Apparatus for producing a composite signal from real moving picture and still picture video signals

A video signal processing apparatus has an input terminal receiving a real moving picture video signal, for example, from a video camera, a memory for storing at least one field of the real moving picture video signal so as to form a still picture video signal, a key signal generator which may be constituted by an additional memory storing data characteristic of a key picture, and a circuit responsive to reading of the data stored in the additional memory for switching between the real moving picture video signal and the still picture video signal and thereby forming a composite video signal therefrom.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to video signal processing 
apparatus and, more particularly, is directed to a video signal processing 
apparatus adapted for incorporation in a home video camera. 
2. Description of the Prior Art 
In a known home video camera, a binary value signal, for example, 
representing characters, indicia and the like to be used in creating a 
title, is generated in advance and converted into a color signal which is 
mixed or composed with a real moving picture video signal so as to provide 
a composite signal that may be displayed as a title picture. In such known 
home video camera, it is desirable to be able to mix other video signals 
as well as the generated binary value signal with the real moving picture 
video signal. 
Further, it has been proposed to reduce noise in a video signal by using a 
so-called field memory, for example, as disclosed in Japanese Patent 
Published Gazette No. 62-3639. An example of a previously-proposed noise 
reducing circuit employing a field memory is shown in FIG. 1 in which a 
video signal Y applied to an input terminal 1 is supplied directly 
therefrom to an adder 2 having its output signal Y' supplied to an output 
terminal 3 and also to a field memory 4. Further, a video signal Y.sub.D 
delayed, for example, one field period, by the field memory 4, is supplied 
from the latter to one input of a subtractor 5 which, at its other input 
receives the video signal Y applied to the input terminal 1. Thus, the 
video signal Y applied to the input terminal 1 is subtracted from the 
delayed video signal Y.sub.D, and the result of such subtraction, that is, 
(Y.sub.D -Y), is supplied to a coefficient generator 6. The coefficient 
generator 6 provides, as its output, a signal k (Y.sub.D -Y) in which k is 
a coefficient provided in the generator 6 and which is selected in 
response to the magnitude of the difference or output (Y.sub.D -Y) from 
the 10 subtractor 5. Such output k (Y.sub.D -Y) from the coefficient 
generator 6 is applied to another input of the adder 2 so that the signal 
Y' appearing at the output of the adder 2, and hence derived at the output 
terminal 3, is expressed by the following noise reducing equation: 
EQU Y'=Y+k (Y.sub.D -Y) 
or 
EQU Y'=(1-k)Y+kY.sub.D ( 1) 
Therefore, noise can be reduced by properly selecting the value of the 
coefficient k in response to the magnitude of the difference (Y.sub.D -Y) 
between the signal Y at the input and the delayed signal Y.sub.D. More 
specifically, the value of the coefficient k is selected so as to provide 
a characteristic substantially as shown on FIG. 2, in which the 
inclination of the illustrated curve represents the coefficient k. In the 
characteristic curve shown on FIG. 2, the portion corresponding to a 
relatively large magnitude of the difference (Y.sub.D -Y) corresponds to a 
real moving picture and, accordingly, the value of the coefficient k is 
decreased. On the other hand, a portion of the curve or graph shown on 
FIG. 2 for a relatively small magnitude of the difference (Y.sub.D -Y) 
corresponds to a still picture and, accordingly, the coefficient k is then 
selected to be near 1.0, with the result that the amount of feedback 
through the field memory 4 is increased for reducing the noise in the 
output video signal. 
In a practical embodiment of the coefficient generator 6, the latter may 
include, for example, a read only memory (ROM) from which there are 
derived output data k(Y.sub.D -Y) in response to the application to the 
ROM of the value (Y.sub.D -Y) as address data therefor. Further, in order 
to provide for varying the degree of noise reduction, the ROM may have a 
plurality of data patterns established therein which are selectively 
addressed. 
It will be appreciated that, in the prior art noise reducing circuit 
described above with reference to FIG. 1, the field memory 4 thereof is 
used to mix video signals. If a so-called video image memory is employed 
as the field memory 4, such video image memory is generally arranged to 
generate data of a lower address from the inside of the memory in order to 
facilitate generation of address data at the outside of the memory, with 
data being written and/or read in units of, for example, 60 blocks. For 
the foregoing reason, if a so-called video image memory is used to mix the 
video signals in the noise reducing circuit, the signal cannot be readily 
rewritten in pixel units so that the video signals cannot be conveniently 
mixed. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved video signal processing apparatus which can avoid the above 
described disadvantages of the prior art. 
More specifically, it is an object of the present invention to provide a 
video signal processing apparatus in which video signals transmitted 
through a single signal line can be made composite by means of a 
relatively simple circuit arrangement. 
Another object of the present invention is to provide a video signal 
processing apparatus, as aforesaid, which can also serve as a noise 
reducing circuit. 
Still another object of the present invention is to provide a video signal 
processing circuit which can also function as a drop-out compensating 
circuit. 
In accordance with an aspect of the present invention, a video signal 
processing apparatus comprises means, such as an image pick-up device, for 
providing a real moving picture video signal which is supplied to an input 
terminal, a memory for storing therein at least one field of the real 
moving picture video signal so as to form a still picture video signal, 
means for generating a key signal, and means responsive to such key signal 
for selectively switching between the real moving picture video signal and 
the still picture video signal so as to form a mixed video signal supplied 
to an output terminal. 
The above, and other objects, features and advantages of the present 
invention, will be apparent in the following detailed description of 
preferred embodiments when read in conjunction with the accompanying 
drawings, in which the same reference numerals are used to identify 
corresponding or similar parts in the several views.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring now to FIG. 3, it will be seen that, in a first embodiment of a 
video signal processing apparatus according to the invention, a noise 
reducing circuit similar to that described previously with reference to 
FIG. 1 is utilized and has its several parts identified by the same 
reference numerals. More specifically, in the embodiment of FIG. 3, an 
input video signal Y, for example, from an image pick-up portion or 
element 11 of a video camera -0, is supplied through a single signal line 
to an input terminal 1 from which, as before, the video signal is supplied 
directly to respective inputs of an adder 2 and a subtractor 5. However, 
the video signal applied to the input terminal 1 in FIG. 3 is also 
supplied to a binary memory 12 having a bit number which corresponds to 
the number of pixels or picture elements in, for example, one field of a 
video signal. 
As before, the output Y' of the adder 2 is applied to the output terminal 3 
and also to the field memory 4, and the output Y.sub.D from the field 
memory 4 is applied to a respective input of the subtractor 5 which, in 
turn, has its output (Y.sub.D -Y) applied to a coefficient generator 6. 
However, in the embodiment of the present invention illustrated on FIG. 3, 
the output of the coefficient generator 6 is supplied to one fixed contact 
13a of a change-over switch 13 which further has a movable contact 13c 
alternately engageable with the fixed contact 13a or with another fixed 
contact 13b to which a signal representing the logic value "0" is 
supplied. The change-over switch 13 is controlled by a key signal KEY read 
out from the binary memory 12, and the movable contact 13c is connected to 
a respective input of the adder 2. 
Further, in the embodiment of the invention shown on FIG. 3, the 
coefficient generator 6 is provided with a "throughmode" in which input 
address data is directly output from generator 6. Thus, when the 
coefficient generator 6 is in its through-mode, that is, the change-over 
switch 13 is positioned or conditioned by the key signal KEY to engage its 
movable contact 13c with the fixed contact 13a, it is the equivalent of 
providing the coefficient k of the coefficient generator 6 with the logic 
value "1". In such case, the previously described noise reducing equation 
(1) can be rewritten as: 
##EQU1## 
Therefore, when the coefficient generator 6 is in its through-mode or the 
switch 13 engages its fixed contact 13a so that the coefficient k equals 
"1", the data output from the terminal 3 and contemporaneously written in 
the field memory 4 corresponds to the data of the preceding field, that 
is, the data of the preceding field is stored in the field memory 4 and a 
still picture video signal is output at the terminal 3. On the other hand, 
when the switch 13 engages its movable contact 13cwith the fixed contact 
13b, this is the equivalent of providing the coefficient k of the 
coefficient generator 6 with the value "0". In such case, the noise 
reducing equation (1) is rewritten as: 
##EQU2## 
Therefore, the data being supplied to the input terminal 1 is 
contemporaneously outputted at the output terminal 3 and also 
contemporaneously written in the field memory 4, that is, data stored in 
the field memory 4 is replaced with new data whenever the switch 13 
engages its fixed contact 13b. 
It will be appreciated that the switching operation of the change-over 
switch 13 is controlled in pixel units, that is, pixel-by-pixel, by the 
key signal KEY read from the memory 12. Thus, for each pixel, the movable 
contact 13c of the change-over switch 13 engages either the fixed contact 
13a corresponding to k ="1", or the fixed contact 13b corresponding to 
k="0". At any pixel for which movable contact 13c engages fixed contact 
13a, that is, k="1", the output Y' of the adder 2 is equal to the delayed 
signal Y.sub.D from the field memory 4 (equation 2), so that the data 
being read from the memory 4 for the respective pixel is written again in 
the field memory. On the other hand, at any pixel for which the movable 
contact 13c of the switch 13 is made to engage the fixed contact 13b, that 
is, k="0", the output Y' of the adder 2 is equal to the input video signal 
Y for that pixel (equation 3). Therefore, only the video signal for the 
pixel at which the key signal KEY causes the switch 13 to engage its fixed 
contact 13b is written as new data in the field memory 4. It will be 
appreciated from the foregoing that, in the video signal processing 
apparatus embodying the present invention, as shown on FIG. 3, data can be 
written in pixel units in the field memory 4 irrespective of the writing 
and/or reading system of such field memory. 
The operation of the video signal processing apparatus described above with 
reference to FIG. 3 will now be described with reference to FIGS. 4A-4D. 
Initially, and as indicated at 10A on FIG. 4A, the video camera is aimed 
at a black and white key picture 15 which, for example, defines a 
heart-shaped area 15a, and the corresponding binary values of the pixels 
representing the key picture 15 are stored in the memory 12. Then, as 
indicated at 10B in FIG. 4B, the video camera is directed at a suitable 
scene, for example, a background of flowers as indicated at 16, while the 
change-over switch 13 is suitably controlled to continuously engage its 
movable contact 13c with the fixed contact 13a, with the result that the 
video image picked up by the video camera in the position 10B is stored as 
a still picture in the field memory 4. Thereafter, and as indicated at 10C 
in FIG. 4C, the video camera is employed for providing a real moving 
picture video signal, for example, of moving figures indicated at 17, 
while the key signal stored in the memory 12 and corresponding to the key 
picture 15 is output from the memory 12 and used for controlling the 
change-over switch 13. As a result of the foregoing, a mixed or composite 
video signal is obtained at the output terminal 3 for providing a 
composite video picture, as shown in FIG. 4D, and in which a real moving 
picture 17' is superimposed, within the heart-shaped area 15'a, upon a 
still picture 16'. 
It will be apparent from the above described operation of the video signal 
processing apparatus of FIG. 3 that, in accordance with the invention, a 
still picture video signal stored in the memory 4 and a real moving 
picture video signal being provided by the video camera 10 are switched or 
alternated on the basis of the key signal KEY from the memory 12, so that 
the still and moving picture video signals are composed or multiplexed by 
a simplified arrangement for transmission through a single signal line 
from the output terminal 3. 
Although the change-over switch 13 is controlled pixel-by-pixel, the field 
memory 4 may be a video image memory in which the writing and reading are 
performed in block units. 
Further, as shown in FIG. 3B, the coefficient generator 6 and the 
changeover switch 13 may be constituted by a multiplier 6' and a read only 
memory (ROM) having data patterns of k="1" and k="0" which are selected in 
response to the key signal KEY and then employed in the multiplier for 
multiplying the input signal (Y.sub.D -Y) and providing the output k 
(Y.sub.D -Y) to the respective input of the adder 2. 
Furthermore, as shown in FIG. 3A, a drop-out detector 12A for sensing a 
drop out in the input video signal Y may be employed in place of the 
memory 12 to provide a drop out detecting signal S.sub.D instead of the 
key signal KEY for controlling the change-over switch 13. In such case, 
the described video signal processing apparatus can be used as a drop out 
compensating circuit in which the movable contact 13c of the switch 13 
normally engages its fixed contact 13b to provide at the output terminal 3 
an output signal Y' corresponding to the input signal Y. On the other 
hand, when a drop out is detected, the resulting drop out detecting signal 
S.sub.D causes the movable contact 13c of the switch 13 to engage the 
fixed contact 13a with the result that the signal Y' then appearing at the 
output terminal 3 corresponds to the signal Y.sub.D of the preceding field 
so as to compensate for the detected drop out. 
If a video signal processing apparatus embodying this invention does not 
need to serve as a noise reducing circuit, such apparatus may be arranged 
as shown in FIG. 5 in which parts corresponding to those described with 
reference to FIG. 3 are identified by the same reference numerals In the 
apparatus of FIG. 5, the video signal applied to the input terminal 1 is 
supplied directly to the fixed contact 13a of the change-over switch 13, 
and is also supplied through a switch 14 to an input of the field memory 4 
which has its output connected to the fixed contact 13b. Further, the 
movable contact 13c of the switch 13 is connected to the output terminal 3 
and the switch 13 is again controllable by a key signal KEY read from the 
memory 12 which has an input connected with the input terminal 1. 
Initially, a key picture, for example, a shown in FIG. 4A, is picked by 
the image pick-up element or portion 11 of a video camera, and a 
corresponding key picture signal is written in the memory 12. Thereafter, 
the switch 14 is suitably closed while the video camera is directed at a 
background scene 16, as at 10B in FIG. 4B, with the result that a 
corresponding still picture signal is written in the field memory 4. 
Finally, the switch 13 is controlled by the key signal KEY read out from 
the memory 12 while a real moving picture is picked up by the image 
pick-up portion 11 of the video camera, as at 10C in FIG. 4C, with the 
result that a mixed video signal is obtained at the output terminal 3 for 
providing a mixed video picture, again as shown in FIG. 4D, and in which a 
real moving picture 17' is superimposed, within the heart-shaped area 
15'a, upon a still picture 16'. 
It will be understood that, in the above described apparatus of FIG. 5, the 
heart-shaped area 15a of the key picture may be increased or reduced in 
size, for example, as shown in dotted lines at 15b and 15c, respectively, 
on FIG. 6A, by suitably controlling the read addresses of the memory 12, 
whereby a so-called wipe effect is achieved. Alternatively, a wipe effect, 
in which the key picture is moved laterally from left to right as shown in 
FIG. 6B, or vertically upward or downward, can be similarly achieved by 
suitably controlling the read addresses of the memory 12. Furthermore, if 
the key picture is a simple geometric figure, as described above, the 
memory 12 may be replaced by a suitable key signal generator, such as, a 
ROM or the like which is addressed for providing the desired key picture 
signal KEY for controlling the switch 13. 
In the embodiments of this invention shown on FIGS. 3 and 5, the input 
video signal applied to the input terminal 1 has been shown to be derived 
from the image pick-up portion or element 11 of a video camera 10. 
However, the video signal processing apparatus embodying the invention may 
be also incorporated in a video tape recorder (VTR), editing apparatus or 
the like, in which, for example, the input video signal is derived from a 
magnetic head or the like which reproduces a video signal recorded on a 
magnetic tape or other medium. 
Although illustrative embodiments of the invention have been described in 
detail herein with reference to the accompanying drawings, it is to be 
understood that the invention is not limited to those precise embodiments, 
and that various changes and modifications may be effected therein by one 
skilled in the art without departing from the scope or spirit of the 
invention as defined in the appended claims.