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Digital Camera Patent Abstract
A quick focusing method for a digital camera calculates a plurality
of resolutions corresponding to a plurality of view-finding locations.
The method finds a location for the optimal location by comparing
the resolutions and determines the optimal location with reference
to the slopes of lines connecting those view-finding locations.
The quick focusing method can advantageously reduce focusing time.
Digital Camera Patent Claims
I claim:
1. A quick focusing method for a digital camera to move an image-fetching
unit to an optimal location with a motor, the method comprising
the steps of: a) moving the image-fetching unit to a first view-finding
location, a second view-finding location and a third view-finding
location, respectively, with the step motor; b) calculating a first
resolution corresponding to the first view-finding location, a second
resolution corresponding to the second view-finding location and
a third resolution corresponding to the third view-finding location;
c) determining a location for the optimal location by comparing
the three resolutions; d) determining the optimal location according
to the first view-finding location, the second view-finding location
and the third view-finding location.
2. The quick focusing method for a digital camera as in claim 1,
wherein in step a) the first view-finding location, the second view-finding
location and the third view-finding location have a same separation
therebetween.
3. The quick focusing method for a digital camera as in claim 1,
wherein in step a) the first view-finding location, the second view-finding
location and the third view-finding location have different separations
therebetween.
4. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises the substeps of: when the first
resolution is larger than the second resolution, setting the optimal
location between the first view-finding location and the second
view-finding location; setting the optimal location closer to the
first view-finding location when a special condition occurs; and
setting the optimal location at the first view-finding location
when a boundary condition occurs.
5. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises substeps of: when the first resolution
is smaller than the second resolution, the second resolution is
larger than the third resolution, and the first resolution is larger
than the third resolution, setting the optimal location between
the first view-finding location and the second view-finding location.
6. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises substeps of: when the first resolution
is smaller than the second resolution, the second resolution is
larger than the third resolution, and the first resolution is equal
to the third resolution, setting the optimal location at the second
view-finding location.
7. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises substeps of: when the first resolution
is smaller than the second resolution, the second resolution is
larger than the third resolution, and the first resolution is smaller
than the third resolution, setting the optimal location between
the second view-finding location and the third view-finding location.
8. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises substeps of: when the second resolution
is smaller than the third resolution and the third view-finding
location is a last view-finding location for the step motor, setting
the optimal location between the second view-finding location and
the third view-finding location, the optimal location being closer
to the third view-finding location or at the third view-finding
location.
9. The quick focusing method for a digital camera as in claim 1,
wherein step c) further comprises substeps of: when the second resolution
is smaller than the third resolution and the third view-finding
location is not a last view-finding location for the step motor,
replacing the first view-finding location with the second view-finding
location; replacing the second view-finding location with the third
view-finding location; setting a location beyond the third view-finding
location as a fourth view-finding location and the replacing the
third view-finding location with the fourth view-finding location;
and repeating step (b).
10. The quick focusing method for a digital camera as in claim
1, wherein step d) further comprises substeps of: calculating a
first slope of a first line connecting the second view-finding location
and the third view-finding location; forming a second line passing
the first view-finding location and having a slope identical to
the first slope; finding an intersection point of the first line
and the second line; and setting the intersection point as the optimal
location.
11. The quick focusing method for a digital camera as in claim
1, wherein step d) further comprises substeps of: calculating a
first slope of a line connecting the first view-finding location
and the second view-finding location; forming a second line passing
through the third view-finding location and having a slope identical
to the first slope; finding an intersection point of the first line
and the second line; and setting the intersection point as the optimal
location.
12. The quick focusing method for a digital camera as in claim
1, wherein step d) further comprises substeps of: setting a location
beyond the third view-finding location as a fourth view-finding
location; calculating a fourth resolution of the fourth view-finding
location; finding an intersection point of a line connecting the
first view-finding location and the second view-finding location
and a line connecting the third view-finding location and the fourth
view-finding location; and setting the intersection point as the
optimal location.
Digital Camera Patent Description
FIELD OF THE INVENTION
[0001] The present invention relates to a quick focusing method
for a digital camera, and especially to a quick focusing method
for a digital camera that uses fewer view-finding locations, thus
decreasing focusing time.
BACKGROUND OF THE INVENTION
[0002] In accord with the rapid progress of digital electronic
and semiconductor process, many conventional consumer products are
digitalized. For example, digital imaging devices such as digital
still cameras (DSC) and digital video cameras (DV) are becoming
increasingly mature and popular.
[0003] The digital still camera uses electronic imaging device
such as a CCD (charge coupled device) to replace conventional film
for image capture. Moreover, focusing lens is also crucial component
in a digital still camera and is generally controlled by a step
motor. FIG. 1 shows a flowchart of the control process for a prior
art focusing lens by a step motor in 50 pitches. In other words,
the focusing lens is moved forward or backward 50 pitches with a
step motor.
[0004] In step 101, the focusing lens is moved forward (or backward)
with the step motor by one pitch for a first view-finding of an
object. In step S103, the electronic imaging device such as a CCD
is exposed. In step S105, the photo resolution for first-time view-finding
is calculated. Step S107 determines whether the focusing lens can
be further moved forward (or backward). If the focusing lens can
be further moved, the procedure goes to step S101 for view-finding
again (S101), exposing again (S103) and resolution calculating again
(S105). If the focusing lens cannot be moved, the focusing lens
has already been moved forward or backward 50 pitches by the step
motor. Step S109 subsequently determines the optimal resolution
to provide the optimal view-finding location among the 50 pitches.
[0005] However, in above-mentioned procedure to control the focusing
lens, the steps of view finding, exposing and resolution calculating
must be repeated for each movement of lens by the step motor. This
is time consuming, especially in the step of exposing the electronic
imaging device such as a CCD.
SUMMARY OF THE INVENTION
[0006] It is an object of the present invention to provide a quick
focusing method for a digital camera that uses less focusing time
for obtaining an optimal location of the image-fetching unit.
[0007] To achieve the above object, the present invention provides
a quick focusing method for a digital camera to move an image-fetching
unit to an optimal location by a step motor, the method comprising
the steps of a) moving the image-fetching unit to a first view-finding
location, a second view-finding location and a third view-finding
location, respectively, with the step motor; b) calculating a first
resolution corresponding to the first view-finding location, a second
resolution corresponding to the second view-finding location and
a third resolution corresponding to the third view-finding location;
c) determining a location for the optimal location by comparing
the three resolutions; and d) determining the optimal location by
the first view-finding location, the second view-finding location
and the third view-finding location.
BRIEF DESCRIPTION OF DRAWINGS
[0008] The foregoing aspects and many of the attendant advantages
of this invention will be more readily appreciated as the same becomes
better understood by reference to the following detailed description,
when taken in conjunction with the accompanying drawings, wherein:
[0009] FIG. 1 is a flowchart describing the view-finding process
according to the prior art;
[0010] FIG. 2 shows a perspective view of a conventional digital
still camera;
[0011] FIG. 3 shows the resolution curve corresponding to the first
embodiment of the present invention;
[0012] FIG. 4 shows the slope curve corresponding to the first
embodiment of the present invention;
[0013] FIG. 5 shows the resolution curve corresponding to the second
embodiment of the present invention;
[0014] FIG. 6 shows the slope curve corresponding to the second
embodiment of the present invention;
[0015] FIG. 7 shows the resolution curve corresponding to the third
embodiment of the present invention;
[0016] FIG. 8 shows the resolution curve corresponding to the fourth
embodiment of the present invention;
[0017] FIG. 9 shows the resolution curve corresponding to the fifth
embodiment of the present invention;
[0018] FIG. 10 shows the resolution curve corresponding to the
sixth embodiment of the present invention;
[0019] FIG. 11 shows the resolution curve corresponding to the
seventh embodiment of the present invention; and
[0020] FIG. 12 shows the flowchart of the quick focusing method
for a digital camera according to the present invention
DETAILED DESCRIPTION OF THE INVENTION
[0021] FIG. 2 shows a perspective view of a digital still camera
(DSC) 50, which comprises a step motor (not shown) to move an image-fetching
unit 10 such as a lens, such that a taken picture can be displayed
on a display 20.
[0022] The present invention presets a plurality of view-finding
locations along a movement path of the image-fetching unit 10 for
taking photos. Taking a motor of 100 pitches as an example, the
view-finding locations in the present invention are separated by
10 pitches. Therefore, there are 10 view-finding locations on the
movement path.
[0023] The above-mentioned process is to reduce exposure times
of the digital still camera (DSC). The separation between the view-finding
locations is fixed in above description. However, the separation
between the view-finding locations can also be variable.
[0024] After setting up the view-finding locations, the image-fetching
unit 10 calculates the resolution and contrast for the taken photo
at those view-finding locations. Therefore, the optimal view-finding
location can be determined and the view-finding location can be
determined to be an ordinary case, a special case or a boundary
case. FIG. 3 shows the resolution curve according to the first preferred
embodiment of the present invention for the ordinary case, in which
the ordinate is the resolution and the abscissa is the view-finding
location.
[0025] After the image-fetching unit 10 is moved to the first view-finding
location Y1 and second view-finding location Y2 by the step motor,
the first resolution and the second resolution corresponding to
the first view-finding location Y1 and second view-finding location
Y2 are calculated. As shown in this figure, the second resolution
is larger than the first resolution, therefore, the step motor further
moves the image-fetching unit 10 beyond the second view-finding
location Y2 to a third view-finding location Y3. Moreover, the third
resolution corresponding to the third view-finding location Y3 is
compared to the first resolution and the second resolution corresponding
to the first view-finding location Y1 and second view-finding location
Y2.
[0026] When the third resolution corresponding to the third view-finding
location Y3 is smaller than the second resolution corresponding
to the second view-finding location Y2, the resolution decreases.
The third resolution corresponding to the third view-finding location
Y3 is again compared with the first resolution corresponding to
the first view-finding location Y1 to determine whether the optimal
view-finding location is located between the first view-finding
location Y1 and second view-finding location Y2, or between the
second view-finding location Y2 and the third view-finding location
Y3.
[0027] As shown in the example of FIG. 4, the optimal view-finding
location is judged to be located between the second view-finding
location Y2 and the third view-finding location Y3 because the third
resolution of the third view-finding location Y3 is larger than
the first resolution of the first view-finding location Y1. In the
present invention, this condition is referred to as an ordinary
condition and a fourth resolution is calculated by further moving
the view-finding location to a fourth view-finding location Y4 beyond
the third view-finding location Y3.
[0028] When the image-fetching unit 10 calculates the fourth resolution
corresponding to the fourth view-finding location Y4, the view-finding
location is not further moved and a slope approach is used to save
focusing time. As shown in FIG. 4, a first extension line is obtained
by connecting the first view-finding location Y1 and second view-finding
location Y2, and a second extension line is obtained by connecting
the view-finding location Y3 and fourth view-finding location Y4.
The optimal location M is the intersection of the two extension
lines.
[0029] As shown in FIG. 4, the four view-finding locations Y1,
Y2, Y3, and Y4 have the same separation such as 10 pitches. The
x between the second view-finding location Y2 and the optimal location
M is an unknown value. Provided that the view-finding locations
Y1, Y2, Y3, and Y4 have ordinates Y1, Y2, Y3, and Y4 and the optimal
location M has an ordinate m and the fixed separation is z, the
distance x can be determined as follows: 1 1. m - y1 z + x = m -
y2 x 2. m - y4 2 z - x = m - y3 z - x
[0030] By computing the two equation, 2 x = z ( 2 y3 - y2 - y4
) ( y2 - y1 + y3 - y4 )
[0031] The optimal location M can be obtained by added x to Y2.
[0032] FIG. 5 shows the resolution curve corresponding to the second
embodiment of the present invention, which corresponds to a special
condition. As shown in this figure, the third view-finding location
Y3 is smaller than the first resolution of the first view-finding
location Y1. This means the resolution is decreasing and the view-finding
location is not moved further.
[0033] In this special condition, the third view-finding location
Y3 is smaller than the first resolution of the first view-finding
location Y1. The optimal view-finding location is therefore located
between the first view-finding location Y1 and second view-finding
location Y2. In this case, the extension line passing the first
view-finding location Y1 is assumed to have the same slope as the
extension line connecting the second view-finding location Y2 and
the view-finding location Y3. Therefore, the optimal location M
is the intersection of the two extension lines, which are two sides
of an isosceles triangle.
[0034] As shown in FIG. 5, the three view-finding locations Y1,
Y2, and Y3 have the same separation z, and the optimal location
M has a separation x with respect to the second view-finding location
Y2. The distance x can be determined as follows: 3 m - y1 z - x
= m - y2 x = y2 - y3 z , x = z ( y1 - y3 ) 2 ( y2 - y3 )
[0035] The optimal location M can be obtained by subtracting x
from Y2.
[0036] Moreover, when the second resolution of the second view-finding
location Y2 is larger than the first resolution of the first view-finding
location Y1, the third resolution of the third view-finding location
Y3 is compared with the second resolution of the second view-finding
location Y2. If the third resolution of the third view-finding location
Y3 is larger than the second resolution of the second view-finding
location Y2, the digital camera 50 judges whether the third view-finding
location Y3 is an end point of the step motor. If it is not, the
second view-finding location Y2 replaces the first view-finding
location Y1, the third view-finding location Y3 replaces the second
view-finding location Y2 and a view-finding location Y4 beyond the
third view-finding location Y3 is set as the new third view-finding
location Y3.
[0037] The step mentioned above is used to judge whether the evolution
should proceed in a case where the resolution is still increasing.
The evolution is further moved to the next view-finding location
if no end point is found.
[0038] FIG. 7 shows the resolution curve corresponding to the third
embodiment of the present invention, which corresponds to a boundary
condition and the optimal location M is at a boundary point. The
boundary point may correspond to the first view-finding location
or the last view-finding location. The image-fetching unit 10 first
calculates the resolution corresponding to the first view-finding
location Y1, which is an initial boundary point (the first point
for the step motor) and then calculate the resolutions corresponding
to the second view-finding location Y2 and the third view-finding
location Y3. The condition is exemplified by the resolution corresponding
to the first view-finding location Y1 being larger than the resolutions
corresponding to the second view-finding location Y2 and the third
view-finding location Y3. The slope m1 of the line connecting the
resolutions of the first view-finding location Y1 and the second
view-finding location Y2 and the slope m2 of the line connecting
the resolutions of the second view-finding location Y2 and third
the view-finding location Y3 are compared. If m1 is equal to m2,
then the first view-finding location Y1 corresponds to the optimal
location M. If m1/m2 is larger than 1, the first view-finding location
Y1 corresponds to the optimal location M.
[0039] As shown in right portion of FIG. 7, when the optimal location
M is at the last boundary point, the criterion should be reversed.
If the slope ratio of the line connecting Y1 and Y2 and the line
connecting Y2 and Y3 is smaller than or equal to 1, the third view-finding
location Y3 corresponds to the optimal location M.
[0040] FIG. 8 shows the resolution curve corresponding to the fourth
embodiment of the present invention, in which the slope of line
connecting Y1 and Y2 is smaller than the slope of line connecting
Y2 and Y3. In this situation, the optimal location M is between
the first view-finding location Y1 and the second view-finding location
Y2 and near the first view-finding location Y1. This is similar
to the special condition shown in FIG. 5 and the optimal location
M can be determined by the method of isosceles triangle as shown
in FIGS. 5 and 6.
[0041] FIG. 9 shows the resolution curve corresponding to the fifth
embodiment of the present invention, in which the slope of line
connecting Y1 and Y2 is larger than the slope of line connecting
Y2 and Y3. In this situation, the slope of line connecting Y1 and
Y2 is calculated and applied to the third view-finding location
Y3 by the isosceles triangle method as shown in FIGS. 5 and 6. The
optimal location M is the apex of the isosceles triangle.
[0042] FIG. 10 shows the resolution curve corresponding to the
sixth embodiment of the present invention, in which the slope of
the line connecting Y1 and Y2 is zero. In this situation, the optimal
location M is the midpoint of the first view-finding location Y1
and the second view-finding location Y2.
[0043] FIG. 11 shows a condition in which the optimal location
M can be quickly discovered. In this situation, the resolutions
of the first view-finding location Y1 and the third view-finding
location Y3 are the same, but they both are smaller than the resolution
of the second view-finding location Y2. The optimal location M can
be quickly known at the second view-finding location Y2.
[0044] FIG. 12 shows the flowchart of the quick focusing method
for a digital camera according to the present invention. At step
S201, at least a first view-finding location Y1, a second view-finding
location Y2 and a third view-finding location Y3 are preset for
the image-fetching unit 10. In step S203, the first resolution corresponding
to the first view-finding location Y1, the second resolution corresponding
to the second view-finding location Y2 and the third resolution
corresponding to the third view-finding location Y3 are calculated.
In step S205, the resolutions are compared to determine whether
the condition is an ordinary, special or boundary condition. In
step S207, the optimal location is calculated by the three view-finding
locations Y1, Y2 and Y3, and slope therebetween.
[0045] To sum up, the quick focusing method for a digital camera
according to the present invention can quickly find the optimal
location of the image-fetching unit for the digital camera. The
focusing time can be reduced.
[0046] Although the present invention has been described with reference
to the preferred embodiment thereof, it will be understood that
the invention is not limited to the details thereof. Various substitutions
and modifications have suggested in the foregoing description, and
other will occur to those of ordinary skill in the art. Therefore,
all such substitutions and modifications are intended to be embraced
within the scope of the invention as defined in the appended claims. |