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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and device for detecting an
image in an auto-focusing apparatus in which focusing condition is judged
by using an image sensor, such as a CCD line sensor.
Various auto-focusing methods have been proposed, in which a CCD line
sensor or like image sensor is used to detect an image. In order to ensure
proper auto-focusing operation, an image zone relevant for auto-focusing
operation should be projected so that the image sensor receives the light
projecting through the such image zone. For instance, if an image zone
having a monotoneous brightness or a substantially constant density is
projected to be sensed by the image sensor, precise auto-focusing
operation cannot be performed leading to erroneous operation. Accordingly,
prior to performing auto-focusing operation, it becomes necessary to judge
whether or not the image zone sensed by the image sensor is a zone
relevant for auto-focusing operation.
2. Prior Art Statement
One known method of judging whether or not the image zone sensed by the
image sensor is a zone relevant for auto-focusing operation or not is the
method wherein the output signal from the image sensor is binarized
(bilevel coded) by a predetermined threshold level to know the reversing
number indicating the number of times for the image signal to be changed
from a value under/over the threshold level to a value over/under the
threshold level (in other words, the number of times for the sensed image
zone to be changed from black to white or white to black), and it is
judged that an image is present in the sensed image zone when the
reversing number is more than a programmed number. However, in this known
method, it becomes necessary to determine the density of the background,
since the threshold level for binarization must be shifted depending on
the density of the background and also depending on whether the original
is a negative or positive picture.
Another known method involves the steps of pre-scanning the entire area of
the original to make a histogram, and determining the density of the
background by referring to the histogram. However, this known method is
detrimental in that the time costed for the pre-scanning operation is
redundantly long since the entire area of the original image must be
pre-scanned for making the histogram. Although it is expected to save the
time for pre-scanning by decreasing the area to be pre-scanned, the
accuracy in determination of background density is lowered.
The accuracy is seriously lowered particularly when the background density
is determined by pre-scanning an image zone having a relatively high
density, e.g. an image zone containing a row of letters, and the slice
level (threshold level) for binarization is set by referring to the thus
determined background density.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, a first object of this invention is to provide a method of
detecting an image in an auto-focusing apparatus for judging precisely and
rapidly the presence or absence of an image in the sensed image zone by
using image signals of relatively small area, even when the density of the
background of the original is fluctuated or even when it is unknown
whether the original is a negative film or a positive film.
A second object of this invention is to provide an image detecting device
to be assembled in an auto-focusing apparatus for performing such a method
as described in the preceding paragraph.
The first object of this invention is achieved in the method of detecting
an image in an auto-focusing apparatus in which a projection lens is
controlled to focus the image by scanning the light projecting through the
original image with an image sensor and by utilizing the image signals
generated from said image sensor, an improvement which comprises:
(a) the step of making a histogram which represents the number of picture
elements in relation of the image signal values sensed by said image
sensor in one focus zone;
(b) the step of judging whether or not an image is present in said one
focus zone on the basis of a profile of said histogram;
(c) the step of setting a binarization level using said histogram when it
is judged that no image is present at the preceding step (b);
(d) the step of counting the reversing number N of which the image signals
of another focus zone change from a value under/over said binarization
level to a value over/under said binarization level; and
(e) the step of judging that an image is present in said another focus zone
when the image reversing number N counted at the preceding step (d) is
more than a programmed number M.
The second object of this invention is achieved by the provision of an
image detecting device to be assembled in an auto-focusing apparatus in
which a projection lens is controlled to focus the image by scanning the
light projecting through the original image with an image sensor and by
utilizing the image signals generated from said image sensor, an improved
image detecting device which comprises:
(a) histogram means for making a histogram which represents the number of
picture elements in relation of the image signal value sensed by said
image sensor in one focus zone;
(b) discriminator means for judging the presence or absence of an image in
said one focus zone on the basis of a profile of said histogram;
(c) focus zone shifting means for shifting the focus zone from said one
focus zone to another focus zone when said discriminator means judges that
no image is present;
(d) binarization level setting means for setting a binarization level using
said histogram;
(e) reversing number counting means for counting the reversing number N of
which the image signals of another focus zone change from a value
under/over said binarization level to a value over/under said binarization
level; and
(f) comparator means for comparing said reversing number N with a
programmed number N; said image detecting device judging that an image is
present when said reversing number N is more than said programmed number N
.
DESCRIPTION OF THE DRAWINGS
The above and other objects and advantages of this invention will be
apparent from the following detailed description of the presently
preferred embodiments with reference to the appended drawings, in which:
FIG. 1 is a schematic illustration showing a reader-printer in which a
first embodiment of this invention is incorporated;
FIG. 2 is a block diagram showing a control system for the auto-focusing
system incorporated in the reader-printer of FIG. 1;
FIGS. 3A, 3B are flow charts showing the processing sequence of the first
embodiment of the auto-focusing system;
FIG. 4-N is a chart showing the wave form of output from the image sensor
when the original is a negative film;
FIG. 4-P is a chart showing the wave form of output from the image sensor
when the original is a positive film;
FIG. 5-N1 is a chart showing the wave form of output from the image sensor
and FIGS. 5-N2 and 5-N3 are charts showing the histograms when the
original is a negative film. These Figures are given for explaining the
principle of the invention;
FIG. 5-P1 is a chart showing the wave form of output from the image sensor
and FIGS. 5-P2 and 5-P3 are charts showing the histograms when the
original is a positive film. These Figures are given for explaining the
principle of the invention;
FIG. 6. is a block diagram showing the operation sequence of the first
embodiment of the image detecting device of the invention;
FIG. 7 is a block diagram showing the operation sequence of an embodiment
of the discriminator means for discriminating presence or absence of
image;
FIG. 8 is a block diagram showing the operation sequence of an embodiment
of the binarization level setting means;
FIGS. 9A, 9B are flow charts showing the operation sequence of a second
embodiment of the auto-focusing system; and
FIG. 10 is a block diagram showing the operation sequence of the
discriminator means 12B of the second embodiment for discriminating
presence or absence of image.
DESCRIPTION OF THE INVENTION
According to this invention, presence or absence of an image in one focus
zone is discriminated or judged on the basis of the profile of a histogram
which represents the number of picture elements in relation of the image
signal value sensed by an image sensor. When it is judged that no image is
present in one focus zone, a binarization level is set while making use of
the histogram made for the aforementioned one focus zone. The reversing
number in another focus zone is counted by binarizing the image signal of
the another focus zone by the thus set binarization level to eliminate the
necessity of making a new histogram for another focus zone.
Presence or absence of an image in a certain focus zone may be judged on
the basis of the profile of the histogram either by a first or second
method. In the first method, presence or absence of an image is judged on
the basis of the distribution range of frequencies (indicated by the
length along the abscissa of the histogram). In the second method,
presence or absence of an image is judged on the basis of the maximum peak
value in the histogram.
Principle of the Methods of the Invention:
The principles of the first and second methods will now be described in
detail while referring to FIGS. 5-N1 to 5-N3 and FIGS. 5-P1 to 5-P3.
FIGS. 5-N1 and 5-P1 show changes in output signals V from the CCD sensor
assembled in a microfilm reader-printer in terms of time t. FIGS. 5-N2 and
5-P2 are histograms corresponding, respectively, to FIGS. 5-N1 and 5-P1.
FIGS. 5-N1 and 5-N2 show the wave form of output signal V and the
corresponding histogram when the original is a negative film, whereas
FIGS. 5-P1 and 5-P2 show the wave form of output signal V and the
corresponding histogram when the original is a positive film.
The original has, in general, a blackening percentage of about 6%, the
blackening percentage being up to 20 or 30% at the most. Accordingly, a
preponderantly larger number of picture elements representing the
background is sensed by a line sensor. The fluctuation of the background
density is relatively little in one film or throughout one roll film, so
that the output signal corresponding to the background density and fed
from the line sensor is relatively stable. As a result, the histograms
(see FIGS. 5-N2 and 5-P2) showing the numbers of picture elements n in the
form of the frequency of output signals V (corresponding to densities D)
have the maximum peak values A and B at the densities D.sub.1 and D.sub.2
indicating the background densities. In case where an image relevant for
auto-focusing operation is not present in the sensed or scanned zone, the
maximum peak value in the histogarm becomes exceedingly large. On the
contrary, an image relevant for auto-focusing operation is present in the
sensed or scanned zone, the maximum peak value in the histogram becomes
relatively small and the distribution range of frequencies (indicated by
the length along the abscissa of the histogram) is widened. Accordingly,
it is possible to judge that an image is present when the length along the
abscissa of the histogram (showing the distribution of output signals from
the line sensor and also showing the distribution of densities of picture
elements) is longer than a predetermined length L.sub.0, and to judge that
an image is not present in the scanned zone when the length along the
abscissa of the histogram is shorther than L.sub.0. Meanwhile, the area
defined by the histogram curve and the abscissa is constant and
corresponding to the number of picture elements sensed by the line sensor.
When the background density D.sub.1 or D.sub.2 and the binarization level a
or b are determined from the histogram, it is desirous for improving the
accuracy to utilize a portion of the histogram having a higher and
narrower maximum peak A or B since such portion of the histogram
corresponds to the area containing a large number of picture elements
representing the background.
Accordingly, in the first method of this invention, presence or absence of
an image in the scanned focus zone is judged on the basis of the
distribution range along the abscissa of the histogram. More specifically,
in the first method of this invention, the total length L of the output
signal range where the frequency n of the histogram equal to or is more
than a programmed value x.sub.0 is determined, and then the length L is
compared with a predetermined length L.sub.0 to judge that an image is
present in the scanned focus zone when L is equal to or longer than
L.sub.0. As an advantageous result, the time required for detecting an
image, and hence the time required for auto-focusing operation, can be
considerably decreased.
On the other hand, in the second method of this invention, presence or
absence of an image in the scanned focus zone is judged on the basis of
the maximum peak value of the histogram. In the second method, the
following feature of the histogram is utilized. If an image relevant for
auto-focusing operation is not present in the scanned focus zone, the
maximum peak value of the histogram becomes higher; whereas the maximum
peak value of the histogram becomes lower and the distribution range of
frequencies in the histogram is widened if an image is present in the
scanned focus zone. Making use of this feature of the histogram, according
to the second method of this invention, the maximum peak value of the
histogram is determined, and the maximum peak value is compared with a
programmed value x.sub.1 to judge that an image is present in the scanned
focus zone when the maximum peak value is not higher than the programmed
value x.sub.1 and to judge that an image usable for auto-focusing
operation is not present in the scanned focus zone when the maximum peak
value is higher than the programmed value x.sub.1.
When the total length L is less than the predetermined length L.sub.0 in
the first method or the maximum peak value of the histogram is more than
the programmed value x.sub.1 in the second method and it is thus judged
that an image usable for auto-focusing operation is not present in the
scanned focus zone, a binarization level a or b is set from the histogram
for scanning another focus zone. It is hereby noted that the histogram for
a zone containing no image has a higher and narrower maximum peak and is
therefore suited for precise determination of the background density. As
will be seen from FIG. 5-N3, when the original is a negative film, an
image is present in the range representing the frequencies of picture
elements having densities higher than the density D.sub.1 of the maximum
peak in the histogram. When the original is a positive film, it will be
seen from FIG. 5-P3 that an image is present in the range representing the
frequencies of picture elements having densities lower than the density
D.sub.2 of the maximum peak in the histogram. Accordingly, the
binarization level a for a negative film is set by adding a constant
.alpha. to the image signal value which is the larger one of the crossing
points of the maximum peak curve of the histogram with a horizontal line
indicating the programmed value x.sub.2 ; whereas the binarization level b
is set by subtracting a constant .beta. from the image signal value which
is the smaller one of the crossing points of the maximum peak curve of the
histogram with a horizontal line indicating the programmed value x.sub.2.
First Embodiment
A first embodiment of this invention will now be described in detail with
reference to FIGS. 1 to 4.
Initially referring to FIGS. 1 and 2, reference numeral 10 designates an
original in the form of a microfishe or a frame of a micro roll film. A
light from a light source 12 passes through a condenser lens 14, a heat
shield filter 16 and a reflector 18 onto the lower face of the original
10. In the reader mode use, the light transmitting through the original
10, i.e. the image projecting light, passes through a projection lens 20
and reflectors 22, 24 and 26 to a light-transmitting screen 28 on which an
enlarged image of the original is focused. In the printer mode use, the
reflector 24 is moved to a position shown by dots-and-dash line in FIG. 1
so that the image projecting light is reflected by the reflectors 22, 30
and 32 to be projected on a surface of photosensitive recording means. In
the illustrated example, the recording means is a slit exposure type
printer 34 of PPC system. The printer 34 has a photosensitive drum 36
which is rotated in synchronism with the movements of the reflectors 22
and 30 so that a latent image is formed on the surface of the
photosensitive drum 36. The thus formed latent image is developed by the
use of a toner having a predetermined polarity, and the developed toner
image is transferred onto a paper sheet 38.
A focus controlling optical system 50 comprises a half-mirror 52 disposed
on the optical axis of the image projecting light, a projection lens 54, a
CCD line sensor 56 used as an image sensor, and a servo motor 58. A
portion of the image projecting light transmitting through the projection
lens 20 is reflected by the half-mirror 52, and passes through the
projection lens 54 to the line sensor 56. The line sensor 56 can be moved
in the plane perpendicular to the optical axis of the image projecting
light by means of the servo motor 58. The projection lens 54 has a focal
distance so that a precisely focused image is incident upon the
photosensitive surface of the line sensor 56 when the projection lens 20
is moved to the position at which a focused image projecting light is
incident upon the screen 28 or upon the surface of the photosensitive drum
36.
The auto-focusing system in the illustrated embodiment has an additional
servo motor 60 for moving the projection lens 20 in the direction parallel
to the optical axis of the image projecting light, and the servo motor 60
is actuated by the control means 48 so that the image projecting light is
precisely focused on the screen 28 or on the surface of the photosensitive
drum 36.
The construction of the control means 48 is shown in FIG. 2. The line
sensor 56 is actuated by a CCD driver 64 in synchronism with a clock pulse
fed from a clock 62. The line sensor 56 generates, for every scanning
operation, a series of output pulses having voltages varied in response to
the incident light quantities from respective picture elements. The
voltages of output pulses are varied due to the difference in
characteristics of respective picture elements even when the light
quantity of the projecting light is constant. The output pulses are
processed by a signal processing circuit 66 to correct the difference in
characteristics of respective picture elements and to be shaped into wave
forms which are shown in FIGS. 5-N1 and 5-P1 as the output signals V.
Each of the output signals V processed by and fed from the signal
processing circuit 66 is converted into a digital signal by an A/D
converter 68, and then fed through an input interface 70 to a CPU (central
processor unit) 72. The CPU 72 is connected with a ROM 74 for storing the
control program for CPU 72 and other necessary data, a RAM 76 and an
output interface 78. The output interface 78 is connected through a D/A
converter 80 and a driver 84 to the servo motor 58, and also connected
through a D/A converter 82 and a driver 60 to the servo motor 60.
Referring now to FIG. 2, comparators 100 and 102 are shown and have
non-reverse input terminals for receiving output signals V and reverse
input terminals for receiving the binarization levels a and b (see FIGS.
5-N3 and 5-P3), respectively for a negative film and for a positive film,
calculated by the CPU 72. The outputs from these comparators 100 and 102
are in high levels as shown by c and d in FIG. 4 when V>a and V>b. A
monostable multi-vibrator 108 generates constant width pulses e indicating
reversion of the signal value from a level under the binarization level a
to a level over the binarization level a in synchronism with the rise of
the output pulses c from the comparator 100. Likewise, a monostable
multi-vibrator 110 generates constant width pulses f indicating reversion
of the signal value from a level under the binarization level b to a level
over the binarization level b in synchronism with the rise of the output
pulses d from the comparator 102. These pulses b or d are integrated by a
counter 112 or 114 for every scanning operations by the line sensor 56.
The result of integration by the counter 112 and 114 are reversing numbers
N.sub.n and N.sub.p which are passed to comparators 120 and 122 where they
are compared with programmed numbers M.sub.n and M.sub.p programmed by
program means 116 and 118. If the reversing number N.sub.n is equal to or
more than the programmed number M.sub.n or the reversing number N.sub.p is
equal to or more than the programmed number M.sub.p, it is judged that an
image is present in the scanned zone. In such a case, the comparator 120
feeds a signal g of high level or the comparator 122 feeds a signal h of
high level. It is desirous that the programmed numbers M.sub.n and M.sub.p
are determined in consideration of the influences by the dusts or defects
of the original 10. The signals g and h are fed in an OR circuit 124 which
decides that an image relevant for auto-focusing operation is present upon
receipt of either one of the signals g or h of high level to feed an
information signal indicating the presence of such an image to the CPU 72,
and simultaneously the signal g or h is passed to the CPU 72 by which it
is judged whether the original is a negative film or a positive film
depending on the receipt of signal g or signal h. When the signal g of
high level is received, it is judged that the original is a negative film
and thus the auto-focusing operation is performed by utilizing the
binarization level a. When the signal h of high level is received, it is
judged that the original is a positive film and thus the auto-focusing
operation is performed by utilizing the binarization level b.
The operation of this embodiment will be described with reference to FIG.
3. The control means 48 controls the servo motor 58 so that the line
sensor 56 receives light projecting through a focus zone addressed by the
CPU 72. When the user selects the reader mode, the reflector 24 is moved
to the position denoted by the real line in FIG. 1 so that the target
original is projected on the screen 28 (Step 200 in FIG. 3). A portion of
the light projecting through the original is reflected by the half-mirror
52 to be passed to the line sensor 56.
The control means 48 reads and stores the output signals V from the line
sensor 56 (Step 202), and measures the exposure light quantity based on
the output signals V (Step 204). In detail, the output signals V from the
signal processing circuit 66 are passed through the input interface 70 to
the CPU 72 which controls the exposure light quantity. When it is found by
the Step 206 that the exposure light quantity is not appropriate, the
exposure light quantity is varied (Step 208) and then the measurement of
exposure light quantity is repeated. The exposure light quantity may be
controlled by adjusting the light quantity from the light source 12 so
that the output signal corresponding to the background picture element has
a constant voltage.
Thereafter, the control means 48 judges whether or not an image relevant
for auto-focusing operation is present in the zone scanned by the line
sensor 56. Histograms shown in FIGS. 5-N2 and 5-P2 are made in relation of
the output image signals V (Step 210), followed by determination of the
total length L of the output signal range within which the frequency n
along the ordinate of the histogram is more than a programmed value
x.sub.0, namely the range within which the picture elements have the
densities higher than a threshold density corresponding to the programmed
value x.sub.0. The total length L is compared with a predetermined length
L.sub.0 (Step 212), and when L is longer than L.sub.0 it is judged that an
image relevant for auto-focusing operation is present in the scanned zone
so that the control means 48 performs the auto-focusing operation (Step
216).
The auto-focusing operation may be controlled by various methods. For
example, the position of the projection lens 20 for providing the maximum
contrast is determined from the output image signals V to find the focused
position (Step 218).
By selecting the printer mode while maintaining the system under the
focused condition (Step 220), the reflector 24 swings to the position
shown by the dots-and-dash line in FIG. 1 so that the image of the
original can be transferred onto the paper sheet 38 to form a hard copy.
When it is found that the total length L is shorter than a predetermined
length L.sub.0 at the step 212, it is judged that an image relevant for
auto-focusing operation is not present in the scanned zone. In such a
case, the control means 48 sets the binarization level a for negative film
or the binarization level b for positive film (Step 222) while making use
of each histogram. As has been described hereinbefore, the binarization
level a for negative film is set by adding a constant .alpha. to the image
signal value which is larger one of the crossing points of the maximum
peak curve of the histogram with a horizontal line indicating the
programmed value x.sub.2, and the binarization level b for positive film
is set by subtracting a constant .beta. from the signal value which is the
smaller one of the crossing points of the maximum peak curve of the
histogram with a horizontal line indicating the programmed value x.sub.2.
The CPU 72 feeds a signal for actuating the servo motor 58 to move the
line sensor 56, so that the zone to be scanned by the line sensor 56 is
shifted to a second focus zone (Step 224). The second focus zone is then
scanned, and output image signals V generating as the result of scanning
the second focus zone are binarized by a real time processing (Step 226),
and the reversing numbers N.sub.n and N.sub.p are integrated,
respectively, by the counters 112 and 114 (Step 228). When the integrated
reversing number N.sub.n is larger than the programmed value M.sub.n, a
signal g of high level indicating the presence of an image is fed from the
comparator 120 to the OR circuit 124 and to the CPU 72; and when the
integrated reversing number N.sub.p is larger than programmed value
M.sub.p, a signal h of high level indicating the presence of an image is
fed from the comparator 122 to the OR circuit 124 and to the CPU 72 (Step
230). When both of the signals g and h are not of high level so that the
output from the OR circuit 124 is of low level, the CPU 72 judges that an
image relevant for auto-focusing operation is not present in the second
focus zone. In such a case, a signal for shifting the line sensor 56 to
scan a new third zone is generated from the CPU 72, and the operation
sequence of Step 226 to Step 230 will be repeated. When either one of the
signals g or h is of high level, it is judged that an image relevant for
auto-focusing operation is present (Step 214), and then the control means
48 performs the auto-focusing operation (Steps 216 and 218). By selecting
the printer mode while maintaining the system under the focused condition,
a hard copy may be reproduced (Step 220).
In the embodiment described above, since the binarization level a for
negative film and the binarization level b for positive film are set and
the output signal value are simultaneously binarized by both of the
binarization levels a and b to determine the reversing number N.sub.p and
N.sub.p respectively for the negative and positive films, either one of
the signals g or h is of high level is supplied to the CPU 72 to enable to
find whether the original is a negative film or a positive film. However,
within the scope of this invention, it is possible to set the system
suited for using either one of the negative or positive films manually by
pushing a selection button on the operation console so that the output
image signal is binarized only by the selected one of the binarization
levels a or b.
The image sensor used in this invention should not be necessarily limited
to a CCD line sensor, but sensors of other type such as, a MOS type line
sensor or an area sensor, may also be used in this invention.
The present invention will now be described more specifically by referring
to FIGS. 6 to 8 in which: FIG. 6 is a block diagram showing the operation
sequence of an embodiment of the image detecting device of the invention;
FIG. 7 is a block diagram showing the operation sequence of an embodiment
of the discriminator means for discriminating presence or absence of
image; FIG. 8 is a block diagram showing the operation sequence of an
embodiment of the binarization level setting means.
In these Figures, a histogram means is denoted by 10A which performs the
function or operation of Step 210(see FIG. 3). Reference numeral 12A
designates a discriminator means for judging presence or absence of an
image in the scanned zone and performs the function or operation shown by
the block diagram encircled by the dot-and-dash lines in FIG. 7. Referring
to FIG. 7, the discriminator means 12A comprises a program means 122A for
setting the programmed value x.sub.0 which is fed to a comparator means
120A. The levels of the image signals are compared with the programmed
value x.sub.0 by the comparator means 120A and the results of comparison
are fed to a counter 124A to know the total length L indicating the range
where the frequency n of the histogram is more than the programmed value
x.sub.0. In a comparator means 126A, the total length L is compared with a
predetermined length L.sub.0 fed from a program means 128A to the
comparator means 126A. Presence or absence of an image in the scanned zone
is judged depending on the result of comparison between L and L.sub.0
(Step 212 shown in FIG. 3).
When it is judged that an image is present in the scanned zone,
auto-focusing operation is performed by an auto-focusing means 14A (see
FIG. 6). When it is judged that an image relevant for auto-focusing
operation is not present in the scanned zone, the binarization levels a
and b are set by a binarization level setting means 16A. This means 16A
comprises a comparator means 160A and an adder-subtracter means 166A as
shown in FIG. 8. A programmed value x.sub.2 is fed from a program means
162A to the comparator means 160A. Data of the maximum peak curve of the
histogram are fed to the comparator means 160A and compared with the
programmed value x.sub.2 to find the output signal values corresponding to
the crossing points of the curve with a line indicating the programmed
value x.sub.0. A constant .alpha. is added to the output signal value
corresponding to the larger one of the crossing points to set the
binarization level a; and a constant .beta. is subtracted from the output
signal value corresponding to the smaller one of the crossing points to
set the binarization level b (Step 222 shown in FIG. 3). Constants .alpha.
and .beta. are predetermined by a programmed means 164A.
Reference numeral 18A designates a focus zone shifting means which
comprises a servo motor 58 for moving the line sensor 56 of the focus
controlling optical system 50. When the focus zone is shifted by the means
18A., the reversing numbers N.sub.n and N.sub.p are detected by a
reversing number counting means 20A in which the output signal values from
the line sensor 56 are binarized by the binarization levels a and b.
Reference numeral 22A designates a further comparator means for comparing
the reversing number N.sub.n with the constant value M.sub.n and for
comparing the reversing number N.sub.p with the constant value M.sub.p to
judge the presence or absence of an image relevant for auto-focusing
operation in the scanned zone. When the comparator means 22A judges that
an image relevant for auto-focusing operation is present, a signal for
commencing the auto-focusing operation is fed therefrom. Constant values
M.sub.n and M.sub.p are fed from program means 24A.
Second Embodiment
The operation of a second embodiment will now be described with reference
to FIG. 9. The second embodiment is distinctive from the first embodiment
in the operation of CPU 72, particularly the operation for discriminating
presence or absence of an image from the histograms in the second
embodiment is different from that in the first embodiment. However, since
the construction of hardware used in the second embodiment is the same as
used in the first embodiment and shown in FIGS. 1 and 2, the description
of the hardware used in the second embodiment will not be repeated.
Likewise, since the steps 200 to 208 are the same as described with
reference to FIG. 3, the description thereof will not be repeated here.
Now referring to FIG. 9, after the completion of adjustment of exposure
light quantity by the steps 200 to 208, presence or absence of an image in
the scanned zone is judged by the control means 48 based on the principle
as described hereinbefore as the second method. The histograms shown in
FIGS. 5-N2 and 5-P2 are made, and the maximum peak values thereof are
compared with the programmed value x.sub.1 (Step 310). When either one of
the maximum peak values of the histograms is lower than the programmed
value x.sub.1, it is judged that an image relevant for auto-focusing
operation is present in the scanned focus zone (Step 312) and the control
means 48 performs the auto-focusing operation (Step 314). After confirming
that the image is brought to the focused condition (Step 316) and the user
selects the printer mode (Step 318), a hard copy is reproduced.
When it is found that both of the maximum peak values of the histograms are
higher than the programmed value x.sub.1 at the step 312, it is judged
that an image relevant for auto-focusing operation is not present in the
scanned focus zone. In such a case, binarization levels a for negative
film and b for positive film are set from the histograms by the control
means 48 (Step 320). The binarization level a for negative film is set by
adding a constant .alpha. to the signal value which is the larger one of
the crossing points of the maximum peak curve of the histogram with a
horizontal line indicating the programmed value x.sub.2 ; and the
binarization level b for positive film is set by subtracting a constant
.beta. from the smaller one of the crossing points of the maximum peak
curve of the histogram with a horizontal line indicating the programmed
value x.sub.2.
After setting the binarization level a or b (Step 320), the CPU 72
generates a signal for actuating the servo motor 58 to move the line
sensor 56 so that a new focus zone is selected (Step 322). The output
signals V obtained by scanning the new focus zone are binarized by the
binarization level a or b by a real-time operation (Step 324), and the
reversing number N.sub.n or N.sub.p is integrated by the counter 112 or
114 (Step 326). In the Step 328, when the integrated reversing number
N.sub.n is equal to or larger than the programmed value M.sub.n, a signal
g of high level is fed from the comparator 120 to the OR circuit 124 and
the CPU 72 to indicate the presence of a negative image; and when the
integrated reversing number N.sub.p is equal to or larger than the
programmed value M.sub.p, a signal h of high level is fed from the
comparator 122 to the OR circuit 124 and the CPU 72 to indicate the
presence of positive image. When both of the signals g and h are not in
high level, the output from the OR circuit 124 is of low level to indicate
that an image relevant for auto-focusing operation is not present in the
scanned new focus zone. The reversing numbers N.sub.n and N.sub.p are
stored in the RAM 76 together with the positional data of the new focus
zone. Then, the line sensor 56 is moved to scan a further different focus
zone, and the operations of Steps 322 to 330 are repeated until a focus
zone containing an image relevant for auto-focusing operation is found. A
focus zone containing an image relevant for auto-focusing operation is
discriminated by finding that either one of the signals g or h is of high
level at the Step 328. After finding a focus zone containing an image
relevant for auto-focusing operation, the control means 48 generates
signals for commencing the auto-focusing operation (Steps 314 and 316).
In case where both of the signals g and h are not of high level in all of
the scanned focus zones (Step 332), the CPU 72 reads the data of N.sub.n
and N.sub.p stored in the RAM 76 to find the location of the focus zone
having the maximum N.sub.n or N.sub.p (Step 334). The line sensor 56 is
moved to scan the focus zone | | |
