U.S. patent application number 15/085247 was filed with the patent office on 2016-10-06 for display control apparatus, display control method, and image capturing apparatus.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Kazunori Ishii.
Application Number | 20160295122 15/085247 |
Document ID | / |
Family ID | 57016199 |
Filed Date | 2016-10-06 |
United States Patent
Application |
20160295122 |
Kind Code |
A1 |
Ishii; Kazunori |
October 6, 2016 |
DISPLAY CONTROL APPARATUS, DISPLAY CONTROL METHOD, AND IMAGE
CAPTURING APPARATUS
Abstract
A display control apparatus, comprises: a focus detection unit
configured to detect, based on an image signal obtainable from an
image sensor, a focus state and reliability of the image signal;
and a display control unit configured to display in a display unit,
when focus adjustment is performed by a manual operation, an index
that indicates the focus state that was detected by the focus
detection unit, wherein the display control unit changes a display
format of the index according to the reliability.
Inventors: |
Ishii; Kazunori;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
57016199 |
Appl. No.: |
15/085247 |
Filed: |
March 30, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04N 5/23212 20130101;
H04N 5/232939 20180801; H04N 9/04557 20180801; H04N 5/36961
20180801; H04N 5/23293 20130101; H04N 5/232122 20180801 |
International
Class: |
H04N 5/232 20060101
H04N005/232 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2015 |
JP |
2015-077147 |
Mar 4, 2016 |
JP |
2016-042829 |
Claims
1. A display control apparatus, comprising: a focus detection unit
configured to detect, based on an image signal obtainable from an
image sensor, a focus state and reliability of the image signal;
and a display control unit configured to display in a display unit,
when focus adjustment is performed by a manual operation, an index
that indicates the focus state that was detected by the focus
detection unit, wherein the display control unit changes a display
format of the index according to the reliability.
2. The display control apparatus according to claim 1, wherein the
focus detection unit detects a defocus amount and a direction to an
in-focus position, and the display control unit displays, as the
index that indicates the focus state, in a case where the
reliability is more than a first threshold value that has been
determined in advance, an index that indicates the defocus amount
and the direction.
3. The display control apparatus according to claim 2, wherein the
first threshold value is set to a value for judging whether or not
it is possible to rely on the defocus amount.
4. The display control apparatus according to claim 2, wherein the
display control unit displays, as the index that indicates the
focus state, in a case where the reliability is the first threshold
value or less and is more than a second threshold value that is
less than the first threshold value, an index that indicates the
direction without indicating the defocus amount.
5. The display control apparatus according to claim 4, wherein the
second threshold value is set to a value for judging whether or not
it is possible to rely on the direction.
6. The display control apparatus according to claim 4, wherein the
display control unit does not display, as the index that indicates
the focus state, in a case where the reliability is the second
threshold value or less, an index that indicates the defocus amount
and the direction.
7. The display control apparatus according to claim 4, wherein the
display control unit displays, in a case where the reliability is
more than the second threshold value and the defocus amount is
outside of a range that has been determined in advance, an index
that indicates the defocus amount, fixed at a position that has
been determined in advance.
8. The display control apparatus according to claim 2, wherein the
display control unit performs display that indicates the defocus
amount by performing display so as to move the index by a movement
amount corresponding to the defocus amount, relative to a reference
position.
9. The display control apparatus according to claim 8, wherein the
display control unit changes a defocus amount that corresponds to a
unit movement amount of the index, according to at least any of the
defocus amount that was detected by the focus detection unit and an
image shooting state.
10. The display control apparatus according to claim 9, wherein the
display control unit performs control such that, in a case where
the defocus amount that was detected by the focus detection unit is
a first value, the defocus amount that corresponds to the unit
movement amount of the index is increased in comparison to a case
of a second value that is less than the first value.
11. The display control apparatus according to claim 9, wherein the
image shooting state includes an aperture state, and the display
control unit performs control such that, in a case of a first
aperture value, the defocus amount that corresponds to the unit
movement amount of the index is increased in comparison to a case
of a second aperture value on a full-open aperture side relative to
the first aperture value.
12. The display control apparatus according to claim 11, wherein
the display control unit performs display such that, in a case
where the defocus amount that was detected by the focus detection
unit is within a predetermined range, the index moves by a movement
amount corresponding to the defocus amount, and the predetermined
range is set larger in the case of the first aperture value than in
the case of the second aperture value.
13. The display control apparatus according to claim 9, wherein the
image shooting state includes an illuminance state, and the display
control unit performs control such that, in a case of a first
illuminance, the defocus amount that corresponds to the unit
movement amount of the index is increased in comparison to a case
of a second illuminance that is brighter than the first
illuminance.
14. The display control apparatus according to claim 9, wherein the
image shooting state includes a state of focal length, and the
display control unit performs control such that, in a case of a
first focal length, the defocus amount that corresponds to the unit
movement amount of the index is increased in comparison to a case
of a second focal length on a wide angle side relative to the first
focal length.
15. The display control apparatus according to claim 14, wherein
the display control unit performs display such that, in a case
where the defocus amount that was detected by the focus detection
unit is within a predetermined range, the index moves by a movement
amount corresponding to the defocus amount, and the predetermined
range is set larger in the case of the first focal length than in
the case of the second focal length.
16. The display control apparatus according to claim 9, wherein a
defocus amount that corresponds to a unit movement amount of the
index is determined based on a depth of focus.
17. The display control apparatus according to claim 15, wherein
the predetermined range is determined based on a depth of
focus.
18. The display control apparatus according to claim 9, wherein the
display control unit calculates an average value of defocus amounts
that were obtained by a plurality of instances of detection, and
based on the average value of a predetermined number of the defocus
amounts, determines the defocus amount that corresponds to the unit
movement amount of the index.
19. The display control apparatus according to claim 18, wherein
the display control unit changes the predetermined number according
to at least any of the defocus amount detected by the focus
detection unit, an aperture state, and an illuminance state.
20. The display control apparatus according to claim 19, wherein
the display control unit increases the predetermined number
according to satisfaction of at least any of a case where the
defocus amount is more than a predetermined value, a case where the
aperture is on a small aperture side relative to a predetermined
aperture value, and a case where illuminance is less than a
predetermined illuminance.
21. The display control apparatus according to claim 9, wherein the
display control unit calculates, a plurality of times, a movement
amount of the index relative to the reference position, and based
on an average value of a predetermined number of the movement
amounts, determines a position to display the index.
22. The display control apparatus according to claim 21, wherein
the display control unit changes the predetermined number according
to at least any of the defocus amount detected by the focus
detection unit, an aperture state, and an illuminance state.
23. The display control apparatus according to claim 22, wherein
the display control unit increases the predetermined number
according to satisfaction of at least any of a case where the
defocus amount is more than a predetermined value, a case where the
aperture is on a small aperture side relative to a predetermined
aperture value, and a case where illuminance is less than a
predetermined illuminance.
24. The display control apparatus according to claim 1, further
comprising an in-focus state determination unit configured to set
an in-focus range of the defocus amount used for determining
in-focus state based on the defocus amount that was detected by the
focus detection unit, wherein the in-focus state determination unit
changes the in-focus range in accordance with a focal length.
25. The display control apparatus according to claim 24, wherein
the in-focus state determination unit performs control such that,
in a case of a third focal length, the in-focus range is increased
in comparison to a case of a fourth focal length on a wide angle
side relative to the third focal length.
26. The display control apparatus according to claim 24, wherein
the in-focus state determination unit changes the in-focus range
further based on a depth of focus.
27. An image capturing apparatus, comprising: an image sensor
having a plurality of pixels provided with a plurality of
photoelectric converters for a single microlens, the image sensor
receiving luminous flux incident through an imaging optical system
with the plurality of photoelectric converters and outputting a
pair of image signals; and a display control apparatus that
comprises: a focus detection unit configured to detect, based on
the par of image signals output from the image sensor, a focus
state by performing focus detection using a phase difference method
and reliability of the pair of image signals; and a display control
unit configured to display in a display unit, when focus adjustment
is performed by a manual operation, an index that indicates the
focus state that was detected by the focus detection unit, wherein
the display control unit changes a display format of the index
according to the reliability.
28. A display control method, comprising: performing focus
detection to detect, based on an image signal obtainable from an
image sensor, a focus state and reliability of the image signal;
and performing display control to display in a display unit, when
focus adjustment is performed by a manual operation, an index that
indicates the focus state that was detected in the focus detection,
wherein in the display control, a display format of the index is
changed according to the reliability.
29. A computer-readable storage medium storing a program for
causing a computer to execute a display control method, comprising:
performing focus detection to detect, based on an image signal
obtainable from an image sensor, a focus state and reliability of
the image signal; and performing display control to display in a
display unit, when focus adjustment is performed by a manual
operation, an index that indicates the focus state that was
detected in the focus detection, wherein in the display control, a
display format of the index is changed according to the
reliability.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a display control apparatus
provided with a configuration that detects a focus state and a
configuration that controls display of the focus state, and a
display control method, and an image capturing apparatus.
[0003] 2. Description of the Related Art
[0004] A focus control apparatus of a high definition video camera
or the like that is compatible with recent full HD, 4K, or the like
has higher resolving power than ever before, and so when a
photographer focuses on a subject using a manual focus operation
(ME operation), it is not easy to focus exactly. In particular,
when performing a focus operation while checking focus using a
viewfinder, a display panel, or the like provided in the camera,
there are cases where focus offset occurs to a degree that cannot
be checked with the viewfinder, the display panel, or the like, and
thus it is difficult to judge whether or not an intended focus
state has been established.
[0005] Consequently, a focus assist method that assists an MF
operation has been proposed. Japanese Patent Laid-Open No.
2007-248615 proposes a method in which when performing an MF
operation, a focus state evaluation value is calculated, and a
degree of focus state is displayed in a bar display. Also, Japanese
Patent Laid-Open No. 2005-140943 proposes, as focus assist methods
in an image capturing apparatus, a plurality of display methods
that indicate changes in focus state accompanying movement of a
focusing lens.
[0006] On the other hand, Japanese Patent Laid-Open No. 2001-083407
describes an image capturing apparatus utilizing an on-imaging
plane phase difference detection method as a method for detecting
the focus state, and in this image capturing apparatus a live view
mode is considered in which image shooting is performed while
displaying a shot image on a rear monitor or the like.
[0007] However, in a case where, as in Japanese Patent Laid-Open
No. 2001-083407, focus detection is performed using an on-imaging
plane phase difference detection method in an image capturing
apparatus capable of image display in a live view mode, phase
difference is detected on the imaging plane, so detection accuracy
decreases according to a blur state of the subject.
[0008] For example, when a subject image as shown in FIG. 12A was
shot, in a pair of signals used in the phase difference detection
method, two peak-like shapes are seen in the vicinity of being in
focus, as shown in FIG. 12B. Also, in the vicinity of being in
focus, where reference sign 1201 denotes an A image and reference
sign 1202 denotes a B image, the A image 1201 and the B image 1202
have about the same shape. Accordingly, by applying the phase
difference detection method and calculating the offset amount of
these two images, it is possible to calculate a defocus amount with
high detection accuracy.
[0009] On the other hand, when focus is greatly blurred (large
blur), for example, as shown in FIG. 12C, the two mountain-like
shapes collapse, becoming one mountain-like shape. Further, that
mountain-like shape has a broad base, and the shape differs between
the A image 1201 and the B image 1202. Therefore, in a large blur
state, the degree of coincidence of the A image and the B image
worsens, so detection accuracy decreases.
[0010] Detection accuracy also decreases depending on aperture. The
reason for this is that, even if distance to the subject is the
same, as the aperture changes from a full-open aperture to a small
aperture, the offset amount of the A image and the B image
decreases and resolving power in phase difference detection becomes
more coarse. Also, when there is low illuminance, the S/N ratio
decreases, and so the detection accuracy decreases.
[0011] As described above, the accuracy of focus detection by an
on-imaging plane phase difference detection method differs
depending on the image shooting state, so when performing focus
assist display, there are cases where it is not possible to display
stable information. In addition, there are some cases where a user
may feel uncomfortable when performing focus adjustment while
monitoring information display due to differences in focus ring
operability and in the depth of focus determined by the focal
length of an attached lens.
SUMMARY OF THE INVENTION
[0012] The present invention has been made in consideration of the
above situation, and realizes a focus assist function that is
stable when performing manual focus adjustment.
[0013] According to the present invention, provided is a display
control apparatus, comprising: a focus detection unit configured to
detect, based on an image signal obtainable from an image sensor, a
focus state and reliability of the image signal; and a display
control unit configured to display in a display unit, when focus
adjustment is performed by a manual operation, an index that
indicates the focus state that was detected by the focus detection
unit, wherein the display control unit changes a display format of
the index according to the reliability.
[0014] Furthermore, according to the present invention, provided is
an image capturing apparatus, comprising: an image sensor having a
plurality of pixels provided with a plurality of photoelectric
converters for a single microlens, the image sensor receiving
luminous flux incident through an imaging optical system with the
plurality of photoelectric converters and outputting a pair of
image signals; and a display control apparatus that comprises: a
focus detection unit configured to detect, based on the pair of
image signals output from the image sensor, a focus state by
performing focus detection using a phase difference method and
reliability of the pair of image signals; and a display control
unit configured to display in a display unit, when focus adjustment
is performed by a manual operation, an index that indicates the
focus state that was detected by the focus detection unit, wherein
the display control unit changes a display format of the index
according to the reliability.
[0015] Further, according to the present invention, provided is a
display control method, comprising: performing focus detection to
detect, based on an image signal obtainable from an image sensor, a
focus state and reliability of the image signal; and performing
display control to display in a display unit, when focus adjustment
is performed by a manual operation, an index that indicates the
focus state that was detected in the focus detection, wherein in
the display control, a display format of the index is changed
according to the reliability.
[0016] Further, according to the present invention, provided is a
computer-readable storage medium storing a program for causing a
computer to execute a display control method, comprising:
performing focus detection to detect, based on an image signal
obtainable from an image sensor, a focus state and reliability of
the image signal; and performing display control to display in a
display unit, when focus adjustment is performed by a manual
operation, an index that indicates the focus state that was
detected in the focus detection, wherein in the display control, a
display format of the index is changed according to the
reliability.
[0017] Further features of the present invention will become
apparent from the following description of exemplary embodiments
(with reference to the attached drawings).
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the description, serve to explain
the principles of the invention.
[0019] FIG. 1 is a block diagram that shows a schematic:
configuration of an image capturing system according to an
embodiment of the present invention;
[0020] FIG. 2 is a schematic view of a pixel array of an image
sensor according to an embodiment;
[0021] FIGS. 3A to 3D show an example of focus assist display
according to a first embodiment;
[0022] FIGS. 4A and 4B illustrate a flowchart that shows a main
flow of focus assist display control according to the first
embodiment;
[0023] FIG. 5 is a flowchart that shows focus detection processing
according to the first embodiment;
[0024] FIGS. 6A to 6D show an example of a focus detection area and
image signals obtained from the focus detection area according to
the first embodiment;
[0025] FIGS. 7A and 7B illustrate a correlation operation method
according to the first embodiment;
[0026] FIGS. 8A and 8B illustrate a correlation operation method
according to the first embodiment;
[0027] FIGS. 9A to 9D show a relationship between a defocus amount
and a display position of an index in focus assist display
according to the first embodiment;
[0028] FIGS. 10A and 10B show a relationship between a focus ring
operation and an index of focus assist display according to a
second embodiment;
[0029] FIGS. 11A to 11C are flowcharts and a table that show
processing to set an amount of conversion from a defocus amount to
an index position in the second embodiment; and
[0030] FIGS. 12A to 12C show an example of image signals obtained
in an on-imaging plane phase difference detection method.
DESCRIPTION OF THE EMBODIMENTS
[0031] Exemplary embodiments of the present invention will be
described in detail in accordance with the accompanying drawings.
Note that the embodiments described, below are only one example of
means for realizing the present invention, and may be revised or
modified as appropriate depending on the configuration of an
apparatus where the present invention is to be applied or various
conditions, and the present invention is not limited by the below
embodiments.
[0032] Configuration of Image Capturing System
[0033] FIG. 1 is a block diagram that shows a schematic
configuration of an image capturing system provided with a focus
assist function according to an embodiment of the present
invention. Note that in the present embodiment, an interchangeable
lens-type image capturing system is described, but an image
capturing apparatus having a fixed lens may also be used.
[0034] As shown in FIG. 1, the image capturing system in the
present embodiment is configured from a lens unit 10 and a camera
main body 20. Also, data communications are performed between a
lens control unit 106 that performs unified control of operation of
the lens unit 10 as a whole, and a camera control unit 207 that
performs unified control of operation of the image capturing system
as a whole.
[0035] First is a description of the configuration of the lens unit
10. The lens unit 10 has an imaging optical system configured from
a fixed lens 101, an aperture 102, a focusing lens 103, a zoom lens
(not shown), and the like. The aperture 102 is driven by an
aperture drive unit 104, and controls an amount of light incident
on an image sensor 201, described later. The focusing lens 103 is
driven by a focusing lens drive unit 105, and is used for focus
adjustment. An unshown zoom lens is driven by a zoom lens drive
unit, and is used for zoom adjustment. Note that in the present
embodiment, the zoom lens and the zoom lens drive unit are not
essential configurations, and may be omitted.
[0036] The aperture drive unit 104, the focusing lens drive unit
105, and the zoom lens drive unit are controlled by the lens
control unit 106, and thus an opening diameter of the aperture 102,
and positions of the focusing lens 103 and the zoom lens, are
controlled. When a user has performed a focus operation, a zoom
operation, or the like by operating a focus ring, a zoom ring, or
the like provided in a lens operation unit 107, the lens control
unit 106 performs control corresponding to the user operation. The
lens control unit 106, according to control commands and control
information received from the camera control unit 207 described
later, performs control of the aperture drive unit 104, the
focusing lens drive unit 105, and the zoom lens drive unit, and
transmits lens information to the camera control unit 207.
[0037] Next is a description of the configuration of the camera
main body 20 provided with a focus assist function according to the
present embodiment. In the camera main body 20, the image sensor
201 is configured with a CCD or CMOS sensor, where luminous flux
that has passed through the imaging optical system of the lens unit
10 is formed as an image on a light-receiving face of the image
sensor 201. Also, a subject image that has been formed is
photoelectrically converted to an electric charge according to the
incident light amount by photodiodes (photoelectric converters) of
the image sensor 201, and accumulated. The electric charge that has
been accumulated in each photodiode is sequentially read out from
the image sensor 201 as a voltage signal corresponding to the
electric charge based on a drive pulse conferred from a timing
generator 209 according to an instruction of the camera control
unit 207. Note that while the detailed configuration of the image
sensor 201 will be described later, the image sensor 201 in the
present embodiment, other than ordinary image signals, can output a
pair of focus detection signals that can be used for focus
detection by a phase difference method.
[0038] An image signal and a focus detection signal that have been
read out from the image sensor 201 are input to a CDS/AGC circuit
202, and correlated double sampling for removing reset noise, gain
adjustment, and signal digitization are performed. The CDS/AGC
circuit 202 outputs a processed image signal to a camera signal
processing unit 203, and outputs a focus detection signal to a
focus signal processing unit 204.
[0039] The camera signal processing unit 203 performs various image
processing on an image signal that has been output from the CDS/AGC
circuit 202, and generates a video signal. A display unit 205 is a
display device such as an LCD or organic EL display device, and
displays an image based on the video signal that was output from
the camera signal processing unit 203. Also, when in a recording
mode in which an image signal is recorded, the image signal is
transmitted from the camera signal processing unit 203 to a
recording unit 206, and is recorded to a recording medium such as
an optical device, a semiconductor memory, or a magnetic tape.
[0040] The focus signal processing unit 204 performs a correlation
operation based on a pair of focus detection signals that have been
output from the CDS/AGC circuit 202 to detect a focus state. Here,
a correlation amount, a defocus amount, and reliability information
(degree of coincidence between two images, steepness of two images,
contrast information, saturation information, defect information,
and the like) are calculated. The calculated defocus amount and
reliability information are output to the camera control unit 207.
Also, the camera control unit 207, based on the obtained defocus
amount and reliability information, notifies the focus signal
processing unit 204 of a change in settings used to calculate the
defocus amount and reliability information. Note that the details
of the correlation operation will be described later with reference
to FIGS. 6A to 6D through FIGS. 8A and 8B.
[0041] The camera control unit 207 performs control by exchanging
information with each configuration within the camera main body 20.
In addition to processing within the camera main body 20, the
camera control unit 207 controls power ON/OFF, settings changes,
and recording according to input from a camera operation unit 208
that was operated by a user. Further, the camera control unit 207
executes various functions corresponding to user operation such as
switching between autofocus (AF) control and manual focus (MF)
control, checking recorded video, and the like. Also, as described
above, the camera control unit 207 exchanges information with the
lens control unit 106 within the lens unit 10, transmits control
commands and control information of the imaging optical system, and
obtains information within the lens unit 10.
[0042] Image Sensor Configuration
[0043] FIG. 2 shows a schematic view of a pixel array of the image
sensor 201 in the present embodiment. In FIG. 2, a pixel array of a
two-dimensional CMOS sensor used as the image sensor 201 in the
present embodiment is shown in a range of four columns.times.four
rows of image capturing pixels (a range of eight columns.times.four
rows as an array of focus detection pixels).
[0044] In the present embodiment, a pixel group 200 includes two
columns.times.two rows of pixels, and is covered by a Bayer array
color filter. In each pixel group 200, a pixel 200R having spectral
sensitivity to red (R) is positioned at the upper left, pixels 200G
having spectral sensitivity to green (G) are positioned at the
upper right and the lower left, and a pixel 200B having spectral
sensitivity to blue (B) is positioned at the lower right. Further,
in the image sensor 201 of the present embodiment, in order to
perform focus detection by an on-imaging plane phase difference
method, each pixel holds a plurality of photodiodes (photoelectric
converters) for one microlens 215. In the present embodiment, each
pixel is configured with two photodiodes 211 and 212 arranged in
two columns.times.one row.
[0045] By having many pixel groups 200, each including two
columns.times.two rows of pixels (four columns.times.two rows of
photodiodes) shown in FIG. 2, arranged on the imaging plane, the
image sensor 201 is enabled to obtain image signals and focus
detection signals.
[0046] In each pixel having this sort of configuration, luminous
flux is split by the microlens 215 and formed as an image on the
photodiodes 211 and 212. A signal (A+B signal) obtained by adding
signals from the two photodiodes 211 and 212 is used as an image
signal, and two signals (A and B image signals) respectively read
out from the individual photodiodes 211 and 212 are used as focus
detection signals. Note that the image signal and the focus
detection signals may be respectively read out, but in the present
embodiment, in consideration of processing load, the following sort
of configuration may also be adopted. That is, the image signal
(A+B signal), and a focus detection signal from either one of the
photodiodes 211 and 212 (for example, the A signal), are read out,
and by taking the difference between those signals, the other focus
detection signal (for example, the B signal) is obtained.
[0047] Note that in the present embodiment, a configuration is
adopted in which in each pixel, there are the two photodiodes 211
and 212 for the one microlens 215, but the number of photodiodes is
not limited to two, and a configuration may also be adopted in
which the number of photodiodes is three or more. Also, a
configuration may be adopted in which there are a plurality of
pixels having a different opening position of a light receiving
portion for the microlens 215. That is, a configuration is
preferable in which, as a result, two signals used for phase
difference detection such that it is possible to detect the phase
difference between the A image signal and the B image signal are
obtained. Also, the present invention is not limited to a
configuration in which, as shown in FIG. 2, all pixels have a
plurality of photodiodes; a configuration may also be adopted in
which focus detection pixels as shown in FIG. 2 are discretely
provided within normal pixels included in the image sensor 201.
First Embodiment
Display Format of Focus Assist
[0048] Next is a description of a display format of focus assist in
the present embodiment, with reference to FIGS. 3A to 3D. In the
present embodiment, the types of focus assist display include four
display formats from first to fourth display formats, and focus
states that were detected are indicated by display parts 301 to
317.
[0049] FIG. 3A shows an example of the first display format, and
shows a state in which a subject was determined to be in focus. In
a state determined to be in focus, the position of the inward
pointing display part 301 coincides with the position of the
outward pointing display part 302 (here, stopped at the top). Also,
when determined to be in an in-focus state, for example, the
display part 301 and the display part 302 may be displayed in a
different color (for example, green) than the color in other
display formats (for example, white).
[0050] FIG. 3B shows an example of the second display format, in
which the subject is not in focus, and in a case where the
reliability of focus detection results is high, shows the direction
to an in-focus position and the size of a defocus amount. For
example, in a case where focus is set to an infinite distance side
(rear focus) relative to the subject, in a state with the inward
pointing display part 303 stopped at the top, the outward pointing
display parts 304 and 305 move with bilateral symmetry on the
circumference. The positions of the display part 304 and the
display part 305 indicate the size of the defocus amount, and
indicate a larger defocus amount the further they are separated
from the position of the display part 303 (reference position).
Note that the display part 303 corresponds to the display part 301,
and a state with the display parts 304 and 305 overlapping each
other corresponds to the display part 302.
[0051] On the other hand, in a case where focus is set to a near
side (front focus) relative to the subject, in a state with the
outward pointing display part 306 stopped at the top, the inward
pointing display parts 307 and 308 move with bilateral symmetry on
the circumference. The positions of the display part 307 and the
display part 308 indicate the size of the defocus amount, and
indicate a larger defocus amount the further they are separated
from the position of the display part 306 (reference position).
Note that the display part 306 corresponds to the display part 302,
and a state with the display parts 307 and 308 overlapping each
other corresponds to the display part 301. As described above, in
the second display format, the size of the defocus amount can be
indicated by the positions of the display parts that move. Also,
the direction to the in-focus position (defocus direction) can be
indicated by the direction in which the display part stopped at the
top is pointing.
[0052] FIG. 3C shows an example of the third display format, in
which only the direction to the in-focus position is shown in a
case where the reliability of focus detection results is moderate.
Here, the display parts 309 to 314 are fixed at predetermined
positions regardless of the defocus amount. Also, in the case of
rear focus, the inward pointing display part 309 is fixed at the
top, and in the case of front focus, the outward pointing display
part 312 is fixed at the top. That is, in the third display format,
the size of the defocus amount is not indicated, and the direction
to the in-focus position is indicated by the direction in which the
display part fixed at the top is pointing.
[0053] FIG. 3D shows an example of the fourth display format, and
shows a case where the reliability of focus detection results is
low. In this case, both the size of the defocus amount and the
defocus direction are not shown, so a user is allowed to see that
focus detection is not possible. Here, the display parts 315 to 317
are displayed in a different color (for example, gray) than the
color in other display formats, and the display parts 315 to 317
are fixed at predetermined positions. Also, the shapes of the
display part 316 and the display part 317 are made different than
the shapes in other display formats.
[0054] Note that the focus assist display shown in FIGS. 3A to 3D
is only an example, and the present invention is not limited to
this display.
[0055] Focus Assist Display Control
[0056] Next is a description of focus assist display control
executed by the camera control unit 207. FIGS. 4A and 4B illustrate
a flowchart that shows a procedure of main processing of focus
assist display control executed by the camera control unit 207.
This processing is executed in a predetermined cycle according to a
computer program that has been stored in the camera control unit
207. For example, this processing is executed in a cycle of reading
out an image signal (each vertical synchronizing period) from the
image sensor 201 in order to generate an image of one frame (or one
field). This processing may also be repeated a plurality of times
within a vertical synchronizing period.
[0057] In step S101 a focus detection area is set, and next, the
focus signal processing unit 204 confirms whether the focus signal
has been updated (step S102). If the focus signal has been updated,
focus detection processing is performed in the focus signal
processing unit 204 (step S103). Then, as a result of focus
detection processing, a defocus amount and reliability are
obtained.
[0058] Here, the focus detection processing performed in step S103
will be described with reference to FIGS. 5 to 8A and 8B. FIG. 5 is
a flowchart that shows focus detection processing, and is performed
by the focus signal processing unit 204. First, in step S201, the
focus signal processing unit 204 obtains a pair of focus detection
signals from the focus detection area that was set in step S101.
Next, in step S202, a correlation amount is calculated from the
pair of focus detection signals that were obtained in step S201.
Next, in step S203, a correlation change amount is calculated from
the correlation amount that was calculated in step S202. Then, in
step S204, a focus offset amount is calculated from the correlation
change amount that was calculated in step S203. Also, in step S205,
reliability of the focus detection signals that were obtained in
step S201 is calculated. This reliability corresponds to a
reliability that expresses the extent to which it is possible to
rely on the focus offset amount that was calculated in step S204.
Then, in step S206, the focus offset amount is converted to a
defocus amount.
[0059] Note that the defocus amount may be expressed as an absolute
distance from the in-focus position, or as a number of pulses
necessary in order to move the focusing lens 103 to the in-focus
position, or may be an expression of a different dimension and
units as such an expression, or may be a relative expression. That
is, it is preferable to express the defocus amount such that it is
possible to judge the distance from the in-focus state, or possible
to judge how much focus control needs to be performed to move to
the in-focus state.
[0060] Next, the focus detection processing described in FIG. 5
will be described in detail with reference to FIGS. 6A to 6D, and
FIGS. 7A and 7B. FIG. 6A shows an example of a focus detection area
402 that has been set on a pixel array 401 used to configure the
image sensor 201. In an operation area 404, where focus detection
signals necessary for performing a correlation operation described
later are read out, the focus detection area 402 is combined with
shift areas 403 necessary for the correlation operation. In FIG.
6A, reference signs p, q, s, and t respectively indicate
coordinates in the x-axis direction, and the operation area 404
corresponds to the range from p to q, and the focus detection area
402 corresponds to the range from s to t.
[0061] FIGS. 6B to 6D show an example of focus detection signals
that were obtained from the operation area 404 that was set in FIG.
6A. The range from s to t corresponds to the focus detection area
402, and the range from p to q corresponds to the operation area
404 necessary for the correlation amount operation, which is based
on a shift amount. Solid line 501 indicates an A image signal, and
broken line 502 indicates a B image signal.
[0062] FIG. 6B shows the A image signal 501 and the B image signal
502 prior to shifting as waveforms. In FIG. 6C, the waveforms of
the A image signal 501 and the B image signal 502 are shifted in a
plus direction with respect to the positions prior to the shifting
shown in FIG. 6B, and in FIG. 6D, the waveforms of the A image
signal 501 and the B image signal 502 are shifted in a minus
direction with respect to the positions prior to the shifting shown
in FIG. 6B. When calculating a correlation amount, the A image
signal 501 and the B image signal 502 are shifted bit by bit in the
directions of the respective arrows.
[0063] Next is a description of a calculation method of a
correlation amount COR in step S202. First, as described in FIGS.
6C and 6D, the A image signal 501 and the B image signal 502 are
shifted bit by bit, and in each shift state, a sum of absolute
values of the difference between the A image signal 501 and the B
image signal 502 in the focus detection area 402 that was set is
calculated. Here, a minimum number of shifts is represented by p-s,
and a maximum number of shifts is represented by q-t. Also, where
the shift amount is represented by i, start coordinates of the
focus detection area are represented by x, and final coordinates of
the focus detection area are represented by y, it is possible to
calculate the correlation amount COR with below expression (1).
COR [ i ] = k = x y A [ k + i ] - B [ k - i ] { ( p - s ) < i
< ( q - t ) } ( 1 ) ##EQU00001##
[0064] FIG. 7A shows an example of change of the correlation
amount, in which the shift amount is shown on the horizontal axis
of the graph and the correlation amount is shown on the vertical
axis. In a correlation amount waveform 601, reference signs 602 and
603 indicate the vicinity of local minimums. Even within such a
vicinity, it can be said that as the correlation amount decreases,
the degree of coincidence of the A image signal 501 and the B image
signal 502 increases.
[0065] Next is a description of a calculation method of a
correlation change amount .DELTA.COR in step S203. First, a
correlation change amount is calculated from a difference in
correlation amounts when skipping one shift from the correlation
amount waveform shown in FIG. 7A. Here, a minimum number of shifts
is represented by p-s in FIGS. 7A and 7B, and a maximum number of
shifts is represented by q-t in FIGS. 7A and 7B. Where the shift
amount is represented by i, it is possible to calculate the
correlation change amount .DELTA.COR with below expression (2).
.DELTA.COR[i]=.DELTA.COR[i-1]-.DELTA.COR[i+1]
(p-s+1)<i<(q-t-1) (2)
[0066] FIG. 7B shows an example of the correlation change amount
.DELTA.COR, in which the shift amount is shown on the horizontal
axis of the graph and the correlation change amount is shown on the
vertical axis. In a correlation change amount waveform 604,
reference signs 605 and 606 indicate the vicinity where the
correlation change amount changes from plus to minus. A state where
the correlation change amount becomes zero in the portion 605 and
the portion 606 is called a zero cross, and in this state the
degree of coincidence of the A image signal 501 and the B image
signal 502 is largest, and a focus offset amount can be obtained
based on the shift amount at that time.
[0067] FIG. 8A shows an enlarged view of the portion 605 in FIG.
7B, in which reference sign 607 denotes a portion of the
correlation change amount waveform 604. A calculation method of a
focus offset amount PRD in step S204 will be described with
reference to FIG. 8A. First, the focus offset amount PRD is divided
into an integer portion .beta. and a fractional portion .alpha..
The fractional portion .alpha. can be calculated with below
expression (3), from the relationship of triangle ABC and triangle
ADE in FIG. 8A.
AB : AD = BC : DE .DELTA. COR [ k - 1 ] : .DELTA. COR [ k - 1 ] -
.DELTA. COR [ k ] = .alpha. : k - ( k - 1 ) .alpha. = .DELTA. COR [
k - 1 ] .DELTA. COR [ k - 1 ] - .DELTA. COR [ k ] ( 3 )
##EQU00002##
[0068] On the other hand, the integer portion .beta. can be
calculated with below expression (4), from FIG. 8A.
.beta.+k-1 (4)
[0069] It is possible to calculate the focus offset amount PRD from
the sum of .alpha. and .beta. that were obtained in the above
manner.
[0070] Also, in a case where a plurality of zero crosses exist as
in FIG. 7B, a location having a larger steepness MAXDER of the
change in the correlation amount at the zero cross is used as a
first zero cross. This steepness MAXDER is an index that indicates
the ease of specifying the in-focus position, and indicates that
this is a point, where it is easier to specify the in-focus
position when the value of the index is larger. The steepness
MAXDER can be calculated with below expression (5).
MAXDER=|.DELTA.COR[k-1]|+|.DELTA.COR[k]| (5)
[0071] As described above, in a case where a plurality of zero
crosses exist, the first zero cross is determined from the
steepness at the zero crosses.
[0072] Next is a description of the method of calculating
reliability of the image signal in step S205. This corresponds to
reliability of the defocus amount, but the calculation method
described below is only an example, and reliability may also be
calculated using another publicly known method. Reliability can be
defined using the above-described steepness and a degree of
coincidence FNCLVL (referred to below as a `degree of two image
coincidence`) between the A image signal and the B image signal.
The degree of two image coincidence is an index that indicates
accuracy of the focus offset amount, and accuracy is better when
the index has a smaller value.
[0073] FIG. 8B shows an enlarged view of the portion of local
minimum vicinity 602 in FIG. 7A, in which reference sign 608
denotes a portion of the correlation amount waveform 601. The
degree of two image coincidence can be calculated with below
expression (6).
(i) when .DELTA.COR[k-1].times.2.ltoreq.MAXDER:
FNCLVL=COR[k-1]+.DELTA.COR[k-1]/4
(ii) when .DELTA.COR[k-1].times.2>MAXDER:
FNCLVL=COR[k]-.DELTA.COR[k]/4 (6)
[0074] When focus detection processing as described above ends in
step S103, processing proceeds to step S104. In step S104, whether
or not the defocus amount is within a first predetermined range,
and reliability is higher than a first threshold value that was
determined in advance, are discriminated. When the defocus amount
is within the first predetermined range and reliability is higher
than a first threshold value Th_A (Yes in step S104), the focus
assist display is set to the first display format shown in FIG. 3A
(step S105).
[0075] The first predetermined range is a range for discriminating
whether or not the position of the focusing lens 103 has entered
the in-focus range for the subject, and for example, is set based
on the depth of focus. Here, the first predetermined range is
adopted as the depth of focus. Also, as reliability of the defocus
amount, a level such that it is possible to judge that the accuracy
of the defocus amount that was calculated is certain is set as the
first threshold value Th_A. In a case where the defocus amount
reliability is higher than the first threshold value Th_A, for
example, contrast of the A image signal and the B image signal is
high, and in this state the shapes of the A image signal and the B
image signal are similar (degree of two image coincidence is high),
or the main subject image is already in focus.
[0076] On the other hand, in a case where the defocus amount is
outside of the first predetermined range, or reliability is the
first threshold value Th_A or less (No in Step S104), processing
moves to step S106.
[0077] In step S106, whether or not the defocus amount is within a
second predetermined range, and reliability is higher than the
first threshold value Th_A, are discriminated. When the defocus
amount is within the second predetermined range and reliability is
higher than the first threshold value Th_A (Yes in step S106), in
order to set an index that indicates a direction and amount to an
in-focus state in focus assist display, an index orientation is
calculated from the defocus direction (step S107). Then, positions
for displaying display parts are calculated from a defocus amount
as described later (step S108). Here, the display parts whose
display positions are calculated are the display parts that move in
the second display format described in FIG. 3B. Then, focus assist
display is set to the second display format shown in FIG. 3B (step
S109). On the other hand, in a case where the defocus amount is
outside of the second predetermined range, or reliability is the
first threshold value Th_A or less No in Step S106), processing
moves to step S110.
[0078] Note that in the second predetermined range, a defocus
amount is set that can be detected without reliance on the subject.
This is because, for example, it is conceivable that the detectable
defocus amount differs between a high contrast subject and a low
contrast subject. In such a case, the state that can be displayed
in the second display format differs depending on the subject, so
the user feels uneasy. Therefore, by setting the second
predetermined range, an amount is set whereby a defocus amount can
generally be obtained regardless of the subject. For example, in
the present embodiment the defocus amount is set to 2 mm. However,
the manner of setting the defocus amount is not limited to this,
and differs also depending on the shift amount when obtaining a
focus offset amount. It is not necessary to set the shift amount in
a case where it is not possible to detect a defocus amount that
exceeds 2 mm, and in that case the second predetermined range may
be infinitely large.
[0079] Also, the defocus amount may be determined in consideration
of operability of the focus assist display. In the second display
format, the display parts that move indicate how much the present
state is offset from an in-focus state. Therefore, when performing
display to a position far from the display part fixed at the top,
it is difficult for the user to know how far the present position
is from the in-focus position. Also, depending on the display
method, when the size of focus assist display on a screen also
becomes large, the screen becomes difficult to view, so the defocus
amount may be determined in consideration of these matters.
[0080] In step S110, whether or not reliability is the second
threshold value Th_B or less is discriminated. When reliability is
not the second threshold value Th_B or less (No in Step S110), an
orientation of the index of focus assist display is calculated from
the defocus direction (step S111), and focus assist display is set
to the third display format shown in FIG. 3C (step S112).
[0081] Thus, in a case where reliability is the first threshold
value Th_A or less (threshold value or less), and is higher than
the second threshold value Th_B (reliability is moderate), it is
determined that the defocus direction indicating the direction that
the in-focus position is expected to exist is certain. Note that a
case where reliability of the defocus amount is the first threshold
value Th_A or less, and is higher than the second threshold value
Th_B, is the following sort of state. That is, although the degree
of two image coincidence level calculated with the focus signal
processing unit 204 is less than a predetermined value, there is a
definite tendency for the correlation amount obtained by relatively
shifting the A image signal and the B image signal, so it is
possible to rely on the defocus direction. For example, the above
determination is often made when there is a small amount of blur of
the main subject.
[0082] On the other hand, in a case where reliability is the second
threshold value Th_B or less (Yes in step S110), it is determined
that it is not possible to rely on the defocus amount and the
defocus direction. Then, focus assist display is set to the fourth
display format shown in FIG. 3D (step S113). A case where
reliability is the second threshold value Th_B or less, for
example, is state in which the A image signal and the B image
signal have low contrast, and the degree of two image coincidence
is also low. This state often occurs when the subject is greatly
blurred, and so calculation of a defocus amount is difficult.
[0083] In step S114, based on any of the first through fourth
display formats that were set by the above processing, parameters
necessary for focus assist display such as color information of
focus assist display, and index orientation and position, are set,
and notice of these parameters is given to the display unit
205.
[0084] Next is a description of the method for calculating
positions of display parts of focus assist display in step S108 in
FIG. 4B, with reference to FIGS. 9A to 9D. In FIGS. 9A to 9D,
defocus amount is shown on the horizontal axis, and display part
positions (index position) are shown on the vertical axis. Note
that here the index position indicates, as an angle, a movement
amount of the display parts that move (display parts 301, 305, 307,
and 308), with respect to the position of the display part that is
fixed at the top in the second display format described in FIG.
3B.
[0085] If the detection accuracy is constant regardless of the
defocus amount that was detected, when the defocus amount and the
index position are expressed linearly as indicated by dotted line
702 in FIG. 9A, an operating amount of a focus ring, for example,
matches to the display positions of display parts, and thus a focus
operation is easy to perform. However, in the case of an on-imaging
plane phase difference detection method, as described above,
detection accuracy decreases as the defocus amount increases.
Therefore, in a case where a display part was displayed at a
position corresponding linearly to the defocus amount that was
output, it is conceivable that the relationship between the actual
focus state and the display part position will vary due to the
decrease in detection accuracy. In this case, the user. sometimes
feels discomfort, and operability worsens.
[0086] Therefore, in the first embodiment, a configuration is
adopted in which, as indicated by solid line 701 in FIG. 9A,
movement of the display part position is made less sharp as the
defocus amount increases. That is, the change in position
(conversion amount) of the display part relative to the defocus
amount is reduced as the defocus amount increases. In other words,
as the defocus amount increases, the defocus amount that
corresponds to the position change per unit angle (unit movement
amount) of the display part is increased. For example, in the case
of focus assist display as indicated by the solid line 701, when
the display part position is indicated as an angle, a defocus
amount of 0.02 mm per one degree is indicated up to a defocus
amount of 0.5 mm. Also, a defocus amount of 0.04 mm per one degree
is indicated up to a defocus amount of 1 mm, and a defocus amount
of 0.08 mm per one degree is indicated up to a defocus amount of 2
mm. Also, when one degree is indicated based on the depth of focus,
one degree is indicated as the depth of focus up to a defocus
amount of 0.5 mm, two times the depth of focus per one degree is
indicated up to a defocus amount of 1 mm, and four times the depth
of focus per one degree is indicated up to a defocus amount of 2
mm. By controlling the index position in this way, it is possible
to realize stable focus assist display regardless of the defocus
amount.
[0087] Next, FIG. 9B illustrates control of the index position
according to aperture. As described above, in the case of an
on-imaging plane phase difference detection method, as the aperture
changes from a full-open aperture to a small aperture, the focus
offset amount of the A image signal and the B image signal differs
even in cases where a certain subject was shot at the same distance
to the subject. The focus offset amount is largest and the
detection accuracy is highest in the case of a full-open aperture.
Therefore, in a case where a defocus amount that has been detected
was converted as-is to an index, it is conceivable that the
relationship between the actual focus state and the display part
position will vary more with a smaller aperture. Therefore, as
indicated by lines 701, 703, and 705 in FIG. 9B, movement of the
display part position is changed according to the aperture. That
is, the change in position (conversion amount) of the display part
relative to the defocus amount is reduced as the aperture changes
from a full-open aperture to a small aperture. For example,
conversion is performed such that the defocus amount per one degree
doubles when the aperture is F5.6 relative to when the aperture is
F2.8. Thus, it is possible to realize stable focus assist display
regardless of the aperture.
[0088] Further, because the depth of focus deepens as the aperture
changes from a full-open aperture to a small aperture, the subject
becomes less likely to blur in comparison to a case where the
aperture is on the full-open aperture side. In this case, it is
conceivable that on the small aperture side, there is less
influence of image collapse in a case where the focusing lens was
moved from the in-focus position, and so detection is possible up
to a large defocus amount. Therefore, as shown in FIG. 9C, the
second predetermined range used in the determination in step S106
in FIG. 4A is widened on the small aperture side indicated by line
704 in comparison to a case of the full-open aperture side
indicated by line 701. By adopting such a configuration, the
display part movement in focus assist display changes less between
the full-open aperture side and the small aperture side for a given
image blur. Thus, the display part movement in focus assist display
is stabilized for the video image viewed by the user, and
operability improves.
[0089] FIG. 9D illustrates a state of low illuminance and a state
of a non-low illuminance. As described above, in a state of low
illuminance, the signal levels of the A image signal and the B
image signal decrease. Also, due to increasing ISO sensitivity a
noise component increases and the S/N ratio decreases, so detection
accuracy also decreases. In this case as well, it is conceivable
that the relationship between the actual focus state and the
display part position will vary. Therefore, in a state of low
illuminance, as indicated by line 705, the change in the display
part position for a given defocus amount is reduced. For example,
line 705 indicates that the defocus amount per one degree is
doubled in a state of low illuminance relative to a state of
non-low illuminance.
[0090] In the first embodiment, for example, whether low
illuminance or not is determined using the below four determination
methods. In the first determination method, it is determined
whether or not ISO sensitivity has been set to a predetermined
value or more. When ISO sensitivity is a predetermined value or
more, it is determined that low illuminance shooting is being
performed, and when ISO sensitivity is less than the predetermined
value, it is determined that low illuminance shooting is not being
performed. In the second determination method, it is determined
whether or not a peak value of luminance of a video signal is a
predetermined value or more. When the peak value of luminance of
the video signal is the predetermined value or more, it is
determined that low illuminance shooting is not being performed,
and when the peak value of luminance of the video signal is less
than the predetermined value, it is determined that low illuminance
shooting is being performed. In the third determination method, it
is determined whether or not an exposure value is a predetermined
value or less. When the exposure value is the predetermined value
or less, it is determined that low illuminance shooting is being
performed, and when the exposure value is more than the
predetermined value, it is determined that low illuminance shooting
is not being performed. In the fourth determination method, it is
determined whether or not a gain setting is a predetermined value
or more. When the gain setting value is the predetermined value or
more, it is determined that low illuminance shooting is being
performed, and when the gain setting value is less than the
predetermined value, it is determined that low illuminance shooting
is not being performed.
[0091] Note that calculation of the display part position in focus
assist display according to the above-described states of defocus
amount, aperture, low illuminance, and the like may be implemented
by any method, or may be implemented by combining a plurality of
methods.
[0092] By thus changing movement properties of the index in focus
assist display according to the defocus amount, aperture, and
illuminance, it is possible to realize stable focus assist display,
and improve user operability.
[0093] Note that it is conceivable that if the display part
position that was calculated as described above is displayed as-is
in the display unit 205 each time a position is calculated, it will
not be possible to realize smooth index movement, and so the
display will appear crude. Therefore, an average value of index
positions (or movement amounts from the reference position) that
were calculated a plurality of times is calculated, and notice of
that result is given. The number of past index positions used to
calculate this average value may be changed according to the image
shooting state, such as the above-described defocus amount,
aperture, low illuminance, and the like. For example, an average
value of the past two index positions is used up to a defocus
amount of 1 mm, and an average value of the past three index
positions is used up to a defocus amount of 2 mm. Also, for
example, an average value of a double number of index positions is
used on the small aperture side of F11 compared to an aperture
between a full-open aperture and F11. For example, in a state of
low illuminance, an average value of a double number of index
positions is used compared to a state of non-low illuminance.
[0094] Also, in order to stably express the index of focus assist
display, it is conceivable to average the defocus amount used for
calculation of the index position with past defocus amounts, and
use that average value. Thus, it is possible to suppress variation
in the defocus amount. By changing the number of these past defocus
amounts to be averaged according to the image shooting state, such
as the above-described defocus amount, aperture, low illuminance,
and the like, it is possible to perform even more stable focus
assist display.
[0095] For example, an average value of the past two defocus
amounts is used up to a defocus amount of 1 mm, and an average
value of the past three defocus amounts is used up to a defocus
amount of 2 mm. Also, for example, an average value of a double
number of defocus amounts is used on the small aperture side of F11
compared to an aperture between a full-open aperture and F11. For
example, in a state of low illuminance, an average value of a
double number of defocus amounts is used compared to a state of
non-low illuminance.
[0096] According to the first embodiment as described above, in an
image shooting apparatus having a focus assist function when
performing manual focus control, a defocus amount and defocus
direction within a focus detection range, and reliability, are
detected by performing focus detection processing of an on-imaging
plane phase difference detection method. By changing focus assist
display that indicates the defocus amount and defocus direction
according to reliability, a stable function is realized, and it is
possible to improve operability. When doing so, by changing display
properties of an index of focus assist display that indicates a
movement amount from a current focusing lens position to an
in-focus position according to the defocus amount and image
shooting state, a stable index display is realized, and thus it is
possible to reduce user discomfort.
Second Embodiment
[0097] Next is a description of the second embodiment of the
present invention. Note that in display control of focus assist
display in the second embodiment, processing to calculate an index
position in focus assist display in step S108 in FIG. 4B differs
from the first embodiment. Accordingly, below, differing points
will be described, but a description of configurations of the image
capturing apparatus and display control that are the same as in the
first embodiment will be omitted here.
[0098] Operability is better for a user if movement of display
parts in focus assist display changes linearly relative to movement
of a focus ring. For example, it is preferable that a movement
amount 1001 of a display part in focus assist display in FIG. 10A
is the same as a movement amount 1002 from point A to point B of a
focus ring in FIG. 10B, where point B is the in-focus position.
However, in the case of an interchangeable lens-type image
capturing apparatus, ring operability of the focus ring differs
depending on the attached lens, so operation linked to movement of
the display part of focus assist display is difficult.
Consequently, in this second embodiment, lens information is
communicated from the lens control unit 106 to the camera control
unit 207, and based on the lens information, a conversion amount of
the defocus amount per one unit (one degree) of display position of
the display part is set.
[0099] A first method is to determine the conversion amount
depending on lens type. For each lens type, whether or not a
rotation angle of the focus ring is large is stored in advance in
the camera main body 20, and the type of the attached lens unit 10
is transmitted from the lens control unit :106 to the camera
control unit 207. Then, the conversion amount for converting from
the defocus amount to the display position of the display part is
changed according to the lens type that was obtained.
[0100] FIG. 11A is a flowchart of conversion amount setting
processing in the first method, and FIG. 11B shows an example of a
chart of maximum display angles (maximum movement amounts) for lens
types (lens IDs). First, in step S301, lens type information is
obtained from the lens unit 10 that has been attached. In step
S302, a maximum display angle that is stored in advance in the
camera main body 20 is set from the lens type information. In step
S303, a defocus amount per one degree of angle is set from the
maximum display angle. For example, in a case where a lens has been
attached that has a lens ID of 1104 in the chart in FIG. 11B, the
maximum display angle is discriminated to be 60 degrees. Then a
defocus amount per one degree when the defocus amount set in the
second predetermined range is expressed with the maximum display
angle is calculated. When the second predetermined range has a
defocus amount of 2 mm, the defocus amount per one degree is about
0.033 mm. This is similarly true in a case where the second
predetermined range is based on focus depth.
[0101] A second method is to determine the conversion amount
depending on the maximum defocus amount and the rotation angle when
the focusing lens 103 has been moved from the near end to the
infinite end of the focus ring, and FIG. 11C shows a flowchart of
setting processing in the second method. In step S401, the maximum
defocus amount and the rotation angle of the focus ring are
obtained. In step S402, a defocus amount per one degree of rotation
angle of the focus ring is calculated. In step S403, the defocus
amount that was obtained in step S402 is set as a defocus amount
per one degree of the display part in focus assist display. In step
S404, an in-focus position, and the angle of the display part
position in the defocus amount of the second predetermined range,
are calculated.
[0102] In step S405, it is determined whether or not the angle that
was calculated in step S404 exceeds a maximum angle that has been
set in advance for the index of focus assist display. When the
angle exceeds the maximum angle for the index of focus assist
display (Yes in step S405), a defocus amount per one degree is
calculated based on the maximum angle of the index. Here, it is
determined whether or not the maximum angle for the index of focus
assist display is exceeded, and when determined that the maximum
angle is exceeded, the defocus amount per one degree is increased.
However, conversely, the second predetermined range may be set to a
defocus amount calculated from the defocus amount per one degree of
angle of the index that was calculated in step S403 and the maximum
angle that has been set in advance for the index of focus assist
display.
[0103] In step S108 in FIG. 4B, the defocus amount that was
obtained in step S103 is converted to an index position, based on
the defocus amount per one degree of the index that was obtained as
described above.
[0104] The second embodiment was described as an interchangeable
lens-type image capturing system, but similar control can also be
performed in a fixed lens-type image capturing apparatus. In that
case, it is not necessary to transmit lens information from the
lens control unit 106 to the camera control unit 207.
[0105] According to this second embodiment as described above, in
addition to similar effects as the first embodiment, by changing
display properties of the index of focus assist display using lens
information, it is possible to perform focus assist display that is
suitable for operability of the focus ring. Thus, it is possible to
improve user operability in the image capturing apparatus.
Third Embodiment
[0106] Next is a description of the third. embodiment of the
present invention. Note that in display control of focus assist
display in the third embodiment, processing to calculate an index
position in focus assist display in step S108 in FIG. 4B differs
from the first and second embodiments. Accordingly, below,
differing points will be described, but a description of
configurations of the image capturing apparatus and display control
that are the same as in the first and second embodiments will be
omitted here.
[0107] In general, the depth of focus at the time of focusing on a
subject located at a predetermined distance differs depending on
the focal length. The depth of focus is deep when the focal length
is in the wide angle side, and the depth of focus becomes narrower
as the focal length approaches the telephoto end.
[0108] In step S104 in FIG. 4B, if the defocus amount is within the
first predetermined range, it is determined that an in-focus state
is attained, however, in a case where the depth of focus is deep,
the range of distance where a subject located at a predetermined
range of distance is in focus is wide, and a period of time when
the first display format is maintained becomes long with respect to
an amount of operation of a focus ring. As a result, it becomes
difficult to focus on a point at which the subject located at a
predetermined distance is most focused.
[0109] Accordingly, the first predetermined range is changed with
respect to the focal length. More specifically, as the focal length
is changed toward the telephoto end, the first predetermined range
is widened. For example, in a case where the focal length is less
than 50 mm, then the first predetermined range is set to .times.0.7
of the depth of focus; in a case where the focal length is greater
than or equal to 50 mm and less than 85 mm, then the first
predetermined range is set to .times.0.8 of the depth of focus; in
a case where the focal length is greater than or equal to 85 mm and
less than 135 mm, then the first predetermined range is set to
.times.0.9 of the depth of focus; and in a case where the focal
length is greater than or equal to 135 mm, then the first
predetermined range is set to .times.1 of the depth of focus.
[0110] Accordingly, if the depth of focus changes depending on the
focal length, it becomes easier to focus on a position where a
subject is most focused, and by the virtue of this, the user
operability of the image capturing apparatus improves.
[0111] Similarly, in a case where the depth of focus is deep, a
moving amount of the index of the focus assist display becomes
small with respect to an operation amount of the focus ring, and a
user may feel uncomfortable when the focus assist display is in the
second display format.
[0112] Accordingly, in the calculation processing of index position
in the focus assist display in step S108 in FIG. 4B, the defocus
amount per 1 .cndot.degree of the index in the focus assist display
is changed in accordance with the focal length. For example, in a
case where the focal length is less than 50 mm, then the defocus
amount per 1 degree of the index in the focus assist display in the
third embodiment may be set to .times.0.7 of the defocus amount per
1 degree of the index calculated in the first and second
embodiments; set to .times.0.8 of the defocus amount per 1 degree
of the index in a case where the focal length is greater than or
equal to 50 mm and less than 85 mm; set to .times.0.9 of the
defocus amount per 1 degree of the index in a case where the focal
length is greater than or equal to 85 mm and less than 135 mm; and
set to .times.1 of the defocus amount per 1 degree of the index in
a case where the focal length is greater than or equal to 135
mm.
[0113] According to the third embodiment as described above, in
addition to the same effects as those of the first and second
embodiments, it is possible to realize focus assist display
conforming to operability of the focus ring by changing the display
characteristics of the index of the focus assist display in
response to the focal length. By virtue of the above, it is
possible to improve a user operability of the image capturing
apparatus.
Other Embodiments
[0114] Embodiment(s) of the present invention can also be realized
by a computer of a system or apparatus that reads out and executes
computer executable instructions (e.g., one or more programs)
recorded on a storage medium (which may also be referred to more
fully as a `non-transitory computer-readable storage medium`) to
perform the functions of one or more of the above-described
embodiment(s) and/or that includes one or more circuits (e.g.,
application specific integrated circuit (ASIC)) for performing the
functions of one or more of the above-described embodiment(s), and
by a method performed by the computer of the system or apparatus
by, for example, reading out and executing the computer executable
instructions from the storage medium to perform the functions of
one or more of the above-described embodiment(s) and/or controlling
the one or more circuits to perform the functions of one or more of
the above-described embodiment(s). The computer may comprise one or
more processors (e.g., central processing unit (CPU), micro
processing unit (MPU)) and may include a network of separate
computers or separate processors to read out and execute the
computer executable instructions. The computer executable
instructions may be provided to the computer, for example, from a
network or the storage medium. The storage medium may include, for
example, one or more of a hard disk, a random-access memory (RAM),
a read only memory (ROM), a storage of distributed computing
systems, an optical disk (such as a compact disc (CD), digital
versatile disc (DVD), or Blu-ray Disc (BD).TM.), a flash memory
device, a memory card, and the like.
[0115] While the present invention has been described with
reference to exemplary embodiments, it is to be understood that the
invention is not limited to the disclosed exemplary embodiments.
The scope of the following claims is to be accorded the broadest
interpretation so as to encompass all such modifications and
equivalent structures and functions.
[0116] This application claims the benefit of Japanese Patent
Application Nos. 2015-077147, filed on Apr. 3, 2015, and
2016-042829, filed on Mar. 4, 2016 which are hereby incorporated by
reference herein in their entirety.
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