 |
Claims  |
|
|
What is claimed is:
1. An image sensing apparatus for automatically matching the focus relative
to an object, comprising:
image sensing means (2, 8) having a focusing lens and an image sensor for
generating a video signal in response to light incident from said object,
relative position changing means (3, 4) for changing a relative position in
the direction of an optical axis of said focusing lens relative to said
image sensor,
sampling area setting means (13, 15) for setting a first sampling area
located in the center of an image sensed picture and a second sampling
area including said first sampling area and having a larger area than that
of said first sampling area by time division of said video signal,
focus evaluating value detecting means (9, 10, 13, 4, 16, 17) for detecting
every constant time period a level of a high frequency component in a
video signal in each of said first and second sampling areas to supply the
same as a focus evaluating value in the corresponding sampling area,
each of the focus evaluating values taking the maximum value in an in-focus
position,
means (26) for selecting either one of said first and second sampling areas
as a focusing area according to a relative relation between the newest
value of the focus evaluating value in each of said first and second
sampling areas and a variable reference value calculated based on the
previous focus evaluating value in the corresponding sampling area, and
control means (26, 27) for controlling said relative position changing
means based on a focus evaluating value corresponding to the sampling area
selected as said focusing area so as to drive the relative position of
said focusing lens to a position where the focus evaluating value becomes
the maximum value.
2. The image sensing apparatus according to claim 1, wherein said focusing
area selecting means comprises
means for calculating said variable reference value based on the maximum
value of the previous focus evaluating value in said corresponding
sampling area.
3. The image sensing apparatus according to claim 2, wherein said focusing
area selecting means comprises
means for selecting a focusing area depending on which of the difference
between the newest focus evaluating value and the maximum value of the
previous focus evaluating value in said corresponding sampling area and
said variable reference value is larger.
4. The image sensing apparatus according to claim 3, wherein said variable
reference value is a value which is one-n-th (n: positive integer) of the
maximum value of the previous focus evaluating value in said corresponding
sampling area.
5. The image sensing apparatus according to claim 4, wherein said variable
reference value is a value which is one-eight of the maximum value of the
previous focus evaluating value in said corresponding sampling area.
6. The image sensing apparatus according to claim 3, wherein said focusing
area selecting means comprises
means for switching focusing areas when the difference between said newest
focus evaluating value and the maximum value of the previous focus
evaluating value exceeds said variable reference value.
7. The image sensing apparatus according to claim 1, wherein said focus
evaluating value detecting means comprises
first filter means for extracting a level of a first high frequency
component in said video signal,
second filter means for extracting a level of a second high frequency
component including a component at a frequency which is lower than the
frequency of said first high frequency component,
means for alternately selecting outputs of said first and second filter
means every said constant time period, and
means for accumulating every said first and second sampling areas the level
of the first or second high frequency component in said video signal
extracted by said first or second filter means.
8. The image sensing apparatus according to claim 1, wherein said focusing
area selecting means makes selection after the relative position of said
focusing lens is driven once to the position where said focus evaluating
value becomes the maximum value.
9. An image sensing apparatus for automatically matching the focus relative
to an object, comprising:
image sensing means (2, 8) having a focusing lens and an image sensor for
generating a video signal in response to light incident from said object,
relative position changing means (3, 4) for changing a relative position in
the direction of an optical axis of said focusing lens relative to said
image sensor,
sampling area setting means (13, 15) for setting a first sampling area
located in the center of an image sensed picture and a second sampling
area including said first sampling area and having a larger area than that
of said first sampling area by time division of said video signal,
focus evaluating value detecting means (9, 10, 13, 14, 16, 17) for
detecting every constant time period a level of a high frequency component
in a video signal in each of said first and second sampling areas to
supply the same as a focus evaluating value in the corresponding sampling
area,
each of the focus evaluating values taking the maximum value in an in-focus
position,
means (26) for selecting either one of said first and second sampling areas
as a focusing area,
first control means (26) for controlling said relative position changing
means based on a focus evaluating value corresponding to the sampling area
selected as said focusing area so as to drive the relative position of
said focusing lens to a position where the focus evaluating value takes
the maximal value having a predetermined projected amount as compared with
focus evaluating values in relative positions of focusing lens before and
after said position of said focusing lens, and
second control means (26) for comparing the respective maximum values of
the focus evaluating values in said first and second sampling areas per
unit area when the focus evaluating value corresponding to said selected
sampling area does not take said maximal value and controlling said
relative position changing means so as to fix the relative position of
said focusing lens to a position where the focus evaluating value in the
sampling area having the larger maximum value reaches a maximum.
10. The image sensing apparatus according to claim 9, wherein said focusing
area selecting means comprises
means for selecting either one of said first and second sampling areas as a
focusing area according to a relative relation between the newest value of
said focus evaluating value in each of said first and second sampling
areas and a variable reference value calculated based on the previous
focus evaluating value in the corresponding sampling area.
11. The image sensing apparatus according to claim 9, wherein said focus
evaluating value detecting means comprises
first filter means for extracting a level of a first high frequency
component in said video signal,
second filter means for extracting a level of a second high frequency
component including a component at a frequency which is lower than the
frequency of said first high frequency component,
means for alternately selecting outputs of said first and second filter
means every said constant time period, and
means for accumulating every said first and second sampling areas the level
of the first or second high frequency component in said video signal
extracted by said first or second filter means.
12. An image sensing apparatus for automatically matching the focus and the
exposure relative to an object, comprising:
image sensing means (2, 8) having a focusing lens and an image sensor for
generating a video signal in response to light incident from said object,
relative position changing means (3, 4) for changing a relative position in
the direction of an optical axis of said focusing lens relative to said
image sensor,
means (6, 7) for changing exposure relative to said object,
means (13, 15) for setting a plurality of sampling areas divided on an
image sensed picture by time division of said video signal,
focus evaluating value detecting means (9, 10, 13, 14, 16-21) for detecting
every constant time period a level of a high frequency component in a
video signal in each of said plurality of sampling areas to supply the
same as a focus evaluating value in the corresponding sampling area,
each of the focus evaluating values taking the maximum value in an in-focus
position,
exposure evaluating value detecting means (11, 13, 14, 16-21) for detecting
every constant time period a level of a luminance signal in the video
signal in each of said plurality of sampling areas to supply the same as
an exposure evaluating value in the corresponding sampling area,
first selecting means (26) for selecting any one of said plurality of
sampling areas as a focusing area,
first control means (26) for controlling said relative position changing
means based on a focus evaluating value corresponding to the sampling area
selected as said focusing area so as to drive the relative position of
said focusing lens to a position where the focus evaluating value becomes
the maximum value,
second selecting means (26) for selecting as a priority area for exposure
control the sampling area selected by said first selecting means, and
second control means (26) for controlling said exposure changing means such
that the exposure evaluating value corresponding to the sampling area
selected as said priority area coincides with a predetermined target
level.
13. The image sensing apparatus according to claim 12, which further
comprises means for determining based on the exposure evaluating value in
each of said plurality of sampling areas whether or not an abnormal
luminance portion exists in the corresponding sampling area, and
said second selecting means selects as said priority area the sampling area
selected by said first selecting means only when said determining means
determines that no abnormal luminance portion exits.
14. The image sensing apparatus according to claim 13, wherein said
plurality of sampling areas comprises at least a first sampling area
located in the center of the image sensed picture, a second sampling are
including said first sampling area and having a larger area than that of
said first sampling area and a third sampling area defined by excluding
said first sampling area from said second sampling area.
15. The image sensing apparatus according to claim 14, wherein said second
selecting means comprises
means for selecting said first sampling area as the priority area if no
abnormal luminance portion exists in said first sampling area while
selecting said second sampling area as the priority area if an abnormal
luminance portion exists, when said first sampling area is selected as
said focusing area, and
means for selecting said second sampling area as the priority area if no
abnormal luminance portion exists in said second sampling area while
supplying the average value of exposure evaluating values in the remaining
sampling areas where no abnormal luminance portion exists to said second
control means as an exposure evaluating value in the priority area if an
abnormal luminance portion exists, when said second sampling area is
selected as said focusing area.
16. The image sensing apparatus according to claim 14, wherein said
focusing area selecting means comprises
means for selecting either one of said first and second sampling areas as a
focusing area according to a relative relation between the newest value of
said focus evaluating value in each of said first and second sampling
areas and a variable reference value calculated based on the previous
focus evaluating value in the corresponding sampling area. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an image sensing apparatus, and
more particularly, to an image sensing apparatus such as a video camera
having an automatic focusing function for automatically matching the focus
relative to an object in response to a video signal obtained from an image
sensor.
2. Description of the Background Art
Conventionally, in an automatic focusing apparatus used in an image sensing
apparatus such as a video camera, an approach utilizing a video signal
itself obtained from an image sensor for evaluating a state in which the
focus is controlled has been developed. More specifically, in such an
approach, a video signal obtained from an image sensor such as a CCD
(charge coupled device) is passed through a high-pass filter (HPF) or a
band-pass filter (BPF), to detect a high frequency component thereof as a
focus evaluating value every constant time period, for example, every one
field, and control a relative position of a lens and the image sensor such
that the focus evaluating value reaches a peak. In this approach, an area
for detecting the focus evaluating value in an image sensed picture, i.e,
a focusing area is generally fixed as an area of constant size in the
center of a picture.
Meanwhile, considering a case in which this focusing area is set large, if
images of objects at different distances from a lens included in one
picture are sensed or the background of the object has a high contrast,
that is, has a large high frequency component, it is not determined which
object is brought into focus. Thus, an object of interest to a user is not
always brought into focus.
In order to prevent such a situation, it is considered that the focusing
area is set small to bring only an object in the center of the picture
into focus. However, the object frequently moves outside of the focusing
area due to unintentional movement of the hands of the user and slight
movement of the object, which is liable to cause a malfunction of
automatic focusing.
As described in the foregoing, large and small focusing areas have both
advantages and disadvantages, respectively. As means for eliminating the
disadvantages, a technique has been proposed of providing large and small
focusing areas and setting a prescribed level of a focus evaluating value
in each of the areas. More specifically, according to such a technique,
even if an object moves outside of the small focusing area so that the
focus evaluating value in this area attains the prescribed level or less,
an auto-focus operation is carried out based on the focus evaluating value
in the large focusing area provided that the focus evaluating value in the
large focusing area is at the prescribed level or more. Thus, a technique
of switching focusing areas is disclosed in, for example, Japanese Patent
Laying-Open Nos. 17418/1988, 182704/1987 and 183877/1985. More
specifically, according to an in-focus state detecting apparatus disclosed
in Japanese Patent Laying-Open No. 17418/1988, a large focusing area is
selected after determining that the focus can not be detected in a small
focusing area and then, detection of the focus is repeated in the large
focusing area. In addition, according to an automatic focusing apparatus
disclosed in Japanese Patent Laying-Open No. 182704/1987, a focusing area
is enlarged in order to increase a focus evaluating value at the time of a
low contrast to stabilize an automatic focusing operation. Furthermore,
according to a focus detecting apparatus disclosed in Japanese Patent
Laying-Open No. 183877/1985, focusing areas are switched depending on the
focal length of an image sensing optical system.
According to the above described conventional techniques, the prescribed
level of the focus evaluating value in each of the large and small
focusing areas is a fixed value previously set. Therefore, a relative
ratio of a peak value (a value in an in-focus state) of the focus
evaluating value to the prescribed level which is the fixed value varies
depending on the object. As a result, in the case of a high-contrast
object, unless the object is considerably spaced apart from the small
focusing area, the focus evaluating value does not attain the prescribed
level or less so that the large focusing area is not selected. On the
other hand, in the case of a low-contrast object, if the object moves
slightly outside of the small focusing area, the large focusing area is
immediately selected, so that there occurs a difference between movement
of the object and timing of switching focusing areas depending on the
object.
Additionally, if and when the background of the object has a high contrast,
the focus evaluating value is large even in a significantly defocused
state. If the focus evaluating value is beyond the prescribed level in the
small focusing area, a malfunction occurs. More specifically, even if the
object completely moves outside of the small focusing area, the large
focusing area is not selected. In addition, if the object moves outside of
the large focusing area, a new peak detecting operation is not carried
out.
On the other hand, in the conventional automatic focusing apparatus, a
focus evaluating value may have no distinct peak during the auto-focus
operation. In such a case, a position where a focus evaluating value in a
fixed focusing area is slightly projected is considered as an in-focus
position, a lens being fixed therein. Thus, in the conventional automatic
focusing apparatus, the peak of the focus evaluating value due to noises
or the like may be erroneously judged to be the in-focus position, so that
a malfunction of automatic focusing is liable to occur.
On the other hand, in an image sensing apparatus such as a video camera,
control of a level of a video signal obtained from an image sensor, i.e.,
exposure control by, for example, adjusting a diaphragm and adjusting the
amplification gain, together with the above described focus control, is a
very important subject. Conventionally, a video camera has been put into
practice which has a function of automatically matching exposure, i.e., an
automatic iris function by adjusting an optical diaphragm and the
amplification factor of an amplifier for amplifying a level of a video
signal obtained from an image sensor based on the average of luminance
levels of the video signal and a level of a peak value.
However, such a conventional automatic iris system has disadvantages. For
example, if a high luminance portion such as a light source exists in a
picture, the diaphragm is driven in the closing direction so that the gain
of the entire picture is decreased, whereby a main object is
insufficiently bright. On the other hand, if the background is very dark,
the diaphragm is driven in the opening direction so that the gain of the
entire picture is increased, whereby the main object becomes too bright.
A method of eliminating the disadvantages is disclosed in, for example,
Japanese Patent Laying-Open No. 110369/1987. According to such a
technique, an optical stop-down mechanism is driven to control the amount
of light incident on an image sensor such that a luminance level of the
entire image sensed picture coincides with a reference level, and a
luminance level in a central area of a picture is weighted, as compared
with a luminance level in a peripheral area thereof to control the
amplification gain of a video signal considering the central area as a
priority area, thereby to decrease the effect of an abnormal luminance
portion such as a light source which exists in the peripheral area on
exposure control.
Meanwhile, if and when the above described automatic focusing apparatus and
exposure control apparatus are equipped with one video camera, the same
area can be set as a focusing area where an object exists and a priority
area where an object exists. However, considering a case in which large
and small focusing areas are provided and switched as described above,
when the priority area is fixed in, for example, the smaller focusing area
and the object laterally moves to be outside of the small focusing area,
the larger focusing area is selected so that an in-focus operation is most
suitably carried out. However, as for exposure control, only exposure in
the smaller focusing area where no object exists becomes most suitable. As
a result, overexposure or underexposure is liable to be obtained with
respect to the object which moves outside of the smaller focusing area.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide an image
sensing apparatus capable of preventing a malfunction of automatic
focusing by switching focusing areas according to an object.
Another object of the present invention is to provide an image sensing
apparatus in which the possibility of carrying out an automatic focusing
operation by erroneously judging a peak of a focus evaluating value due to
noises or the like to be an in-focus state can be decreased.
Still another object of the present invention is to provide an image
sensing apparatus capable of always obtaining exposure most suitable for
an object by taking an area which is a destination of an object to be
moved as a priority area for exposure control.
Briefly stated, the present invention is directed to an image sensing
apparatus for automatically matching the focus relative to an object,
which comprises an image sensing circuit having a focusing lens and an
image sensor for generating a video signal in response to light incident
from the object, a relative position changing apparatus for changing a
relative position in the direction of an optical axis of a focusing lens
with respect to the image sensor, a sampling area setting circuit for
setting a first sampling area located in the center of an image sensed
picture and a second sampling area including the first sampling area and
having a larger area than the first sampling area by time division of the
video signal, a focus evaluating value detecting circuit for detecting
every constant time period a level of a high frequency component in a
video signal in each of the first and second sampling areas to supply the
same as a focus evaluating value in the corresponding sampling area, a
circuit for selecting either one of the first and second sampling areas as
a focusing area according to a relative relation between the newest value
of the focus evaluating value in each of the first and second sampling
areas and a variable reference value calculated based on the previous
focus evaluating value in the corresponding sampling area, and a control
circuit for controlling the relative position changing apparatus based on
a focus evaluating value corresponding to the sampling area selected as
the focusing area such that a relative position of the focusing lens is
driven to a position where the focus evaluating value takes the maximum
value.
In accordance with another aspect of the present invention, an image
sensing apparatus for automatically matching the focus relative to an
object comprises an image sensing circuit having a focusing lens and an
image sensor for generating a video signal in response to light incident
from the object, a relative position changing apparatus for changing a
relative position in the direction of an optical axis of the focusing lens
with respect to the image sensor, a sampling area setting circuit for
setting a first sampling area located in the center of an image sensed
picture and a second sampling area including the first sampling area and
having a larger area than that of the first sampling area by time division
of the video signal, a focus evaluating value detecting circuit for
detecting every constant time period a level of a high frequency component
in a video signal in each of the first and second sampling areas to supply
the same as a focus evaluating value in the corresponding sampling area, a
circuit for selecting either one of the first and second sampling areas as
a focusing area, a first control circuit for controlling the relative
position changing apparatus based on the focus evaluating value
corresponding to the sampling area selected as the focusing area such that
the relative position of the focusing lens is driven to a position where
the focus evaluating value takes a maximal value having a predetermined
projected amount as compared with focus evaluating values in relative
positions of focusing lens before and after the position of the focusing
lens, and a second control circuit for controlling the relative position
changing apparatus such that the respective maximum values of the focus
evaluating values in the first and second sampling areas are compared with
each other per unit area when the focus evaluating value corresponding to
the selected sampling area does not take the maximal value, so that the
relative position of the focusing lens is fixed to a position where the
focus evaluating value in the sampling area having a larger maximum value
reaches a maximum.
In accordance with still another aspect of the present invention, an image
sensing apparatus for automatically matching the focus and exposure
relative to an object comprises an image sensing circuit having a focusing
lens and an image sensor for generating a video signal in response to
light incident from the object, a relative position changing apparatus for
changing a relative position in the direction of an optical axis of the
focusing lens with respect to the image sensor, an apparatus for changing
the exposure relative to the object, a circuit for setting a plurality of
divided sampling areas on an image sensed picture by time division of the
video signal, a focus evaluating value detecting circuit for detecting
every constant time period a level of a high frequency component in a
video signal in each of the plurality of sampling areas to supply the same
as a focus evaluating value in the corresponding sampling area, an
exposure evaluating value detecting circuit for detecting every constant
time period a level of a luminance signal in the video signal in each of
the plurality of sampling areas to supply the same as an exposure
evaluating value in the corresponding sampling area, a first selecting
circuit for selecting any one of the plurality of sampling areas as a
focusing area, a first control circuit for controlling the relative
position changing apparatus based on a focus evaluating value
corresponding to the sampling area selected as the focusing area such that
the relative position of the focusing lens is driven to a position where
the focus evaluating value reaches a maximum, a second selecting circuit
for selecting the sampling area selected by the first selecting circuit as
a priority area for exposure control, and a second control circuit for
controlling the exposure changing apparatus such that an exposure
evaluating value corresponding to the sampling area selected as the
priority area coincides with a predetermined target level.
A principal advantage of the present invention is that since not a fixed
value but a variable value set based on a focus evaluating value in each
area is used as a prescribed level for switching focusing areas, a
focusing area corresponding to an object can be selected, so that a
malfunction of automatic focusing can be prevented.
Another advantage of the present invention is that even if a focus
evaluating value has no distinct peak, an auto-focus operation is carried
out considering as a focusing area a sampling area having the larger
maximum focus evaluating value, so that erroneous detection of an in-focus
position caused by noises or the like can be prevented.
Still another advantage of the present invention is that a priority area
for exposure control is switched which follows switching of focusing
areas, so that exposure most suitable for an object can be obtained
without being affected by an area where no object exists.
The foregoing and other objects, features, aspects and advantages of the
present invention will become more apparent from the following detailed
description of the present invention when taken in conjunction with the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic block diagram showing an automatic focusing/automatic
iris apparatus according to an embodiment of the present invention;
FIG. 2 is a diagram typically showing a manner in which sampling areas are
set on an image sensed picture;
FIG. 3 is a flowchart showing a main routine of the automatic
focusing/automatic iris operation;
FIG. 4 is a flowchart showing a routine of the automatic focusing
operation;
FIG. 5 is a flowchart showing a routine for calculating focus evaluating
values and a relative ratio;
FIG. 6 is a diagram for typically explaining a manner in which the focus
evaluating value and the relative ratio are calculated;
FIG. 7 is a flowchart showing an evaluating value stability confirming
routine;
FIG. 8 is a flowchart showing a direction determining routine;
FIG. 9 is a graph showing a relation between the position of a focusing
lens and a focus evaluating value;
FIG. 10 is flowchart showing a hill-climbing routine;
FIG. 11 is a graph showing the change in focus evaluating value at the time
of return to a peak;
FIG. 12 is a graph showing a relation among the position of a focusing
lens, a focus evaluating value, the rotational speed of a focusing motor,
and a relative ratio of focus evaluating values;
FIG. 13 is a graph showing a relation between the position of a focusing
lens and an accumulated value of outputs of high-pass filters;
FIG. 14 is a graph showing a relation between a relative ratio of focus
evaluating values and the degree of defocusing;
FIG. 15 is a flowchart showing a peak return routine;
FIG. 16 is a flowchart showing an evaluating value fluctuation monitoring
routine;
FIG. 17 is a flowchart showing a peak confirming routine;
FIGS. 18 and 19 are graphs showing fluctuations in focus evaluating value
caused by the change in position of a focusing lens;
FIG. 20 is a diagram for typically explaining a manner in which an object
moves;
FIGS. 21 to 24 are graphs showing fluctuations in focus evaluating value
caused by the change in object; and
FIGS. 25 and 26 are flowcharts showing a routine of an automatic iris
operation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic block diagram showing an automatic focusing/automatic
iris apparatus according to an embodiment of the present invention. In
FIG. 1, a video camera portion 1 comprises a focusing lens 2, a focusing
ring 3 for supporting this focusing lens 2 and moving the same in the
direction of an optical axis, a focusing motor 4 for driving this focusing
ring 3, an endpoint switch 5 for detecting the limit of a range in which
the focusing ring 3 can be driven, a stop-down mechanism 6 for controlling
exposure, an iris motor 7 for driving this stop-down mechanism 6, and an
image sensing circuit 8 having a solid-state image sensor for converting
light incident from an object into a video signal.
A luminance signal in the video signal obtained from the image sensing
circuit 8 is applied to a first high-pass filter (HPF) 9 and a second HPF
10 having different cut-off frequencies, a low-pass filter (LPF) 11, and a
synchronizing separator circuit 12.
A vertical synchronizing signal VD and a horizontal synchronizing signal HD
separated from the luminance signal by the synchronizing separator circuit
12 are supplied to a switching control circuit 13 for setting a sampling
area. This switching control circuit 13 is responsive to the vertical and
horizontal synchronizing signals VD and HD and a fixed output of an
oscillator (not shown) serving as a clock for driving a CCD for outputting
a selection signal S2 to apply the same to a selecting circuit 15 in the
succeeding stage so as to set a rectangular first sampling area A1 in the
center of a picture, a second sampling area A2 including this area A1 and
having an area which is four times that of the area A1, and third to sixth
sampling areas A3, A4, A5 and A6 around this area A2, as shown in FIG. 2.
In addition, the switching control circuit 13 outputs a switching signal
S1 for alternately selecting for each field outputs of the first HPF 9 and
the second HPF 10 and selecting an output of the LPF 11 once per 32 fields
to apply the same to a switching circuit 14.
As a result, the switching circuit 14 alternately selects the outputs of
the first HPF 9 and the second HPF 10 for each field to output the same to
the selecting circuit 15 in the succeeding stage and further selects the
output of the LPF 11 only once per 32 fields to apply the same to the
selecting circuit 15, in response to the switching signal S1.
On the other hand, the selecting circuit 15 is responsive to the selection
signal S2 from the switching control circuit 13 for selectively applying
the output selected by the switching circuit 14 to accumulating circuits
16, 17, . . . , 21 corresponding to sampling areas. More specifically, an
output of each of the filters with respect to the first sampling area A1
and an output of each of the filters with respect to the second sampling
area A2 are respectively applied to the accumulating circuits 16 and 17.
Similarly, outputs of the respective filters with respect to the third to
sixth sampling areas A3, A4, A5 and A6 are respectively applied to the
accumulating circuits 18, 19, 20 and 21.
The accumulating circuit 16 comprises an A/D converter 22, an adder 23, and
a memory circuit 24. The A/D converter 22 sequentially A/D converts the
filter outputs passing through the selecting circuit 15, to apply the same
to the adder 23. The adder 23, together with the A/D converter 22 in the
preceding stage and the memory circuit 24 in the succeeding stage,
constitutes a digital integrator, which adds an output of the memory
circuit 24 to an output of the A/D converter 22 to supply the result of
the addition to the memory circuit 24. The memory circuit 24 is reset for
each field. Thus, the memory circuit 24 holds an output of the adder 23,
i.e., a digitally converted value, corresponding to one field, of a level
of a luminance signal passing through a filter selected in the current
field with respect to the first sampling area A1.
The accumulating circuits 17, 18, . . . , 21 have all the same structures
as that of the accumulating circuit 16. Thus, a memory circuit contained
in each of the accumulating circuits holds an integrated value,
corresponding to one field, of a level of a luminance signal passing
through a filter selected in the current field with respect to each of the
sampling areas. The integrated value in each of the memory circuits is
further applied to the memory circuit 25 in the succeeding stage, to be
collectively stored therein.
Areas where passage through the first HPF 9, the second HPF 10 and the LPF
11 is allowed are respectively set to 600 KHz or more, 200 KHz or more and
2.4 MHz or less. In practice, the areas can be respectively set using BPFs
respectively having pass bands of 600 KHz to 2.4 MHz, 200 KHz to 2.4 MHz,
and 0 to 2.4 MHz. 2.4 MHz is a substantially high frequency independent of
a luminance signal and thus, the LPF 11 can be omitted. Thus, a high
frequency component or a low frequency component, corresponding to one
field, of a luminance signal passing through any one of the first HPF 9,
the second HPF 10 and the LPF 11 is digitally integrated, the integrated
value being stored in a memory circuit 25 as an evaluating value in the
current field for each sampling area. An integrated value of a low
frequency component in a field where the LPF 11 is selected and an
integrated value of a high frequency component in a field where the first
HPF 9 or the second HPF 10 is selected out of the integrated values stored
in the memory circuit 25 are respectively operated by a microcomputer 26
in the succeeding stage as an exposure evaluating value for exposure
control and a focus evaluating value for focus control.
The evaluating values are processed by the microcomputer 26 in a software
manner. Based on the result of this processing, the microcomputer 26
carries out an automatic focusing operation such that the focus evaluating
value reaches a maximum by issuing a command to a focusing motor control
circuit 27, thereby to drive the focusing motor 4 to move the focusing
lens 2. In addition, the microcomputer 26 carries out automatic exposure
control such that the exposure evaluating values becomes a predetermined
value by also issuing a command to an iris motor control circuit 28,
thereby to drive the iris motor 7 to operate the stop-down mechanism 6.
Referring now to a flowchart of FIG. 3, description is made of a main
routine of an automatic focusing operation and an automatic iris
(automatic exposure control) operation by the microcomputer 26.
When a video camera enters an operating state, the microcomputer 26 first
executes a main routine shown in FIG. 3.
First, in the step 30, an integrated value corresponding to the current one
field with respect to each sampling area is read in the microcomputer 26
from the memory circuit 25. Then, in the step 31, the rotational direction
of a zoom motor 101 (see FIG. 1) is detected. In this case, the zoom motor
101 drives rotation of a zoom ring 102 rotatably arranged in a lens barrel
portion projected forward from a main body of the video camera 1 in a
radial direction. This zoom ring 102 supports a zoom lens (not shown)
which is a variable power lens. This zoom lens moves in the direction of
an optical axis according to rotation of the zoom ring 102, which is
movable from a telescope (Tele) region to a wide angle (Wide) region
through a middle region. In general, a user can obtain a desired zoom
position by operating a zoom driving switch (not shown) arranged in the
main body of the camera to a telescope direction or a wide angle direction
to rotate the zoom motor 101 in either direction.
Then, a count value of a counter AECNT provided for performing an automatic
focusing operation and an automatic iris operation in a time divisional
manner is decremented, that is, one is subtracted therefrom (in the step
32), to determine whether or not the count value is zero (in the step 33).
The automatic focusing operation is carried out if the count value is not
zero, while the automatic iris operation is carried out only when the
count value is zero. In addition, if and when it is confirmed in the step
34 that result of the detection of the rotational direction of the zoom
motor 101 i.e., a zoom direction in the step 31 is a wide angle direction
and it is further determined in the step 100 that a code indicating an
operation mode for automatic focusing as described below is "4", that is,
the usual automatic focusing operation has been already completed so that
the focusing lens reaches once a peak of the focus evaluating value, an
automatic focusing routine (in the step 35) for carrying out an automatic
focusing basic operation is not executed, to be skipped. The reason is as
follows: when a zoom mechanism moves toward a wide angle side, the depth
of field gradually becomes larger. Thus, if an in-focus state is achieved
once before a zooming operation, the automatic focusing operation need not
be carried out again during the zooming operation in a wide angle
direction. In addition, if the automatic focusing operation is carried out
in such a case, an unnecessary automatic focusing operation is repeated
due to fluctuations in the focus evaluating value caused by the change in
the angle of field, resulting in an unclear picture. Thus, the unclear
picture must be prevented. If and when the zoom direction is not the wide
angle direction, or the zoom direction is the wide angle direction but the
in-focus state is not achieved immediately before the zooming operation,
the automatic focusing routine (in the step 35) is executed.
When the automatic focusing routine is terminated, it is determined whether
or not the result obtained by subtracting one from the content of the
counter AECNT is zero (in the step 36). If the count value is zero, a
control signal is generated to the switching control circuit 13 from the
microcomputer 26, and the switching control circuit 13 applies the
switching signal S1 for selecting the output of the LPF 11 to the
switching circuit 14 upon receipt of the control signal, so that the
output of the LPF 11 is selected (in the step 37). Consequently, when the
output of the LPF 11 is selected, the microcomputer 26 waits until an
evaluating value obtained corresponding to this selected output of the LPF
11 is read in the memory circuit 25.
On the other hand, when the automatic iris operation is selected in the
step 33, an automatic iris routine (in the step 38) which is the basis of
the automatic iris operation is executed. Thereafter, the counter AECNT is
returned to an initial state (in the step 39) and the output of the first
HPF 9 is further selected (in the step 40), so that the microcomputer 26
waits for accumulation of evaluating values in the next field.
The initial state of the counter AECNT is a state in which an initial value
"32" is set so as to calculate an exposure evaluating value in response to
the luminance signal passing through the LPF 11 for one field every 32
fields.
Referring now to a flowchart of FIG. 4, description is made of the
automatic focusing operation according to the present invention.
If the automatic focusing operation is selected in the step 33 in the main
routine shown in FIG. 3 and the zoom mechanism is not moved to the wide
angle side (in the step 34), the automatic focusing routine (in the step
35) is executed.
First, in the step 41 shown in FIG. 4, focus evaluating values and a
relative ratio thereof are calculated based on integrated values
corresponding to sampling areas stored in the memory circuit 25. Then,
confirming processing of an endpoint switch of the focusing ring is
performed in the step 42 and then, a zoom position which is a zoom region
of a zoom mechanism is confirmed in the step 43. Thereafter, a so-called
hill-climbing control is started.
The hill-climbing control comprises a total of five routines: an evaluating
value stability confirming routine (in the step 45), direction determining
routine (in the step 46), a hill-climbing routine (in the step 47), a peak
return routine (in the step 48) and an evaluating value fluctuation
monitoring routine (in the step 49). Selection among the routines is made
by designating any one of operation mode codes 0 to 4 in the step 44
according to conditions set in the previous field. In general, the
evaluating value stability confirming routine (in the step 45), the
direction determining routine (in the step 46), the hill-climbing routine
(in the step 47), the peak return routine (in the step 48) and the
evaluating value fluctuation monitoring routine (in the step 49) are
executed in that order.
After each of the routines is terminated, the output | | |
