Abstract:
An image processing apparatus comprises an image reader for inputting image data, a memory for storing the image data, a read clock generator for generating a read clock to read out the image data from the memory and a write clock generator for generating a write clock to write the image data into the memory.The read clock generator and the write clock generator vary the frequencies of their respective clocks in accordance with a magnification/reduction factor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image processing apparatus having a variable magnification/reduction function, and more particularly to a digital image processing apparatus such as a digital copying machine which can electrically magnify or reduce image data. 
     2. Description of the Prior Art 
     FIG. 1 shows a prior art image processing apparatus of the above type. 
     In FIG. 1, an image data is outputted from image reader 1 in synchronism with a frequency fω and the image data is magnified or reduced by a factor of 0 to 2. A clock generator 2 generates a clock signal having the frequency fω and a clock signal having a frequency 2fω which is used to magnify the image data by a factor of up to two. 
     The clock signal having the frequency 2fω is supplied to a clock changing circuit (variable clock circuit) 3 where the frequency of the clock signal is multipled by a factor of M (M=0 to 1) in response to a magnification factor control signal A to produce a write clock signal which is used to write the image data into a memory 4. 
     The written image data is read from the memory 4 in synchronism with a clock signal having a frequency F R  which is generated by the clock generator 5. In the circuit shown in FIG. 1, the image data is written into the memory 4 by the write clock having a frequency higher than fω, that is, the frequency M2fω (0.5≦M≦1) to magnify the image so that the image data is interpolated. 
     On the other hand, to reduce the image, the image data is written into the memory 4 by the write clock having the frequency M2fω (0≦M&lt;0.5) which is lower than the frequency fω so that the image data is interlaced. When the frequency of the write clock is equal to fω, the image data of the equal scale is produced. 
     In the image processing apparatus which uses the magnification/reduction system shown in FIG. 1, the clock signal having the frequency 2fω is necessary to magnify the image by the factor of two. Accordingly, the variable clock circuit 3 (for example, Texas Instrument rate multiplier 7497) and the memory 4 (for example, Intel 2147 high speed static RAM) must be able to operate in a high frequency region and a problem may arise in a stable operation of the circuit. 
     When fω is 10 MHz and a magnification factor of ten is required, the variable clock circuit 3 and the memory 4 must be operated by the write clock signal having a frequency of as high as 10fω=100 MHz. This is difficult to attain. 
     Further, since the data is interpolated in the magnification mode, the memory needs a capacity equal to the image data multiplied by the magnification factor (&gt;1) in order to magnify the image data. Accordingly, if the number of one line of image data is 4096 bits, the memory 4 needs the capacity equal to 4096×2=8192 its per line in order to magnify the image data by the factor of two in a main scan direction. When the Intel RAM 2147 is used, two such RAM&#39;s are required. This increases the cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to eliminate such drawbacks as above-mentioned. 
     It is another object of the present invention to provide an inexpensive image processing apparatus having a magnification/reduction function. 
     It is another object of the present invention to provide an image processing apparatus which operates in a stable manner. 
     It is another object of the present invention to provide an image processing apparatus of simple construction having a magnification/reduction function. 
     It is another object of the present invention to provide an image processing apparatus having a magnification/reduction function which is simple in construction yet operates in a stable manner. 
     It is a further object of the present invention to provide an image processing apparatus capable of magnifying or reducing an image with a relatively small capacity memory. 
     Other objects of the present invention will be apparent from the following description made in conjunction with the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a prior art image processing apparatus having a magnification/reduction function, 
     FIG. 2 shows an external view of a copying machine to which the present invention is applicable, 
     FIG. 3 shows a sectional view of a readerprinter, 
     FIG. 4 shows an image processing apparatus in accordance with one embodiment of the present invention, and 
     FIG. 5 shows an image processing apparatus having a dither processing circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 2 shows an external view of a copying machine to which the present invention is applicable. It comprises two basic units, a reader A and a printer B. The reader and the printer are mechanically and functionally separated so that they can be separately and individually used. They are connected through electrical cables. The reader B includes a control panel by which a magnification/reduction factor and the number of copies are selected. 
     FIG. 3 shows a sectional view of the reader A and the printer B. An original sheet is placed in a face-down attitude on an original sheet glass 33. A reference mount position is at the left inside as viewed from a front. The original sheet is pressed to the glass 33 by an original sheet cover 34. The original sheet is illuminated by a fluorescent lamp 32 and a light reflected thereby is focused on a plane of a CCD 31 through mirrors 35 and 37 and a lens 36. The mirrors 37 and 35 are moved at relative velocities of two to one. An optical unit comprising the light source 32 and the mirrors 35 and 37 is moved from left to right at a constant velocity through a PLL by a DC servo motor to sub-scan the original sheet. 
     A main scan direction is orthogonal to the sub-scan direction. In the present apparatus, the original sheet is electrically main-scanned by a CCD array sensor. 
     The printer B located below the reader A in FIG. 3 is now explained. A bit-serial image signal processed in the reader is transmitted to the printer in synchronism with an output clock and supplied to a laser scan optical unit 25 which comprises a laser driver, a semiconductor laser, a collimater lens, a rotating polygonal mirror, an F-θ lens, a correction optical system and so on. The image signal is supplied to the laser driver of the laser scan optical unit 25. The laser driver drives the semiconductor laser in accordance with the image signal to generate a light which is modulated by &#34;0&#34; and &#34;1&#34; image signals. The modulated light is directed to the rotating polygonal mirror in the laser scan optical system 25 so that the main scan is effected as the mirror rotates. The scan output light is directed to a reflection mirror 24 through the F-θ lens and the correction optical system of the laser scan optical unit 25 so that the light is irradiated to a specified position on a photosensitive drum 8 by the reflection mirror 24 to mainscan in the photosensitive plane. 
     The photosensitive drum 8 is rotated in a direction of an arrow at a constant speed so that an image is formed on the photosensitive plane in the sub-scan direction. 
     The photosensitive drum 8 may comprise three layers, namely a conductive layer, a photosensitive layer and an insulative layer. Process components for forming an image are arranged about the drum 8. Numeral 9 denotes a pre-discharger, numeral 10 denotes a pre-exposure lamp, numeral 11 denotes a primary charger, numeral 12 denotes a secondary charger, numeral 13 denotes a flat exposure lamp, numeral 14 denotes a developing unit, numeral 15 denotes a paper cassette, numeral 16 denotes a paper feed roller, numeral 17 denotes a paper feed guide, numeral 18 denotes a registration roller, numeral 19 denotes a transfer charger, numeral 20 denotes a separation roller, numeral 21 denotes a convey guide, numeral 22 denotes a fixing unit and numeral 23 denotes a tray. 
     The positions irradiated by the beam bear the &#34;black&#34; pixel information and they are latently imaged by the high voltage chargers 9, 11, and 12 arranged around the photosensitive drum 8 and visualized by toners of the developing unit 14. 
     When the copy papers have been loaded in the paper cassette 15, the copy paper is fed by the paper registration roller 16 to the vicinity of the photosensitive drum 8 through the paper guide plate 17, and the copy paper passes under the photosensitive drum 8 as the registration roller 18 is operated. The image visualized by the toner is transferred to the copy paper by a transfer high voltage applied by the transfer charger 19, and the copy paper having the toner image transferred thereto is fed to the convey guide 21 through the separation roller 20. Thus, the image signal from the original sheet is transferred to the copy paper. Since the toner is merely deposited on the copy paper at this stage, the copy paper is fed from the convey guide 21 to the fixing unit 22 where the toner image is fixed by a high temperature and a high voltage to form a permanent image. Then, the copy paper is ejected to the tray 23. 
     FIG. 4 shows an embodiment of the image processing apparatus of the present invention, which may be included in the reader A. In FIG. 4, an image reader 31, a clock generator 32, a memory 34 and a clock generator 35 correspond to the image reader 1, the clock generator 2, the memory 4 and the clock generator 5, respectively, of FIG. 1, and the image reader 31 includes a CCD. 
     Differences between FIG. 4 and FIG. 1 reside in that an output of the clock generator 35 is only a clock signal having the frequency fω and the variable clock circuit 3 of FIG. 1 is divided into a variable clock circuit 30 and a variable clock circuit 36. 
     The variable clock circuit 30 varies the frequency fω by a factor of X (0≦X≦1) in response to the magnification/reduction control signal B and the variable clock circuit 36 varies the frequency f R  by a factor of Y (0≦Y≦1) in response to the magnification/reduction control signal C. When X=1 and Y=1, an image of the equal scale is produced. Since the highest frequencies of the clock signals produced by the variable clock circuits 30 and 36 and fω and f R , respectively, a stable circuit operation is assured. 
     When the image is to be reduced, the factor Y is set to unity and only the factor X is varied. That is, the sampling frequency Xfω of the image data is set to be lower than the image data transfer clock frequency fω to interlace the image data to reduce the image. Since the interlaced image data is written into the memory 34, it is read out by the clock signal having the frequency f R  so that the image is reduced by the factor of X. 
     When the image is to be magnified, the factor X is set to unity and only the factor Y is varied. the image data is read from the memory 34 in synchronism with the clock signal having the frequency Yf R  and it is sampled by the output clock having the frequency f R  so that the image data is interpolated. As a result, the image data is magnified. A magnification factor is equal to 1/Y. 
     In the above magnification mode and reduction mode, either one of the factors X and Y is fixed to unity and the other is varied for the sake of simplification of the explanation, although both factors X and Y may be concurrently varied. In the latter case, a magnification factor is given by X/Y. 
     In the present embodiment, the transfer clock frequency fω and the read clock frequency f R  are different because the transfer speed of the input image data from the CCD and the scan speed in the main scan direction of the printer are different. If the transfer speed of the input image data and the scan speed of the printer are the same, the same clock frequency may be used. 
     The magnification/reduction in the sub-scan direction will be explained below. In the present embodiment, since the rotating speed of the photosensitive drum 8 of the printer B is constant, the magnification/reduction in the sub-scan direction is readily attained by switching the scan speed in the sub-scan direction of the optical unit of the reader A. By reducing the scan speed of the optical unit, the reproduced image is magnified in the sub-scan direction, and by increasing the scan speed of the optical unit, the reproduced image is reduced in the sub-scan direction. By independently setting the magnification/reduction factor in the main scan direction and the magnification/reduction factor in the sub-scan direction, the longitudinal size and the lateral size of the original image can be independently magnified or reduced. 
     The control signals B and C may be produced by a microcomputer in accordance with a specified magnification/reduction factor, or they may be produced by a switch linked to a magnification/reduction specifying lever or key. The control signals Band C may be determined by an original sheet size and/or a copy paper size. 
     The memory 34 may be a page memory, or may have two lines of capacity in the main scan direction if the apparatus processes the image on a real time basis. 
     By processing the magnified or reduced image data to dither-process by a dither processing circuit 40 as shown in FIG. 5, the image can be magnified or reduced without destroying the dither pattern. In this case, the output clock is a timing signal for the dither processing. The &#34;1&#34; and &#34;0&#34; image data after the dither processing are supplied to the printer. 
     The input image data need not be the data from the reader but it may be image data transmitted from an electronic file, a facsimile or the like. 
     As described hereinabove, according to the present invention, the image can be magnified with a simple configuration without using a high frequency clock signal. 
     Since the image data is magnified when it is read from the memory, the capacity of the memory may be small. 
     Since the magnification factor is given by 1/Y when X=1, the limitation of the operating clock 
     is not imposed and the magnification in a wide range can be attained. 
     The present invention provides an inexpensive image processing apparatus having the magnification/reduction function. 
     The present invention is not limited to the illustrated embodiment but many modifications and variations can be made within the scope of the claims.