U.S. patent application number 09/792348 was filed with the patent office on 2001-11-08 for brightness control for auto-focus in an optical system.
Invention is credited to Campbell, David K., Hofer, Gregory V., Ohno, Masahiro, Yamazaki, Yoshihiro.
Application Number | 20010038414 09/792348 |
Document ID | / |
Family ID | 25149157 |
Filed Date | 2001-11-08 |
United States Patent
Application |
20010038414 |
Kind Code |
A1 |
Hofer, Gregory V. ; et
al. |
November 8, 2001 |
Brightness control for auto-focus in an optical system
Abstract
An imaging device includes an image lens, an image sensor, and a
brightness control element. The imaging device receives an image
through the image lens in the optical pathway and detects the image
at the image sensor. Brightness of the light impinging on the image
sensor is adjusted using the brightness control element. In one
automatic focus technique, the brightness control element controls
luminous flux diameter. In another automatic focus technique, the
brightness control element controls light transmittance without
changing the luminous flux diameter. During detection of the
auto-focus (AF) signal for a bright image, a brightness controller
leaves the luminous flux diameter open and inserts a
neutral-density (ND) filter into the optical path to avoid
saturation of the signal from the image sensor. When the neutral
density filter is inserted, an auto-focus controller moves the
focusing lens to the best focus position independent of the
auto-focus (AF) and an automatic-exposure (AE) signals. When the
image is focused, the appropriate aperture diameter (F number) is
inserted based on the automatic-exposure signal.
Inventors: |
Hofer, Gregory V.;
(Loveland, CO) ; Campbell, David K.; (Loveland,
CO) ; Ohno, Masahiro; (Tokyo, JP) ; Yamazaki,
Yoshihiro; (Tokyo, JP) |
Correspondence
Address: |
HEWLETT-PACKARD COMPANY
Intellectual Property Administration
P.O. Box 272400
Fort Collins
CO
80527-2400
US
|
Family ID: |
25149157 |
Appl. No.: |
09/792348 |
Filed: |
February 23, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09792348 |
Feb 23, 2001 |
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09401038 |
Sep 21, 1999 |
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6233506 |
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09401038 |
Sep 21, 1999 |
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08789934 |
Jan 28, 1997 |
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6009355 |
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Current U.S.
Class: |
348/207.99 |
Current CPC
Class: |
B60K 35/00 20130101;
B60K 2370/12 20190501; B60R 2325/205 20130101; B60R 25/042
20130101; B60R 25/102 20130101; B60Q 9/00 20130101; B60R 25/2081
20130101; B60K 2370/11 20190501; B60R 16/0231 20130101; B60R
2325/304 20130101; B60K 2370/148 20190501; B60K 2370/1438 20190501;
B60K 2370/143 20190501; B60K 2370/152 20190501; B60G 2600/76
20130101; B60K 2370/736 20190501; B60H 1/00985 20130101; B60G
2600/70 20130101; B60K 37/06 20130101; B60G 17/0195 20130101; B60K
2370/161 20190501; B60H 1/00642 20130101; B60H 1/00771 20130101;
B60K 2370/154 20190501 |
Class at
Publication: |
348/207 |
International
Class: |
H04N 005/225; H04N
009/04 |
Claims
What is claimed is:
1. An imaging device comprising: an image lens disposed in an
optical path; an image sensor coupled to the optical path and
capable of detecting illumination passing through the image lens
and generating an image signal based on the detected illumination;
and a brightness controller coupled along the optical path, the
brightness controller capable of executing an auto-focus operation
that generates an auto-focus signal based on the image signal, a
brightness control operation that controls luminous flux diameter
along the optical path, and a light transmittance control operation
that controls light transmittance without changing the luminous
flux diameter, the auto-focus operation determining a focus
condition without changing the luminous flux diameter.
2. An imaging device according to claim 1 further comprising: a
controllable aperture that is controlled to modify the luminous
flux diameter.
3. An imaging device according to claim 1 further comprising: a
neutral density filter that can be inserted and removed from the
optical path to control light transmittance without changing the
luminous flux diameter.
4. An imaging device according to claim 1 further comprising: a
controllable aperture that is controlled to modify the luminous
flux diameter; and a neutral density filter that can be inserted
and removed from the optical path to control light transmittance
without changing the luminous flux diameter, both the controllable
aperture and the neutral density filter being disposed along the
optical path.
5. An imaging device according to claim 1 further comprising: a
focusing lens disposed in the optical path between the image lens
and the image sensor.
6. An imaging device according to claim 1 wherein: the imaging
device is a still image imaging device.
7. An imaging device according to claim 1 wherein: the auto-focus
operation and the light transmittance control operation are
performed concurrently.
8. An imaging device according to claim 1 further comprising: a
fixed objective lens disposed along the optical path.
9. An imaging device according to claim 1 further comprising: a
zoom lens disposed along the optical path.
10. An imaging device according to claim 1 further comprising: a
controller; and a control process operational in the controller,
the control process including: a processing logic capable of
detecting illumination at the image sensor and producing a signal
indicative of the amount of light impinging on the image sensor; a
processing logic capable of generating an automatic-exposure signal
based on the detected illumination level in combination with
generation of the auto-focus signal; and a processing logic capable
of responding to an increase in detected illumination intensity by
controlling light transmittance without changing the luminous flux
diameter.
11. An imaging device according to claim 10 further comprising: a
processing logic capable of reducing the detected light to a level
within a desired range.
12. An imaging device according to claim 10 further comprising: a
zoom lens disposed in the optical path; a processing logic capable
of detecting changes in system setting of the imaging device; and a
processing logic responsive to the detected changes in system
setting and capable of positioning the zoom lens along the optical
path in response to the changed system settings.
13. An imaging device according to claim 10 further comprising: a
processing logic capable of detecting changes in system setting of
the imaging device; and a processing logic responsive to the
detected changes in system setting and capable of modifying the
illumination level of light reaching the image sensor in some
circumstances by changing the aperture in other circumstances by
inserting the neutral density filter into the optical path.
14. An imaging device according to claim 10 further comprising: a
focusing lens disposed in the optical path; a processing logic
capable of detecting changes in system setting of the imaging
device; and a processing logic responsive to the detected changes
in system setting and capable of modifying the position of the
focusing lens and detecting the auto-focus signal at different
positions along the optical path.
15. A control process executable in an imaging device that includes
an imaging lens disposed in an optical path, an image sensor
coupled to the optical path and capable of detecting illumination
passing through the image lens and generating an image signal based
on the detected illumination, and a brightness controller coupled
along the optical path, the control process comprising: a
processing logic capable of executing an auto-focus operation that
generates an auto-focus signal based on the image signal; a
processing logic capable of executing a brightness control
operation that controls luminous flux diameter along the optical
path; and a processing logic capable of executing a light
transmittance control operation that controls light transmittance
without changing the luminous flux diameter, the auto-focus
operation determining a focus condition without changing the
luminous flux diameter.
16. A control process according to claim 15 further comprising: a
processing logic capable of detecting illumination at the image
sensor and producing a signal indicative of the amount of light
impinging on the image sensor; a processing logic capable of
generating an automatic-exposure signal based on the detected
illumination level in combination with generation of the autofocus
signal; and a processing logic capable of responding to an increase
in detected illumination intensity by controlling light
transmittance without changing the luminous flux diameter.
17. A control process according to claim 15 further comprising: a
processing logic capable of reducing the detected light to a level
within a desired range.
18. A control process according to claim 15 further comprising: a
zoom lens disposed in the optical path; a processing logic capable
of detecting changes in system setting of the imaging device; and a
processing logic responsive to the detected changes in system
setting and capable of positioning the zoom lens along the optical
path in response to the changed system settings.
19. A control process according to claim 15 further comprising: a
processing logic capable of detecting changes in system setting of
the imaging device; and a processing logic responsive to the
detected changes in system setting and capable of modifying the
illumination level of light reaching the image sensor in some
circumstances by changing the aperture in other circumstances by
inserting the neutral density filter into the optical path.
20. A control process according to claim 15 further comprising: a
focusing lens disposed in the optical path; a processing logic
capable of detecting changes in system setting of the imaging
device; and a processing logic responsive to the detected changes
in system setting and capable of modifying the position of the
focusing lens and detecting the auto-focus signal at different
positions along the optical path.
21. A method of controlling brightness in an imaging device
including an image lens and an image sensor, the method comprising:
detecting illumination passing through the image lens; generating
an image signal based on the detected illumination; generating an
auto-focus signal based on the image signal; controlling luminous
flux diameter along the optical path; and controlling light
transmittance without changing the luminous flux diameter, the
auto-focus operation determining a focus condition without changing
the luminous flux diameter.
22. A method according to claim 21 further comprising: detecting
illumination at the image sensor and producing a signal indicative
of the amount of light impinging on the image sensor; generating an
automatic-exposure signal based on the detected illumination level
in combination with generation of the auto-focus signal; and
responding to an increase in detected illumination intensity by
controlling light transmittance without changing the luminous flux
diameter.
Description
CROSS-REFERENCE
[0001] The present invention is related to subject matter disclosed
in the following co-pending patent applications:
[0002] 1. United States patent application entitled, "Zoom and
Focus Control Method and System" (HP Docket No. 10006921-1), naming
Michelle Ogg, Gregory V. Hofer, and David K. Campbell as inventors
and filed on even date herewith; and
[0003] 2. United States patent application entitled, "Zoom and
Focus Control System in an Optical System" (HP Docket No.
10006923-1), naming Gregory V. Hofer, David K. Campbell, Masahiro
Ohno, and Yoshihiro Yamazaki as inventors and filed on even date
herewith.
BACKGROUND OF THE INVENTION
[0004] Electronic imaging devices such as electronic cameras and
digital cameras acquire and record images using an electrical image
sensor. Usage of an electrical image sensor permits beneficial
functionality such as automatic focusing. For example, a digital
camera can use the signal from the electrical image sensor to
detect characteristics of light within the optical path of the
camera. The automatic focus operation involves analysis of the
spatial distribution of the light impinging on the detector, and
the intensity of light at the various positions in the spatial
field. Analysis of the light distribution can be used to create an
auto-focus signal and the auto-focus signal can be used to adjust
the position of an image lens to a focus position, thereby
adjusting the focus.
[0005] An optimum signal for properly and effectively focusing is a
signal that is easily detected by sensing circuitry. Control
circuits generally use various triggering techniques to determine
whether conditions are proper for actuating a control signal. For
example, a trigger signal is often used to detect some system
characteristic. In the case of an automatic focusing operation,
what is desired is a signal that precisely determines whether an
image is in focus.
[0006] Fidelity of the automatic focus signal depends largely on
the lens F number, which corresponds to the amount of light
entering the optical path of the camera. When the optical aperture
of the camera is closed, the electrical image sensor detects a
signal that is spread uniformly over the two-dimensional surface of
the sensor. The focal depth is great and the small differences
between detected signal at different spatial positions does not
permit fine detection of the focused condition. When the aperture
is open, the focus condition is more easily detected because the
depth of focus is much shallower. Thus an open aperture is highly
advantageous for detecting a suitable auto-focus signal. However,
if a bright image is detected, for example such as occurs in a
highly reflective condition such as a ski slope scene with bright
sun, then the brightness may overflow the range of the electrical
image sensor. The brightness causes the sensor to saturate, making
detection of a suitable auto-focus signal difficult.
[0007] An automatic focus camera typically adjusts the brightness
control by changing the electrical shutter speed of the camera. In
very bright conditions brightness control by modification of
shutter speed is difficult to control.
SUMMARY OF THE INVENTION
[0008] What is needed is an automatic focus device that accurately
determines a focus condition without decreasing the automatic
focusing accuracy even for bright objects in the image field.
[0009] In accordance with an aspect of the present invention, an
imaging device includes an image lens, an image sensor, and a
brightness control element. The imaging device receives an image
through the image lens in the optical pathway and detects the image
at the image sensor. Brightness of the light impinging on the image
sensor is adjusted using the brightness control element. In one
automatic focus technique, the brightness control element controls
luminous flux diameter. In another automatic focus technique, the
brightness control element controls light transmittance without
changing the luminous flux diameter. During detection of the
auto-focus (AF) signal for a bright image, a brightness controller
leaves the luminous flux diameter open and inserts a
neutral-density (ND) filter into the optical path to avoid
saturation of the signal from the image sensor. When the neutral
density filter is inserted, an auto-focus controller moves the
focusing lens to the best focus position independent of the
auto-focus (AF) and an automatic-exposure (AE) signals. When the
image is focused, the appropriate aperture diameter (F number) is
inserted based on the automatic-exposure signal.
[0010] In accordance with an embodiment of the present invention,
an imaging device includes an image lens disposed in an optical
path, an image sensor coupled to the optical path and capable of
detecting illumination passing through the image lens and
generating an image signal based on the detected illumination, and
a brightness controller coupled along the optical path. The
brightness controller is capable of executing an auto-focus
operation that generates an auto-focus signal based on the image
signal and a brightness control operation that controls luminous
flux diameter along the optical path. A light transmittance control
operation controls light transmittance without changing the
luminous flux diameter. The auto-focus operation determines a focus
condition without changing the luminous flux diameter.
[0011] In accordance with another embodiment of the present
invention, a control process is executable in an imaging device
that includes an imaging lens disposed in an optical path, an image
sensor coupled to the optical path, and a brightness controller.
The image sensor is capable of detecting illumination passing
through the image lens and generating an image signal based on the
detected illumination. The control process includes a processing
logic capable of executing an auto-focus operation, a processing
logic capable of executing a brightness control operation, and a
processing logic capable of executing a light transmittance control
operation. The auto-focus operation generates an auto-focus signal
based on the image signal. The brightness control operation
controls luminous flux diameter along the optical path. The light
transmittance control operation controls light transmittance
without changing the luminous flux diameter, the auto-focus
operation determining a focus condition without changing the
luminous flux diameter.
[0012] The described automatic focusing operation and apparatus
attain a highly suitable focus result for images with a wide range
of brightness without decreasing the auto-focus accuracy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a schematic block diagram that illustrates an
electronic imaging device that is suitable for implementing a
brightness and auto-focus control system in accordance with an
embodiment of the present invention.
[0014] FIG. 2 is a simplified, highly schematic pictorial diagram
that depicts an optical path of an imaging device in accordance
with an embodiment of the present invention.
[0015] FIG. 3 is a signal intensity graph showing an auto-focus
signal which is indicative of the intensity of light sensed at the
image sensor for a range of positions of the focus lens.
[0016] FIG. 4 is a schematic flow chart illustrating an automatic
focus technique for usage in an imaging device.
[0017] FIG. 5 is a schematic block diagram that illustrates another
electronic camera also suitable for implementing a brightness and
auto-focus control system in accordance with an alternative
embodiment of the present invention.
DESCRIPTION OF THE EMBODIMENT(S)
[0018] Referring to FIG. 1, a schematic block diagram illustrates
an electronic camera 102 that is also suitable for implementing a
zoom and focus control system 100 in accordance with an alternative
embodiment of the present invention. A sensor such as a
charge-coupled device (CCD) photo sensor 104 that detects light
passing through a lens system 106 to form an image. The alternative
illustrative zoom and focus control system 100 has a lens system
106 that also includes a plurality of lens groups, each of which
includes one or more lenses. The present example also has three
lens groups, first lens group 108, second lens group 110, and third
lens group 112. The first lens group 108 is a fixed-objective lens.
The second lens group 110 is a moving group lens that contains an
aperture stop (not shown). The second lens group 110 moves in
conjunction with the third lens group 112 to cause magnification to
change when the lens system 106 moves. THE second lens group 110
moves in a nonlinear manner to hold the image plane in a relatively
constant position as the lens system 106 is zoomed. The second lens
group 110 is also moved to focus the lens system 106 after reaching
a particular focal length. The third lens group 112 is also a
moving group of lenses in the lens system 106. The third lens group
112 is also a moving lens group. The third lens group 112 moves in
a linear manner to change the focal length of the camera as the
lens zooms.
[0019] The CCD photo sensor 104 is a two-dimensional array of
charge-coupled photo sensors that captures an image focused onto
the photo sensors by the lens system 106. Individual photo sensor
sites are pixels with an associated color such as red, green, or
blue. CCD photo sensor 104 is exposed to light and charge
integrates at the individual pixel site proportional to the number
of photons received at the site. Clock drivers 114 are connected to
the CCD photo sensor 104 and convey clock signals to control the
read-out process of CCD photo sensor 104. Image processing hardware
(not shown) generates the clock signals and sends the clock signals
from the image processing hardware through the clock drivers 114 to
the CCD photo sensor 104. The clock drivers 114 supply clock
signals with high current and sufficient frequencies to drive
highly capacitive CCD control lines.
[0020] A low pass filter 116 is connected to the CCD photo sensor
104 for anti-alias filtering to avoid optical moire effects
resulting from the discrete CCD pixel structure. An example of the
low pass filter 116 includes two birefringent quartz plates (not
shown) and a quarter-wave plate (not shown). One birefringent quart
plate produces filtering with respect to a horizontal direction of
the CCD array. The other birefringent plate filters in a vertical
direction of the CCD array. The quarter-wave plate functions is a
depolarizer. The term low-pass filter indicates imaging of only a
low spatial frequency image.
[0021] The CCD photo sensor 104 generates image signals and passes
the signals through an analog to digital converter (ADC) 118 to the
image processing hardware. Row-by-row pixel image data from the CCD
photo sensor 104 are an analog voltage passed to the analog to
digital converter 118. The analog to digital converter 118
amplifies and digitizes the image signal. The digitization process
generates an N-bit digital word for each pixel. The analog to
digital converter 118 clocks pixel data into the image processing
hardware.
[0022] A shutter/aperture module 120 is interposed between the
second lens group 108 and the third lens group 110. The
shutter/aperture module 120 includes a shutter 122, apertures 124,
and a neutral density filter 126. The shutter 122 is a blade
switched into the optical path 128 of the lens system 106 to
prevent light from reaching the CCD photo sensor 104. The shutter
122 blocks light at the end of an exposure time to complete image
capture and when the camera is powered off to protect the CCD photo
sensor 104 from receiving excessive light and damaging individual
sensor elements.
[0023] The apertures 124 are multiple blades, each containing a
hole. Different blades typically have different diameter holes.
Different apertures can be switched into the optical path 128 to
reduce the light transmitted through the lens system 106 to the CCD
photo sensor 104. Different apertures 124 are used to control light
exposure and focus depth of field. A typical still-image electronic
camera has one or two aperture blades. In other designs, the
aperture 124 may be composed of a diaphragm with continuously
variable aperture hole sizes to supply a greater number of
selectable apertures.
[0024] The neutral density filter 126 is an additional blade that
can be switched into the optical path 128. The neutral density
filter 126 also reduces the light passed through the lens system
106 to the CCD photo sensor 104. The aperture 124 and the neutral
density filter 126 function similarly, but differ in that the
neutral density filter 126 can be used to reduce the amount of
light passing through the lens system 106 without affecting the
focus depth of field. In contrast, usage of an aperture to reduce
light to the CCD photo sensor 104 changes the depth of focus. The
neutral density filter 126 can be used in conjunction with the
apertures 124 to further reduce the level of light passing to the
CCD photo sensor 104.
[0025] The shutter/aperture module 120 is controlled by signals
passed from a camera control element (not shown) via solenoids 130.
Individual blades of the shutter 122, the apertures 124, and the
neutral density filter 126 are actuated in and out of the lens
optical path 128 by a plurality of solenoids including a shutter
solenoid 129, an aperture solenoid 130, and a neutral density
filter solenoid 131. The solenoids are driven by coil drivers 132
which supply voltage and current for actuating the blades into
position in a timely manner. The coil drivers 132 are controlled by
signals from a processor (not shown) such as a central processing
unit (CPU), a microcontroller, or control logic. The camera control
element may be software or firmware that executes on the
processor.
[0026] The processor determines relative positioning of the second
lens group 110, and the third lens group 112, thus controlling zoom
and focus functionality. The processor executes application
programs that supply control information to a motor driver 134, an
executing program code supplying control signals to a first stepper
motor 138 and a second stepper motor 140. The stepper motors 138
and 140 physically control the position of the second lens group
110 and the third lens group 112, respectively.
[0027] In the illustrative electronic camera 102, the motor driver
134 sends signals to the stepper motor 138 that is connected to the
second lens group 110 by gear reduction 150 and a lead screw 152.
Similarly, the motor driver 134 sends signals to the stepper motor
138 that is connected to the third lens group 112 also by gear
reduction 150 and a lead screw 152. The stepper motors 138 and 140
receive signals from the processor via the motor driver 134 that
determine the position and motion of the second lens group 110 and
the third lens group 112. In alternative systems, other types of
motors and drive mechanisms can be used to controls lens position
adjustment of the second and third lens groups 110 and 112. Photo
sensors 154 are connected to the motor and drive mechanism for the
second and third lens groups 110 and 112 to monitor positioning of
the lens groups 110 and 112. The processor determines the initial
positions of the second and third lens groups 110 and 112 by moving
the lens groups toward the photo sensors 154 and detecting when
flag 156 mounted on the second and third lens groups 110 and 112
reaches the photo sensors 154. The position at which the photo
sensors 154 detect the flags is a home position. The processor
measures the positions of the second and third lens groups 110 and
112 relative to the home position. The processor tracks the number
of steps the stepper motors 138 and 140 execute in all moves
relative to the home position.
[0028] The motor drivers 134 supply voltage and current to the
stepper motors 138 and 140, thus determining the position and
motion of the second lens group 110 and the third lens group 112.
The motor drivers 134 are controlled by signals from the
processor.
[0029] Referring to FIG. 2, a simplified, highly schematic
pictorial diagram depicts an optical path 202 of an imaging device
200 in accordance with an embodiment of the present invention.
Arranged along an optical axis 204 are an image lens 206, a neutral
density filter 208, an aperture 209, a focus lens 210, and an image
sensor 212. The simplified diagram is used for illustrative
purposes and omits additional components such as additional lenses,
for example a zoom lens that may be included in some devices. The
image lens 206 and focus lens 210 may be single lenses or compound
lenses. When the aperture 209 is open, light passes along the
optical path 202 to the image sensor 212, a two-dimensional array
of sensor elements.
[0030] Referring to FIG. 3 in conjunction with FIG. 2, a signal
intensity graph depicts an auto-focus signal 300 which is
indicative of the intensity of light sensed at the image sensor 212
for a range of positions of the focus lens 210. The focus lens 210
scans under control of a focus control element (not shown) in the
imaging device 200 from a position adjacent the aperture 209
through a range of focus lens positions toward the image sensor
212. The illumination signal as a function of focus lens position
is called an auto-focus (AF) signal and is used to focus the
imaging device 200.
[0031] When the aperture 209 is closed, the illumination detected
by the image sensor 212 is relatively low in intensity and is
generally distributed across the range of focus lens positions. For
the closed aperture, so that the AF signal 302 at a focus position
does not greatly exceed the amplitude when the image is not in
focus. Automatic focusing control is typically implemented using
electronic circuits that detect a suitable indication of a focused
condition and control positioning of pertinent components such as
the focus lens 210 to acquire images in the focused condition.
Generally, triggering circuits are used to monitor the AF signal
and detect suitable focus conditions. Various aspects of the AF
signal may be used to determine the focused condition. A peak
detector may be used to detect the maximum AF signal although the
closed-aperture AF signal 302 does not greatly differ across the
range of focus lens positions so that proper focusing is difficult
to achieve. Peak detection is highly sensitive to noise, increasing
the difficulty in attaining a focused condition. Other aspects of
the AF signal may be monitored to determine the focus condition,
such as the slope of the AF signal. The closed-aperture AF signal
302 has a small slope, or derivative, signal throughout the focus
position range so that facility of detection is not greatly
improved over peak detection.
[0032] When the aperture 209 is open, the illumination signal
detected by the image sensor 212 is relatively high in intensity
near the focus position of the focus lens 210 and low outside a
suitable focus region. A wide aperture thus results in a narrow
field for the open-aperture AF signal 304. The open-aperture
auto-focus signal 304 is therefore highly preferable over the
closed-aperture AF signal 302 for detecting a focused condition.
Both peak detection and slope detection are facilitated by usage of
the open-aperture AF signal 304 to detect a focused condition. The
problem with usage of the open-aperture AF signal 304 for detecting
a focused condition is that the AF signal can be saturated due to
high illumination, creating drop-outs and noise that obscure the
focused condition.
[0033] The illustrative imaging device 200 improves auto-focus
capabilities by using the neutral density filter 208 to reduce the
level of illumination detected by the image sensor 212 so that the
open-aperture AF signal 304 can be used to determine a focused
condition. Accordingly, the imaging device 200 detects the
auto-focus signal by maintaining the aperture 209 at a desired
preselected setting and reducing light intensity detected by the
image sensor 212 through usage of the neutral density filter 208.
The user sets the imaging device 200 to acquire images at a
selected aperture setting, or F number, and monitors the AF signal
while the F number is maintained at the same setting, thereby
maintaining the same luminous flux diameter. The neutral density
filter 208 is inserted while the AF signal is monitored so that the
AF signal has reduced or removed distortion from saturation
effects. Usage of the neutral density filter 208 controls the
amount of light to reach the image sensor 212 without changing the
aperture 209 setting. In the illustrative example, the neutral
density filter 208 appears to reduce the intensity of incident
light on the image sensor 212 at an amount that approximates the
light reduction of changing the aperture setting by two F
stops.
[0034] Referring to FIG. 4, a schematic flow chart illustrates an
automatic focus technique 400 for usage in an imaging device. The
automatic focus technique 400 can be executed as a firmware or
software program or routine in a processor connected to an imaging
system such as the systems shown in FIGS. 1, 2, and 5.
Alternatively, the automatic focus technique 400 can be performed
in a controller or logic circuit. In a typical application, the
automatic focus technique 400 can operate continuously in response
to various signals produced by the imaging system, timing elements
(not shown), and the processor.
[0035] In a detect illumination operation 402, the image sensor
detects illumination at the sensor elements and produces a signal
indicative of the amount of light impinging on the sensor elements.
The detected illumination level is used to generate an
automatic-exposure (AE) signal as well as the AF signal. If the
amount of detected light is increased, according to logic block
404, the neutral density filter is interposed 406 into the optical
path to reduce the detected light to a level within a desired
range. In response to any changes in system settings 408, the
imaging device performs various zoom 410, auto-exposure 412, and
auto-focus 414 tasks. Generally the zoom task 410 changes the
position of a zoom lens to a desired position. The auto-exposure
task 412 modifies the illumination level of light reaching the
image sensor in some circumstances by changing the aperture in
other circumstances by inserting the neutral density filter into
the optical path. The auto-focus task 414 modifies the position of
a focusing lens and detects the AF signal at different positions.
The auto-focus task 414 detects a desired AF signal condition, for
example the maximum AF signal or the maximum slope AF signal, and
determines that a suitable position of the focus lens on that
basis.
[0036] Although in the illustrative examples, the second and third
lenses are used for zooming and the second lens is used for focus.
In other embodiments, the lenses may be used in a different manner.
For example, the first and second lens groups may be used for
zooming and the third lens group used for focusing.
[0037] Referring to FIG. 5, a schematic block diagram illustrates
another electronic camera 502 that is suitable for implementing a
zoom and focus control system 500 in accordance with an embodiment
of the present invention. An image is detected at a sensor, for
example a charge-coupled device (CCD) photo sensor 504 that detects
light passing through a lens system 506. In the illustrative zoom
and focus control system 500, the lens system 506 includes a
plurality of lens groups, each of which includes one or more
lenses. One example has three lens groups, first lens group 508,
second lens group 510, and third lens group 512. The second lens
group 510, termed a variator, changes the effective focal length of
the lens and moves in a linear manner. The first lens group 508
moves in a nonlinear manner relative to the linear motion of the
second lens group 510 and functions as a compensator. The first
lens group 508 functions to hold the image plane relatively
constant as the lens is zoomed over the range of focal lengths of
the lens system 506. The third lens group 512 is a positive is a
positive element that is moved to focus the lens system 506.
[0038] The CCD photo sensor 504 is a two-dimensional array of
charge-coupled photo sensors used to capture the image that is
focused onto the photo sensors by the lens system 506. The
individual photo sensor sites are defined as pixels and have an
associated color such as red, green, or blue. As the CCD photo
sensor 504 is exposed to light, charge integrates at the individual
pixel site proportional to the number of photons received at the
site. Clock drivers 514 are connected to the CCD photo sensor 504
and propagate clock signals that are used to control the read-out
process of the CCD photo sensor 504. Image processing hardware (not
shown) generates the clock signals. The clock signals propagate
from the image processing hardware through the clock drivers 514 to
the CCD photo sensor 504. The clock drivers 514 supply clock
signals with high levels of current at sufficient frequencies to
drive highly capacitive CCD control lines.
[0039] A low pass filter 516 is connected to the CCD photo sensor
504 for usage as an anti-aliasing filter to avoid optical moire
effects that occur due to the discrete nature of the CCD pixel
structure. One suitable example of the low pass filter 516 includes
two birefringent quartz plates (not shown) and a quarter-wave plate
(not shown). One of the birefringent quart plates produces
filtering with respect to a horizontal direction of the CCD array.
The second birefringent plate produces filtering in a vertical
direction of the CCD array, 90.degree. shifted from the horizontal
direction. The quarter-wave plate functions as a depolarizer. The
term low-pass filter indicates imaging of only a low spatial
frequency image.
[0040] The CCD photo sensor 504 generates image signals that are
passed through an analog to digital converter (ADC) 518 to the
image processing hardware. Row-by-row pixel image data is read from
the CCD photo sensor 504 as an analog voltage and is passed to the
analog to digital converter 518. The analog to digital converter
518 amplifies and digitizes the image signal. The digitization
process generates an N-bit digital word for each pixel. The analog
to digital converter 518 clocks the digital words for the pixels
into the image processing hardware.
[0041] A shutter/aperture module 520 is interposed between the
first lens group 508 and the second lens group 510. The
shutter/aperture module 520 includes a shutter 522, apertures 524,
and a neutral density filter 526. The shutter 522 is a blade that
is switched into the optical path 528 of the lens system 506 to
prevent light from reaching the CCD photo sensor 504. The shutter
522 typically is controlled to block the light at the end of an
exposure time to complete image capture. The shutter 522 is also
closed when the camera is powered off to protect the CCD photo
sensor 504 from receiving excessive light, potentially causing
damage to the individual sensor elements.
[0042] The apertures 524 are multiple blades containing different
diameter holes. An aperture blade can be switched into the optical
path 528 to reduce the amount of light transmitted through the lens
system 506 to the CCD photo sensor 504. Different apertures 524 are
used to control light exposure and to control the focus depth of
field. A typical electronic camera that is used for still image
reception has one or two aperture blades. Alternatively, the
aperture 524 may be composed of a diaphragm with continuously
variable aperture hole sizes to supply a greater number of
selectable apertures.
[0043] The neutral density filter 526 is an additional blade that
can be switched into the optical path 528. The neutral density
filter 526 also reduces the amount of light that is transmitted
through the lens system 506 to the CCD photo sensor 504. Although
an aperture 524 and the neutral density filter 526 are similar in
function, the neutral density filter 526 can be used to reduce the
amount of light passing through the lens system 506 without
affecting the focus depth of field. Usage of an aperture to reduce
light to the CCD photo sensor 504 always affects the depth of
focus. The neutral density filter 526 can be used in conjunction
with the apertures 524 to further reduce the level of light passing
to the CCD photo sensor 504.
[0044] The shutter/aperture module 520 is controlled by signals
passed from a camera control block (not shown) via solenoids (not
shown). Individual blades of the shutter 522, the apertures 524,
and the neutral density filter 526 are actuated in and out of the
lens optical path 528 by a solenoid. The individual solenoids are
driven by a solenoid driver (not shown) which supplies the voltage
and current for actuating the blades into position in a timely
manner. The solenoid drivers are controlled by signals from a
processor (not shown) such as a central processing unit (CPU), a
microcontroller, or control logic. The camera control block may be
software or firmware that executes on the processor.
[0045] The processor determines relative positioning of the first
lens group 508, the second lens group 510, and the third lens group
512, thus controlling zoom and focus functionality. The processor
executes application programs that supply control information to a
motor driver 534, an executing program code supplying control
signals to a DC motor 536 and a stepper motor 538. The DC motor 536
physically controls the position of the first lens group 508 and
the second lens group 510 of the lens system 506. The stepper motor
538 physically controls the position of the third lens group 512.
The first lens group 508 and the second lens group 510 are held by
a lens barrel 540. DC motor 536 is connected to the lens barrel 540
and drives the rotation of the lens barrel 540 via a set of gears
(not shown) between the lens barrel 540 and the DC motor 536. As
the lens barrel 540 rotates, the positions of the first lens group
508 and the second lens group 510 are adjusted through the
operation of cam slots (not shown) inside the lens barrel 540. A
lens cam switch 542 is mounted on the lens barrel 540 and sends
signal transitions to the processor as the lens barrel 540 rotates
through a plurality of zoom positions. In one example, the
electronic camera 502 has three zoom positions of wide, tele, and
retract. A slider potentiometer 544 is connected to the lens barrel
540. As the lens barrel 540 rotates between the wide and tele zoom
positions, the slider potentiometer 544 produces a fine zoom
position information. A cam slot 546 in the lens barrel 540 drives
the slider potentiometer 544 depending on the position of the wide
and tele zoom position. The processor determines the fine zoom
position by reading the voltage obtained from the center tap of the
slider potentiometer 544 via an analog-to-digital converter (ADC)
548. Fine zoom position values produced by the slider potentiometer
544 are calibrated by recording the slider potentiometer values
when the lens cam switch 542 is positioned at the tele and wide
positions.
[0046] In the illustrative electronic camera 502, the motor driver
534 sends signals to the stepper motor 538 that is connected to the
third lens group 512 by gear reduction 550 and a lead screw 552.
The stepper motor 538 receives signals from the processor via the
motor driver 534 that determine the position and motion of the
third lens group 512. In alternative systems, other types of motors
and drive mechanisms can be used to controls lens position
adjustment of the third lens group 512. Photo sensors 554 are
connected to the motor and drive mechanism for the third lens group
512 to monitor positioning of the third lens group 512. The
processor determines the initial position of the third lens group
512 by moving the lens group toward the photo sensor 554 and
detecting when flag 562 mounted on the third lens group 512 reaches
the photo sensor 554. The position at which the photo sensor 554
detects the flag is a home position. The processor measures the
position of the third lens group 512 relative to the home position.
The processor tracks the number of steps the stepper motor 538
executes in all moves relative to the home position.
[0047] The motor driver 534 supplies voltage and current to the DC
motor 536 and the stepper motor 538, thus determining the position
and motion of the first lens group 508 and second lens group 510,
and the third lens group 512. The motor driver 534 is controlled by
signals from the processor.
[0048] A temperature sensor 560 inside the electronic camera 502
measures temperature and is connected to the processor. The
processor includes a processing logic that is capable of adjusting
a starting position of the lenses to adjust focus for temperature
differences.
[0049] While the invention has been described with reference to
various embodiments, it will be understood that these embodiments
are illustrative and that the scope of the invention is not limited
to them. Many variations, modifications, additions and improvements
of the embodiments described are possible. For example, those
having ordinary skill in the art will readily implement the steps
necessary to provide the structures and methods disclosed herein,
and will understand that the process parameters, materials, and
dimensions are given by way of example only and can be varied to
achieve the desired structure as well as modifications which are
within the scope of the invention. Variations and modifications of
the embodiments disclosed herein may be made based on the
description set forth herein, without departing from the scope and
spirit of the invention as set forth in the following claims. For
example, one or ordinary skill in the art could similarly apply the
first and second quality-of-service techniques to the other
interconnect structures described herein.
[0050] In the claims, unless otherwise indicated the article "a" is
to refer to "one or more than one".
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