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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a movement detection device suitable for
use with (i) a camera having a vibration-proof device for compensating for
the movement of an image being picked-up by the camera due to trembling of
the hand or other vibrations, (ii) an automatic tracking apparatus for
tracking a moving object, or (iii) an automatic focus detection apparatus
for detecting a focusing state from an image pick-up signal.
2. Related Background Art
Recently, image instruments such as a video camera or electronic camera
have been remarkably developed in which, to enable a more reliable and
appropriate photographing operation, a movement correction device has been
adopted which allows the photographing of higher quality images without
fluctuation by correcting the movement of the image due to trembling of
the hand or other vibrations.
The movement correction method for the movement correction device involves
(i) a mechanical correction method of using inertia to maintain the axes
of the lens and image sensor fixed against the rotation of camera body,
(ii) an optical correction method of using an optical member such as a
variable apex angle prism, and (iii) an image processing correction method
for making the correction by moving the image with image processing.
According to the mechanical correction method, a special structure for
supporting the lens and a pick-up system is required. According to the
optical correction method, a special optical member such as a variable
apex prism is required, while in the image processing correction method,
no special mechanical structure or optical members are necessary. In the
image processing correction method, the movement is corrected only with
signal processing using electrical circuitry, and this method is expected
to be widely used in the future.
However, the movement correction device with the above-mentioned
conventional image processing method has the following disadvantage,
compared with the mechanical or optical device. That is, in performing the
movement correction with the image processing method, an image has some
movement at the pick-up stage (with an image sensor or pick-up tube),
whereby in the post-pick-up processing, the movement of the image within
an image screen is removed by shifting the image in accordance with the
amount of image movement.
Thus, as the image obtained in the pick-up stage yields some unfocused
portions, final resolution of the image is low even if the movement of the
image is corrected in the post-pick-up processing, so that a poor quality
of image is output.
Recently, in video instruments such as a video camera or an electronic
camera, an automatic focusing adjustment apparatus for adjusting the focus
by detecting the focusing state from a pick-up signal has been adopted,
but as above described, the movement of the image may reduce a high
frequency component varied with the focusing state from the pick-up
signal, thereby decreasing the sharpness, and degrading the performance of
automatic focusing adjustment apparatus, whereby there is a risk of a
malfunction. Thus, it is quite important to detect and correct the
movement of the image in the signal processing using the pick-up signal.
SUMMARY OF THE INVENTION
The present invention is intended to resolve the above problems, and it is
a first object to provide a movement detection device which can compensate
for the degradation of resolution due to the movement of the image.
A second object of the present invention is to provide a movement detection
device capable of providing an image without fluctuation or deflection and
having high resolution, with the movement corrected, and which can
compensate for the degradation of resolution with the movement of the
image by means of filtering.
A third object of the present invention is to provide a movement detection
device capable of providing a high quality image (with its movement
corrected) by performing filtering adaptively by the use of a movement
vector of the image obtained from a movement amount detection device
especially useful for the correction of movement.
A fourth object of the present invention is to provide a movement detection
device having the effect of providing a high quality image by compensating
for the degradation of image quality resulting from the movement of the
image by means of filtering, and increasing the resolution of the output
image for a movement correction device.
A fifth object of the present invention is to provide a movement detection
device in which the quality of the image can be made excellent, almost
optimal, without an increase of the cost, by changing adaptively the
characteristics of a filter used in the filtering processing, particularly
based on a movement vector to be obtained for the correction of movement.
To achieve such objects, a preferred embodiment of the present invention
features a movement detection device for detecting the movement of an
image and compensating for the movement of the image, comprising movement
detection means for detecting a movement of an image, correction means for
correcting the movement of the image based on an output of said detection
means, and filter means for performing a filtering processing compensating
for degradation of resolution with the movement of the image.
A sixth object of the present invention is to provide a focus detection
apparatus capable of making a high precision focus detection while
avoiding the decrease of accuracy due to the movement of the image,
wherein the movement of the image is detected and the focus detection is
made using a signal for which the degradation of the resolution with the
movement of the image has been compensated.
A seventh object of the present invention is to provide a stable focus
detection apparatus with high precision at all times, in which the
apparatus is not subject to the influence of camera vibration or object
movement because it is possible to prevent the degradation of accuracy in
focus detection means caused by a signal decreasing in accordance with the
focusing state, such as unclearness of an edge portion or a decrease of
the high frequency component owing to the movement of the image.
To accomplish such objects, a preferred embodiment of the present invention
features a focus detection apparatus for detecting a focusing state based
on a pick-up signal output from pick-up means, comprising movement
detection means for detecting a movement of an image from the pick-up
signal, movement correction means for correcting the movement of the image
based on an output of the movement detection means, and focus detection
means for performing focus detection by extracting a signal component
varying with the focusing state from the pick-up signal having its
movement component corrected by the movement correction means.
Additional objects and feature of the present invention will become
apparent from the following description and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a first example of a movement detection
device according to the present invention.
FIG. 2 is a view showing the movement of an image.
FIG. 3 is a view showing the movement of an optical image.
FIGS. 4A to 4C are characteristic views showing the filter characteristic
for filtering.
FIG. 5 is a characteristic view showing the inverse filter characteristic.
FIG. 6 is a characteristic view showing the Wiener filter characteristic.
FIG. 7 is a block diagram showing a second example of the present
invention.
FIG. 8 is a view showing images containing a plurality of movements.
FIG. 9 is a view showing area decision results.
FIG. 10 is a block diagram showing a third example of a movement correction
device according to the present invention.
FIG. 11 is a view showing the movement of the image.
FIG. 12 is a view showing the movement of an optical system.
FIG. 13 is a view showing a point image distribution function with the
movement of the image.
FIG. 14 is a view showing the correction of an edge width.
FIG. 15 is a block diagram showing a fourth example of the present
invention.
FIGS. 16A and 16B are schematic graphs showing a focus detection method
using a conventional image processing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of a movement correction device according to the present
invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing a first embodiment of a movement
correction device according to the present invention.
In FIG. 1, 1 is an object, 2 is a pick-up lens, and 3 is a pick-up element
(or pick-up tube) such as a CCD for outputting a pick-up signal by
photoelectrically converting an object image formed on a pick-up plane by
the pick-up lens 2. 4 is an amplifier for amplifying the pick-up signal
output from the pick-up element 3 to a predetermined level, 5 is an A/D
converter for converting the input analog pick-up signal to a digital
signal, 6 is a frame memory for storing the image signal converted into
the digital signal by the A/D converter 5, and 7 is a movement amount
detection circuit for obtaining a movement vector from the image signal
which has been converted from analog to digital form. Exemplary of a
method of calculating the movement vector is that method used in a
so-called representative point matching method or gradient method. 8 is a
memory reading circuit for reading an image signal form the frame memory 6
by generating a read address and executing the reading.
9 is a parameter setting circuit for setting parameters for prevention of
image degradation, and 10 is a filter.
11 is a D/A converter for converting the digital image signal passing
through the filter 10 to an analog image signal, 12 is a synchronism
signal adding circuit for adding a synchronism signal of the image signal,
and 13 is an output video signal.
The pick-up leans 2 forms an image of object 1 on the pick-up plane of
pick-up element 3. The image on the pick-up element 3 includes movements
owing to the movement of the lens 2, pick-up element 3, or object 1. The
image signal output from the pick-up element 3 is amplified by the
amplifier 4, converted to the digital signal by the A/D converter 5, and
then stored in the frame memory 6, temporarily.
The digital image signal which is an output of A/D converter 5 is also
transferred to the movement amount detection circuit 7. Movement vector
data obtained by the movement amount detection circuit 7 are transferred
to the memory reading circuit 8 and the parameter setting circuit 9.
The movement detection circuit 7 requires data of an image screen of one
frame or one field prior to the current screen for calculating the amount
of movement, thereby requiring a frame memory. This frame memory may be
constructed in common with the frame memory 6, or separately provided.
The memory reading circuit 8 creates the address for reading the frame
memory 6 multiplied by the offset based on movement vector data. Thereby,
data read from the frame memory 6 are read out in such a way so as to move
data almost reversely to the movement of the image, so that the movement
of the image can be corrected. That is, the correction of image deflection
can be achieved in the memory.
The parameter setting circuit 9 determines parameters such as filter
coefficients based on the movement vector obtained from the movement
amount detection circuit 7, and sends them to the filter 10. The filter 10
filters the image signal having the corrected movement read from the frame
memory 6, so as to reduce the unfocused part resulting from the movement
of the image on the pick-up element 3, i.e., the degradation of
resolution.
Also, the filter 10 has the characteristics of a high-pass filter and a
band-pass filter, as will be described later.
The image signal output from the filter 10 is converted to an analog signal
by the D/A converter 11, synthesized with a synchronism signal by the
synchronism signal adding circuit 12, and output as the video signal 13.
The improvement of resolution with the filtering will be described in the
following.
FIG. 2 is a plan view showing the movement of an image.
21 is an output screen. The output screen 21 has a fixed coordinate system
which is useful as a reference to perform the processing such as vibration
isolation. Here, a monitor display screen can be assumed, for example.
22 is a previous image, and 23 is a current image. 24 is a movement vector
when the previous image 22 moves to the current image 23.
In the output screen 21, a video signal 13 of FIG. 1 is displayed. For
example, an image displayed with trembling of the hand shows the movement
from previous image 22 to current image 23 if time has passed from one
clock to another when the object 1 is stationary.
With the movement correction method in the image processing, the movement
correction is performed in such a manner that the movement vector 24 is
calculated in the movement amount detection circuit 7, data is shifted by
the amount of movement vector 24 on the output screen 21 when date of
current image 23 is read from the frame memory 6, and the offset is added
to the read address so that current image 23 can be superimposed almost on
previous image 22.
As current image 23 includes movement, the value of each pixel is
integrated in a direction of movement vector 24. Accordingly, in practice,
current image 23 of FIG. 2 only shows approximately a gravitational center
position of sides of each pattern.
FIG. 3 is a front view showing the movement of the optical system. In the
same figure, 31 is one cell when the pick-up element is a solid-state
pick-up element such as a CCD. For the convenience of explanation, it is
assumed that the movement direction of the image coincides with a
direction of the array for one cell in the pick-up element 3. The pick-up
element 3 converts a pattern of the optical image thereon during a
predetermined period of exposure. 32 is an optical image at the start of
exposure, and 33 is an optical image at the termination of exposure. The
optical image 32 at the start of exposure is moved to the optical image 33
at the termination of exposure because the image moves during exposure as
shown in FIG. 2.
The movement vector 24 as shown in FIG. 3 indicates the movement between
the optical image 32 at the start of exposure and the optical image 33 at
the termination of exposure. This is almost the same as that of FIG. 2,
but more strictly, slightly different. That is, the movement vector as
shown in FIG. 2 is one taken at nearly intermediate times of respective
exposure periods for two images. On the contrary, the movement vector as
shown in FIG. 3 is one taken for an image of interest from the start of
exposure to the termination of exposure. Accordingly, when the amount of
image movement changes abruptly, both movement vectors will have different
values. Generally, both of the values can be almost the same, but the
movement vector 24 as shown in FIG. 3 may be used after some slight
correction when required in the parameter setting circuit 9, because the
movement vector 24 obtained from the movement detection circuit 7 is one
as shown in FIG. 2.
FIGS. 4A-4C are graphs showing the filter characteristics for the filtering
in the filter 10 for correcting the degradation of the image.
In FIG. 4A, 41 is a point image distribution function with the movement of
the image. The axis of abscissa x in the spatial coordinate system is
taken along the movement direction. The length of the movement vector 24
is assumed to be a. Then, the image generated by one point of object 1
moves during the exposure period, approximately following the point image
distribution function 41.
Representing that function as h(x)
h(x)=Rect(x/a) (1)
42 in FIG. 4B is a frequency characteristic showing the degradation of the
image.
Representing the frequency as f and the frequency characteristic 42 as
H(f),
H(f)=(sin.pi.af)/.pi.f (2)
because H(f) is a Fourier transform of the point image distribution
function h(x).
43 in FIG. 4C is a frequency characteristic of the filter, and representing
it as P(f),
##EQU1##
Such a filter is called as an inverse filter.
That is, H(f).multidot.P(f)=1, which means that the filtering of P(f) can
compensate for the degradation of the image with H(f).
By filtering with filter 10, the resolution of output video signal 13 is
enhanced and an excellent quality image can be obtained. However, the
inverse filter can be realized only approximately because it has infinite
value at the frequency where the Fourier transform H(f) is zero, and the
frequency range can be a range where the frequency spectrum exists.
As clearly seen from FIGS. 4A-4C and expressions (2) and (3), the
characteristic of degradation H(f) and the characteristic of compensation
filter P(f) contain the size a of movement vector 24 as a parameter. The
x-axis and f-axis are each taken along the direction of movement vector
24, which reveals that P(f) depends on the size and direction of movement
vector 24.
Accordingly, it is desirable that the filter 10 has its filter
characteristic changed adaptively depending on the movement vector 24.
The filter 10 has two methods of performing the filtering processing. One
of them is filtering on the axis of frequency, in which the Fourier
transform is taken of the image signal read out from the frame memory 6
with an FFT (Fast Fourier Transform), which is then multiplied by the
inverse filter P(f), and the inverse Fourier transform is taken so that a
filtered image signal is obtained.
Another filtering method is filtering on the axis of time, performed in
such a way that the impulse response is obtained by the inverse Fourier
transformation of inverse filter P(f), and convoluted to the image signal
from the frame memory 6 so that a filtered output can be obtained.
When the inverse filter is realized with the convolution in the axis of
time, an impulse response S(x) of the filter in the following expression
can be used.
##EQU2##
Where K is a proportional constant, .delta.(x) is a delta function, and
.delta.'(x) is a derivative of the delta function. And "*" is a symbol
indicating the convolution, and sign(x) indicates a sign such that
##EQU3##
Note that the expression (4) is obtained by taking the Fourier transform
of expression (3) using the delta function.
FIG. 5 is a graph showing the impulse response of an inverse filter.
51 is an impulse response of the inverse filter, representing the
expression (4).
The expression (4) must be truncated midway because it continues infinitely
in the direction of the x-axis. Therefore, it is desirable to use that
function in the filtering processing after multiplication of the window
function such as a hamming window.
In the inverse filter, the frequency area where the image information is
almost lost with the degradation of the image, i.e., where the value of
frequency characteristic 42 is zero, and the high frequency area where
there is only a little image information by nature may be given the
characteristic of a large gain so that the output image often has a poor
S/N ratio. Therefore, in the filter 10, the Wiener filter can be
substituted.
The frequency characteristic of the Wiener filter R(f) can be represented
in the following expression.
##EQU4##
Where .PHI..sub.n (f) and .PHI..sub.s (f) indicate the power spectrum of
noise and image signal, respectively, and * indicates the complex
conjugate.
Here, as it is difficult to obtain .PHI..sub.n (f) and .PHI..sub.s (f)
correctly, .PHI..sub.n (f) is set to be constant by assuming white noise,
and .PHI..sub.s (f) is set to be the Gaussian type. Or they can be
predetermined with the assumption that .PHI..sub.n (f)/.PHI..sub.s (f) is
constant over all frequencies.
In the Wiener filter, at the frequency where the signal component is
sufficiently larger than the noise component, the value is almost the same
as that of the inverse filter, or conversely, it is close to zero at the
frequency where the noise component is larger than the signal component.
FIG. 6 is a graph showing the frequency characteristic of a Wiener filter.
61 is a frequency characteristic of the Wiener filter. Compared with the
frequency characteristic 43 of the inverse filter, it can be seen that the
gain is smaller at the frequency area with the poor S/N ratio. And in the
Wiener filter, like the inverse filter, it is desirable that the
characteristic may be adaptively changed depending on the movement vector
24.
Various filter characteristics of the filter 10 have generally the
characteristic of a high-pass filter or a band-pass filter.
FIG. 7 is a block diagram showing a second embodiment of the present
invention.
The second embodiment shows a device which is effective when there are a
moving area and a stationary area in an image, and further when the moving
area is separated into a plurality of regions which have different
movement vectors.
71 is an output of the movement amount detection circuit 7, i.e., the
movement vector for each block or pixel within a screen. 72 is an area
discrimination circuit, 73 is its output, i.e., an address offset signal,
74 and 75 are other outputs of the area discrimination circuit 72, i.e.,
the area signal and movement vector within the area, respectively. 76 is a
switch for sending the input signal to either of two output lines. 77 is
an output video signal being processed for each area.
The stages where the input image signal is converted from analog to digital
form, stored into the frame memory 6, and transferred to the movement
amount detection circuit 7 are the same as in the first embodiment.
The movement amount detection circuit 7 transfers the movement vector 71 to
the area discrimination circuit 72.
The area discrimination circuit 72 divides the screen into the stationary
area and a plurality of moving areas having different movement vectors,
based on the movement vector 71. The area discrimination circuit 72
selects a desired area of divided areas, and sends the movement vector of
the selected area as an address offset signal 73 to the memory reading
circuit 8. The memory reading circuit 8 reads the image signal from the
frame memory 6 by offsetting the address, based on the received signal.
Thereby, the entire screen is shifted.
The area discrimination circuit 72 sends the area signal 74 and the
movement vector 75 within the area to the parameter setting circuit 9, and
the parameter setting circuit 9 sets a different filter characteristic for
each area to the filter 10. The area signal 74 is also sent to the switch
76, which sends the image signal from the frame memory 76 to the D/A
converter 11 for the stationary area or to the filter 10 for the moving
area. The output of filter 10 is subsequently sent to the D/A converter
11. That is, only for the moving area is the filtering processing
performed.
Note that the switch 76 can be integrated into the filter 10 by using a
filter which allows the transmission of a whole frequency band, if the
stationary area is considered as a special case in the filter 10.
The analog signal output of the D/A converter 11 has a synchronism signal
added by the synchronism signal adding circuit 12, and is sent out as the
output video signal 77 being processed for each area.
FIG. 8 is a plan view showing images containing a plurality of movements.
In this figure, 81 is an output screen which corresponds to a monitor
display screen.
82 and 83 are first and second images of a previous screen, respectively.
84 and 85 are first and second images of a current screen, respectively.
86 is a background image composed of small squares arranged in FIG. 8.
In transferring from the previous screen to the current screen, the first
and second images 82, 83 of the previous screen are moved to the first and
second images 84, 85 of the current screen on the output screen 81,
respectively. However, the moving directions and sizes of the two images
are different. The background image 86 is not moved herein, i.e.,
coincident between the previous screen and the current screen.
FIG. 9 is a plan view showing the area discrimination result.
91 and 92 are first and second moving areas, respectively. 93 and 94 are
the movement vectors within areas of the moving areas 91, 92. 95 is a
stationary area.
The area discrimination circuit 72 of FIG. 7 performs the area division and
the calculation of the movement vector within the area as shown in FIG. 9.
That is, the first and second moving areas 91, 92 and the stationary area
95 are divided, and the movement vectors 93, 94 within the areas are
obtained for the first and second moving areas 91, 92.
When the device as shown in FIG. 7 is a tracking device, the tracking of a
specified image is performed. If it is assumed that the second image 83 is
tracked in the current screen, the area discrimination circuit 72 sends
the movement vector 94 within the area of the second moving area 92 to the
memory reading circuit as an address offset signal 73. At this time, as a
result of shifting of the image due to the offset applied in reading the
image signal from the frame memory 6, the second image 84 of the current
screen is displayed at the same place as the first image 83 of the
previous screen on the output screen 81. The images of other areas are
shifted.
The switch 76 sends the image signal of the first and second moving areas
91, 92 to the filter 10, and that of the stationary area 95 directly to
the D/A converter.
The filter 10 has its filter set with a different characteristic by the
parameter setting circuit 9, depending on the movement vectors 93, 94
within the areas, for the images of the first and second moving areas 91,
92, in order to perform the filtering processing. The settings of the
filter and parameters used in the filter 10 are the same as in the first
embodiment.
As described above, the movement detection device of the present invention
can compensate for the degradation of image quality resulting from the
movement of the image with filtering processing, so that there is an
effect of increasing the resolution of the output image with the movement
correction device, thereby providing a high quality image.
Further, the filtering characteristic useful for the filtering processing
has such an effect that the image quality is made excellent, nearly
optimal, by changing it adaptively based on the movement vector to be
obtained especially for the movement correction, and without increasing
the cost.
Next, to accomplish the sixth and seventh objects of the present invention,
an embodiment in which the movement detection device is applied to a focus
detection apparatus to improve the focus detection accuracy will be
described.
Recently, image equipment such as a video camera or an electronic camera
have been remarkably developed, and it is a requisite for its function to
have an automatic focus adjustment device.
By the way, for the focus detection device, there are provided a device of
the passive type in which the focusing signal is obtained by taking the
correlation of the image picked up by a twin-lens optical system, or an
automatic focus adjustment device of the active type in which the focusing
is judged from a position of a spot generated by reflected light flux by
radiating an infrared light onto an object.
On the other hand, in the pick-up device such as a television camera, a
focus detection device has been developed in which the focus detection is
performed by carrying out the image processing of the image signal. In
such a device using image processing, the signal for detecting the
focusing state is obtained from the image signal, whereby there is a
feature that the focus detection is allowed irrespective of the distance
from an object, without special elements or a circuit for providing the
infrared projection, and with high precision, so that its development has
rapidly progressed.
FIGS. 16A-16B are views for explaining an embodiment of a focus detection
method with conventional image processing, illustrating the intensity
distribution for the edge portion of an object image in the unfocused and
focused states, in which FIG. 16A shows the unfocused state and FIG. 16B
shows the focused state.
In FIG. 16A, EO shows an intensity distribution of the edge portion for an
object image in the unfocused state, with a vague distribution due to the
unfocused condition and a large width of the edge portion.
Also, in FIG. 16B, EI shows an intensity distribution of the edge portion
for an object image in the focused state and at the same place as for the
intensity distribution EO of an unfocused edge portion. In the focused
state, it shows a narrow and steeply rising-up edge.
Accordingly, the width of the edge portion for the object image is
detected, and focusing and unfocusing are judged from this edge width.
That is, focusing can be judged by making use of the property of a narrow
edge width.
The edge intensity distribution EO in the unfocused state is a distribution
of the edge portion detected from the image signal, where the edge width
is represented by the following expression.
l.sub.l =d.sub.l /(dI.sub.l (x)/dx) (6)
Where d.sub.l indicates an intensity difference of the edge portion.
I.sub.l (x) is a function for representing the intensity distribution of
the edge in the unfocused state, whereby Di.sub.l (x)/dx indicates a slope
of the edge. This slope of the edge can be used by taking the average of
the slopes of focusing in a range from a portion where the edge rises up
to a portion where it becomes flat again.
Also, when focused, the width of edge l.sub.2 can be calculated from the
intensity distribution EI for the focused state, using the following
expression.
l.sub.2 =d.sub.2 /(Di.sub.2 (x)/dx) (7)
Where d.sub.2 is an intensity difference of the edge portion, I.sub.2 (x)
is a function for representing the intensity distribution El of the edge
in the focused state, and Di.sub.2 (x)/dx is a slope of the edge. d.sub.2
has almost the same value as d.sub.l, and Di.sub.2 (x)/dx is larger than
Di.sub.l (x)/dx.
Accordingly, since l.sub.2 is a smaller value than l.sub.1, it can be seen
that the edge width becomes smaller and the focusing has been adjusted.
In this way, generally, a method (in which the edge width is calculated
from a density difference and a slope of the edge portion, and the state
is judged nearer to the focused state if the value is smaller) is
practiced as one method of performing focus detection with image
processing.
However, in the above-mentioned focus detection method, when an image has
movement, i.e., when an object is moving, or when the whole screen has
shifted as a result of trembling of the hand and/or panning, the image
becomes unfocused due to the movement, whereby there is a disadvantage
that the width of the edge is widened due to the movement, and correct
detection of the focus state can not be made.
The following embodiment has been made to resolve the above-mentioned
problems, and is characterized by focus detection apparatus comprising
movement detection means for detecting a movement of an image from the
image pick-up signal, movement correction means for correcting the
movement of the image based on the output of the detection means, and
focus detection means for performing the focus detection by extracting a
signal component which varies with the focusing state from the pick-up
signal having its movement component corrected by the movement correction
means.
Thereby, a high precision focus detection apparatus can be realized without
decreasing its precision owing to the movement of the image, in which the
focus detection can be performed by detecting the movement of an image
from an image signal, and using the signal for which the degradation of
resolution due to the movement of the image is compensated.
A focus detection apparatus of this example will be described in detail
below with reference to the drawings.
FIG. 10 is a block diagram showing a third example in which a movement
detection device of the present invention is applied to the focus
detection apparatus. In the same figure, 101 is an object, 102 is a
pick-up lens, and 103 is a pick-up element (or pick-up tube) such as a CCD
for outputting a pick-up signal by photoelectrically converting an object
image formed on a pick-up plane by the pick-up lens 2. 104 is an amplifier
for amplifying the pick-up signal output from the pick-up element 3 to a
predetermined level, 105 is an A/D converter for converting an input
analog pick-up signal to the digital signal, 106 is a movement vector
operation circuit for obtaining the movement vector of the image from the
image signal which has been converted to the digital signal by the A/D
converter 105, 107 is an x-axis projection circuit for projecting the
movement vector on the x-axis that is a horizontal direction of the
screen, and 108 is an x component of the movement vector.
109 is an edge detection circuit for detecting the width of the edge
portion for an object image, 110 is an edge width detection circuit for
detecting the width of the edge portion detected by the edge detection
circuit 109, and 111 is an edge width signal.
112 is a comparator, and 113 is a memory. 114 is a lens control circuit,
115 is a lens control signal, and 116 is a lens driving circuit for moving
the pick-up lens 102 in a direction of the optical axis to adjust the
focus.
On the other hand, 117 is a video signal processing circuit for outputting
a standard television signal by performing signal processing such as gamma
correction or various filtering of the pick-up signal output from the A/D
converter 105, 118 is a D/A converter for converting the digital signal
output by the video signal processing circuit 117 to an analog signal, and
119 is a synchronism signal adding circuit for adding a synchronism signal
to the image signal output from the D/A converter 118, and 120 is an
output video signal.
With the above constitution, the pick-up lens 102 forms an image of object
101 on the pick-up plane of pick-up element 103, and the pick-up element
103 converts photoelectrically the image of the object to output an image
signal. The image formed on the pick-up element 103 includes movement
owing to the movement of the pick-up lens 102, pick-up element 103, or
object 101.
The image signal output from the pick-up element 103 is amplified by the
amplifier 104, and converted to a digital signal by the A/D converter 105.
A part of the digitized image signal is input into the movement vector
operation circuit 106. The movement vector operation circuit 106 contains
a frame memory where the image of a previous frame is stored, and in which
the movement vector of the image is calculated by comparing the image of
the current frame with that of the previous frame stored in the frame
memory. Exemplary of the method of calculating the movement vector is that
used in a so-called representative point matching method, or a gradient
method can be used.
The x-axis projection circuit 107 gives an x-axis component signal 108 from
the movement vector obtained by the movement vector operation circuit 106.
The digitized image signal is sent to an edge portion detection circuit
109. The edge portion detection circuit 109 detects an edge portion from
the information such as a slope for the image signal, and selects an edge
having the largest slope with respect to the x-axis, for example, as the
edge for judgement of the focusing. The edge width operation circuit 110
calculates the width of the edge from a density difference of the edge and
a slope of the edge, as above-described, and outputs it as an edge width
signal 111. The edge width signal 111 is subtracted from the x-axis
component signal 108 of the movement vector and then sent to the
comparator 112. The signal sent to the comparator 112 is an edge width
signal with the movement of the image corrected. And the comparator 112
compares the input corrected edge width signal with data within the memory
113.
Within the memory 113, the corrected edge width signal in the previous
field or frame is stored.
The comparator 112 sends a control signal to the lens control circuit, as
well as writing a smaller edge width signal of two corrected edge width
signals into the memory 113.
The control signal is one in which driving of the current pick-up lens 102
is continued in the same direction when a newly input edge width signal is
smaller than the previous edge width signal, or driving is performed in a
reverse direction when it is larger than the previous edge width signal.
Also, it may be permitted to send a signal in which the amount of driving
the lens is gradually changed depending on the amount of variation in the
corrected edge signal. Or when the amount of variation is quite small, a
control signal for stopping the driving of the lens can be sent by
deciding on the focusing state if the amount of variation is changed from
negative to positive. In order to make the fine control, it is desirable
that corrected edge signals (as much as several frames) should be stored
in the memory 113.
The lens control circuit 14 issues a lens driving signal 115, based on a
control signal sent from the comparator 112, in accordance with which the
lens driving circuit 116 drives the pick-up lens 102.
On the other hand, the digitized image signal is input into the video
signal processing circuit 117, is then input into the D/A converter 118
for conversion into the analog signal, has a synchronism signal added in
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