JP2007158846A - Image reading device and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image reader capable of selecting a line sensor to be reference of delay time for delaying an output of the line sensor arbitrarily. <P>SOLUTION: A main control part 21 selects a line sensor shown by line sensor specifying information set in a memory such as a semiconductor memory included in the main control part 21, that is, a line sensor having the worst CTF (contrast transfer function) value as a reference line sensor. The main control part 21 calculates delay time of each line sensor in accordance with a reduction ratio of an image with the selected reference line sensor as reference and instructs a corresponding line memory unit on the calculated delay time of each line sensor. Each line memory unit delays an output of each line sensor as much as delay time instructed from the main control part 21, performs interpolation with a weighting value instructed from the main control part 21 and sends the output to an image processing part 22. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image reading apparatus and method for reading an image such as a document.

An image reading apparatus, for example, an image reading apparatus included in an image forming apparatus such as a copying machine or a facsimile, uses a line sensor that reads an image line by line in order to read an image at high speed. An image reading apparatus for reading a color document includes a plurality of line sensors such as RGB
Read the document using line sensors that read the three colors (Red-Green-Blue).

  FIG. 7 schematically shows the configuration of the image reading apparatus 9 according to the first conventional technique. The image reading device 9 includes a document reading unit 90, a main body unit 20, and a document table 31. The document reading unit 90 reads the document 30 placed on the document table 31 and sends the read image information to the main body unit 20. And memorized.

  The document reading unit 90 includes a charge coupled device (CCD) 11, a line memory unit G16, and a line memory unit R17. The CCD 11 is included in a scanner including a lamp unit that irradiates light on the document 30, and reads the document 30 placed on the document table 31. In the image reading apparatus 9 shown in FIG. 7, the original 30 is moved in the sub-scanning direction with respect to the scanner to read the image. However, the original 30 may be fixed and the scanner may be moved.

  The CCD 11 includes three line sensors 11a to 11c for three colors of RGB, and the three line sensors 11a to 11c are arranged in parallel in the sub-scanning direction, that is, the direction orthogonal to the direction in which the document 30 moves. The reading portion A of the original 30 sequentially passes through the reading positions of the line sensors 11a to 11c and is read by each line sensor. That is, the image at the reading location A is read in the order of the line sensor 11a, the line sensor 11b, and the line sensor 11c.

  The line memory unit G16 includes a line memory for four lines, and can delay the output of the line sensor 11b by a maximum of four lines. The line memory unit R17 includes a line memory for 8 lines, and can delay the output of the line sensor 11a by a maximum of 8 lines. The delay time delayed by the line memory unit G16 and the line memory unit R17 is changed by an instruction from the main control unit 21. The output of the line memory unit G16, the output of the line memory unit R17, and the output of the line sensor 11c are sent to the image processing unit 22. Since the line sensor 11c reads the image latest, there is no need to delay the output of the line sensor 11c, and there is no line memory unit at the subsequent stage of the line sensor 11c.

  The main body unit 20 receives the output of the main control unit 21, the line memory unit G16, the line memory unit R17, and the line sensor 11c, that is, image information from the document reading unit 90, which controls the document reading unit 90, and receives the received image information. The image processing unit 22 that stores image information that has been processed or received in the image memory 23, the image memory 23 that includes information instructed by the image processing unit 22, for example, a semiconductor memory that stores image information, and the like An operation display unit 24 including an operation button for giving an instruction to the image reading device 9 and a liquid crystal display for displaying information to the user, and a printing unit for outputting information instructed from the image processing unit 22 to a printing paper or the like 25.

  FIG. 8 shows the positional relationship between the line sensors 11a to 11c shown in FIG. 7 and the output time relationship. Fig.8 (a) shows the positional relationship of the line sensors 11a-11c. The line sensors 11a to 11c are arranged in parallel at intervals of the time difference T. The original 30 advances from the position of the original 30a to the position of the original 30b, and further advances to the position of the original 30c. In FIG. 8A, the document 30 is illustrated at a position away from each line sensor (hereinafter also referred to as a CCD line sensor), but actually passes through the position of each line sensor.

  FIG. 8B is a time chart showing the reading timing at which the line sensors 11a to 11c read images. The line sensor 11a, that is, the line sensor reading timing for reading the R color in order from the top, the second is the line sensor 11b, that is, the reading timing of the line sensor for reading the G color, and the third is the line sensor 11c, that is, the line for reading the B color. This is the sensor reading timing.

  One cycle of the clock indicating the read timing, that is, the read cycle t is a time from when the CCD line sensor reads an image for one line until an image for the next one line is read. The time difference between the line sensor 11a and the line sensor 11b and the time difference between the line sensor 11b and the line sensor 11c are both time differences T. In the same magnification mode, that is, the mode in which the image is not reduced or enlarged, the time difference T = 4t. . That is, the output of the line sensor 11a needs a delay of time 8t with respect to the output of the line sensor 11c, and the output of the line sensor 11b needs delay of time 4t with respect to the output of the line sensor 11c. At this time, the distance between the line sensor 11a and the line sensor 11b and the distance between the line sensor 11b and the line sensor 11c are distances obtained by integrating the moving speed of the document 30 and the time 4t.

  In forming an image, there is an image forming apparatus that can enlarge or reduce the size of an image to be formed to a size that is free with respect to the document size. When the image is reduced, the image may be read by increasing the relative moving speed of the scanner including the line sensor with respect to the original according to the reduction ratio. Since the time difference between the outputs of the line sensors that read the image at the same position is inversely proportional to the moving speed of the scanner unit, it is necessary to change the delay time of the output of the line sensor in accordance with the moving speed. For example, when the copying magnification is 50%, that is, when the moving speed of the scanner unit is twice, the time difference between the output of the R line sensor 11a and the output of the B line sensor 11c (hereinafter abbreviated as RB) is the same in the same magnification mode. The time difference is 1/2, that is, T = 4t, and the time difference between the output of the G line sensor 11b and the output of the B line sensor 11c (hereinafter abbreviated as GB) is T = 2t. That is, when the copy magnification is 50%, the delay time needs to be ½ of the normal magnification mode.

  The size to be reduced can be changed in increments of 1%, for example, and the moving speed is also changed in increments of 1%. Therefore, the delay time must also be set to a delay time corresponding to 1% increments of the reduced size. For example, when the reduction ratio is 88%, the delay time needs to be 0.88 times the delay time in the normal magnification mode. That is, the delay time between RBs is 8t × 0.88 = 7.04t, and the delay time between GBs is 4t × 0.88 = 3.52t. In this case, it is necessary to delay the output of the R line sensor 11a by about 7.0 and delay the output of the G line sensor 11b by about 3.5t.

  However, since an image to be read has a reading cycle of 1t, an image having a time difference of 3.5t is not read. When the time difference is not an integral multiple of the reading period t, for example, when the time difference is 3.5 t, interpolation data with a time difference of 3.5 t is calculated by interpolation with images before and after the time difference is an integral multiple of the reading period t. Ask for.

  FIG. 9 shows a configuration of the line memory unit R17 shown in FIG. The line memory unit R17 includes eight line memories 171, a selector A172, a selector B173, and an interpolation data creation unit 174.

  The eight line memories 171 are connected in series, and delay the output from the CCD line sensor 11a input to the first-stage line memory by one line, that is, by a reading cycle t. The output of the first line memory is input to the next line memory. Thereafter, the output of the previous line memory is input up to the eighth line memory. In either line memory, the input is delayed by one line, that is, by a reading cycle t.

  Outputs from the CCD line sensor 11a and outputs from the eight line memories 171 are also input to the selector A172 and the selector B173. The selector A 172 and the selector B 173 select and output the inputs indicated by “select value 1” and “select value 2”, respectively, which are instructed from the main control unit 21 from among the nine inputs. The outputs of the selector A 172 and the selector B 173 are input to the interpolation data creation unit 174.

  The interpolation data creation unit 174 generates and outputs interpolation data of the output “value A” of the selector A 172 and the output “value B” of the selector B 173 based on the “weighting value” instructed from the main control unit 21. . Specifically, “value A” is multiplied by (1− “weighting value”), “value B” is multiplied by “weighting value”, and the sum thereof is obtained as interpolation data. The weighting value is a numerical value less than the decimal point of the delay amount. The delay amount is a value obtained by dividing the delay time by the reading cycle t, and the unit is a line.

  For example, when the delay amount is 3.7 lines, that is, the delay time is 3.7 t, the main control unit 21 indicates that the selector A 172 selects the output of the line memory delayed by 3 lines. “Value 1” is instructed, and “select value 2” indicating that the output of the line memory delayed by 4 lines is selected to the selector B 173. The selector A 172 selects the output of the third line memory and outputs it as “value A”, and the selector B 173 selects the output of the fourth line memory and outputs it as “value B”.

  Next, the main control unit 21 instructs the interpolation data creation unit 174 to “weight”, for example, “0.7”. Assuming that the output “value A” of the selector A 172 and the output “value B” of the selector B 173 are, for example, “100” and “50”, respectively, the interpolation data creation unit 174 selects 30% of the output “100” of the selector A 172 and the selector Interpolation data is obtained by adding 70% of the output “50” of B173. That is, the interpolation data becomes “65” from the calculation formula 100 × 0.3 + 50 × 0.7.

  As a second conventional technique, the relative positional shifts of the three CCD line sensors that convert the light separated into R component, G component, and B component into electrical signals are determined according to the amount of positional shift. There is a color image forming apparatus that can correct an electrical signal from a line sensor by delaying and form an output image without color misregistration (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 5-75792

  In the first conventional technique, the output of the line sensor for the R and G colors is delayed with reference to the line sensor for the B color that reads the image latest, so that the delay amount when the image is reduced is small. If it is not an integer, interpolation is performed on the output of the delayed R and G line sensors. In general, image quality deteriorates when interpolation is performed. Specifically, the deterioration of the image quality appears remarkably as a color change of a thin line in a character or the like. For example, a black character is colored or a colored character is black. In this case, since there is a problem that a line sensor that does not perform interpolation, that is, a line sensor that is a reference for the delay amount that delays the output of the line sensor cannot be arbitrarily selected, the output of the line sensor that performs interpolation is If it is lowered, the image quality is further deteriorated.

  The second conventional technique reduces the occurrence of color misregistration due to misregistration during the manufacture of the CCD line sensor by delaying the output of each CCD line sensor in accordance with the misregistration amount. The delay is individually performed according to the positional deviation of each CCD line sensor, and does not adjust the difference in reading time between the CCD line sensors, but uses a line sensor that is a reference for the delay amount of the output of the line sensor. Absent.

  An object of the present invention is to provide an image reading apparatus and method that can arbitrarily select a line sensor that is a reference of a delay time for delaying the output of the line sensor.

The present invention reads an image in line units composed of pixels arranged in a straight line, and a plurality of line sensors arranged in parallel;
Delay means for each line sensor for delaying the output of the image read by the line sensor at a predetermined reading cycle;
One line sensor corresponding to a delay means for delaying the output of the line sensor by an integer multiple of the reading cycle is selected as a reference line sensor from the plurality of line sensors, and each delay is performed based on the selected reference line sensor. Control means for calculating a delay time to delay the means, and instructing each delay means to the calculated delay time,
Any one of the plurality of line sensors can be selected as a reference line sensor.

  According to the present invention, an image is read in a line unit composed of pixels arranged in a straight line by a plurality of line sensors arranged in parallel, and the line sensor reads the image at a predetermined read cycle by a delay unit for each line sensor. The output of the line sensor is delayed, and the control means delays the output of the line sensor from the plurality of line sensors that can be selected as the reference line sensor by the control means for a time that is an integral multiple of the read cycle. One line sensor corresponding to the means is selected as a reference line sensor, a delay time is calculated for delaying each delay means with reference to the selected reference line sensor, and the calculated delay time is calculated for each delay means. Instructed.

  As described above, since the delay means for delaying the output of the line sensor is provided in all the line sensors, the line sensor that becomes a reference for the delay time of the output of the line sensor, for example, a line sensor that does not need to perform interpolation is provided. Can be arbitrarily selected.

  In the invention, it is preferable that the control means selects a line sensor having the worst evaluation value for evaluating the output of the line sensor as a reference line sensor.

  According to the present invention, since the line sensor having the worst evaluation value is the reference line sensor, that is, the line sensor that delays the time output of an integral multiple of the reading cycle in which the line sensor reads an image, the output of the line sensor having the worst evaluation value is obtained. Therefore, it is possible to prevent the output from deteriorating due to the interpolation.

Further, the present invention increases the relative movement speed between the image and the line sensor to a movement speed corresponding to the reduction magnification at which the image is reduced, and sets the delay time of each delay means when reading the image for each predetermined reduction magnification. Further includes storage means for storing delay time information calculated for each line sensor using each line sensor as a reference line sensor,
The control means instructs each delay means of a delay time corresponding to a reduction ratio indicated by delay time information of a line sensor selected as a reference line sensor.

  According to the present invention, the delay time information calculated for each line sensor using each line sensor as a reference line sensor is stored in the storage means as the delay time for delaying the output of each line sensor for each predetermined reduction ratio. When the reduction ratio is instructed, the delay time can be obtained from the delay time information stored in the storage means.

The present invention also includes setting means for setting line sensor specifying information for specifying the line sensor having the worst evaluation value.
The control means selects a line sensor specified by the line sensor specifying information set in the setting means as a reference line sensor.

  According to the present invention, since the reference line sensor is selected based on the line sensor specifying information set in the setting means, that is, the information for specifying the line sensor having the worst evaluation value, the line sensor specifying information is The line sensor with the worst evaluation value can be used as the reference line sensor simply by setting the setting means.

  Further, the invention is characterized in that the evaluation value is an evaluation value obtained by CTF measurement.

  According to the present invention, the evaluation value is an evaluation value obtained by CTF measurement, that is, the output value of each line sensor obtained by reading a basic chart in which a wide black rectangle and a narrow black rectangle are formed on a white background is added, subtracted, multiplied, and divided. Since the evaluation value is obtained simply by doing, it can be easily evaluated based on the same standard.

Further, the present invention is an evaluation value calculation step of reading an image in line units composed of pixels arranged in a straight line, and calculating an evaluation value for evaluating outputs of a plurality of line sensors arranged in parallel.
A reference in which an output of an image read by a line sensor in a predetermined reading cycle is delayed by an integral multiple of the reading cycle, with the line sensor having the worst evaluation value calculated in the evaluation value calculating step among the plurality of line sensors. A selection process to select as a line sensor;
Calculate the delay time to delay the output of the image read by each line sensor based on the reference line sensor selected in the selection process, and instruct the calculated delay time to the delay unit for delaying the output of each line sensor And an image reading method characterized by including a control step.

  According to the present invention, in the evaluation value calculation step, an evaluation value for evaluating the output of a plurality of line sensors arranged in parallel is a line sensor that reads an image in units of lines composed of pixels arranged in a straight line. In the calculating and selecting step, the output of the image read by the line sensor in a predetermined reading cycle is selected as an integer of the reading cycle, the line sensor having the worst evaluation value calculated in the evaluation value calculating step among the plurality of line sensors. Select as a reference line sensor that is delayed by twice the time, and in the control process, calculate the delay time to delay the output of the image read by each line sensor based on the reference line sensor selected in the selection process The delay time is instructed to a delay unit for delaying the output of each line sensor.

  In this way, the line sensor with the worst evaluation value is used as the reference line sensor, that is, the line sensor that delays the time output that is an integral multiple of the reading cycle in which the line sensor reads the image, so the output of the line sensor with the worst evaluation value is interpolated. It is not necessary to carry out the process, and output deterioration due to interpolation can be prevented.

  According to the present invention, it is possible to arbitrarily select a line sensor as a reference for the delay time of the output of the line sensor, so even if there is a line sensor with a low output, the line sensor is selected as the reference line sensor. By doing so, the clearness of the color corresponding to each line sensor, for example, RGB can be made substantially uniform.

  Further, according to the present invention, it is not necessary to interpolate the output of the line sensor having the worst evaluation value, and deterioration of the output due to the interpolation can be prevented. Therefore, when reading at an increased moving speed in order to reduce the image, Even if there is a line sensor with a poor evaluation value, it is possible to suppress the color change of the thin line caused by the interpolation.

  Further, according to the present invention, when the reduction ratio is instructed, the delay time can be obtained from the delay time information stored in the storage means, so that the delay time can be obtained in a short time without performing calculation.

  Further, according to the present invention, if a document reading unit provided with setting means in which line sensor identification information is set is purchased, the main body unit can be used as a reference only by connecting the document reading unit to the main body unit including the main control unit. Therefore, when connecting the document reading unit to the main body, it is not necessary to set a line sensor having the worst evaluation value, and productivity can be improved.

  Further, according to the present invention, since the evaluation can be easily performed based on the same standard, the same evaluation value can be easily obtained even if the measurers who measure the CTF are different.

  Further, according to the present invention, it is not necessary to interpolate the output of the line sensor having the worst evaluation value, and deterioration of the output due to the interpolation can be prevented. Therefore, when reading at an increased moving speed in order to reduce the image, Even if there is a line sensor with a poor evaluation value, it is possible to suppress the color change of the thin line caused by the interpolation.

  FIG. 1 shows a schematic configuration of an image reading apparatus 1 according to an embodiment of the present invention. The image reading apparatus 1 is an image reading apparatus included in a single image reading apparatus such as a scanner apparatus or an image forming apparatus such as a copying machine or a facsimile. The image reading apparatus 1 includes a document reading unit 10, a main body unit 20, and a document table 31. The document reading unit 10 reads a document 30 placed on the document table 31 and sends the read image information to the main body unit 20. And memorized.

  The document reading unit 10 includes a charge coupled device (CCD) 11, a line memory unit B12, a line memory unit G13, and a line memory unit R14. The CCD 11 is included in a scanner (not shown) including a lamp unit (not shown) that irradiates the document 30 with light, and reads the document 30 placed on the document table 31. In the image reading apparatus 1 shown in FIG. 1, the original 30 is moved in the sub-scanning direction with respect to the scanner to read the image. However, the original 30 may be fixed and the scanner may be moved. The scanner is included in the document reading unit 10.

  The CCD 11 includes three line sensors 11a to 11c for three colors of RGB (Red-Green-Blue). The three line sensors 11a to 11c are arranged in a direction perpendicular to the sub-scanning direction, that is, the direction in which the document 30 moves. They are arranged in parallel. The document 30 sequentially passes through the reading positions of the line sensors 11a to 11c and is read by each line sensor. That is, an image at the same position is read in the order of the line sensor 11a, the line sensor 11b, and the line sensor 11c.

  Since the positional relationship and output time relationship of the line sensors 11a to 11c are the same as the positional relationship and output time relationship of the line sensors 11a to 11c shown in FIG. 8, for example, detailed description will be omitted.

  The line sensors 11a to 11c are arranged in parallel at intervals of the time difference T. One cycle of the clock indicating the read timing, that is, the read cycle t is a time from when the CCD line sensor reads an image for one line until an image for the next one line is read. In the same magnification mode, that is, the mode in which the image is not reduced or enlarged, the time difference T = 4t. That is, the output of the line sensor 11a needs a delay of time 8t with respect to the output of the line sensor 11c, and the output of the line sensor 11b needs delay of time 4t with respect to the output of the line sensor 11c. At this time, the distance between the line sensor 11a and the line sensor 11b and the distance between the line sensor 11b and the line sensor 11c are distances obtained by integrating the moving speed of the document 30 and the time 4t.

  The line memory unit B12 includes a line memory for one line, and can delay the output of the line sensor 11c by a maximum of one line. The line memory unit G13 includes a line memory for five lines, and can delay the output of the line sensor 11b by a maximum of five lines. The line memory unit R14 includes a line memory for 9 lines, and can delay the output of the line sensor 11a by a maximum of 9 lines. The delay time delayed in the line memory unit B12, the line memory unit G13, and the line memory unit R14 is changed by an instruction from the main control unit 21. The output of the line memory unit B12, the output of the line memory unit G13, and the output of the line memory unit R14 are sent to the image processing unit 22.

  The configuration of these line memory units is the same except for the number of line memories included in the line memory unit 17 shown in FIG. The line memory unit B12 has one line memory, the line memory unit G13 has five line memories, and the line memory unit R14 has nine line memories. Thus, since the line memory unit is provided for the output of the B line sensor 11c, the output of the B line sensor 11c can also be delayed. That is, since the interpolation data can be generated for the output of the B line memory 11c, the R or G line sensor can be used as a reference line sensor.

  The main unit 20 receives the output of the line memory unit, that is, image information from the document reading unit 10 and performs image processing on the received image information or receives the image data. The image processing unit 22 for storing the image information in the image memory 23, the image memory 23 configured by information instructed from the image processing unit 22, for example, a semiconductor memory for storing the image information, etc. An operation display unit 24 including an operation button for giving an instruction and a liquid crystal display for displaying information to the user, and a printing unit 25 for outputting information instructed from the image processing unit 22 to printing paper or the like are included.

  In this way, the line sensor for the color B that reads the image most slowly is also provided with a line memory unit or delay means for delaying the output of the line sensor. That is, the output of the line sensor is supplied to all the line sensors. Since the delay means for delaying is provided, it is possible to arbitrarily select a line sensor that is a reference for the delay time of the output of the line sensor, for example, a line sensor that does not require interpolation. Therefore, even if there is a line sensor with a low output, by selecting the line sensor as a reference line sensor, the clearness of the color corresponding to each line sensor, such as RGB, can be made substantially uniform.

  Generally, even if each line sensor of RGB has the same configuration, there is a difference in the characteristics of the optical system, so that there is a difference in the output of the line sensor although it is within an allowable range. In order to evaluate this output difference, a CTF (Contrast Transfer Function) is used.

  FIG. 2 shows how to obtain the CTF for evaluating the output of the CCD 11 shown in FIG. The CTF is an evaluation value for evaluating the output of the line sensor. For example, a basic chart in which a wide black rectangle and a narrow black rectangle are formed on a white background is read by the line sensor of the CCD 11, and each output value is calculated. It can be determined by comparison.

  FIG. 2A shows an output value when the line sensor of the CCD 11 reads a sufficiently wide black rectangle to obtain an output closest to the ideal output. The ideal value, that is, the ideal output value, is a rectangular output in which the output value obtained by reading the white background portion is the MAX value 80, and the output value obtained by reading the black rectangular portion is the MIN value 20. The output of the line sensor varies depending on the response characteristics during the transition period from the white background to the black rectangle and during the transition period from the black rectangle to the white background. Is the MAX value 80, and the output value obtained by reading the black rectangular portion is the MIN value 20.

  FIG. 2B shows an output value when the line sensor of the CCD 11 reads a narrow black rectangle. The width of the black rectangle is such that the difference in reading ability of each line sensor can be discriminated. Specifically, the difference due to the quality of the line sensor appears in the output value of the line sensor when the black rectangular portion is read. Narrow width. As for the output of the line sensor, the output value obtained by reading the white background portion is the MAX value 80, and the output value obtained by reading the black line portion is the MIN value 40.

  FIG. 2C shows an arithmetic expression for obtaining the CTF value. If the difference between the MAX value and the MIN value when a wide black rectangle is read is a, and the difference between the MAX value and the MIN value when a narrow black rectangle is read is b, the CTF value is b. Is obtained by dividing by. From FIG. 2A, a = 80-20 = 60, and from FIG. 2B, b = 80-40 = 40. Therefore, the CTF value is 40/60, which is about 67%.

  The CTF is measured for each line sensor of the CCD 11 at the stage where the image reading apparatus 10 is assembled before shipment, for example. A line sensor having a bad CTF value is identified based on the CTF measurement result. Line sensor specifying information for specifying the line sensor having the worst CTF value is input from the operation display unit 24. The input line sensor specifying information is sent from the operation display unit 24 to the main control unit 21, and the main control unit 21 The received line sensor specifying information is set in a memory such as a semiconductor memory (not shown) included in the main control unit 21.

  When the image is reduced, reading is performed by increasing the relative moving speed between the document 30 and the CCD 11. Therefore, the delay time of the R and G line sensors with respect to the B line sensor 11c is a reading cycle t indicating the reading timing for reading the image. May be a time that is an integral multiple of the time from when the line sensor reads an image for one line until the next image for one line is read. The output of the line sensor whose delay time is not an integral multiple of the reading cycle t needs to be interpolated.

  Since each of the line sensor unit B12, the line sensor unit G13, and the line sensor unit R14 includes the selector A, the selector B, and the interpolation data creation unit illustrated in FIG. 9, the output of any line sensor performs interpolation. be able to.

  Assuming that the reference line sensor serving as a reference for the delay time is the B line sensor 11c that reads the image latest, interpolation is performed by the R and G line sensors. If the line sensor that is the reference for the delay time is the G line sensor 11b, interpolation is performed by the B and R line sensors, and the line sensor that is the reference for the delay time is the R line sensor 11a, the G and B line sensors are interpolated. Interpolation is performed by the line sensor. Since the delay time of the reference line sensor is a time that is an integral multiple of the reading cycle t, no interpolation is necessary, and the interpolation is performed because the delay time for the reference line sensor is not an integral multiple of the reading cycle t. It is.

  The main control unit 21 selects the line sensor indicated by the line sensor specifying information set in the memory included in the main control unit 21, that is, the line sensor having the worst CTF value, as the reference line sensor. Since the delay time of the reference line sensor is a time that is an integral multiple of the reading cycle, it is not necessary to perform interpolation, and deterioration of image quality due to interpolation can be prevented.

  The main control unit 21 calculates the delay time of each line sensor according to the image reduction magnification with reference to the selected reference line sensor. Specifically, first, the reduction ratio is set to the delay time 8t of the R line sensor 11a and the delay time 4t of the G line sensor 11b in the equal magnification mode when the reference line sensor is the B line sensor 11c. Multiplication is performed to calculate a delay time considering the reduction ratio. Next, the delay time of each line sensor is adjusted so that the delay time of the reference line sensor becomes an integral multiple of the reading cycle t.

  For example, when the reduction ratio is 88%, the delay time of the R line sensor 11a with respect to the B line sensor 11c (hereinafter referred to as the delay time between RBs) is 7.0t if a fractional number of two digits or less is omitted. The delay time of the G line sensor 11b with respect to the B line sensor 11c (hereinafter referred to as the delay time between GBs) is 3.5 t if a fractional number of two decimal places or less is omitted. If the reference line sensor is the G line sensor 11b, the delay time of each line sensor is adjusted after the delay time of the G line sensor 11b is set to an integral multiple of the reading cycle t.

  The delay time at which the delay time of the G line sensor 11b is an integral multiple of the reading cycle t is an integer greater than and closest to the delay time between GBs when the reference line sensor is the B line sensor. Double the delay time. That is, since the delay time between GB is 3.5 t, the delay time of the G line sensor 11 b is 4 t. The delay time of the B line sensor 11c is 0.5t because the delay time between GB is 3.5t, and 3.5t is subtracted from the delay time 4t of the G line sensor 11b. The delay time of the R line sensor 11a is such that the delay time between RBs is 7t and the delay time between GBs is 3.5t, that is, the delay time between RGs is 3.5t. 3.5t is added to the delay time 4t of 7.5 to obtain 7.5t.

  The main control unit 21 instructs the calculated delay time of each line sensor to the corresponding line memory unit. Each line memory unit delays the output of each line sensor by the delay time instructed from the main control unit 21, further performs interpolation with the weighting value instructed from the main control unit 21, and sends it to the image processing unit 22. When the weighting value instructed from the main control unit 21 is “0” or “1”, data without interpolation is output.

  FIG. 3 shows the time transition of the output value of each line memory unit shown in FIG. A time transition of an output value of each line memory unit when a black rectangular image (hereinafter abbreviated as BK image) is read by each RGB line sensor is shown. FIG. 3A shows a case where the output values of all RGB are ideal. The output values of any of RGB indicate the lowest output value at a position near the center of the BK image. At this time, the CTF values of the outputs of the RGB line sensors all coincide with each other at a high value.

  FIG. 3B shows a case where the CTF value of the output of the G line sensor 11b is bad, and the output of any line sensor is not interpolated. The G output value is slightly higher than the G output value shown in FIG. 3A at a position near the center of the BK image. If printing is performed based on the RGB output values, the C (Cyan) component and the Y (Yellow) component are larger than the M (Magenta) component, so that there are many C and Y components, not black characters. It becomes a character of color.

  FIG. 3C shows a case where the output of the G line sensor 11b having a bad CTF value and the output of the R line sensor 11a are interpolated by the conventional technique. That is, it is a case where the B line sensor that reads the image latest is used as a reference. The output value of G is slightly higher at the position near the center of the BK image than the output value of G shown in FIG. 3B by interpolation, and the output value of R is also changed by interpolation as shown in FIG. Is slightly higher at the position near the center of the BK image than the output value of R shown in FIG. The sharpness of the G color is further reduced by the interpolation, and the degree of color change is deteriorated.

  FIG. 3D shows a case where the present invention is applied and the G line sensor 11b having a bad CTF value is used as a reference line sensor. The output of the R line sensor 11a and the output of the B line sensor 11c are interpolated. The output value of R becomes a little higher at the position near the center of the BK image than the output value of R shown in FIG. 3B by interpolation, and the output value of B is also interpolated by interpolation. The output value of B is slightly higher at the position near the center of the BK image. The RGB output values are approximately the same at positions near the center of the BK image. Therefore, it is possible to suppress a change in color by preventing the deterioration of the sharpness of the G color and bringing the sharpness of the R and B colors close to the sharpness of the G color.

  In this way, the line sensor with the worst evaluation value is used as the reference line sensor, that is, the line sensor that delays the time output that is an integral multiple of the reading cycle in which the line sensor reads the image, so the output of the line sensor with the worst evaluation value is interpolated. It is not necessary to carry out the process, and output deterioration due to interpolation can be prevented. Therefore, when reading at an increased moving speed to reduce the image, even if there is a line sensor with a poor evaluation value, it is possible to suppress the color change of the thin line caused by the interpolation.

  Furthermore, the evaluation value is obtained by simply adding, subtracting, and dividing the output value of each line sensor obtained by reading a basic chart in which a wide black rectangle and a narrow black rectangle are formed on a white background, that is, an evaluation value obtained by CTF measurement. Therefore, it is possible to easily evaluate with the same standard. Therefore, the same evaluation value can be easily obtained even if the measurers who measure the CTF are different.

  FIG. 4 shows a delay amount table used in the image reading apparatus 1 according to the second embodiment of the present invention. The configuration of the image reading apparatus 1 is the same as the configuration shown in FIG. 1, but the main control unit 21 includes a semiconductor memory such as a ROM (Read Only Memory) (not shown), for example, and this ROM has a delay amount table. It is remembered. The delay amount table is a table in which the delay amount for delaying the output of each line sensor is summarized for each line sensor using each line sensor as a reference line sensor for each predetermined copy magnification, for example, for each reduction magnification. The delay amount is a value obtained by dividing the delay time by the reading cycle t, and is a value obtained by converting the reading cycle t into one line.

  FIG. 4A shows a delay amount for delaying each line sensor when the B line sensor 11c is used as a reference. With respect to the copy magnification in 1% increments between 50% and 100%, the delay amount between GB, that is, the delay amount with respect to the B line sensor 11c of the G line sensor 11b, the delay amount between RBs, that is, the R line sensor. The delay amount for the B line sensor 11c of 11a and the delay amount of the B line sensor are indicated by the number of lines.

  For example, when the copying magnification is 100%, the delay amount between GB is 4 lines, the delay amount between RBs is 8 lines, and the delay amount of the B line sensor is 0 line. When the copy magnification is 88%, the lines are 3.5 lines, 7.0 lines, and 0.0 lines, respectively. When the copy magnification is 52%, the lines are 2.1 lines, 4.2 lines, and 0.0 lines, respectively. Yes, when the copy magnification is 51%, they are 2.0 lines, 4.1 lines, and 0.0 lines, respectively, and when the copy magnification is 50%, they are 2, 4, and 0 lines, respectively. These delay amounts can be obtained by multiplying the copy amount by a delay amount of 100% copy magnification.

  FIG. 4B shows a delay amount for delaying each line sensor when the G line sensor 11b is used as a reference. The amount of delay between GB, the amount of delay between RBs, and the amount of delay of the B line sensor are indicated by the number of lines for the copy magnification in 1% increments between 50% and 100%.

  For example, when the copying magnification is 100%, the delay amount between GB is 4 lines, the delay amount between RBs is 8 lines, and the delay amount of the B line sensor is 0 line. When the copy magnification is 88%, the lines are 4.0 lines, 7.5 lines, and 0.5 lines, respectively. When the copy magnification is 52%, the lines are 3.0 lines, 5.1 lines, and 0.9 lines, respectively. Yes, when the copy magnification is 51%, they are 2.0 lines, 4.1 lines, and 0.0 lines, respectively, and when the copy magnification is 50%, they are 2, 4, and 0 lines, respectively.

  FIG. 4C shows a delay amount for delaying each line sensor when the R line sensor 11a is used as a reference. The amount of delay between GB, the amount of delay between RBs, and the amount of delay of the B line sensor are indicated by the number of lines for the copy magnification in 1% increments between 50% and 100%.

  For example, when the copying magnification is 100%, the delay amount between GB is 4 lines, the delay amount between RBs is 8 lines, and the delay amount of the B line sensor is 0 line. When the copy magnification is 88%, the lines are 3.5 lines, 7.0 lines, and 0.0 lines, respectively. When the copy magnification is 52%, the lines are 2.9 lines, 5.0 lines, and 0.8 lines, respectively. Yes, when the copy magnification is 51%, they are 2.9 lines, 5.0 lines, and 0.9 lines, respectively, and when the copy magnification is 50%, they are 2, 4, and 0 lines, respectively.

  When the copy magnification is instructed from the operation display unit 24, the main control unit 21 obtains a delay amount for each line sensor, that is, a delay time from this delay amount table, and instructs each line memory unit. Since the main control unit 21 can obtain the delay amount of each line sensor from the delay amount table, it is not necessary to calculate the delay amount every time the copy magnification is instructed.

  As described above, the delay means that delays the output of each line sensor, that is, the delay time, is calculated for each line sensor using each line sensor as a reference line sensor for each predetermined reduction ratio. For example, since it is stored in the memory included in the main control unit 21, when a reduction ratio is instructed, the delay time can be obtained from the delay time information stored in the storage means. Therefore, when the reduction magnification is instructed, the delay time can be obtained in a short time without performing calculation.

  FIG. 5 shows a schematic configuration of an image reading apparatus 2 according to the third embodiment of the present invention. The image reading apparatus 2 includes a document reading unit 40, a main body unit 20, and a document table 31 (not shown). The document reading unit 40 reads the document 30 placed on the document table 31, and the read image information is the main body unit 20. Sent to and memorized. The main body 20 is the same as that shown in FIG.

  The document reading unit 40 includes a CCD 11, a line memory unit B 12, a line memory unit G 13, a line memory unit R 14, and a setting unit 15. The CCD 11, the line memory unit B12, the line memory unit G13, and the line memory unit R14 are the same as those shown in FIG.

  The setting unit 15 as setting means is configured by, for example, a DIP SW (Dual Inline Package Switch), that is, a DIP type switch, and sets line sensor information for identifying a line sensor having a bad CTF value. The main sensor 21 can refer to the line sensor specifying information set in the setting unit 15. The main control unit 21 calculates the delay time of each line sensor using the line sensor indicated by the line sensor specifying information set in the setting unit 15 as a reference line sensor.

  In the embodiment shown in FIG. 1, the line sensor specifying information is instructed from the operation display unit 24, and the instructed line sensor specifying information is set in the memory included in the main control unit 21, but the third embodiment In the form, it is set in the setting unit 15 included in the document reading unit 40. Setting in the setting unit 15 is performed, for example, when the original document reading unit 40 is assembled. First, the CTF value of the output of each line sensor is obtained, and the line sensor having the worst CTF value among the obtained CTF values is determined. Next, the setting unit 15 such as DIP SW is set so that line sensor specifying information for specifying the determined line sensor is output. Specifically, a switch corresponding to each line sensor is provided in the DIP SW, the switch of the line sensor having the worst CTF value is turned on, and the switches of the other line sensors are turned off. Alternatively, a code for identifying each line sensor may be determined and the code may be set.

  As described above, since the reference line sensor is selected based on the line sensor specifying information set in the setting unit 15 as the setting means, that is, the information for specifying the line sensor having the worst evaluation value, the line sensor is selected. The line sensor with the worst evaluation value can be used as the reference line sensor simply by setting the specific information in the setting means. Therefore, if an original reading unit provided with setting means in which line sensor identification information is set is purchased, the main body unit can be used as a reference line sensor only by connecting the original reading unit to the main body unit including the main control unit. Since the selection can be made, it is not necessary to set a line sensor having the worst evaluation value when connecting the document reading unit to the main body, and productivity can be improved.

  In the above-described embodiment, the CTF is measured at the time of manufacturing the image reading apparatus, and the line sensor specifying information is set in the image reading apparatus. However, the basic chart for measuring the CTF value, for example, a wide black rectangle and a width A chart in which a narrow black rectangle is formed on white paper is attached to the image reading apparatus, and during maintenance, the image reading apparatus is caused to read the basic chart, and the output value of each line sensor is measured. The CTF value may be calculated based on the measured output value. In this case, the CTF value calculation program is stored in a memory such as a ROM included in the main control unit 21, and the CTF value is obtained based on the measured output value by executing this program.

  FIG. 6 is a flowchart of an image reading method according to the fourth embodiment of the present invention. This flowchart shows processing steps performed by the image reading apparatus 1 or the image reading apparatus 2. For example, when the basic chart is read during maintenance or the like, the process proceeds to step S1.

  In step S1, the basic chart is read, the output value of each line sensor is measured, and the CTF value is calculated based on the measured output value. The calculated CTF value is stored in a memory included in the main control unit 21. For example, the CTF value may be calculated in advance when the apparatus is manufactured and stored in a memory included in the main control unit 21 or may be set in the DIP SW or the like and referenced by the main control unit 21. You may be able to do that. In step S2, the line sensor having the worst calculated CTF value is selected as a reference line sensor that delays the output of the line sensor for a time that is an integral multiple of the reading period at which the line sensor reads an image.

  In step S3, the delay time of each line sensor is calculated on the basis of the selected reference line sensor when reading at an increased reading speed to reduce the image. In step S4, the calculated delay time is instructed to each line memory unit. In step S5, the output from the line memory unit is stored in the image memory 23 and the process ends.

  In this way, the line sensor with the worst evaluation value is used as the reference line sensor, that is, the line sensor that delays the time output that is an integral multiple of the reading cycle in which the line sensor reads the image, so the output of the line sensor with the worst evaluation value is interpolated. It is not necessary to carry out the process, and output deterioration due to interpolation can be prevented. Therefore, when reading at an increased moving speed to reduce the image, even if there is a line sensor with a poor evaluation value, it is possible to suppress the color change of the thin line caused by the interpolation.

1 shows a schematic configuration of an image reading apparatus 1 according to an embodiment of the present invention. A method for obtaining a CTF for evaluating the output of the CCD 11 shown in FIG. 1 will be described. The time transition of the output value of each line memory unit shown in FIG. 1 is shown. The delay amount table used with the image reading apparatus 1 which is the 2nd Embodiment of this invention is shown. 3 shows a schematic configuration of an image reading apparatus 2 according to a third embodiment of the present invention. It is a flowchart of the image reading method which is the 4th Embodiment of this invention. 1 schematically shows a configuration of an image reading apparatus 9 according to a first conventional technique. The positional relationship of the line sensors 11a-11c shown in FIG. 7 and the time relationship of an output are shown. 8 shows a configuration of the line memory unit R17 shown in FIG.

Explanation of symbols

1, 2, 9 Image reading device 10, 40, 90 Original reading unit 11 CCD
12 Line sensor unit B
13, 16 Line sensor unit G
14, 17 Line sensor unit R
DESCRIPTION OF SYMBOLS 15 Setting part 20 Main part 21 Main control part 22 Image processing part 23 Image memory 24 Operation display part 25 Printing part 30 Original 31 Original stand 171 Line memory 172 Selector A
173 Selector B
174 Interpolation data creation unit

Claims (6)

A plurality of line sensors arranged in parallel to read an image in line units composed of pixels arranged in a straight line,
Delay means for each line sensor for delaying the output of the image read by the line sensor at a predetermined reading cycle;
One line sensor corresponding to a delay means for delaying the output of the line sensor by an integer multiple of the reading cycle is selected as a reference line sensor from the plurality of line sensors, and each delay is performed based on the selected reference line sensor. Control means for calculating a delay time to delay the means, and instructing each delay means to the calculated delay time,
An image reading apparatus characterized in that any one of the plurality of line sensors can be selected as a reference line sensor.   The image reading apparatus according to claim 1, wherein the control unit selects a line sensor having the worst evaluation value for evaluating the output of the line sensor as a reference line sensor. The delay time of each delay means when reading the image by increasing the relative movement speed between the image and the line sensor to a movement speed corresponding to the reduction magnification at which the image is reduced is set for each line sensor for each predetermined reduction magnification. A storage unit that stores delay time information calculated for each line sensor as a reference line sensor;
The image reading apparatus according to claim 1, wherein the control unit instructs each delay unit of a delay time corresponding to a reduction ratio indicated by delay time information of a line sensor selected as a reference line sensor. Including setting means for setting line sensor specifying information for specifying the line sensor having the worst evaluation value;
The image reading apparatus according to claim 2, wherein the control unit selects a line sensor specified by the line sensor specifying information set in the setting unit as a reference line sensor.   The image reading apparatus according to claim 2, wherein the evaluation value is an evaluation value obtained by CTF measurement. An evaluation value calculation step of reading an image in line units composed of pixels arranged in a straight line and calculating an evaluation value for evaluating the outputs of a plurality of line sensors arranged in parallel;
A reference in which an output of an image read by a line sensor in a predetermined reading cycle is delayed by an integral multiple of the reading cycle, with the line sensor having the worst evaluation value calculated in the evaluation value calculating step among the plurality of line sensors. A selection process to select as a line sensor;
Calculate the delay time to delay the output of the image read by each line sensor based on the reference line sensor selected in the selection process, and instruct the calculated delay time to the delay unit for delaying the output of each line sensor An image reading method comprising: a control step.

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