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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to a method of changing image magnification,
and more particularly to a method of enlarging or reducing image
information produced from a light sensor after it has read an original
image as modified in size by optical means, at a desired magnification
ratio with electric means, so that an image which is magnified at a
desired ratio can be reproduced highly accurately and inexpensively.
In the field of printing plate-making, for example, there has been employed
an image scanning recording and reproducing system for electrically
processing image information on an original to produce an original film
plate in order to carry out the plate-making process efficiently and
improving the image quality.
The image scanning recording and reproducing system is basically composed
of an image reading device and an image reproducing device. In the image
reading device, image information on an original which is fed in an
auxiliary scanning direction is scanned in a main scanning direction by a
light sensor, which converts the image information to an electric signal.
Then, the photoelectrically converted image information is subjected to
gradation correction, profile emphasis, and other image processing in the
image reproducing device according to given plate-making conditions.
Thereafter, the image information is converted to a light signal such as a
laser beam signal which is applied to a recording medium comprising a
photosensitive material such as a photographic film to record the image
information thereon. The image on the recording medium is developed by an
image developing device, and the recording medium will be used as a film
plate in a printing process.
It is preferable that the image information carried on the original be
reproduced at an enlarged or reduced size by selecting a desired
magnification ratio. One method of changing the magnification ratio of
image information is to use a zoom lens in the optical system for focusing
the image information on the light sensor and vary the magnification ratio
by operating the zoom lens.
A magnification ratio for image information can be changed as desired by
the zoom lens. However, where image information is greatly enlarged by the
zoom lens, the image information focused on the light sensor suffers from
various optical defects such as spherical aberration, distortion, and the
like, resulting in a reduction image accuracy. It would be technically
difficult and highly expensive to produce a zoom lens having minimum
aberrations and capable of magnifying image information in a wide
magnification range.
It is also possible to employ a fixed-focus lens, instead of a zoom lens,
and to displace the fixed-focus lens and the light sensor with respect to
an original for thereby changing the magnification ratio.
With this method, however, the lens and the light sensor must be displaced
greatly in order to greatly enlarge or reduce the original image, and a
wide space is necessary to accommodate such a large displacement of the
lens and the light sensor. Where the magnification of the original image
is increased, optical defects or aberrations are produced to lower the
image accuracy, as with the zoom lens.
An electric process may be employed for changing an image magnification
ratio. For example, image information photoelectrically converted by a
light sensor and stored in a memory may be reproduced in a 1/2 size by
reading the stored information from every other address of the memory.
Likewise, stored image information may be reproduced in a reduced size at
a magnification ratio of 1/3, 1/4, . . . Conversely, an image may be
reproduced at a magnification ratio which is a multiple of an integer by
reading image information several times from each address of the memory.
It is however impossible to continuously change the magnification ratio to
obtain magnification of x 1.3 or x 3.8, for example, since available
magnification ratios are multiples of an integer. An enlarged reproduced
image is not smooth and continuous because it is reproduced by reading the
stored information several times from each address of the memory.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of changing
the magnification ratio of an image by reading, with a light sensor, an
original image produced at a desired size by optical means, changing the
magnification of the image from the light sensor with electric means to
produce an image signal at a desired size, so that an image which is
magnified in a wide magnification range can be reproduced highly
accurately and inexpensively.
Another object of the present invention is to provide a method of changing
the magnification ratio of image information carried on an original for
reproduction at a desired magnification ratio, the method comprising the
steps of reducing or enlarging the image information to a prescribed size
with optical means, thereafter, photoelectrically converting the image
information with a light sensor, and selectively picking up the
photoelectrically converted image information or determining data between
adjacent items of the photoelectrically converted image information by
interpolation, thereby obtaining image information at a desired size.
Still another object of the present invention is to provide a method of
changing the magnification ratio of image information, wherein the optical
means comprises a fixed-focus lens, the light sensor and the fixed-focus
lens being displaceable with respect to the original to change the
magnification ratio of the image information with respect to the light
sensor.
Yet another object of the present invention is to provide a method of
changing the magnification ratio of image information, wherein the optical
means comprises a zoom lens for changing the magnification ratio of the
image information with respect to the light sensor.
A further object of the present invention is to provide a method of
changing the magnification ratio of image information, wherein
magnification ratios established by the optical means and magnification
ratios established by the electric means are stored in combination in a
magnification table.
A yet further object of the present invention is to provide a method of
changing the magnification ratio of image information, wherein the data
between the adjacent items of the photoelectrically converted image
information is produced by using an interpolation table set up according
to enlarging magnification ratios established by the electric means.
A still further object of the present invention is to provide a method of
changing the magnification ratio of image information, wherein the
interpolation table is composed of interpolated data produced for each of
the magnification ratios established by the electric means, the
interpolated data being selected according to an enlarging magnification
ratio established by the electric means to interpolate the image
information.
The above and other objects, features and advantages of the present
invention will become more apparent from the following description when
taken in conjunction with the accompanying drawings in which a preferred
embodiment of the present invention is shown by way of illustrative
example.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view, partly in block form, of an image reading
device which employs a method of changing the magnification ratio of an
image according to the present invention;
FIG. 2 is a perspective view of the image reading device shown in FIG. 1;
FIG. 3 is a block diagram of a magnification converting circuit shown in
FIG. 1;
FIG. 4 is a view showing a magnification table produced in the method of
the invention;
FIG. 5 is a view of an interpolation table produced in the method of the
invention; and
FIG. 6 is a diagram illustrating linear interpolation effected in the
method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
FIG. 1 shows an image reading device in which a method of changing the
magnification ratio of an image according to the present invention is
carried out. The image reading device essentially comprises an image
reader 10 for optically reading image information carried on an original S
and an image processor 12 for electrically processing the image
information read by the image reader 10.
The image reader 10 includes a light sensor 14 in the form of a CCD for
photoelectrically converting light from the image information carried on
the original S, and a fixed-focus lens 16 for focusing the image
information at a varied magnification ratio on the CCD 14. The CCD 14
comprises a linear array of photoelectric transducer elements, and is
disposed parallel to a main scanning direction indicated by the arrow X
(FIG. 2) for the original S to scan the original S which is fed in an
auxiliary scanning direction indicated by the arrow Y.
The CCD 14 is displaceable by a step motor 18a to move along an optical
axis 20 of the lens 16. More specifically, the step motor 18a is
operatively coupled to a drum 26a through a belt 24a. A wire 28a has one
end wound around the drum 26a and an opposite end fixed to the frame of
the image reader 10 and trained around a pulley 32a which is urged by a
spring 30a to move in a direction away from the drum 26a, the pulley 32a
being fixed to the CCD 14.
The lens 16 is displaceable by a step motor 18b in a direction along the
optical axis 20. Rotative drive power from the step motor 18b is
transmitted to the lens 16 by a mechanism which is identical to the power
transmitting mechanism associated with the CCD 14. Therefore, various
parts of the power transmitting mechanism associated with the lens 16 are
denoted by identical reference numerals with a suffix b and will not be
described in detail. The magnification ratio of image information focused
on the CCD 14 is optically variable by displacing the CCD 14 and the lens
16 along the optical axis 20 with the step motors 18a, 18b.
The image processor 12 comprises an A/D converter 34 for converting the
image information which has been photoelectrically converted by the CCD 14
to a digital signal, a line memory 36 serving as a buffer for temporarily
storing the digital image information from the A/D converter 34, a
magnification converter 38 for electrically processing the image
information to change its magnification, an I/O port 40 for applying
control signals to the step motors 18a, 18b of the image reader 10, and a
magnification table 42 containing selected combinations of magnification
ratios. These components of the image processor 12 are controlled by a CPU
44. The magnification table 42 contains magnification ratios that can be
varied by the image reader 10 and magnification ratios that can be varied
by the magnification converter 38 in combination with desired
magnification ratios for image information.
The magnification converter 38 is arranged as shown in FIG. 3. The
magnification converter 38 comprises a sequencer 46 for controlling an
operation sequence of the magnification converter 38, a pair of latches
48, 50 for latching image data items fetched from the line memory 36 based
on an addressing command from the sequencer 46, a subtractor 52 for
calculating the difference between the image data items latched in the
latches 48, 50, an interpolation table 54 for producing interpolated data
based on the difference calculated by the subtractor 52, and an adder 56
for adding the image data latched in the latch 48 and the interpolated
data and applying the sum data to an image memory (not shown). The
interpolation table 54 stores linear interpolation data items with respect
to predicted values for the calculated data from the subtractor 52, in
association with the magnification ratios in the magnification converter
38.
A method of changing the magnification ratio of an image is carried out by
the above arrangement as follows:
A magnification ratio for image information carried on the original S is
expressed as the product of a magnification ratio optically established in
the image reader 10 and a magnification ratio electrically established by
the magnification converter 38 of the image processor 12. Assuming that
the image reader 10 has a range of magnification ratios of from 100% to
200% in increments of 1% and the magnification converter 38 can establish
magnification ratios of 100%, 200%, and 300%, combined magnification
ratios for a reproduced image are as shown in FIG. 4. The combined
magnifications range from 100% to 600% in increments of 1 through 3%.
These combinations of magnification ratios are stored as the magnification
table 42 in a memory. The combinations of the magnification ratios
established in the image reader 10 and the magnification ratios
established in the magnification converter 38 are selected such that the
quality of reproduced images will be optimum.
A magnification ratio is converted by the magnification converter 38 based
on the interpolation table 54. The interpolation table 54 is set up as
illustrated in FIG. 5 assuming that the magnification ratio established by
the magnification converter 38 is 300%. If image data is represented by 8
bits, the image data can be expressed by 256 level. Assuming that the Nth
image data is indicated by D.sub.N and the (N+1)th image data adjacent to
the Nth image data is indicated by D.sub.N+1, the value of (D.sub.N+1
-D.sub.N) can be expressed by 511 levels from -255 to 255. In order to
obtain image data which is magnified at a magnification ratio of 300%, the
interval between the Nth image data D.sub.N and the (N+1)th image data
D.sub.N+1 is divided into three segments and interpolated data r.sub.i
(i=0, 1, 2) with respect to the image data D.sub.N at points of division i
(i=0, 1, 2 ) is obtained by linear interpolation. The deviation of the
interpolated data item r.sub.0 from the image data is zero. Where the
image data D.sub.N is represented by p and the image data D.sub.N+1 is
represented by q, the interpolated data items r.sub.1, r.sub.2 are
expressed as follows:
r.sub.1 =(q-p)/3 (1)
r.sub.2 =2(q-p)/3 (2)
An interpolation table 54 with respect to the magnification ratio of 300%
is prepared in this manner and stored in the memory. Likewise,
interpolation tables 54 with respect to magnification ratios of 100%, 200%
are prepared in the same manner. As the interpolation table for the
magnification ratio of 100%, the interpolation table for the magnification
table of 200% or the interpolation table 54 for the magnification table of
300% with i=1 may be used.
After the magnification table 42 and the interpolation table 54 have been
prepared, the original S is scanned to produce image data at a desired
magnification ratio. By way of example, image information is magnified
150% by the image reader 10 and then magnified 300% by the magnification
converter 38, so that image information is reproduced at a combined
magnification of 450%.
First, desired magnification data 450% is applied from an input device (not
shown) to the image processor 12. The image processor 12 then selects a
magnification ratio of 150% optically established by the image reader 10
and a magnification ratio of 300% electrically established by the
magnification converter 38, from the magnification table 42 (FIG. 4).
Then, the CPU 44 applies a control signal corresponding to the
magnification ratio of 150% established by the image reader 10 to the step
motors 18a, 18b through the I/O port 40. In response to the applied
control signal, the step motors 18a, 18b rotate the drums 26a, 26b through
the respective belts 24a, 24b to displace the respective wires 28a, 28b in
directions of the arrows. Since the wires 28a, 28b are trained around the
respective pulleys 32a, 32b, the CCD 14 and the lens 16 are displaced by
the pulleys 32a, 32b in the directions of the arrows A. As a result, the
conjugate lengths between the CCD 14 and the lens 16 and between the lens
16 and the original S are varied to focus the image information carried by
the original S onto the CCD 14 at the magnification ratio of 150%.
The image information which is photoelectrically converted by the CCD 14 is
converted by the A/D converter 34 to a digital signal which is stored in
the line memory 36.
The sequencer 46 of the magnification converter 38 is supplied with a clock
signal, a synchronizing signal, and a magnification signal in timed
relation to the image scanning operation effected by the CCD 14. As the
magnification signal, a magnification signal indicative of 300%
established by the magnification table 42 shown in FIG. 4 is applied. The
sequencer 46 then specifies data addresses of the line memory 36 based on
the clock signal. The line memory 36 thus addressed by the sequencer 46
supplies Nth image data D.sub.N to the latch 48 and also supplies (N+1)th
image data D.sub.N+1. The image data items D.sub.N, D.sub.N+1 latched by
the respective latches 48, 50 are then supplied to the subtractor 52 which
then calculates their difference according to (D.sub.N+1 -D.sub.N).
A prescribed interpolation table 54 is selected on the basis of the
magnification signal which is established by the magnification table 42
for the magnification converter 38. At this time, the interpolation table
54 with respect to 300% as shown in FIG. 5 is selected. In the
interpolation table 54, levels corresponding to the difference (D.sub.N+1
-D.sub.N) calculated by the subtractor 52 are selected, and interpolated
data items r.sub.i (i=0, 1, 2) at these levels are successively indicated
by the sequencer 46 and applied to the adder 56.
The adder 56 adds the image data D.sub.N from the latch 48 and the
interpolated data items r.sub.i (i=0, 1, 2). As a result, two new image
data items are produced between the image data D.sub.N, D.sub.N+1.
In the above manner, the image information of the original S is enlarged
150% by the lens 16 of the image reader 10, and thereafter enlarged 300%
by the magnification converter 38. As a consequence, the image information
is enlarged 450% and stored in the image memory. The enlarged image
information is then supplied to an image reproducing device in which is
reproduced highly accurately without optical defects or aberrations.
While in the above embodiment image information is obtained at the
magnification ratio of 450%, image information may be obtained at other
magnification ratios that can be established by the magnification table
42. The magnification table 42 is shown as having combined magnification
ratios of 100% or larger. However, it is easy to obtain image information
at a combined magnification ranging from 50% to 100%. For example, in
order to have a combined magnification ratio of 50%, image information may
be reduced 50% in size by the optical means, or the magnification ratio
according to the optical means may be selected to be 100%, and every other
image data may be selected by the electric means for storage in the image
memory.
With the arrangement of the present invention, as described above, an
original image is reduced or enlarged in size by optical means, and read
by a photoelectric transducer device, and then magnified image information
from the photoelectric transducer device is selectively picked up or data
between image information items are interpolated by electric means, so
that image information can be obtained at a desired magnification ratio.
Accordingly, image information can be reduced or enlarged highly
accurately without optical defects or aberrations in a wide range of
magnification ratios. The arrangement required to perform the above method
is inexpensive since an expensive zoom lens is not employed as optical
means to change magnification ratios. When image information is enlarged,
image data between adjacent pixels of the original image is produced by
linear interpolation. Therefore, a smooth enlarged image of continuous
gradation can be reproduced at a large magnification ratio.
The drive system or mechanism in the image reader 10 may be simplified by
employing a relatively inexpensive zoom lens in place of the fixed-focus
lens 16.
Although a certain preferred embodiment has been shown and described, it
should be understood that many changes and modifications may be made
therein without departing from the scope of the appended claims.
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