JP2779804B2 - Color image reader - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image reading apparatus, and more particularly, to a color density included in a digital color copying machine or the like and representing the intensity of red light, green light, and blue light, respectively. The present invention relates to a color image reading apparatus that forms signals and generates signals representing the ink amounts of cyan, magenta, and yellow based on these color signals. 2. Description of the Related Art Conventionally, as this type of color image reading apparatus, for example, the one shown in FIG. 2 is known. In FIG. 2, reference numeral 1 denotes an original on which a color image is drawn. The original 1 is irradiated with white light of a light source 4 which moves in the direction of arrow 3 by receiving a driving force from a motor 2, and its reflected light is indicated by an arrow. In the image sensor 5 composed of a plurality of CCD elements arranged at right angles to the three directions, the intensity of each of the red, green and blue colors of the reflected light is converted into color signals R, G, and B, each of which represents a voltage value. Is converted. These color signals R, G, B are converted from the reflection intensity of each color into density values of each color by a logarithmic conversion circuit 6 and output as color density signals (the reflectance value is Rf, and the color density signal value is Assuming that D, the logarithmic conversion circuit calculates D = -logRf.) These color density signals are converted from analog values to digital values by the A / D converter 7, and digital color density signals DR ', D
G 'and DB' are sent to the shading circuit 8. The shading circuit 8 corrects the digital color density signals DR ″, DG ″, D after correcting errors caused by uneven light emission of the light source 4 and variations in the characteristics of the CCD elements constituting the image sensor 5.
B "is supplied to the masking processing circuit 9. In the masking processing circuit 9, the digital color density signal D
Output signals C, M, and Y representing the ink amounts of cyan, magenta, and yellow are formed based on R ", DG", and DB ", and these output signals C, M, and Y are subjected to a halftone process such as dither processing. It is supplied to a printing device (not shown) via a processing circuit 10. Reference numeral 11 denotes a central processing unit for controlling the circuits 7 to 10 and the motor 2. As a specific example of the masking processing circuit 9, For example, as disclosed in JP-A-60-216670, the result of multiplication of coefficients a00 to a22 representing the characteristics of the printing ink and the digital color density signals DR ", DG", DB "is fixed for each color. It is composed of a read-only memory for temporarily storing coefficients and an adder for adding outputs of these read-only memories. In general, the coefficients a00 to a22 are set so that the hues of pixels printed with respect to various color samples are close to each other. Specifically, each of the coefficients a00 to a22 is (L
*, A *, b *) The square error ΔE ² ΔE ² = Σ ｛(L * −) between a number of color samples represented by the values and the (L * ′, a * ′, b * ′) values of the print color. L * ′) ² + (a * −a * ′) ² + (b * −b * ′) ²・ ・ ・ (Equation 1) is set to be minimum. [INVENTION Problems to be Solved point] However, in the conventional masking processing circuit 9, the value of the coefficient a00~a22 is the squared error Delta] E ² calculated was set to a minimum at (Equation 1) Therefore, although a good result can be obtained for a document containing various hues on average, a document having a biased hue (for example, a document containing many sea and sky images, or a person However, there is a problem that a natural sensation cannot always be given to the original document centering on the image. SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a color image reading apparatus capable of obtaining a natural copy image even in an original having a biased hue. Means for Solving the Problems The present invention has been made in view of the fact that a natural image can be obtained by selectively using a coefficient that improves the reproducibility of the main hues in a document. The gist of this is that a determination means for determining a dominant hue in a color document, a memory storing a plurality of color masking coefficients set according to the hue, and a plurality of color masking coefficients stored in the memory A color masking coefficient corresponding to the hue determined by the determination means is selected from among the above, and using the selected color masking coefficient, the red, green, and blue color signals obtained by reading the color original are cyan, And color signal forming means for converting into magenta and yellow print signals. [Operation of the Invention] In the color image reading apparatus according to the above configuration, since the color masking coefficient is selected based on the dominant hue in the document, the color shift of the printed image with respect to the predetermined hue is reduced. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings. 1 and 3 are views showing a color image reading apparatus according to one embodiment of the present invention. In the figure, reference numeral 21 denotes a document glass table on which a document 22 depicted in a color image is placed, and a copying machine for the document 22 has an exposure lamp 23, a first mirror 24,
An optical system 29 including a second mirror 25, a third mirror 26, a lens 27, and an image sensor 28 is a central processing unit (CPU) 30.
The driving force is obtained from the motor 31 controlled by the controller 31 and the motor 31 is repeatedly moved in the arrow 32 direction. As the optical system 29 moves, the original 22 is irradiated with white light, and the reflected light is reflected by first, second, and third mirrors.
The light passes through 24, 25, 26 and the lens system 27 and is supplied to the image sensor 28. The image sensor 28 is composed of three rows of CCD elements each having a filter for selectively transmitting red light (R), green light (G), and blue light (B). Output analog color signals R, G, and B, each representing the intensity of a red component, a green component, and a blue component in the reflected light by a voltage value. The scanning of the document 22 is performed three times for one document. The reason that the scanning is performed three times for one document is to perform printing with cyan ink based on the first scanning and magenta based on the second scanning. This is because printing with ink is performed and printing with yellow ink is performed based on the third scan. The analog color signals R, G, output from the image sensor 28,
B is converted from an analog value to an 8-bit digital value by A / D converters 33, 34, 35 every three scans, and is converted to digital color signals DR, DG, DB by shading circuits 36, 37, 38. Sent out. Shading circuits 36, 37, 38 are exposure lamps
After correcting errors due to uneven light emission of the light source 23 and variations in the characteristics of the CCD elements constituting the image sensor 28, the corrected digital color signals DR, DG, and DB are supplied to a color masking circuit 39. The color masking circuit 39 includes a random access memory (random access memory (hereinafter, simply referred to as a ram)) having an 8-bit address terminal and an 8-bit data input terminal as shown in FIG. Prepare each digital color signal DR, DG, DB,
It includes a configuration in which the output signals of 41 and 42 are supplied in parallel to the input terminal of the adder 43. The color masking circuit 39 supplies the digital color signals DR, DG, and DB to the address terminals of the rams 40, 41, and 42, respectively, as described in detail below, and is represented by the digital color signals DR, DG, and DB. The data OR, OG, and OB for the respective ink amounts of the cyan ink, magenta ink, and yellow ink corresponding to the intensity of the red component, the intensity of the green component, and the intensity of the blue component of the reflected light are output, and these cyan inks, The output signals C1 and M1 representing the ink amounts of the cyan, magenta and yellow inks by respectively adding the data on the ink amounts of the magenta and yellow inks.
Form Y1. As described above, in this embodiment, one original
Since only the ink amount of cyan ink, magenta ink or yellow ink is calculated in the scan of 22, the data of the rams 40, 41, 42 must be rewritten after the end of each scan and before the start of the next scan. As shown in FIG. 6, selectors 44, 45, 46 are provided between the shading circuits 36, 37, 38 and the rams 40, 41, 42, and the rams 40, 41, 42
Selectors 47, 48, and 49 are interposed between the adder 43 and the adder 43, respectively, and stored in a read-only memory (hereinafter simply referred to as ROM) 50 under the control of the central processing unit 30. Based on a22, the central processing unit 30 performs a predetermined operation to calculate data related to inks of different colors,
Transfer to 40,41,42. The output of the color masking circuit 39 is supplied to a printing device (not shown) via a binary / halftone processing circuit 51 for performing dither processing and the like, and is supplied to a printing device (not shown) via predetermined processing. Therefore, in the present embodiment, the optical system 29 and the A / D converters 33, 34, 3
5 constitutes a color signal forming section as a whole, and the rams 40, 4
Reference numerals 1 and 42 constitute a conversion table. Next, data on the amount of ink held in the rams 40, 41, 42 will be described. Data on ink amount This is a logarithmic value of the operation result on the right side when the digital color signals DR, DG, and DB are changed using the determinant shown below. Note that a0
0 to a02 are constant coefficients determined in advance by the spectral reflection characteristics, printing characteristics, etc. of the cyan ink used in the printing device (not shown), and a10 to a12 are also the spectral reflection characteristics, printing characteristics, etc. of the magenta ink. Is a constant coefficient determined by Also, a20
A22 are constant coefficients determined by the spectral reflection characteristics, printing characteristics, and the like of the yellow ink. These coefficients a00 to a22 are stored in the read-only memory 50 for a plurality of sets corresponding to a plurality of hues for which reproducibility is important, as will be described in detail later. Further, C, M, and Y indicate the amounts of cyan ink, magenta ink, and yellow ink, respectively. Continuing with the description of the data regarding the ink amount, when printing with cyan ink, the logarithmic value of the calculation result of a00 × DR when the value of the digital color signal DR is changed is stored in the RAM 40 and the RAM 40. 41 has a digital color signal DG
The logarithmic value of the calculation result of a01 x DG when the value of is changed is stored, and the log 42 of the calculation result of a02 x DB when the value of the digital color signal DB is changed is stored in the RAM 42. Have been. On the other hand, when printing with magenta ink, when the values of the digital color signals DR, DG, and DB are respectively changed, 10a × DR,
The logarithmic values of the calculation results of a11 × DG and a12 × DB are held in rams 40, 41, and 42, respectively. Similarly, when printing with yellow ink, the values of digital color signals DR, DG, and DB are stored. A20 × DR, a21 × DG, a22 × D when
The logarithmic value of each operation result of B is stored in the rams 40, 41, and 42, respectively. When reading the data relating to the ink amount from these rams 40, 41, 42, the rams 40, 41, 42 are switched to the read mode in response to the write / read control signal W / R supplied from the central processing unit 30. Selectors 44-49
Supplies signals supplied from the shading circuits 36 to 38 to the address terminals of the rams 40, 41, 42 by a bus control signal supplied from the central processing unit 30, and outputs the output signals of the rams 40, 41, 42 to an adder 43. , So that the digital color signals DR, DG,
Data relating to the ink amount stored at the address indicated by the value of DB is output to the adder 43 from the data input / output terminal. On the other hand, when the address signal is supplied from the central processing unit 30, the rams 40, 41, and 42 are in the write mode, and the central processing unit 30 is in charge of the new ink amount supplied to the data input / output terminal via the data bus DB. Data is sequentially written to addresses appearing on the address bus AB.
An example of data relating to the amount of ink held in the rams 40, 41, 42 in this manner is shown in the table below. In the table below, a00 = 10110
010 and the digital color signal value from 00000000 to 1111111
The data on the amount of ink when it is changed to 1 is shown. The data on the ink amount read from each of the rams 40, 41, and 42 is supplied to the adder 30.
43 is added. Therefore, the adder 43
The output signal output from the printer indicates the amount of cyan ink, magenta ink or yellow ink. Based on the output signal from the adder 43, a printing device (not shown) outputs a partial image of cyan, magenta and yellow. When the partial images for each color are combined, the image drawn on the original 22 is duplicated. Next, the coefficient for calculating the data on the amount of ink
a00 to a22 will be described. As described above, the coefficients a00 to a22 of the present embodiment enhance the reproducibility of a specific hue over the reproducibility of other hues. Specifically, (L *, a *) of a color sample in a uniform color space , b *) value and (L * ', a *', b
* ') Square error ΔE ² with a load of color k applied to the value
A00 to a22 (hereinafter, 式 aij｝ k
Is selected. ΔE ² = {Mk} (Lk * −Lk * ′) ² + (ak * −ak * ′) ² + (bk * −bk * ′) ² ｝ (Equation 2) The coefficients a00 to a22 are specific colors (for example, blue) ), And the coefficient is set so that the chromaticity deviation of the specific hue is smaller than the chromaticity deviation of the other hues. Therefore, a plurality of sets of such coefficients {aij} k are prepared for each different hue, and are stored in the read-only memory 50. At the time of printing, a specific set is selected from a plurality of sets as described later in detail, and the central processing unit 30 calculates data on the ink amount while sequentially reading out the coefficients a00 to a22 constituting the set. In this embodiment, the read-only memory 50 stores the coefficients a00 to a22 of the above-described sets.
Storage capacity of 50 can be relatively small as about 6 bytes, the data is stored directly relating to the ink amount in the read only memory 50, as 8-bit each data storage capacity of 2 ⁸ × 6 = 1.5 (kilobytes) Is required for each set {aij} k, which causes an increase in the storage capacity of the read-only memory 50. The color image reading device according to the present embodiment further includes line rams 52, 5 connected in parallel to shading circuits 36, 37, 38.
The outputs of the line rams 52, 53, 54 are supplied to a data input / output terminal of the central processing unit 30. These line rams 52, 53, and 54 are each composed of a predetermined coefficient set 係数 ai
The digital color signals DR, DG, and DB output from the shading circuits 36, 37, and 38 are temporarily stored when j｝ k is selected, and the central processing unit 30 determines the dominant hue of the document 22. Provide data for That is, when the user of the color image reading apparatus according to the present embodiment specifies the pre-scan mode with a mode designating switch (not shown) prior to copying the original document 22, the central processing unit 30 communicates via the communication system 55. In response to the transmitted pre-scan mode signal, the printer deactivates a printing device (not shown), and gives an operation command to the optical system 29 to start scanning the document 22. The digital color signals DR, DG, and DB are supplied to the line rams 52, 53, and 54 via the A / D conversion circuits 33, 34, and 35 and the shading circuits 36, 37, and 38 along with the scanning of the document 22, so that the central The processing device 30 forms a histogram of the hues of the document 22, determines the dominant hue of the document 22, and then determines the coefficient set {aij} k. When copying is started without specifying the prescan mode, a set of hue coefficients directly specified by the operator or a set of average hue coefficients expressed by (Equation 1) is specified. Next, the operation of this embodiment will be sequentially described with reference to the flowcharts shown in FIGS. When the operator desires color copying of the original 22 and places the original 22 at a predetermined position on the original glass table 21 and selects the prescan mode, the central processing unit 30 selects the prescan mode in step S1. Detected (Y), a pre-scan subroutine SR1 described later is executed. If the result of the determination in step S1 is no (N), it is determined whether or not coefficient data for a specific hue is designated ( Step S
2) If the determination result of step S2 is YES (Y), the switch for hue designation is scanned to read the hue designated by the operator, and the switch operated from a plurality of coefficient sets based on the switch operation Is selected (step S3). On the other hand, when the hue designating switch is not operated, an averaged optimized coefficient set determined according to (Equation 1) is selected (step S).
Four). When the pre-scan mode SR1 starts, as shown in FIG. 8, the central processing unit 30 initializes a histogram set in a predetermined memory space (step S1).
5) Then, an instruction is given to turn on the exposure lamp 23 (step S6). The motor 31 starts normal rotation in response to an instruction from the central processing unit 30, and starts pre-scanning of the document 22 (step S7). By the start of the prescan, the shading circuits 36, 37, and 38 output digital color signals DR, DG, and DB appropriately corrected. Accordingly, the central processing unit 30 reads the hues of the respective pixels from the line rams 52, 53, 54 (step S8), and determines to which of the spaces Ri the hue of the read pixels divides the uniform color space into a predetermined number. (Step S9), it is added to the histogram (Step S10). In this way, while performing the prescan for the entire range of the document 22 while creating the histogram (steps S8 to S10), the process waits until the result of the determination in step S11 becomes YES. Eventually, when the scanning of the entire range of the document 22 is completed, the determination result of step S11 becomes YES (Y), so that the central processing unit 30 gives an instruction of reversal to the motor 31 and returns the optical system 29 to the initial position (step S12). Thereafter, control returns to the main routine shown in FIG. When the histogram is completed in this way, the central processing unit 30 determines the hue that appears most frequently based on the histogram, and determines a set of coefficients corresponding to the hue (step S13). When the set of coefficients for the dominant color of the document 22 is determined in this way, the central processing unit 30 calculates data on the cyan ink using the coefficient ｛aij｝ k, and Write to 41 and 42 (Step S1
Four). Eventually, when the switch for starting copying is operated, the central processing unit 30 instructs the exposure lamp 23 to light up, instructs the motor 31 to rotate forward, and starts the first scan (step S1).
Five). When the first scan is completed in this way, the central processing unit 30 repeats steps S14 to S15 to calculate data relating to the magenta ink, and performs the second scan. Similarly, when the printing for the magenta ink is completed, steps S14 to S15 are repeated again to perform printing with the yellow ink. In the above embodiment, the data relating to the amount of ink held in the rams 40, 41 and 42 is rewritten each time the document is scanned. However, the data relating to the amount of ink for three colors is stored in the large-capacity ram. May be. Further, in the above embodiment, the description regarding the sign of a00 to a22 is omitted, but since it may be negative depending on the coefficient, it is preferable to use a type that can perform signed addition as the adder 43. . At this time, as coefficient data to be written to the ram, the most significant bit is a sign bit, and it is known in advance whether a complement is written or which data is a negative number. , 42 and the adder 43, and for the negative coefficient, the central processing unit 30 may control the sign control circuit to perform a negative operation. [Effects of the Invention] As described above, according to the present invention, the data relating to the amount of ink can be changed according to the dominant hue of the original, so that the original having a characteristic hue can be copied in a natural state. The effect that can be obtained is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block circuit diagram showing a configuration of a color image reading device according to an embodiment of the present invention, and FIG. 2 is a block circuit diagram showing a configuration of a conventional color image reading device. FIG. 3 is a block diagram showing a detailed configuration of an optical system of the color image reading apparatus according to one embodiment; FIG. 4 is a plan view showing a pin arrangement of a ram used in a masking processing circuit according to one embodiment; FIG. 5 is a block circuit diagram showing a schematic configuration of a color masking circuit of one embodiment, FIG. 6 is a block circuit diagram showing a detailed configuration of a color masking circuit of one embodiment, and FIG. 7 is a main routine of one embodiment. FIG. 8 is a flowchart showing a prescan subroutine of one embodiment. 21: Original glass table, 22: Original, 28: Image sensor, 29: Optical system, 30, Central processing unit, 33-35, A / D converter, 36-38, Shading circuit, 39: color masking circuit, 40 to 42: ram, (conversion table), 43: adder, 50: read-only memory, 52 to 54: line ram.

Claims (1)

(57) [Claims] Determining means for determining a dominant hue in a color document; a memory storing a plurality of color masking coefficients set in accordance with the hue; and a plurality of color masking coefficients stored in the memory. While selecting a color masking coefficient according to the determined hue, using the selected color masking coefficient, the red, green, and blue color signals obtained by reading the color original are cyan, magenta,
A color image reading apparatus comprising: a color signal forming unit that converts each of the yellow print signals. 2. The color masking coefficients stored in the memory are set so that a chromaticity difference between a target color and a print color in a certain hue is smaller than a chromaticity difference in another hue. Item 2. The color image reading device according to Item 1.