a predetermined value, it is decided that the first field may be a duplicate field. The result of the cumulative addition of the second field is multiplied with a coefficient greater than 1 and compared with the result of cumulative addition of the first field. When the result of comparison is smaller than a predetermined value, it is decided that the second field may be a duplicate field. In such case, the duplicate field discriminating signal
205
is turned ON. It is also decided that when each of the above-mentioned results of comparison is greater than the predetermined value, the fields are not duplicated fields and the duplicate field discriminating signal
205
is turned OFF.
The threshold value determining means
18
decides a threshold value in correspondence to the threshold value decision signal
206
and outputs a threshold value signal
207
. The duplicate field determining means
15
compares the cumulative addition signal
203
with the threshold value signal
207
and decides that the signal is a duplicate field when the cumulative addition signal
203
is smaller than the threshold value signal
207
and the duplicate field discriminating signal
205
is turned ON to output the duplicate field discriminating signal
103
. Such arrangement allows the duplicate field to be detected without being affected by noise because the threshold value signal
207
is controlled in correspondence to an amount of conversion noise generated in converting the movie film signal into the telecinema signal and because whether or not the signal is a duplicate field depends on this threshold value signal
207
and the duplicate field discriminating signal
205
.
However, the prior art television signal converter, constructed as described above, has had a problem because no large difference is produced between the cumulative value of the difference signal of the first field and the cumulative value of the difference signal of the second field. Namely, when the motion of a scene of the movie film is temporarily small or when a still scene appears, the ratio, even when found, becomes close to 1. Therefore, the input signal erroneously may be recognized as a duplicate field of the telecinema signal.
Further, because many of the movie image signals are displayed
Kato Yoshiaki
Murakami Tokumichi
Yamada Yoshihisa
Miller John
Mitsubishi Denki & Kabushiki Kaisha
Natnael Paulos
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