JP3733241B2 - Image reading apparatus and computer-readable storage medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus suitable for use in an image reading apparatus having an RGB 3 line sensor and a computer-readable storage medium used in the apparatus.
[0002]
[Prior art]
Conventionally, in an image reading apparatus that reads an original image while scanning and moving an RGB three-line color sensor, a phase shift occurs between output RGB signals due to uneven scanning speed, vibration, sensor placement accuracy, and the like. Occurs. This phase shift may occur or change due to component accuracy during assembly, temperature, changes with time, and the like. As a result, the color blurs at the edge portion of the output image, and a failure such as a malfunction of the character area determination circuit appears. For this reason, it is necessary to make the accuracy stricter as the read pixel accuracy increases.
[0003]
On the other hand, in the past, firstly, it has been dealt with by increasing the accuracy of parts. Secondly, RGB signals are taken out of the apparatus while scanning a document, taken into a computer, and RGB phases are measured to obtain information for correction.
[0004]
[Problems to be solved by the invention]
However, the first method for increasing the accuracy of the component leads to an increase in the cost of the component. Further, in the future, as the pixel reading density increases, it is necessary to improve the component accuracy, and there is a problem that a solution that does not depend on the density is required.
[0005]
In addition, the method of extracting the RGB signals from the outside of the product and causing the computer to process it is necessary to provide an interface circuit for signal extraction that is not necessary for the product, leading to an increase in cost and size of the product. In addition, it takes a lot of time and effort to import the image into a computer, calculate the amount of phase shift, and input the correction amount to the product side. There was a problem.
[0006]
The present invention has been made to solve the above-described problem, and aims to improve reading accuracy when a three-line sensor reads the same pixel.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the image reading apparatus according to the present invention, the first, second, and third color signals are respectively scanned and read to output first, second, and third color signals. Image reading means, first calculation means for multiplying and adding each pixel value adjacent to the sub-scanning direction in the first color signal by a coefficient, and pixel value adjacent to the sub-scanning direction in the second color signal The image is obtained by comparing the absolute value of the signal obtained from the second calculation means for multiplying and adding each by a coefficient, the outputs of the first and second calculation means and the third color signal with a threshold value. A determination unit that determines whether the color is chromatic or achromatic, and outputs a determination signal; a count unit that counts the determination signal that determines the chromatic color; and each image while sequentially changing the coefficient of the achromatic image Let the reading means read The Create a counting means count value and a table showing the relationship between the coefficient of, are provided and control means for said count value to detect a coefficient which minimizes this table when.
[0008]
In the computer-readable storage medium according to the present invention, the image is main-scanned and read by the first, second, and third image reading means, and the first, second, and third color signals are output. Image reading processing, first calculation processing for multiplying each pixel value adjacent in the sub-scanning direction in the first color signal by a coefficient, and pixel value adjacent in the sub-scanning direction in the second color signal The image is obtained by comparing the absolute value of a signal obtained from the second calculation process for multiplying and adding each by a coefficient, the output of the first and second calculation processes, and the third color signal with a threshold value. A determination process for determining a chromatic color or an achromatic color and outputting a determination signal; a count process for counting the determination signal for determining the chromatic color; and each image while sequentially changing the coefficient of the achromatic image Reader To create a table showing the relationship between the count value of the count process at that time and the coefficient, and to cause the computer to execute a control process for detecting the coefficient that minimizes the count value from the table. I remember the program.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a reading unit of a color copying machine according to an embodiment of the present invention.
FIG. 2 shows the configuration of the CCD line sensors 101 to 103 in FIG. 1, where DB is the distance between the B sensor and the G sensor, and here it is a distance of 8 pixels at the same magnification scanning. DR is a distance between the R sensor and the G sensor, and here is a distance of 8 pixels at the same magnification scanning.
[0010]
In FIG. 1, reference numerals 101 to 103 denote CCD line sensors that read an image of a document in the main scanning direction, and output R, G, and B signals, respectively. Reference numerals 104 to 106 denote amplifiers that amplify the outputs of the line sensors 101 to 103. Reference numerals 107 to 109 denote A / D converters that convert the output signals of the amplifiers 104 to 106 into 8-bit digital signals. Reference numerals 110 to 112 denote shading correction circuits that correct luminance unevenness between the sensor and the optical system.
[0011]
Reference numeral 113 denotes an R signal line delay unit. Since the distance between the RGs of the line sensors 101 and 102 is 8 pixels and the GB distance is 8 pixels at the same magnification scanning, the delay is 8 + 8 = 16 lines. Do. The number of delay lines can be changed by the CPU 135.
[0012]
Reference numeral 114 denotes a G signal line delay unit. Since the distance between GBs of the line sensors 102 and 103 is equal to 8 pixels at the same magnification scanning, a delay of 8 lines is performed here. The number of delay lines can be changed by the CPU 135.
[0013]
With these configurations, in the case of an ideal optical system, the output of the delay unit 113 (R: first color signal), the output of the delay unit 114 (G: third color signal), and the shading correction circuit 112 outputs (B: second color signal) are output to the same pixel at the same timing. That is, the phases in the RGB sub-scanning direction match.
[0014]
The output R signal of the R line delay unit 113 is then input to the 1 line delay unit 115, and the output value is multiplied by the value (1-p) of the coefficient register 117 by the multiplier 121. Further, the R signal not delayed by one line is multiplied by the value (p) of the coefficient register 118 and the multiplier 122. The output values of the multipliers 121 and 122 are added by the adder 125.
[0015]
The output B signal of the shading correction circuit 112 is then input to the 1-line delay unit 116, and the output value is multiplied by the value (1−q) of the coefficient register 119 by the multiplier 123. Further, the B signal not delayed by one line is multiplied by the value (q) of the coefficient register 120 by the multiplier 124. The output values of the multipliers 123 and 124 are added by the adder 126. The coefficient registers 117 to 120 can be rewritten by the CPU 135.
[0016]
Next, the output value (R) of the adder 125, the output value (G) of the delay unit 114, and the output value (B) of the adder 126 are input to the input masking circuit 127, and the following calculation is performed.
R ′ = a00 × R + a01 × G + a02 × B
G ′ = a10 × R + a11 × G + a12 × B
B ′ = a20 × R + a21 × G + a22 × B (1)
Here, a00, a01, a02, a10, a11, a12, a20, a21, a22 are coefficients.
[0017]
The output value of the input masking circuit 127 is input to the color space conversion circuit 128, and the following calculation is performed to obtain L, CA, and CB signals.
L = (R + 2G + B) / 4
CA = (RG) / 2
CB = (R + G-2B) / 4 (2)
The output value of the color space conversion circuit 128 is input to the spatial filter circuit 129 and the color determination circuit 133.
[0018]
The color determination circuit 133 compares the absolute values of CA and CB with predetermined threshold values Tca and Tcb, and if both are equal to or greater than these threshold values, outputs an IRO signal as 1 as a chromatic color. When the color is achromatic, the IRO signal is output as 0.
This IRO signal is input to the counter circuit 134, and the number of 1's of the IRO signal is counted.
[0019]
The IRO signal is also input to the spatial filter 129. The spatial filter 129 performs edge enhancement or smoothing processing. Spatial filter coefficients can be switched by an IRO signal.
[0020]
The output signal of the spatial filter 129 is input to the color space conversion circuit 130, and the following calculation is performed to obtain RGB output.
R = (4L + 5CA + 2CB) / 4
G = (4L-3CA + 2CB) / 4
B = (4L + CA + 6CB) / 4 ─── (3)
[0021]
The output signal of the color space conversion circuit 130 is subjected to data conversion by the LOG conversion and output masking circuit 131 to obtain C, M, Y, and K signals. This is done by table conversion. These CMYK signals are output to the printer 132 and printed. The CPU 135 executes processing by a control program stored in the storage medium 136 constituting the present invention.
[0022]
Next, the color misregistration automatic correction operation will be described. This is an operation mode used when the amount of color misregistration is likely to change when an optical system is assembled at a factory, or when parts of the optical system are replaced on the market.
First, a test document containing a plurality of black lines parallel to a white background is placed on the document table so that the black lines are parallel to the line sensor. Then, the line sensor is scanned in a direction (sub-scanning direction) perpendicular to the line sensor at a speed at which an equal-magnification image is obtained. Here, if the optical system is ideal with respect to the luminance of the document, the RGB signals should overlap, but in reality, the signals are shifted by a certain distance. It is also conceivable that the three colors do not overlap because the MTF is different for the three colors.
[0023]
FIG. 3 shows an output example of the RGB line sensor when the black line is read. In the example of FIG. 3, R and B are shifted by 3 pixels each centering on G. In FIG. 3, if one address is 0.1 pixel, the R signal is shifted by 0.3 pixel from the G signal, and the B signal is shifted by 0.3 pixel from the G signal.
[0024]
In this case, when the read image is reproduced as it is, color components appear on both sides of the black line. Therefore, when such a document image is scanned and read, the counter circuit 134 counts chromatic color pixels.
[0025]
The above information is obtained by setting the R line delay unit 113 to 16 line delay as described later, the G line delay unit 114 to 8 line delay, and the coefficients p and q of the coefficient register to 1.
In this example, since the images are read in the order of RGB, if R is brought closer to G by 0.3 pixels, that is, if the pixel distance between R and G is 7.7 pixels, the phase of R and G Will match. Similarly, if B is brought closer to G by 0.3 pixels, that is, if the pixel distance between G and B is 7.7 pixels, the phases of G and B match. In this way, there can be no color misregistration.
[0026]
In terms of R, the interpolation is performed on two lines. For R, the pixel on the seventh line is multiplied by a coefficient of 0.3, the pixel on the eighth line is multiplied by a coefficient of 0.7, and these are added. Can be obtained. G can be obtained by multiplying the pixel on the seventh line by a coefficient of 0.3, multiplying the pixel on the eighth line by a coefficient of 0.7, and adding them.
In order to obtain this result, the delay amount of the R line delay unit 113 is set to 16 lines, p of the coefficient registers 117 and 118 is set to 0.7, the delay amount of the G line delay unit 114 is set to 8 lines, and the coefficient register 119 is set. , 120 by setting q to 0.7.
[0027]
According to the above description, when color misregistration occurs, even when a black and white document is read, chromatic colors are counted at the image edge portion in the sub-scanning direction. Will not be counted. In an actual image reading apparatus, vibration occurs when the sensor moves. For this reason, in addition to the amount of color shift when there is no vibration (due to scanning speed accuracy and magnification accuracy of the optical system), color shift due to vibration is added.
[0028]
For this reason, even if the values of p and q are optimized, a certain amount of chromatic colors are counted when a black and white document is read. That is, even if the count value is not 0, the minimum condition can be considered as the minimum color shift condition. In the embodiment of the present invention, the coefficients p and q that minimize the color misregistration are obtained from the chromatic color count value without adding any hardware.
[0029]
Next, a first embodiment of the present invention will be described.
First, the test document is read with the R and G pixel distance of 7.5 pixels and the B and G pixel distance of 7.5 pixels, and the count value at this time is read. This is repeated 4 times and the count value is added. The reason for reading a plurality of times is that the count value obtained by reading is not constant due to electrical noise and vibration of the optical system, and is averaged. Next, with the pixel distance between R and G being 7.5 pixels, the pixel distance between B and G is 7.6 pixels, the count value is read, this is repeated four times, and the count value is added.
[0030]
Similarly, while changing the pixel distance of R and G from 7.5 pixels to 8.5 pixels, the pixel distance of B and G is sequentially changed from 7.5 pixels to 8.5 pixels, and counting is performed under each condition. Find the sum of values.
Then, a condition that minimizes the count value is found from the table created by the above procedure, and is set as the pixel distance to be corrected.
[0031]
These obtained correction values are stored in a memory that is not erased even when the power is turned off. This eliminates the need to obtain the correction value again when the power is turned on next time. In addition, since it is not necessary to extract the RGB signal to the outside of the product, it is not necessary to provide an interface circuit for signal extraction. Further, an image is captured into the computer, the phase shift amount is calculated, and the correction amount is input to the product side. Thus, the operation can be simplified and the working time can be shortened.
[0032]
The test document used at this time can be output as a specific pattern from a printer to which the present apparatus is connected. Accordingly, it is not necessary to have a specific document even when the above adjustment is performed in the market, and it is possible to prevent an erroneous document from being used.
Further, since the original for adjustment is merely drawn with a black straight line, even if a low-resolution printer is used, it is not affected by jaggies and can be used without any problem.
[0033]
At the time of the copy operation, whether to perform the color copy operation or the monochrome copy operation is determined depending on whether or not the document includes chromatic color pixels. Therefore, the original is scanned before the copying operation is performed, and the count value of the counter circuit 134 is read by the CPU. If this count value is equal to or greater than a predetermined value, it is determined that the original is a color original, and a color copy operation is performed. This is a color / monochrome automatic identification operation that has been performed conventionally.
[0034]
Next, a second embodiment of the present invention will be described.
In the first embodiment, when the minimum value is obtained from the count value table, the count value is not constant, and a different result may be obtained for each sampling. The cause is considered to be large electrical noise and vibration of the optical system. In this case, there is a high possibility that the minimum value of the count value is not a true correction value.
[0035]
Such a case can be solved by averaging the sampled value with the count value in the adjacent condition. Thereby, the minimum value can be obtained accurately.
[0036]
Next, a third embodiment of the present invention will be described.
In the first embodiment, the count value is obtained while changing both the R and G pixel distances and the B and G pixel distances. However, in this embodiment, the R and G pixel distances are fixed to 8 pixels. Then, the count value is obtained by sequentially changing the pixel distance of B and G from 7.5 pixels to 8.5 pixels, and the minimum value is set as the correction value of the pixel distance of R and G.
According to the present embodiment, the number of operations for obtaining the count value can be reduced, so that the product shipment efficiency at the factory can be improved and the product cost can be reduced.
[0037]
Note that the object of the present invention is to use a storage medium storing software program codes for realizing the above-described embodiments in a system or apparatus, and the program code stored in the storage medium by the CPU of the system or apparatus. It can also be achieved by reading and executing.
In that case, the program code itself read from the storage medium realizes the functions of the above-described embodiment, and a storage medium such as the storage medium 136 shown in FIG. This constitutes the present invention.
[0038]
As the storage medium, a semiconductor memory such as ROM or RAM, an optical disk, a magneto-optical disk, a magnetic medium, or the like may be used. These may be a CD-ROM, a floppy disk, a magnetic medium, a magnetic card, a nonvolatile memory card, or the like. It may be configured and used.
[0039]
Therefore, the above-described implementation is also possible when this storage medium is used in another system or apparatus other than the system or apparatus shown in FIG. 1, and the system or computer reads and executes the program code stored in this storage medium. A function equivalent to this embodiment can be realized, and an equivalent effect can be obtained, thereby achieving the object of the present invention.
[0040]
Further, when an OS or the like running on the computer performs part or all of the processing, or an extended function board in which a program code read from a storage medium is inserted into the computer or an extended function connected to the computer Even when the CPU or the like provided in the extended function board or the extended function unit performs part or all of the processing based on the instruction of the program code after being written in the memory provided in the unit, it is equivalent to the embodiment. A function can be realized and an equivalent effect can be obtained, and the object of the present invention can be achieved.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to perform color misregistration correction without increasing the accuracy of components, and therefore, there is no cost increase and there is no dependence on pixel density.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a configuration diagram of a CCD line sensor.
FIG. 3 is an output characteristic diagram of each line sensor of RGB.
[Explanation of symbols]
101, 102, 103 CCD line sensors 113-116 Line delay units 117-120 Coefficient units 121-124 Multipliers 125, 126 Adders 127 Input masking circuit 128 Color space conversion circuit 133 Color judgment circuit 134 Counder circuit 135 CPU
136 storage media

Claims (18)

First, second, and third image reading means for reading images by main scanning and outputting first, second, and third color signals;
First computing means for multiplying and adding pixel values adjacent to each other in the sub-scanning direction in the first color signal, respectively;
Second computing means for multiplying each pixel value adjacent in the sub-scanning direction in the second color signal by a coefficient,
The absolute value of the signal obtained from the outputs of the first and second arithmetic means and the third color signal is compared with a threshold value to determine whether the image is chromatic or achromatic, and a determination signal is output. A determination means;
Counting means for counting the determination signal for determining the chromatic color;
The achromatic color image is read by each of the image reading means while sequentially changing the coefficient, and a table showing the relationship between the count value of the count means and the coefficient at that time is created. An image reading apparatus comprising: a control unit that detects a coefficient that minimizes the coefficient.   2. The image reading apparatus according to claim 1, wherein the control means causes the image reading means to read the image using the detected coefficient in the first and second calculation means.   2. The image reading apparatus according to claim 1, wherein sampling for creating the table is performed a plurality of times under the same conditions.   2. The image reading apparatus according to claim 1, wherein sampling data for creating the table is averaged between adjacent conditions.   2. The image reading apparatus according to claim 1, wherein the table is a two-dimensional table having each coefficient as an axis, and a combination of coefficients having the smallest count value is obtained from the table.   A table in which the coefficient for the second color signal is changed by fixing the coefficient for the first color signal to a predetermined value is generated, and the coefficient having the minimum count value is detected from the table to detect the first color signal. Create a table with the coefficient for the color signal, the coefficient for the second color signal fixed to a predetermined value and the coefficient for the first color signal changed, and detect the coefficient with the smallest count value from this table The image reading apparatus according to claim 1, wherein the coefficient is a coefficient for the second color signal.   2. The image reading apparatus according to claim 1, wherein the determination means and the counting means constitute image determination means for determining whether the image is a monochrome image or a color image.   The image reading apparatus according to claim 1, further comprising a printer that outputs the achromatic image.   An input masking means for inputting a signal obtained from the outputs of the first and second arithmetic means and the third color signal to the determination means is provided, and a coefficient of the input masking means is changed. The image reading apparatus according to claim 1. An image reading process in which an image is read by main scanning by first, second, and third image reading means, respectively, and first, second, and third color signals are output;
A first calculation process for multiplying and adding a pixel value adjacent to each other in the sub-scanning direction in the first color signal;
A second calculation process of multiplying and adding a pixel value adjacent to each other in the sub-scanning direction in the second color signal;
The absolute value of the signal obtained from the outputs of the first and second arithmetic processing and the third color signal is compared with a threshold value to determine whether the image is chromatic or achromatic, and a determination signal is output. Judgment processing,
A count process for counting the determination signal for determining the chromatic color;
The achromatic image is read by each of the image reading means while sequentially changing the coefficient, and a table showing the relationship between the count value of the count process at that time and the coefficient is created. A computer-readable storage medium storing a program for causing a computer to execute a control process for detecting a coefficient with a minimum value.   11. The computer reading according to claim 10, further comprising a reading process in which each of the image reading means reads the image by using the detected coefficient in the first and second calculation processes. Possible storage medium.   11. The computer-readable storage medium according to claim 10, wherein sampling for creating the table is performed a plurality of times under the same conditions.   11. The computer-readable storage medium according to claim 10, wherein sampling data for creating the table is averaged between adjacent conditions.   11. The computer-readable storage medium according to claim 10, wherein said table is a two-dimensional table having each coefficient as an axis, and a combination of coefficients having the smallest count value is obtained from the table. .   A table in which the coefficient for the second color signal is changed by fixing the coefficient for the first color signal to a predetermined value is generated, and the coefficient having the minimum count value is detected from the table to detect the first color signal. Create a table with the coefficient for the color signal, the coefficient for the second color signal fixed to a predetermined value and the coefficient for the first color signal changed, and detect the coefficient with the smallest count value from this table 11. The computer-readable storage medium according to claim 10, wherein the coefficient is a coefficient for the second color signal.   11. The computer-readable storage medium according to claim 10, wherein an image determination process for determining whether the image is a monochrome image or a color image is executed by the determination process and the count process.   11. The computer-readable storage medium according to claim 10, further comprising a process of outputting the achromatic image from a printer.   11. A process for changing an input masking coefficient for inputting a signal obtained from the outputs of the first and second arithmetic processes and the third color signal to the determination process is provided. The computer-readable storage medium described.

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