Color image reading apparatus with an improved sensor
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to an image reading apparatus for color images, more particularly to a image reading apparatus using one-dimensional color sensors whose one picture element is comprised by three different sensor elements for sensing three primary colors; red, green and blue which respectively are successfully aligned as one image element in series. 
     2. Description of the Prior Art 
     CCD (Charged Coupled Device) one-dimensional image sensors, which are aligned in series in order to sense, for example, the three primary colors; red, green and blue are well known as a color sensor to be used in reading apparatus for color images. Such color sensors contain respective red (R), green (G) and blue (B) filters which are aligned adjacently each picture element by vapor deposition and other techniques, so that fundamentally the data are outputted serially in the order of R→G→B, while the data comprising a set of R, G and B are converted through a color conversion processing into respective data for the three primary colors for printing. 
     In such a conventional color conversion method, however, the density of image reading is equal to the picture element density of the sensor, in other words, the density of image reading can not be increased over the picture element density, for example 16 per 1 mm in general. 
     In the prior art therefore, the read image data are processed electrically in order to generate the picture elements and consequently improve the picture element density, resulting in problems such as a need for complicated software processings and longer processing time. 
     SUMMARY OF THE INVENTION 
     In order to solve the problems described hereinbefore, an object of this invention is to provide a novel image reading apparatus for color images, which realizes the image reading with fine pitch up to three times of the picture element density of the sensor through a hardware configuration only. 
     Another object of this invention is to provide an image reading apparatus for color images, which can read images with variable pitches multiplied by 3, 2 or 1 to the picture element density of the sensor, according to the capacity of a printer to be used. 
     A still further object of this invention is to provide an image reading apparatus for color images, which comprises comparatively cheap hardware for realizing the proceeding objects. 
     This invention is principally based on the fact that one picture element of the color image reading apparatus consist of each one of three different sensor elements corresponding to the three primary colors respectively, namely, this invention applies a technique which increase the apparent picture element number three times to the actual image element number by shifting by one sensor element and duplicating of three different sensor elements which are aligned one-dimensionally and repeatedly in the same order without fixing any picture element to any set of three specified sensor elements. 
     The above and further objects and features of the invention will more fully be apparent from the following detailed description with accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a construction of a scanning system of a general color image reading apparatus. 
     FIG. 2 shows a schematic diagram of an arrangement of CCD sensor arrays of the one-dimensional image sensor used in the scanning system of FIG. 1, 
     FIG. 3 is a block diagram showing the whole configuration of a signal processing system in the color image reading apparatus, 
     FIG. 4 is a schematic diagram showing a relation of the sensor elements constructing the respective picture elements of the color sensor with the respective picture elements during printout, 
     FIG. 5 is a block diagram showing construction of a color conversion processing circuit, 
     FIG. 6 is a block diagram giving a detailed construction containing a multiplying block and an adding block, 
     FIG. 7 is a timing chart explaining the operation of the multiplying block, 
     FIG. 8 is another timing chart explaining the operation of the adding block, 
     FIG. 9 is a block diagram showing construction of an image density conversion circuit, 
     FIG. 10 is a timing chart explaining the operation thereof, 
     FIG. 11 is a block diagram showing another construction of the color conversion processing circuit, and 
     FIG. 12 is a timing chart of the operation thereof. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The color image reading apparatus according to this invention will be hereinafter described in detail with reference to the drawings showing the preferred embodiment. 
     FIG. 1 shows the construction of a well known scanning system for color image reading apparatus and FIG. 2 shows the CCD array pattern of the one-dimensional CCD image sensor thereof, while FIG. 3 is a block diagram showing the entire configuration of a processing circuit for signals being read by the color sensor 1. 
     The original 101 is irradiated by the light source (a fluorescent lamp) 102 and the reflected light is transmitted through the lens array 103 to the one-dimensional CCD color image sensor (hereinafter referred to simply as &#34;color sensor&#34;) 1, sensed as the image information and converted into corresponding electric signals. 
     In the color sensor 1 with the array pattern thereof as shown in FIG. 2, four CCD sensor arrays; CCD1 through CCD4 are aligned with a slight shift in the direction perpendicular to the alignment line of respective sensor elements and combined together so as to make a sensor unit as a whole. 
     Within each picture element of the respective sensor arrays; CCD1 through CCD4, as shown in the magnified sketch of FIG. 1, the filters; R (red), G (green) and B (blue) are vapor-deposited as separate sensor elements in the alignment direction of the picture elements. 
     Moreover, respective sensor elements have the form of a parallelogram instead of quadrate in order to prevent occurrence of moire patterns. 
     Therefore, the respective sensor arrays CCD1 through CCD4 output the signals; R, G and B successively and repeatedly, which are then transmitted to the analog multiplexer 2, which is a means for connecting four CCD sensor arrays; CCD1 through CCD4 selectively with a sample hold circuit 3 so that the respective sensor arrays can operate as if they were one sensor unit as a whole. 
     The sample hold circuit 3 performs a color analysis to the signals; R, G and B, while succeeding signal amplifier 4 executes a differential amplification of black level under sensitivity correction of the signals; R, G and B. The amplified signals are converted respectively through an A/D converter 5 into digital values of 8 bits and transmitted to a color conversion processing circuit 7 after shading correction by the shading correction circuit 6. 
     The color conversion processing circuit 7 converts respective data of the shading-corrected and sensed image signals; R, G and B into C (cyan), M (magenta) and Y (yellow) for printing out by a printer and others. The color conversion processing is represented by the following equation; 
     
         Data to be printed out=r·R+g·G+b·B (1) 
    
     where r, g and b are predetermined constants depending upon respective data of C, M and Y, therefore, the equation (1) can be rewritten as the following determinant (2); ##EQU1## where r 1-3 , g 1-3  and b 1-3  are constants respectively. Namely, the respective constants r, g and b are multiplied with the sensed image data R, G and B and then the data r·R, g·G, and b·B are summed up in the color conversion processing. 
     As described hereinafter in the color image reading apparatus according to this invention, the density of the color picture elements can be increased up to three times by summing up between the adjacent picture elements. As shown in FIG. 4, three types of sensor elements; R n , G n  and B n  are aligned successively for the n-th picture element of the sensor. If it is supposed that the value (C 3n ) of the 3n-th C is calculated from the data (R n , G n , B n ) of the n-th picture element in the following equation; 
     
         C.sub.3n =r.sub.1 ·R.sub.n +g.sub.1 ·G.sub.n +b.sub.1 ·B.sub.n                                         (3) 
    
     the value (C 3n+1 ) of the 3n+1-th C is obtained from the data of the adjacent picture elements, namely, G n , B n  and R n+1  are considered as another picture element, therefore, 
     
         C.sub.3n+1 =r.sub.1 ·R.sub.n+1 +g.sub.1 ·G.sub.n +b.sub.1 ·B.sub.n                                         (4) 
    
     Furthermore, the value (C 3n+2 ) of the 3i+2-th C is obtained from the data of the corresponding adjacent picture elements, namely, B n , R n+1  and G n+1  are considered as another picture element again. 
     
         C.sub.3n+2 =r.sub.1 ·R.sub.n+1 +g.sub.1 ·G.sub.n+1 +b.sub.1 ·B.sub.n                                (5) 
    
     The color conversion processing for M and Y are carried out in the same manner. 
     As described hereinbefore, the color conversion processing is not executed once for respective sensor elements of the picture element, but repeated three times with the data of the adjacent picture elements, resulting in the picture element density equal to three times the sensing density. 
     FIG. 5 shows a block diagram of a color operation circuit 7, where the multiplying block 11 is a block for multiplication of r·R etc. and the results are transmitted successively to three adding blocks I, II and III (12, 13 and 14) from which the respective added values are transmitted respectively to the data compositing circuit 15, the functions of this circuit will be described in the timing chart thereof (FIG. 7). 
     FIG. 6 is a block diagram showing a detailed construction of the multiplying block 11 and an adding block, for example, 12, while two remaining adding blocks with the perfectly same construction are not shown for the purpose of simplification. 
     As shown in the flow chart of FIG. 7, respective data (digital data of 8 bits) of input picture element data R, G and B sensed by the color sensor 1 in the multiplying block 11 are transmitted in serial form by a parallel/serial conversion circuit 21 and then transmitted as the data DA serially to an multiplier 22 in the order of R, G and B and in synchronization with the rise of clock CK1 equal to three times of the dot clock, while a selector 23 selects one among three constants r, g, b (for example, r 1 , g 1 , b 1  in operation of C) and transmits the selected constant to the multiplier 22. The aforesaid selection is executed in synchronization with the rise of constant select clocks CK2 and CK3 generated by a select clock generating circuit 24. 
     Thus, the synchronized data r and R, g and G, and b and B are inputted into the multiplier 22, which executes the multiplications r·R, g·G and b·B successively and transmits these multiplied values through a latch circuit 25 to the adding blocks 12, 13 and 14 in synchronization with the clock CK1 inverted by an inverter 26. 
     The selector 34 in the adding blocks 12, 13 and 14 clears to &#34;zero&#34; the added data DC, which has been processed by an adder 31 and a latch 32, periodically (once for three operations). The data from a selector 34 is latched by a latch 35 and transmitted as the data DC&#39; to the adder 31 in synchronization with the output DB from the multiplying block 11. The adder 31 executes the addition of the data DB and the feed back data DC&#39; and outputs the added data DD through the latches 32, 33 in response to the clock CK1/3. 
     The output DC of the latch 32 is cleared periodically by a selector 34, and is latched by a latch 33 in synchronization with the clearing timing in order to execute the operation as expressed by the equation (1), namely, the adding blocks 12, 13 and 14 output the data r·R+g·G+b·B only to the succeeding processing block while the additions r·R+0, r·R+g·G, and r·R+g·G+b·B are executed. 
     As shown in FIG. 5, the adding blocks on right side of FIG. 6 are actually connected in parallel, however, operation differences of respective adder blocks are limited to timings of &#34;0&#34; selection by the selector 34 and the latching by a latch 35 which takes place simultaneously therewith. Namely, the selector 34 in the adding blocks I, II and III, as shown in the timing chart of FIG. 8, periodically clears to &#34;zero&#34; the output data DC from the adder 31, however, the respective blocks I, II and III have different timings of the &#34;zero&#34; clearing (refer to corresponding DC&#39;s) and the latch 33 of the respective blocks latches the data DC in synchronization with the timing of &#34;zero&#34; clearing in the selector 34 (refer to DD of FIG. 8). 
     Therefore, if the image data r·R n , g·G n  and b·B n  outputted from the adding blocks are simply represented by R&#39; n , G&#39; n  and B&#39; n , the adding block I outputs R&#39; n  +G&#39; n  +B&#39; n  and the adding block II outputs R&#39; n+1  +G&#39; n  +B&#39; n , while the adding block III outputs R&#39; n+1  +G&#39; n+1  +G&#39; n , resulting in the tripled picture element density. 
     If it is supposed that the outputs of the respective blocks I, II, III are DE n , DF n  and DG n , the data compositing circuit 15 of FIG. 5 transmits the outputs of the respective blocks to a printer after successive parallel/serial conversion thereof in the order of the DE n , DF n  and DG n . Thus, the data equal to three times the read picture element density are outputted during the conversion thereof into printing data C, M or Y in the color conversion processing circuit 7. 
     The image reading apparatus for obtaining color information of the original copy to be converted into printing data repeats scannings of the respective printing data C, M and Y in the same scanning line, three times in total. 
     The output data DH of the color conversion circuit 7 is then converted into the picture element density corresponding to the printing dot density of the output side, i.e., the printer side and transmitted to the printer. 
     FIG. 9 is a block diagram of an image density conversion circuit 8 while FIG. 10 shows a timing chart of the operation thereof. 
     This circuit 8 is applied for converting the picture element density in the main scanning direction, i.e., picture element alignment direction of the color sensor 1, while the scanning velocity by the optical system is appropriately changed in the sub scanning direction (the density can be increased when the velocity is reduced). 
     If the reading image density of the color sensor 1 is 16 lines/mm, the output DH of the data compositing circuit 15 will have the density of 48 lines/mm; three times the above density. On the other hand, the dot clock CK4 synchronized with the change of DH generates latch clock in a latch circuit 44 through a clock generating circuit 41 for converting image density. An image density conversion data signal is usually preset (for example, 24 lines/mm) according to the printing dot density in output side. The clock generating circuit 41 for image density conversion generates a clock RCK whose frequency is modified from that of the clock CK4 based on these image density conversion data signals and transmits the clock RCK to an AND gate 42. 
     An image density conversion command signal is a negative logic signal. When the image density conversion command signal is &#34;L&#34;, the clock RCK outputted from the clock generating circuit 41 for image density conversion as the latch clock is transmitted to the latch 44 through the AND gate 42 and the OR gate 43, while when the same is &#34;H&#34;, CK4/3 as the latch clock is transmitted to the latch circuit 44 through the AND gate 45 and the OR gate 43. Therefore, the latch 44 outputs the picture element data equal to or less than 48 lines/mm in response to the image density conversion data according to the printing dot number if the output side of the image density conversion command signal is &#34;L&#34; and outputs the data of 16 lines/mm equal to the density of the reading picture elements if &#34;H&#34;. 
     Moreover, a conventional system as shown in FIG. 11 may be used as the color conversion processing circuit, namely, the color conversion processing circuit 7 can be constructed by three multipliers 51, 52 and 53 and an adder 57. 
     FIG. 12 gives the timing chart of the above circuit, wherein the multipliers are provided for the respective data R, G and B, the respective operation results are synchronized with the latches 54, 55 and 56, while three data r·R, g·G and b·B are added in parallel by the adder 57 and the operation results are latched with the clocks inverted from latch clocks of the above latches 54, 55 and 56 in order to obtain the printing data C, M or Y. If the data from the adder 57 is latched by a thinned-out clock, variable magnification (electric contraction) may be realized, the data C, M and Y being obtained by three times scannings. This circuit has an cost disadvantage in comparison with the system as shown in FIG. 5 because three considerably expensive multipliers are used. 
     As described hereinabove in detail, the color image reading apparatus according to this invention can execute image reading with a density up to three times the picture element density of the one-dimensional color sensor without any complicated and relatively time-consuming software processing. It is also allowed to adjust the reading density lower if the capacity of the printer and others is limited. 
     As this invention may be embodied in several forms without departing from the spirit of essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the meets and bounds of the claims, or equivalence of such meets and bounds thereof are therefore intended to be embraced by the claims.