U.S. patent application number 09/843839 was filed with the patent office on 2002-02-07 for three-dimensional image capturing device.
This patent application is currently assigned to ASAHI KOGAKU KOGYO KABUSHIKI KAISHA. Invention is credited to Seo, Shuzo.
Application Number | 20020015144 09/843839 |
Document ID | / |
Family ID | 18641988 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020015144 |
Kind Code |
A1 |
Seo, Shuzo |
February 7, 2002 |
Three-dimensional image capturing device
Abstract
A three-dimensional image capturing device performs sensing
operations of a first reflected light beam component and a second
reflected light beam component. In the sensing operation of the
first reflected light beam component, the pulse shape of a distance
measuring light beam is triangular. The electric charge
accumulating period starts at the same time as the disappearance of
a pulse of the distance measuring light beam, and ends after the
disappearance of a pulse of the reflected light beam. In the
sensing operation of the second reflected light beam component, the
pulse shape of a correction light beam is rectangular. The electric
charge accumulating period starts at the same time as the
disappearance of a pulse of the correction light beam, and ends
after the disappearance of a pulse of the reflected light beam. A
signal charge obtained by the first reflected light beam component
sensing operation is divided by a signal charge obtained by the
second reflected light beam component sensing operation.
Inventors: |
Seo, Shuzo; (Saitama,
JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1941 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
ASAHI KOGAKU KOGYO KABUSHIKI
KAISHA
Tokyo
JP
|
Family ID: |
18641988 |
Appl. No.: |
09/843839 |
Filed: |
April 30, 2001 |
Current U.S.
Class: |
356/5.01 |
Current CPC
Class: |
G01S 7/483 20130101;
G01S 17/10 20130101; G01C 3/08 20130101; G01C 11/00 20130101; G01S
17/89 20130101 |
Class at
Publication: |
356/5.01 |
International
Class: |
G01C 003/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 2, 2000 |
JP |
P2000-133504 |
Claims
1. A three-dimensional image capturing device, comprising: a
distance measuring light beam irradiating processor that irradiates
a distance measuring light beam to a measurement subject, said
distance measuring light beam being a pulsed beam, the height of
the pulse changing with time, said measurement subject reflecting
said distance measuring light beam to generate a first reflected
light beam pulse; a first reflected light beam component sensing
processor that receives said first reflected light beam pulse for a
first sensing period to sense a first reflected light beam
component; a correction light beam irradiating processor that
irradiates a correction light beam to said measurement subject,
said correction light beam being a pulsed beam, the height of the
pulse being constant, said measurement subject reflecting said
correction light beam to generate a second reflected light beam
pulse; a second reflected light beam component sensing processor
that receives said second reflected light beam pulse for a second
sensing period to sense a second reflected light beam component;
and a distance information calculating processor that divides said
first reflected light beam component by said second reflected light
beam component to obtain the distance from said device to each
point of said surface of said measurement subject.
2. A device according to claim 1, wherein the height of the pulse
of said distance measuring light beam linearly changes.
3. A device according to claim 2, wherein the height of the pulse
of said distance measuring light beam linearly decreases.
4. A device according to claim 2, wherein the pulse of said
distance measuring light beam is saw-toothed.
5. A device according to claim 1, wherein said first sensing period
starts at the extinction of the pulse of said distance measuring
light beam, and said second sensing period starts at the extinction
of the pulse of said correction light beam.
6. A three-dimensional image capturing device, comprising: means
for irradiating a distance measuring light beam to a measurement
subject, said distance measuring light beam being a pulsed beam,
the height of the pulse changing with time, said measurement
subject reflecting said distance measuring light beam to generate a
first reflected light beam pulse; means for receiving said first
reflected light beam pulse for a first sensing period to sense a
first reflected light beam component; means for irradiating a
correction light beam to said measurement subject, said correction
light beam being a pulsed beam, the height of the pulse being
constant, said measurement subject reflecting said correction light
beam to generate a second reflected light beam pulse; means for
receiving said second reflected light beam pulse for a second
sensing period to sense a second reflected light beam component;
and means for dividing said first reflected light beam component by
said second reflected light beam component to obtain the distance
from said device to each point of said surface of said measurement
subject.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a three-dimensional image
capturing device by which a three-dimensional shape of a
measurement subject, which is to be measured, is captured by a
time-of-flight measurement.
[0003] 2. Description of the Related Art
[0004] Conventionally, there is known a three-dimensional image
capturing device, in which distance measuring light beam pulses are
radiated onto a measurement subject for a constant period and the
reflected light beam pulses coming from the measurement subject are
received and integrated by an imaging device such as a CCD. Namely,
each photodiode of the CCD corresponds to each point on the surface
of the measurement subject, and thus electric charge corresponding
to the point is accumulated in the photodiode. Due to this, the
shape of the surface of the measurement subject S is sensed.
[0005] In a conventional three-dimensional image capturing device
as described above, if the device is constructed in such a manner
that information, which is used for correcting a reflectance to
improve the accuracy of the distance measurement, is sensed, it may
be necessary to expand the output range of the imaging device, such
as the CCD. However, merely expanding the output range of the
imaging device will cause further difficulties in sufficiently
improving the accuracy of the distance measurement.
SUMMARY OF THE INVENTION
[0006] Therefore, an object of the present invention is to improve
the accuracy of the distance measurement, when sensing a
three-dimensional shape of a measurement subject, without
substantially expanding the output range of the imaging device.
[0007] According to the present invention, there is provided a
three-dimensional image capturing device, comprising a distance
measuring light beam irradiating processor, a first reflected light
beam component sensing processor, a correction light beam
irradiating processor, a second reflected light beam component
sensing processor and a distance information calculating
processor.
[0008] The distance measuring light beam irradiating processor
irradiates a distance measuring light beam to a measurement
subject. The distance measuring light beam is a pulsed beam. The
height of the pulse changes with time. The measurement subject
reflects the distance measuring light beam to generate a first
reflected light beam pulse. The first reflected light beam
component sensing processor receives the first reflected light beam
pulse for a first sensing period to sense a first reflected light
beam component. The correction light beam irradiating processor
irradiates a correction light beam to the measurement subject. The
correction light beam is a pulsed beam. The height of the pulse is
constant. The measurement subject reflects the correction light
beam to generate a second reflected light beam pulse. The second
reflected light beam component sensing processor receives the
second reflected light beam pulse for a second sensing period to
sense a second reflected light beam component. The distance
information calculating processor divides the first reflected light
beam component by the second reflected light beam component to
obtain the distance from the device to each point of the surface of
the measurement subject.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The objects and advantages of the present invention will be
better understood from the following description, with reference to
the accompanying drawings in which:
[0010] FIG. 1 is a perspective view showing a camera provided with
a three-dimensional image capturing device of an embodiment of the
present invention;
[0011] FIG. 2 is a block diagram showing an electrical construction
of the camera shown in FIG. 1;
[0012] FIG. 3 is a view showing a principle behind a distance
measurement;
[0013] FIG. 4 is a timing chart showing a distance measuring light
beam, a reflected light beam, a gate pulse and a distribution of an
amount of a light beam received by a CCD;
[0014] FIG. 5 is a timing chart of a sensing operation of a first
reflected light beam component;
[0015] FIG. 6 is a timing chart of a sensing operation of a first
noise component;
[0016] FIG. 7 is a timing chart of a sensing operation of a second
reflected light beam component;
[0017] FIG. 8 is a timing chart of a sensing operation of a second
noise component;
[0018] FIGS. 9A and 9B show a flowchart of a distance information
sensing operation;
[0019] FIG. 10 is a view showing the timing of a distance measuring
light beam, a reflected light beam and an electric charge
accumulation period in the sensing operation of the first reflected
light beam component;
[0020] FIG. 11 is a view showing the timing of a correction light
beam, a reflected light beam and an electric charge accumulation
period in the sensing operation of the second reflected light beam
component; and
[0021] FIG. 12 is a view showing the relationship between an
accumulated electric charge and an output range of a CCD.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] The present invention will be described below with reference
to the embodiments shown in the drawings.
[0023] FIG. 1 is an external view of a camera having a
three-dimensional image capturing device of an embodiment of the
present invention.
[0024] On a front surface of a camera body 10, a view-finder window
12 is provided toward a left-upper edge, adjacent to a
photographing lens 11, and an electronic flash 13 is disposed
toward a right-upper edge. On an upper surface of the camera body
10, a light emitting device (i.e., a light source) 14, which
radiates a laser beam (an infrared laser beam, for example, being a
distance measuring light beam) is mounted above the photographing
lens 11. A release switch 15 and a liquid crystal display panel 16
are provided on a left side of the light emitting device 14, and a
mode change dial 17 and a V/D mode switch 18 are provided on a
right side of the device 14. On a side surface of the camera body
10, a card slot 19 is formed into which a recording medium, such as
an IC memory card, is insertable, and a video output terminal 20
and an interface connector 21 are also provided.
[0025] FIG. 2 is a block diagram showing an electrical construction
of the camera shown in FIG. 1.
[0026] An aperture 25 is provided in the photographing lens 11. The
opening degree of the aperture 25 is adjusted by an iris drive
circuit 26. A focusing operation and a zoom operation of the
photographing lens 11 are controlled by a lens drive circuit
27.
[0027] An imaging device (CCD) 28 is disposed on an optical axis of
the photographing lens 11. A subject image is formed on a light
receiving surface of the CCD 28 through the photographing lens 11,
and an electric charge corresponding to the subject image is
generated therein. An operation, such as an accumulating operation
and a reading operation of the electric charge of the CCD 28, is
controlled by a CCD drive circuit 30. An electric charge signal,
i.e., an image signal, read from the CCD 28 is amplified by an
amplifier 31, and is converted from an analog signal to a digital
signal by an A/D converter 32. The digital image signal is
subjected to a process, such as a gamma correction, in the image
signal process circuit 33, and is stored as digital image data in
an image memory 34. The iris drive circuit 26, the lens drive
circuit 27, the CCD drive circuit 30 and the image signal process
circuit 33 are controlled by a system control circuit 35.
[0028] The digital image data are read from the image memory 34,
and supplied to an LCD drive circuit 36, which is operated in
accordance with the digital image data, so that an image
corresponding to the digital image data is indicated on an image
indication LCD panel 37.
[0029] The digital image data read from the image memory 34 are
also transmitted to a TV signal encoder 38, so that the digital
image data can be transmitted to a peripheral monitor device 39,
provided externally to the camera body 10, through a video output
terminal 20. The system control circuit 35 is connected to an
interface circuit 40, which in turn is connected to an interface
connector 21. Therefore, the digital image data read from the image
memory 34 can also be transmitted to a computer 41 connected to the
interface connector 21. Further, the system control circuit 35 is
connected to an image recording device 43 through a recording
medium control circuit 42. Therefore, the digital image data read
from the image memory 34 can be recorded in a recording medium M,
such as an IC memory card, mounted in the image recording device
43.
[0030] An illumination control circuit 44 is connected to the
system control circuit 35. The light emitting device 14 is provided
with a luminous-flux emitting element 14a and an illumination lens
14b, and an operation of the luminous-flux emitting element 14a is
controlled by the illumination control circuit 44. The
luminous-flux emitting element 14a radiates a pulsed laser beam,
which is a distance measuring light beam, and which irradiates a
whole of a measurement subject through the illumination lens 14b.
The pulse shape of the laser beam is rectangular or triangular, as
described later. The laser beam, reflected by the measurement
subject, becomes incident on the photographing lens 11. By
detecting the laser beam with the CCD 28 provided with a plurality
of photo-diodes, which are two-dimensionally disposed on a surface
thereof, a three-dimensional image is sensed, as described later.
Note that, in the sensing operation of the three-dimensional image,
a control of a transferring operation and so on, in the CCD 28, is
performed by the system control circuit 35 and the CCD drive
circuit 30.
[0031] The liquid crystal display panel 16 and a switch group 45,
including the release switch 15, the mode change dial 17 and the
V/D mode switch 18, are connected to the system control circuit
35.
[0032] With reference to FIGS. 3 and 4, a principle behind a
distance measurement in the embodiment is described below. Note
that, in FIG. 4, the abscissa indicates time "t".
[0033] A distance measuring light beam output by a distance
measurement device B is reflected by a measurement subject S, and
the reflected light beam is sensed by a CCD (not shown). The
distance measuring light beam is a pulse, the width of which is
"H". Accordingly, the reflected light beam is a pulse, the width of
which is "H", similar to the distance measuring light beam. The
fall of the pulse of the reflected light beam occurs after the fall
of the pulse of the distance measuring light beam by a time
.delta..multidot.t (.delta. is a delay coefficient). Since the
distance measuring light beam and the reflected light beam have
both traveled a distance "r" between the distance measurement
device B and the measured subject S, the distance "r" is
represented as follows:
r=.delta..multidot.t.multidot.C/2
[0034] wherein "C" is the velocity of light.
[0035] For example, by setting a condition in such a manner that
the reflected light beam can only be sensed from a fall of the
pulse of the distance measuring light beam to a point after a fall
of the pulse of the reflected light beam so as to sense a component
containing the fall of the pulse of the reflected light beam, i.e.,
by providing a gate pulse corresponding to a reflected light beam
detecting period T, an amount "A" of received light from the
reflected light beam becomes a function of the distance "r".
Namely, the greater the distance "r" (or the greater the time
.delta..multidot.t), the greater the received light amount A.
[0036] In this embodiment, by taking advantage of the principle
described above, the received light amount A is sensed using each
of the photo-diodes (photoelectric conversion elements) of the CCD
28, the distance from the camera body 10 to each point on the
surface of the measurement subject S is sensed, and data of the
three-dimensional image, which indicates a topography of the
measurement subject S, can be obtained concurrently.
[0037] FIG. 5 is a timing chart of a sensing operation of a first
reflected light beam component, by which data, corresponding to the
distance from the camera body 10 to each point on a surface of the
measurement subject, is sensed. The sensing operation of the first
reflected light beam component is described below with reference to
FIG. 1, 2 and 5. Note that, in FIG. 4, although the pulse shapes of
the distance measuring light beam and the reflected light beam are
rectangular for the simplicity of the explanation, the actual pulse
shapes are triangular, or saw toothed, as shown in FIG. 5.
[0038] In synchronization with an output of a vertical
synchronizing signal S1, the light emitting device 14 is actuated,
and thus a distance measuring light beam S3, which is a triangular
pulsed beam, is output therefrom. The distance measuring light beam
S3 has a constant pulse width and rises vertically from the
time-axis and linearly decreases to zero for the duration of the
pulse. The distance measuring light beam S3 is reflected by the
measurement subject, and enters the CCD 28 as a reflected light
beam S4. The pulse shape of the reflected light beam S4 is
triangular, similar to the distance measuring light beam S3.
[0039] An electric charge discharging signal (a pulse signal) S2 is
output in synchronization with the time at which each of the
distance measuring light beams S3 disappears. The output of the
electric charge discharging signal S2 is controlled to terminate at
the same time the pulse of the distance measuring light beam S3
disappears. Due to this, unwanted charge accumulated in the
photo-diodes is discharged to the substrate. When a predetermined
time has elapsed since the output of the distance measuring light
beam S3, an electric charge transfer signal (pulse signal) S5 is
output, so that the electric charge accumulated in the photo-diodes
is transferred to the vertical transfer unit. Note that the
electric charge transfer signal S5 is output after the pulse of the
reflected light beam S4 disappears.
[0040] Thus, for a period T.sub.U from the end of the output of the
electric charge discharging signal S2 to the beginning of the
output of the electric charge transfer signal S5, a signal charge
corresponding to the distance from the camera body 10 to the
measurement subject is accumulated in each of the photo-diodes.
Namely, the electric charge accumulating period T.sub.U is started
at the same time as a period T.sub.S ends, for which the distance
measuring light beam S3 is output, and during the electric charge
accumulating period T.sub.U (i.e., a first sensing period), only a
part of the reflected light beam S4, which is a first reflected
light beam component including a part in which the pulse height of
the reflected light beam S4 is relatively low, is detected by the
CCD 28. A signal charge S6, generated by the detected light beam,
corresponds to the distance from the camera body 10 to the
measurement subject. In other words, the signal charge S6,
corresponding to a light beam, which is included in the reflected
light beam S4 coming from the measurement subject and reaches the
photo-diodes within the electric charge accumulation period
T.sub.U, is accumulated in the photo-diodes. The signal charge S6
is transferred to the vertical transfer unit by the electric charge
transfer signal S5.
[0041] After a predetermined time has elapsed since the output of
the electric charge transfer signal S5, the electric charge
discharging signal S2 is again output, so that unwanted charge,
which is accumulated in the photo-diodes after the transfer of the
signal charge S6 to the vertical transfer unit, is discharged to
the substrate. Thus, another charge, due to the next distance
measuring light, is accumulated in the photo-diodes. Then, similar
to the above description, when the electric charge accumulation
period T.sub.U has again elapsed, the signal charge S6 is
transferred to the vertical transfer unit.
[0042] The transferring operation of the signal charge S6 to the
vertical transfer unit is repeatedly performed until the next
vertical synchronizing signal S1 is output. Thus, the signal charge
S6 is integrated in the vertical transfer unit. The signal charge
S6 integrated for one field period, which is between two vertical
synchronizing signals S1, corresponds to distance information of
the measurement subject, on condition that the measurement subject
is stationary for the period between the two vertical synchronizing
signals S1.
[0043] The detecting operation of the signal charge S6 described
above is carried out in all of the photo-diodes provided in the CCD
28. As a result of the detecting operation for one field period,
the distance information sensed by each of the photo-diodes is held
in a corresponding part of the vertical transfer unit, which is
located adjacent to the column of photo-diodes. The distance
information is output from the CCD 28 by a vertical transferring
operation of the vertical transfer units and a horizontal
transferring operation of a horizontal transfer unit (not shown).
The distance information is then output from the three-dimensional
image capturing device, as a three-dimensional image data of the
measured subject.
[0044] The reflected light beam, sensed by the CCD 28 as described
above, maybe affected by a reflectance of the surface of the
measurement subject. Therefore, the distance information, obtained
through the reflected light beam, may contain an error resulting
from the reflectance. Further, the reflected light beam sensed by
the CCD 28 may contain a noise component, such as ambient daylight,
being other than the reflected light beam from the measurement
subject, which can cause an error. Accordingly, in the distance
information sensing operation, it is preferable that influences of
the reflectance of the surface of the measurement subject, the
ambient daylight and so on, are corrected. A distance information
sensing operation, in which the correction is performed, is
described below.
[0045] FIGS. 6, 7 and 8 show sensing operations of a first noise
component, a second reflected light beam component and a second
noise component, respectively. FIGS. 9A and 9B show a flowchart of
the distance information sensing operation. With reference to FIGS.
1, 2, 5, 6, 7, 8, 9A and 9B, the distance information sensing
operation, in which influences of the reflectance of the surface of
the measurement subject, noise and so on, are corrected, is
described.
[0046] When it is recognized in Step 101 that the release switch is
fully depressed, Step 102 is executed in which it is determined
which mode is selected, a video (V) mode or a distance measurement
(D) mode. A change between the modes is carried out by operating
the V/D mode switch 18.
[0047] When the D mode is selected, in Steps 103 through 107, the
sensing operation of the first reflected light beam component is
performed. In Step 103, the vertical synchronizing signal S1 is
output and a distance measuring light beam control is started.
Namely, the light emitting device 14 is driven so that the distance
measuring light beam S3 is intermittingly output as a triangular
pulsed beam. Then, Step 104 is executed so that a sensing operation
control of the CCD 28 is started. Namely, the sensing operation of
the first reflected light beam component, described with reference
to FIG. 5, is started, and thus the electric charge discharging
signal S2 and the electric charge transfer signal S5 are
alternately output, so that the signal charge S6 of the first
reflected light beam component is integrated in the vertical
transfer unit.
[0048] In Step 105, it is determined whether one field period has
elapsed since the beginning of the sensing operation of the first
reflected light beam component, i.e., whether a new vertical
synchronizing signal S1 has been output. When one field period has
passed, the process goes to Step 106 in which the signal charge S6
of the first reflected light beam component is output from the
CCD28. The signal charge S6 is then stored in the image memory 34
in Step 107. Then, in Step 108, the distance measuring light beam
control is turned OFF, and thus the light emitting operation of the
light emitting device 14 is stopped.
[0049] In Steps 109 through 112, the sensing operation of the first
noise component is performed. In Step 109, as shown in FIG. 6, the
vertical synchronizing signal S11 is output, and a sensing
operation control of the CCD 28 is started. Namely, an electric
charge discharging signal S12 and an electric charge transfer
signal S15 are alternately output while the light emitting
operation of the light emitting device 14 is not carried out, i.e.,
while the light source is not illuminated. Although the electric
charge accumulation period Tu is the same as that of the sensing
operation of the first reflected light beam component, which is
shown in FIG. 5, the distance measuring light beam does not
irradiate the measurement subject (reference S13), and thus there
is no reflected light beam (reference S14). Therefore, although a
signal charge of the first reflected light beam component is not
generated, a signal charge S16 corresponding to an interference or
noise component is generated, since a noise component, such as
ambient daylight, etc., enters the CCD 28. Namely, the signal
charge S16 corresponds to the first noise component contained in
the first reflected light beam component.
[0050] In Step 110, it is determined whether one field period has
elapsed since the beginning of the sensing operation of the first
noise component, i.e., whether a new vertical synchronizing signal
S11 has been output. When one field period has passed, the process
goes to Step 111 in which the signal charge S16 of the first noise
component is output from the CCD 28. The signal charge S16 of the
first noise component is then stored in the image memory 34 in Step
112.
[0051] In Steps 113 through 117, the sensing operation of the
second reflected light beam component is performed. In Step 113, as
shown in FIG. 7, a vertical synchronizing signal S21 is output, and
a correction light beam control is started, so that a correction
light beam S23 is intermittently output as a pulsed beam. The pulse
shape of the correction light beam S23 is different from the
distance measuring light beam S3. Namely, the pulse height (i.e.,
the intensity of light) is constant and the output period T.sub.S
is the same as that of the distance measuring light beam S3. In
Step 114, a sensing operation control of the CCD 28 is started, and
thus an electric charge discharging signal S22 and an electric
charge transfer signal S25 are alternately output.
[0052] In the sensing operation of the second reflected light beam
component, the pulse of the correction light beam S23 is
rectangular, and the output timings of the electric charge
discharging signal S22 and the electric charge transfer signal S25,
relative to the correction light beam S23, are the same as those of
the electric charge discharging signal S2 and the electric charge
transfer signal S5, relative to the distance measuring light beam
S3, in the sensing operation of the first reflected light beam
component. Namely, a second sensing period T.sub.U is started at
the same time as period T.sub.S ends, for which the correction
light beam S23 is output. Thus, the second sensing period T.sub.U
is started at the extinction of the pulse of the correction light
beam S23, and the length of the period T.sub.U is the same as that
of the first sensing period. Therefore, similar to the sensing
operation of the first reflected light beam component, only a part
of the reflected light beam S24 (i.e., the second reflected light
beam component) is sensed by the CCD 28. The signal charge S26
generated by the sensed light beam corresponds to the distance from
the camera body 10 to the measurement subject and is transferred to
the vertical transfer unit by the electric charge transfer signal
S25, similar to the signal charge S6 sensed in the sensing
operation of the first reflected light beam component.
[0053] In Step 115, it is determined whether one field period has
elapsed since the beginning of the sensing operation of the second
reflected light beam, i.e., whether a new vertical synchronizing
signal S21 has been output. When one field period has passed, the
process goes to Step 116 in which the signal charge S26 of the
second reflected light beam is output from the CCD 28. The signal
charge S26 is then stored in the image memory 34 in Step 117. Then,
in Step 118, the correction light beam control is turned OFF, and
thus the light emitting operation of the light emitting device 14
is stopped.
[0054] In Steps 119 through 122, the sensing operation of the
second noise component is performed. In Step 119, as shown in FIG.
8, a vertical synchronizing signal S31 is output, and a sensing
operation control of the CCD 28 is started. Namely, an electric
charge discharging signal S32 and an electric charge transfer
signal S35 are alternately output while the light emitting
operation of the light emitting device 14 is not carried out.
Although the length and timing of the electric charge accumulation
period T.sub.U are the same as those of the sensing operation of
the second reflected light beam component, which is shown in FIG.
7, the distance measuring light beam does not irradiate the
measurement subject (reference S33), and thus there is no reflected
light beam (reference S34). Therefore, although a signal charge of
the second reflected light beam component is not generated, a
signal charge S36 corresponding to a noise component, such as the
ambient daylight, is generated in the CCD 28. Namely, the signal
charge S36 corresponds to the second noise component contained in
the second reflected light beam component.
[0055] In Step 120, it is determined whether one field period has
elapsed since the beginning of the sensing operation of the second
noise component, i.e., whether a new vertical synchronizing signal
S31 has been output. When one field period has passed, the process
goes to Step 121 in which the signal charge S36 of the second noise
component is output from the CCD28. The signal charge S36 is stored
in the image memory 34 in Step 122.
[0056] Note that the output timings of the electric charge
discharging signal S32 and the electric charge transfer signal S35
in the sensing operation of the second noise component are the same
as those of the electric charge discharging signal S12 and the
electric charge transfer signal S15 in the sensing operation of the
first noise component, and thus the signal charge S36 of the second
noise component can be deemed to be equal to the signal charge S16
of the first noise component. In this case, the sensing operation
of the second noise component can be omitted.
[0057] The first and second reflected light beam components (the
signal charges S6 and S26) contain the reflected light beam
components, which depend upon the reflectance of the surface of the
measurement subject, and the noise component, such as the ambient
daylight. In Step 123, a calculation process of the distance
measurement (D) data is performed using the first and second
reflected light beam components and the first and second noise
components, which are obtained in Steps 103 through 122. The D data
is output in Step 124, and the sensing operation ends.
[0058] Conversely, when it is determined in Step 102 that the V
mode is selected, the distance measuring light beam control is
turned OFF in Step 125, and a normal photographing operation (i.e.,
CCD video control) using the CCD 28 is turned ON in Step 126. Then,
the sensing operation ends.
[0059] The contents of the calculations executed in Step 123 are
described below with reference to FIGS. 10 and 11. FIG. 10 is a
view, which shows a distance measuring light beam, a reflected
light beam and an electric charge accumulation period in the
sensing operation of the first reflected light beam component,
which is shown in FIG. 5. FIG. 11 is a view, which shows a distance
measuring light beam, a reflected light beam and an electric charge
accumulation period in the sensing operation of the second
reflected light beam component, which is shown in FIG. 7.
[0060] In the sensing operation of the first reflected light beam
component, the electric charge accumulation period Tu (the first
sensing period) starts at the same time as the disappearance of a
pulse of the distance measuring light beam, and ends after the
disappearance of a pulse of the reflected light beam. Namely, a
signal charge S6 (see FIG. 5), corresponding to a time T.sub.D
immediately before the disappearance of the reflected light beam,
is sensed. Here, when it is supposed that the initial intensity of
the distance measuring light beam is I.sub.01, the intensity
I.sub.01T of the distance measuring light beam, which is at a point
of the time T.sub.D before the disappearance of the distance
measuring light beam, is:
I.sub.01T=I.sub.01.multidot.(T.sub.D/T.sub.S) (1)
[0061] When it is supposed that the reflectance of the surface of
the measurement subject is R and the diffusion coefficient of light
is D(r), the intensity I.sub.1 of the reflected light beam, which
is at a point of the time T.sub.D before the disappearance of the
reflected light beam, is:
I.sub.1=R.multidot.D(r).multidot.I.sub.01T (2)
[0062] Accordingly, the signal charge S6 or the output value
(accumulated charge) of the CCD 28, which is generated by the
reflected light beam for the time T.sub.D, is 1 S 1 = k 0 T D I 1 T
= k R D ( r ) I 01 T s 1 2 T D 2 ( 3 )
[0063] wherein k is constant.
[0064] On the other hand, in the sensing operation of the second
reflected light beam component, the electric charge accumulation
period T.sub.U (the second sensing period) starts at the same time
as the disappearance of a pulse of the correction light beam, and
ends after the disappearance of a pulse of the reflected light
beam. Namely, similar to the sensing operation of the first
reflected light beam component, a signal charge S26 (see FIG. 7),
corresponding to a time T.sub.D immediately before the
disappearance of the reflected light beam, is sensed. However,
since the pulse shape of the correction light beam is rectangular,
when it is supposed that the initial intensity of the correction
light beam is I.sub.02, the intensity I.sub.02T of the correction
light beam, which is at a point of the time T.sub.D before the
disappearance of the correction light beam, is:
I.sub.02T=I.sub.02 (4)
[0065] The intensity I.sub.2 of the reflected light beam, which is
at a point of the time T.sub.D before the disappearance of the
reflected light beam, is:
I.sub.2=R.multidot.D(r).multidot.I.sub.02T (5)
[0066] Accordingly, the signal charge S26 or the output value
(accumulated charge) of the CCD 28, which is generated by the
reflected light beam for the time T.sub.D, is 2 S 2 = k 0 T D I 2 T
= k R D ( r ) I 02 T D ( 6 )
[0067] A ratio of the output value S.sub.1 of the first reflected
light beam component to the output value S.sub.2 of the second
reflected light beam component, i.e., the accumulated electric
charge ratio is obtained from the formulae (3) and (6) as
follows:
S.sub.D=S.sub.1/S.sub.2=(1/2T.sub.S).multidot.(I.sub.01/I.sub.02).multidot-
.T.sub.D (7)
[0068] Here, when it is supposed that the distance from the camera
to the measurement subject is "r" and the velocity of light is "C",
the time T.sub.D, which is required for the light radiated from the
camera to return to the camera, is as follows:
T.sub.D=2r/C (8)
[0069] Accordingly, the distance r is expressed as following
formula (9).
[0070] ti
r=C.multidot.T.sub.s.multidot.(I.sub.02/I.sub.01).multidot.S.sub-
.D (9)
[0071] As understood from formulae (7), (8) and (9), the distance r
does not contain the measurement subject, the reflectance R and the
diffusion coefficient of light D(r).
[0072] On the other hand, the output values S.sub.1 and S.sub.2
contain accumulated electric charges corresponding to the first and
second noise components. Therefore, in reality, the accumulated
electric charge ratio S.sub.D is obtained by dividing a first
value, which is obtained by removing an accumulated electric charge
amount corresponding to the first noise component from the output
value S.sub.1, by a second value, which is obtained by removing an
accumulated electric charge amount corresponding to the second
noise component from the output value S.sub.2.
[0073] Thus, in the calculation process of Step 123 of FIG. 9B,
based on the first and second reflected light beam components,
which are obtained in the sensing operations of the first and
second reflected light beam components, and the first and second
noise components, the distance r from the camera to each point of a
surface of the measurement subject, i.e. a three-dimensional shape
of the measurement subject is obtained according to formulae (3),
(6) and (9).
[0074] The amount of the output values S.sub.1 and S.sub.2 of the
first and second reflected light beam components and an output
range of the CCD 28 (FIG. 2) are described below.
[0075] When a subject having a reflectance R is illuminated by a
point light source positioned close to a forming optical system so
that the subject is deemed as a secondary light source of a
luminance L.sub.0, and a subject image is formed on an image sensor
by the forming optical system, if a flare component is neglected,
illuminance Ea of the optical image is as follows:
E.sub.a=(.tau..pi.L.sub.0V.multidot.cos.sup.4.theta.)
/(4F.sup.2(1+m).sup.2) (10)
[0076] wherein ".tau." is transmittance of a lens of the forming
optical system, "V" is vignetting factor, ".theta." is an
inclination angle of the subject relative to the optical axis, "F"
is F-number of the forming optical system and "m" is lateral
magnification of the forming optical system.
[0077] When it is supposed that the subject distance from the
entrance pupil of the lens is "r", the focal length is "f", and a
distance between the entrance pupil and the main axis is "vf" (v is
a constant), the lateral magnification m is expressed as
follows:
m=f/(r-f-vf)
[0078] If vf is neglected because vf has a minute value, formula
(10) can be transformed as follows:
E.sub.a=(.tau..pi.L.sub.0V(r-f).sup.2.multidot.cos.sup.4
.theta.)/(4F.sup.2r.sup.2) (11)
[0079] On the other hand, if a point light source, having luminous
intensity I.sub.01.multidot.(T.sub.D/T.sub.S) (i.e., formula (1)),
is positioned close to the entrance pupil and illuminates a
subject, which is positioned away from the point light source by a
distance r.sub.L, illuminance E.sub.b of the subject is expressed
as follows:
E.sub.b=I.sub.01.multidot.(T.sub.D/T.sub.S).multidot.(cos
.alpha.)/(r.sub.L).sup.2 (12)
[0080] wherein ".alpha." is an angle between the optical axis of
the light source and a normal line on a surface of the subject.
When it is supposed that a reflectance of the surface of the
subject is "R" and the surface is a uniformly diffuse surface, a
luminance L.sub.0 of light, which occurs as the subject is
illuminated to function as a secondary light source, is expressed
as follows:
L.sub.0=RI.sub.01.multidot.(T.sub.D/T.sub.S).multidot.(cos
.alpha.)/(.pi..multidot.r.sub.L.sup.2) (13)
[0081] By substituting formula (13) for formula (11), the following
relationship is obtained: 3 E a = RV ( r - f ) 2 cos 4 4 F 2 r 2 I
01 cos r L 2 T D T S ( 14 )
[0082] The output value S.sub.1, which is obtained by integrating
the electric charge generated during the electric charge
accumulation period T.sub.D, is proportional to the exposure amount
which is a product of the field illumination and the exposure
period, and is obtained as follows: 4 S 1 = h 0 0 T D E a T = h 0
RV ( r - f ) 2 cos 4 4 F 2 r 2 I 01 cos r L 2 2 r 2 T S C 2 ( 15
)
[0083] wherein h.sub.0 is the constant of proportion of the
equation for obtaining the exposure amount.
[0084] Formula (15) can be transformed to formula (16) when it is
deemed that r.sub.L is nearly equal to r and the subject distance
is much greater than the focal length. 5 S 1 h 0 RV cos 4 4 F 2 I
01 cos T S C 2 ( 16 )
[0085] As understood from formula (16), the first reflected light
beam component is approximately constant regardless of a change in
the subject distance.
[0086] On the other hand, regarding the second reflected light beam
component, the illuminance E.sub.b on the surface of the subject is
expressed as follows:
E.sub.b=I.sub.02.multidot.(cos .alpha.)/(r.sub.L).sup.2 (17)
[0087] Therefore, obtaining formula corresponding to formula (16)
by using the method described above, in which formula (17) is used
instead of formula (12), it is understood that the second reflected
light beam component decreases in proportion to the inverse number
of the subject distance.
[0088] FIG. 12 is a view showing a relationship between the
accumulated electric charge amounts (the output values S.sub.1 and
S.sub.2) and the output range of the CCD 28. The abscissa is the
logarithm of the distance r, and the ordinate is the logarithm of
the output values S.sub.1 and S.sub.2.
[0089] The output value S.sub.1 of the first reflected light beam
component is approximately constant, and the logarithm of the
output value S.sub.1 is varied in accordance with the breadth Do of
the luminance of the measurement subject within a range sandwiched
between the solid lines G.sub.1 and G.sub.2. Conversely, the output
value S.sub.2 of the second reflected light beam component is
proportional to 1/r, and the logarithm of the output value S.sub.2
is varied in accordance with the breadth D.sub.0 of the luminance
of the measurement subject within a range sandwiched between the
solid lines G.sub.3 and G.sub.4.
[0090] Accordingly, for performing a distance measurement within a
range between the minimum distance r.sub.min to the maximum
distance r.sub.max, the CCD 28 needs to have the output range shown
by reference D.sub.1. The breadth of the output range D.sub.1 is
greater than the breadth D.sub.0 of the luminance of the
measurement subject by 20 or 30% at most.
[0091] Conversely, as a method in which any influence of the
reflectance of the measurement subject is corrected, the entire
width of each of the pulses of the reflected light beam may be
sensed, which is different from the embodiment (the specification
of U.S. Ser. No. 09/343,392, for example). For example, all of the
reflected light beam S24 may be sensed by starting the sensing
period T.sub.U before the rise of the pulse S24 (see FIG. 7).
However, according to this method, a term, which is in proportion
to 1/r.sup.2 and included in the accumulated electric charge,
becomes relatively large, and as a result it is necessary to expand
the output range of the CCD 28 as shown by reference D.sub.2.
[0092] As described above, in the embodiment, by calculating the
ratio S.sub.D of the first reflected light beam component, obtained
by the sensing operation of the reflected light beam component, to
the second reflected light beam component, obtained by the sensing
operation of the second reflected light beam component, the
influence of the surface of the measurement subject is removed.
Further, prior to the calculation of the ratio S.sub.D, the
corresponding noise components are removed from each of the first
and second reflected light beam components. Therefore, correction
of the noise, such as the reflectance, can be carried out with a
simple calculation, and further, the output range of the imaging
device is restrained as much as possible, so that the distance
measurement accuracy of the three-dimensional shape of the
measurement subject is improved.
[0093] Note that, although the height of each of the pulses of the
distance measuring light beam linearly decreases in the embodiment,
the height may linearly increase. Further, the variation of the
pulse height may be non-linear.
[0094] Although the embodiments of the present invention have been
described herein with reference to the accompanying drawings,
obviously many modifications and changes may be made by those
skilled in this art without departing from the scope of the
invention.
[0095] The present disclosure relates to subject matter contained
in Japanese Patent Application No. 2000-133504 (filed on May 2,
2000) which is expressly incorporated herein, by reference, in its
entirety.
* * * * *