JP5020187B2 - Image reading apparatus, image reading apparatus control method, and program - Google Patents

Description

  The present invention relates to an image reading apparatus having a light quantity adjustment function, a control method for the image reading apparatus, and a program.

  An image reading apparatus including an image sensor such as a CIS or CCD irradiates a document with light from a light source such as an LED or a lamp, and outputs an analog image signal by receiving the reflected light with an image sensor. The electrical signal that has been photoelectrically converted by the image sensor is amplified by a gain controller, converted into a digital signal, and output to the image processing unit.

  By the way, in order to improve the S / N ratio of the image signal and obtain a high-quality image, it is necessary to increase the amplitude of the analog image signal output from the image sensor so as not to be affected by noise.

  To increase the amplitude of the analog image signal output from the image sensor, it is sufficient to increase the light amount of the light source. However, if the light amount is increased too much, the image sensor will be saturated (the light amount and the output signal amplitude are not proportional). .

  Further, when the analog image signal amplitude of the image sensor is increased, the digital output signal of the AFE (analog front end) -IC that receives the signal is saturated (the digital output signal with respect to the input image signal is not proportional).

  Further, the light source has a variation in light output, and the image sensor also has a variation in sensor sensitivity. For this reason, it is assumed that the variation in the light output is maximum, and the sensitivity of the image sensor is assumed to be maximum, and the amplitude of the analog image signal from the image sensor and the digital output signal of the AFE-IC are not saturated. Setting the amount of light causes the following problems. That is, the analog image signal amplitude from the image sensor in the airframe having normal light output and sensor sensitivity becomes small, so that it is easily affected by noise, resulting in low image quality.

  Therefore, a method has been proposed in which the amount of analog image signal from the image sensor is increased by adjusting the amount of light for each image reading device, the S / N ratio of the image signal is improved, and a high-quality image is obtained. .

For example, an image reading apparatus has been proposed in which a movable light shielding plate is disposed in front of a condensing lens that collects reflected light of a document and the light amount is adjusted by moving the light shielding plate (Patent Document 1). . Further, there has been proposed an image reading apparatus that sets a target value of a digital image signal and adjusts a light amount by gradually changing a current value of a light source until the target value of the digital image signal is reached from a saturated output state (patent) Reference 2). Furthermore, an image reading apparatus that adjusts the amount of light by gradually changing the lighting time of a light source has been proposed (Patent Document 3).
JP 2007-251430 A JP 2006-67029 A JP-A-4-261270

  In Patent Document 1, a light shielding plate for shielding reflected light of a document and a driving component for moving the light shielding plate are required, which causes a problem that the apparatus cost is high.

  In Patent Documents 2 and 3, the user can adjust the amount of light. However, since adjustment takes time, there is a problem that it is troublesome to make frequent adjustments such as adjusting the amount of light every time an image is read.

  In this case, as shown in FIG. 8, the inclination is calculated from the output (D402) when the light source is lit with the first light quantity (L1) and the output data (D401) when the light source is not lit, and the digital image signal output A method of determining the light quantity (LT) at the time of image reading from the target value (DT) can be considered.

  However, there is a case where the ideal light amount LT cannot be obtained by the light amount adjustment by the above method. For example, when the light amount setting is performed by changing the lighting time of the light source, as shown in FIG. 9, the lighting drive circuit 602 that drives the lighting of the light source 601 of the reading sensor has a slow response speed such as a general-purpose transistor or an operational amplifier. Suppose that it is composed of a low-cost circuit.

  In this case, as shown in FIG. 10, when the value of the set light quantity is high (the lighting period of the light source is sufficiently long), the light source is turned on even if the response speed of the lighting drive circuit 602 is slow. However, as shown in FIG. 11, the output of the light source lighting signal when the value of the set light amount is low (the light source lighting period is short) does not rise to the output at which the light source can be turned on, and the light source does not light up. Therefore, the relationship between the set light amount and the output of the digital image signal is as shown by the solid line in FIG.

  In FIG. 12, similarly to FIG. 8, the inclination is calculated from the output (D502) when the light is lit with the first light quantity (L1) and the output data (D501) when the light is not lit, and the digital image signal output target value is obtained. It is assumed that the light quantity (LT) at the time of image reading is determined from (DT). In this case, the light amount adjustment is performed in a state where the characteristic is mistakenly recognized as a one-dot chain line in FIG. As a result, an incorrect light amount (LT) is set, and as a result, the output value of the digital image signal becomes an adjustment value (DW) different from the target value (DT).

  Therefore, in order to achieve the same adjustment method as that shown in FIG. 8, it is necessary to configure the circuit with a transistor or an operational amplifier capable of high-speed response of the light source lighting drive circuit 602.

Therefore, the present invention provides a mechanism that can obtain an optimum light amount for obtaining a high-quality image by improving the S / N ratio of an image signal in an image reading apparatus in a short time and at a low cost. With the goal.

In order to achieve the above object, an image reading apparatus according to the present invention includes a reference member having a predetermined reference density, a light source that irradiates light to the reference member, a drive unit that drives the light source to turn on, and the light source. Read means for receiving reflected light of the light irradiated on the reference member and photoelectrically converting it to output an image signal; and controlling the drive means based on the output signal of the read means to read the image at the time of image reading and a control means for adjusting the light quantity of the light source, wherein the control means, the output of the reading means when the light source is turned on the light source in the first light level to be longer than the lighting period required until the lighted a signal, the light source based on an output signal of said reading means at the time of lighting the light source in the second light quantity to be longer than the lighting period of the first light level, the light intensity of the light source at the time of reading the image Adjust, characterized by That.

  According to the present invention, the light amount is adjusted based on the output signal of the reading unit when the light source is turned on with the first light amount and when the light source is turned on with the second light amount. For this reason, the S / N ratio of the image signal can be reduced even in a low-cost lighting driving circuit with a slow response speed that cannot respond to a lighting signal that is input when the value of the set light amount is low and the light source does not light up. The optimum amount of light for improving and obtaining a high-quality image can be obtained in a short time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram for explaining an apparatus configuration of an image reading apparatus according to the first embodiment of the present invention.

  As shown in FIG. 1, the image reading apparatus of the present embodiment includes a main control unit 301, a ROM 302, a light source 303, a reading sensor 304, an AFE 305, an SD-RAM 306, a reference plate 307, and a lighting drive circuit 312.

  The main control unit 301 includes a light amount control unit 309 that adjusts the light amount of the light source 303, a sensor control unit 310 that controls driving of the reading sensor 304, an AFE control unit 311 that controls the AFE 305 and acquires image data output from the AFE 305. Prepare. The main control unit 301 also includes an external IF control unit 308 for communicating image data, control commands, and the like to an external information terminal (not shown), and each of the control units 308 to 311 is based on a program stored in the ROM 302. Take control.

  The lighting drive circuit 312 is a circuit for lighting the light source 303, and includes a general-purpose transistor or an operational amplifier. The reading sensor 303 receives reflected light of light emitted from the light source 303, photoelectrically converts the reflected light, and outputs an analog image signal.

  The AFE 305 adjusts the amplification factor and offset level of the analog image signal output from the reading sensor 304 based on the control of the main control unit 301, performs A / D conversion to a digital image signal, and outputs the digital image signal to the AFE control unit 311. To do.

  The SD-RAM 306 temporarily stores a part of the program of the main control unit 301 and image data acquired by the main control unit 301 from the AFE 305. The reference plate 307 is a reference member having a predetermined reference density for performing shading correction.

  Next, an example of the light amount adjustment operation of the light source in the image reading apparatus according to the present embodiment will be described with reference to FIGS.

  FIG. 2 is a flowchart for explaining an example of the light amount adjustment operation of the light source, and FIG. 3 is a graph showing the relationship between the light amount and the AFE output during the light amount adjustment operation of the light source. 2 is executed by the CPU or the like of the main control unit 301 after the program stored in the ROM 302 or the like is loaded into the SD-RAM 306. In the present embodiment, the light amount control unit 309 performs light amount adjustment by changing the lighting period of the light source 303. Further, the light amount adjustment of the light source 303 is performed, for example, immediately before the start of image reading or before shipment of the image reading apparatus.

  First, adjust the black reference. In step S101, the main control unit 301 controls the AFE control unit 311 to set the register for setting the amplification factor of the AFE 305 to the minimum value and the register for setting the offset level to the intermediate level.

  Next, in step S <b> 102, the main control unit 301 controls the driving of the lighting drive circuit 312 via the light amount control unit 309 to turn off the light source 303.

  Next, in step S103, the main control unit 301 controls the sensor control unit 310 to drive the reading sensor 304. Here, the analog image signal output from the reading sensor 304 is adjusted in amplification factor and offset level by the AFE 305, A / D converted into a digital image signal, and output to the AFE control unit 311. The main control unit 301 acquires the output value D104 of the digital image signal output from the AFE 305 via the AFE control unit 311 and stores it in the SD-RAM 306.

  Next, in step S104, the main control unit 301 controls the AFE control unit 301, and based on the digital image signal output value acquired in step S103, the offset level of the AFE 305 is set to a preset black reference value D104. Change the register that sets. This completes the black reference adjustment.

  Next, the light amount of the light source 303 is adjusted. In step S <b> 105, the main control unit 301 drives the lighting drive circuit 312 via the light amount control unit 312 in the first light amount lighting period L <b> 1 to turn on the light source 303. Here, referring to FIG. 3, the first light quantity lighting period L1 is set in advance to a lighting period longer than the lighting period required for the lighting drive circuit 312 to light the light source 303 and shorter than the second light quantity lighting period L2. Has been.

  Next, in step S106, the main control unit 301 controls the sensor control unit 310 to drive the reading sensor 304. Similarly to the above, the digital image signal output value D106 output from the AFE 305 is acquired via the AFE control unit 311 and stored in the SD-RAM 306 (first acquisition step).

  Next, in step S107, the main control unit 301 drives the lighting drive circuit 312 in the second light amount lighting period L2 via the light amount control unit 312 to light the light source 303. Here, referring to FIG. 3, the second light quantity lighting period L2 is longer than the first light quantity lighting period L1, and the digital image signal output from the AFE 305 or the analog image signal output from the reading sensor 304 is saturated. A lighting period shorter than the lighting period to be set is set in advance.

  Next, in step S108, the main control unit 301 controls the sensor control unit 310 to drive the reading sensor 304. Similarly to the above, the digital image signal output value D108 output from the AFE 305 is acquired via the AFE control unit 311 and stored in the SD-RAM 306 (second acquisition step).

  Next, in step S109, the main control unit 301 calculates the expression (D108-D106) / (L2-L1) from the digital image signal output value D106 acquired in step S106 and the digital image signal output value D108 acquired in step S108. Is used to calculate the slope A. After calculating the slope A, the main control unit 301 calculates the intercept B (see FIG. 3) using the formula D106−L1 × A. Note that the intercept B may be calculated from D108-L2 × A.

  After calculating the slope A and the intercept B, the main control unit 301 calculates (DT−B) / A from the preset target value DT, slope A, and intercept B of the digital image reading signal, and the lighting period of the light source 103. LT is determined. Thus, the adjustment of the lighting period (light quantity) of the light source 103 is completed.

  Finally, adjust the white reference. In step S <b> 110, the main control unit 301 controls the light amount control unit 309 to drive the lighting drive circuit 312 during the lighting period LT calculated in step S <b> 109 to turn on the light source 303.

  Next, in step S111, the main control unit 301 controls the sensor control unit 310 to drive the reading sensor 304, and similarly to the above, the digital image signal output value output from the AFE 305 is passed through the AFE control unit 311. Obtained and stored in the SD-RAM 306.

  Next, in step S112, the main control unit 301 controls the AFE control unit 311, and based on the digital image signal output value acquired in step S109, sets the amplification factor of the AFE 305 so as to become a preset white reference value. Change the register to be set. Thus, the white reference adjustment is completed, and the process ends.

  As described above, in the present embodiment, light amount adjustment at the time of image reading is performed based on the output signal of the reading sensor 304 when the light source 303 is lit with the first light amount and when the light source 303 is lit with the second light amount. For this reason, when the lighting period is controlled to be short, the light source is not lit and the digital signal output value does not increase. / N ratio can be improved. Thereby, the optimal light quantity for obtaining a high quality image can be obtained in a short time.

(Second Embodiment)
Next, an image reading apparatus according to a second embodiment of the present invention will be described with reference to FIGS. In addition, about the part which overlaps with the said 1st Embodiment, a code | symbol is diverted and demonstrated.

  FIG. 4 is a flowchart for explaining an example of the light amount adjustment operation of the light source, and FIG. 5 is a graph showing the relationship between the light amount and the AFE output during the light amount adjustment operation of the light source.

  In the present embodiment, a process of automatically setting the light amount value of the first light amount is added between step S104 and step S105 of FIG. 2 in the first embodiment.

  After completion of the black reference adjustment in step S104 of FIG. 2, in step S901, the main control unit 301 adds an increase LS of the lighting period to the preset lighting period or the current lighting period, and sets the lighting period. Change the setting (see FIG. 5). The lighting period increment LS is preferably a lighting period obtained by dividing the first lighting period L1 obtained empirically or experimentally, but is not limited thereto.

  Next, in step S902, the main control unit 301 controls the light amount control unit 309 to drive the lighting drive circuit 312 in the lighting period set in step S901, thereby lighting the light source 303.

  Next, in step S903, the main control unit 301 controls the sensor control unit 310 to drive the reading sensor 304, and similarly to the above, the digital image signal output value D903 output from the AFE 305 is passed through the AFE control unit 311. Obtained and stored in the SD-RAM 306.

  Next, in step S904, the main control unit 301 determines whether the digital image reading signal output value D903 acquired in step S903 is greater than or equal to the reference value DL1.

  When the digital image reading signal output value D903 is less than the reference value DL1, the main control unit 301 returns to step S901, further adds the lighting period increment LS (see FIG. 5), and performs the processing after step S902. repeat.

  On the other hand, when the digital image reading signal output value D903 is greater than or equal to the reference value DL1, the main control unit 301 proceeds to step S905.

  In step S905, the main control unit 301 sets the lighting period set in step S901 to the first light quantity lighting period L1, and proceeds to step S105 in FIG.

  As described above, in the present embodiment, the light amount of the light source 303 is increased by a certain amount at regular intervals, and the light amount when the signal output value of the reading sensor 304 exceeds a predetermined value is set as the first light amount. The first light amount can be automatically set without setting the first light amount in advance. Note that the present invention includes a case where the increment LS of the lighting period is not a constant value. Further, the present invention includes not only increasing the amount of light but also decreasing it. Other configurations and operational effects are the same as those of the first embodiment.

(Third embodiment)
Next, an image reading apparatus according to a third embodiment of the present invention will be described with reference to FIG. FIG. 6 is a graph showing the relationship between the light amount and the AFE output during the light amount adjustment operation of the light source. In addition, about the part which overlaps with the said 1st and 2nd embodiment, a code | symbol is diverted and demonstrated.

  The present embodiment is an example in which processing for automatically setting the light amount value of the first light amount is added to the first embodiment, similarly to the second embodiment, but step S904 in FIG. 4 is added. The processing of is different.

  That is, in step S904 of FIG. 4, the main control unit 301 calculates a difference value (change amount) DM1 between the digital image reading signal output value acquired in step S903 and the previously acquired digital image reading signal output value, It is determined whether the difference value DM1 is greater than or equal to the reference value DL1. In the present embodiment, the digital image reading signal output value acquired previously is the black reference value D104.

  If the difference value DM1 is less than the reference value DL1 shown in FIG. 6, the main control unit 301 returns to step S901, further adds an increase LS of the lighting period (see FIG. 6), and performs the processing after step S902. repeat.

  On the other hand, if the difference value DM1 is greater than or equal to the reference value DL1, the main control unit 301 proceeds to step S905, sets the lighting period set in step S901 to the first light quantity lighting period L1, and proceeds to step S105 in FIG. .

  In the present embodiment, the difference value DM1 is calculated from the difference between the acquired digital image signal output value and the black reference value D104. However, as shown in FIG. You may use the digital image reading signal output value acquired when it turned on with the light quantity. Further, instead of the black reference value, an average value of the digital image reading signal output values that are turned on with the immediately preceding light amount may be used. Also, a digital image read signal output value acquired at a light quantity several times before may be used instead of just before.

  As described above, in the present embodiment, the light amount of the light source 303 is increased by a certain amount at regular intervals, and the signal output value of the reading sensor 304 at the time of increasing the light amount and the signal output value of the reading sensor 304 acquired previously are calculated. The amount of light when the difference value is equal to or greater than a predetermined value is defined as the first amount of light. Thereby, the first light quantity can be set automatically without setting the first light quantity in advance. Other configurations and operational effects are the same as those of the first and second embodiments.

  In addition, this invention is not limited to what was illustrated by said each embodiment, In the range which does not deviate from the summary of this invention, it can change suitably.

  For example, an image sensor in which the signal output decreases may be used instead of an image sensor in which the signal output increases when the amount of light increases. In this case, for example, a difference obtained by subtracting the signal output from the reference signal output corresponds to the signal output value of the present invention. Further, the present invention includes the case where the light amount is adjusted not by increasing or decreasing the lighting period but by adjusting the voltage / current of a signal for inputting the light emission intensity of the light source.

  The object of the present invention can also be achieved by executing the following processing. That is, a storage medium that records a program code of software that realizes the functions of the above-described embodiments is supplied to a system or apparatus, and a computer (or CPU, MPU, etc.) of the system or apparatus is stored in the storage medium. This is the process of reading the code.

  In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code and the storage medium storing the program code constitute the present invention.

  Moreover, the following can be used as a storage medium for supplying the program code. For example, floppy (registered trademark) disk, hard disk, magneto-optical disk, CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM, DVD-RW, DVD + RW, magnetic tape, nonvolatile memory card, ROM or the like. Alternatively, the program code may be downloaded via a network.

  Further, the present invention includes a case where the function of the above-described embodiment is realized by executing the program code read by the computer. In addition, an OS (operating system) running on the computer performs part or all of the actual processing based on an instruction of the program code, and the functions of the above-described embodiments are realized by the processing. Is also included.

  Furthermore, a case where the functions of the above-described embodiment are realized by the following processing is also included in the present invention. That is, the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer. Thereafter, based on the instruction of the program code, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing.

1 is a block diagram for explaining a device configuration of an image reading apparatus according to a first embodiment of the present invention. It is a flowchart for demonstrating the light quantity adjustment operation example of a light source. It is a graph which shows the relationship between the light quantity at the time of light quantity adjustment operation of a light source, and an AFE output. It is a flowchart for demonstrating the light quantity adjustment operation example of the light source in the image reading apparatus which is the 2nd Embodiment of this invention. It is a graph which shows the relationship between the light quantity at the time of light quantity adjustment operation of a light source, and an AFE output. It is a graph which shows the relationship between the light quantity at the time of light quantity adjustment operation of the light source, and AFE output in the image reading apparatus which is the 3rd Embodiment of this invention. It is a graph which shows the relationship between the light quantity at the time of light quantity adjustment operation of a light source, and an AFE output. It is a graph which shows the relationship between the light quantity and AFE output in the case of performing light quantity adjustment with the output data when the light source is lit with the first light quantity and when it is not lit. It is a block diagram which shows the circuit which drives a light source. It is a graph which shows the output of a light source when the lighting period of a light source is long enough. It is a graph which shows the output of a light source when the lighting period of a light source is short. The graph which shows the relationship between the light quantity and AFE output in case light quantity adjustment is performed with the output data when the light source is turned on with the first light quantity and the light source is not turned on with the AFE output not changing when the set light quantity is low It is.

Explanation of symbols

301 Main controller 302 ROM
303 Light source 304 Reading sensor 305 AFE
306 SD-RAM
307 Reference plate 308 External IF control unit 309 Light amount control unit 310 Sensor control unit 311 AFE control unit 312 Lighting drive circuit

Claims (7)

A reference member having a predetermined reference density, a light source that emits light to the reference member, a driving unit that drives the light source to turn on, and a reflected light of the light emitted from the light source to the reference member is received and photoelectrically received. A reading unit that outputs an image signal by conversion, and a control unit that controls the driving unit based on the output signal of the reading unit to adjust the light amount of the light source during image reading ,
The control means outputs an output signal of the reading means when the light source is turned on with a first light amount so as to be longer than a lighting period required until the light source is turned on, and a lighting period when the light source is the first light amount. wherein at the time of lighting the light source in the second light quantity to be longer than on the basis of the output signal of the reading means, for adjusting the light quantity of the light source at the time of reading the image, the image reading apparatus characterized by. The image reading apparatus according to claim 1, further comprising a unit that changes a light amount of the light source, obtains a light amount at which a signal output value of the reading unit is equal to or greater than a predetermined reference value, and sets the light amount to the first light amount. apparatus. And a means for changing the light amount of the light source by a certain amount, and setting the light amount at which the change amount of the signal output value of the reading means with respect to the change of the constant amount is a predetermined reference value or more as the first light amount. The image reading apparatus according to claim 1. Wherein said control means includes an image reading equipment according to claim 1, characterized in that the light quantity adjustment of the light source before reading by the reading means. The image reading apparatus according to claim 1, wherein the control unit performs black reference adjustment based on an output value when the light source is turned off before the light amount adjustment of the light source . A reference member having a predetermined reference density, a light source that emits light to the reference member, a driving unit that drives the light source to turn on, and a reflected light of the light emitted from the light source to the reference member are received and photoelectrically received. A reading unit that outputs an image signal by converting the image reading apparatus,
A first acquisition step of turning on the light source with a first light amount so as to be longer than a lighting period required until the light source is turned on, and obtaining an output signal of the reading means; and turning on the light source with the first light amount The second acquisition step of turning on the second light amount so as to be longer than the period and acquiring the output signal of the reading means, the output signal acquired in the first acquisition step, and the second acquisition step And a control step of controlling the driving means based on the output signal to adjust the light quantity of the light source during image reading. A reference member having a predetermined reference density, a light source that emits light to the reference member, a driving unit that drives the light source to turn on, and a reflected light of the light emitted from the light source to the reference member are received and photoelectrically received. A program for controlling an image reading apparatus comprising: a reading unit that outputs an image signal by conversion;
A first acquisition step of turning on the light source with a first light amount so as to be longer than a lighting period required until the light source is turned on, and obtaining an output signal of the reading means; and turning on the light source with the first light amount The second acquisition step of turning on the second light amount so as to be longer than the period and acquiring the output signal of the reading means, the output signal acquired in the first acquisition step, and the second acquisition step And a control step of adjusting the light quantity of the light source during image reading by controlling the driving unit based on an output signal.

Images