JP4334372B2 - Image reading apparatus, image forming apparatus, and image reading method - Google Patents

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, and an image reading method using an image sensor as an image reading element.

  Conventionally, in CCD linear image sensors used in image reading devices used in digital copying machines, facsimiles, etc. in addition to a single image scanner, output is alternately performed at odd / even pixel numbers such as ODD / EVEN output. Sorting is done. In other words, an ODD / EVEN two-channel output image sensor and an analog signal processing circuit are provided, and analog image signals output from the image sensors are odd-numbered / even-numbered independently and processed in parallel independently, thereby increasing the reading speed. It has been.

  However, at present, there is an increasing demand for an image reading apparatus having a higher reading speed than before, and it is necessary to realize a reading speed that cannot be achieved by such an ODD / EVEN 2-channel output image sensor.

  For this reason, recently, as a sensor capable of realizing a reading speed twice as high as that of an ODD / EVEN 2-channel output image sensor, in addition to the ODD / EVEN separate reading, the light receiving element array is shifted left and right at the center in the main scanning direction. Dividing into two parts, the first half (First) and the second half (Last), and dividing the whole into four parts to make the pixel frequency 1/4, so-called 4-channel output image sensor (FL type image sensor) Has been proposed (see, for example, Patent Documents 1 and 2).

  In an image reading apparatus using such a 4-channel output image sensor, a level difference occurs between the left and right read signals due to a slight difference in linearity characteristics of each of the output signals of a total of 4 channels. At the border, there will be a step in the read signal level on the left and right. Here, in the case of a conventional ODD / EVEN two-channel output image sensor, even if a signal level difference occurs in ODD / EVEN, a very fine repeated pattern is slightly added to the reproduced image. However, when a step occurs in the read signal level at the left and right division positions, even a slight signal step becomes very conspicuous.

JP-A-11-215298 JP 2002-158837 A

  Therefore, in Patent Document 1, a test pattern output from a printer unit is read by an image reading device, and correction is performed by performing gamma conversion based on the value. That is, when a 4-channel output CCD is used, correction is performed using a left / right correction circuit in which the adjustment of the correction is clarified, and the variation in the left / right CCD characteristics due to the difference in CCD devices is eliminated, and the left / right density between the airframes is eliminated. In order to reproduce a stable image density without any difference, in the gradation pattern reading mode, the gradation pattern reading process of the image processing ASIC reads each gradation data by scanning the scanner unit and reading out the image data of a plurality of pixel parts to obtain an average value. The basic unit CPU performs correction processing calculation based on the difference between the image data corresponding to the left side of the read 4-channel output CCD and the image data corresponding to the right side, and the calculated correction data is corrected to the left and right by the left and right correction circuit. It is set to the table.

  However, the output of the printer unit is indispensable for the correction of the method of Patent Document 1, and this method cannot be applied to a single image reading apparatus. In addition, it is sufficient to prepare a reference document in advance. However, since only a small signal step is at issue now, slight dirt or scratches on the document adversely affect the characteristics of the image reading apparatus. There is a possibility that. Further, Patent Document 1 does not specify the interval at which correction data is updated (execution of the proposed invention). However, if this interval is widened, the correction data does not match when the characteristics of the image reading apparatus change, and the reverse. It is possible that the signal step is converted into a conspicuous direction.

  Here, as a cause of the level difference between the left and right (first half, second half) read signals, there is a difference in sampling points of the CCD output waveform. The ideal CCD output is a waveform that gradually approaches a constant value as shown by the solid line in FIG. 18, but actually, after rebounding with an undershoot as shown by a broken line or an overshoot as shown by a one-dot chain line. It may be a waveform toward convergence. In the case of very high speed driving, there is a case where it does not converge to a constant value within a specified output period. Further, when comparing waveforms between a plurality of output terminals, the convergence ratio is often slightly different even when the rebound waveform is not used. This difference in waveform depends on the input timing of the clock for driving the CCD, the input waveform, etc., and even when viewed at multiple terminals of the same CCD package, it is common that all outputs do not have the same waveform. .

  There is no problem if sampling is performed after convergence (A in FIG. 18) with respect to the CCD output waveform such as a broken line or a one-dot chain line. In some cases, sampling is performed at B in FIG. The CCD basically outputs a voltage proportional to the amount of received light, but cannot accurately obtain a voltage at a point before convergence. As a result, the linearity difference as described above occurs, and in the case of the first half / second half divided CCD, a difference in read signal level between the left and right (first half / second half) occurs.

  An object of the present invention is to correct variations in output value linearity due to output signal distortion during high-speed reading so that a high-quality image can be obtained.

An image reading apparatus according to a first aspect of the present invention includes an image sensor that receives optical image information and outputs an analog image signal corresponding to the received light amount, and an A / D converter that converts the analog image signal into digital image data. Correction means for correcting the converted digital image data to appropriate data by linearity correction data, a drive frequency of the image sensor being a first frequency, slower than the first frequency, and the image sensor Means for changing the relationship between the analog signal to be output and the optical image information to a second frequency that is linear, and output of the digital image data obtained when the drive frequency of the image sensor is the first frequency the output level of the digital image data obtained when the level is set to the second frequency driving frequency of the image sensor The linearity correction data associated such that and means for setting said correction means.

  According to a second aspect of the present invention, in the image reading apparatus according to the first aspect, the image sensor is divided into a first half and a second half at the center in the main scanning direction, and the pixel outputs of the sensor array respectively correspond to each other. Sort output to the A / D converter.

  According to a third aspect of the present invention, in the image reading apparatus according to the second aspect, the image sensor includes a sensor array in which each of the first half and the second half is further divided into an even pixel portion and an odd pixel portion. Are alternately distributed and output to the corresponding A / D converters.

  According to a fourth aspect of the present invention, in the image reading apparatus according to any one of the first to third aspects, the image sensor is a color image sensor having a sensor unit for each of RGB colors.

  According to a fifth aspect of the present invention, in the image reading apparatus according to the second or third aspect, the correction unit corrects the digital image data for each path output from the A / D converters.

  According to a sixth aspect of the present invention, in the image reading apparatus according to the third aspect, the correction means outputs the even-numbered pixel portion and the odd-numbered pixel portion in the first half portion and the second half portion that are output from the A / D converters. The digital image data is corrected for each path synthesized in time series.

  According to a seventh aspect of the present invention, in the image reading apparatus according to any one of the first to sixth aspects, the correction unit corrects the digital image data before shading correction.

  According to an eighth aspect of the present invention, in the image reading apparatus according to the seventh aspect, the correction unit corrects the digital image data after an offset level correction process.

  According to a ninth aspect of the present invention, in the image reading apparatus according to any one of the first to eighth aspects, the correction unit has a lookup correction table in which linearity correction data is set.

According to a tenth aspect of the present invention, in the image reading apparatus according to any one of the first to ninth aspects, the generation / setting operation of the linearity correction data is performed when the apparatus is activated.

An image forming apparatus according to an eleventh aspect of the invention forms an image on a recording medium on the basis of the image reading apparatus according to any one of claims 1 to 10 that reads an image of the original and the read image of the original. A printer engine.

According to a twelfth aspect of the present invention, in the image forming apparatus according to the eleventh aspect , the linearity correction data is generated and set when the process adjustment of the printer engine is executed.

According to a thirteenth aspect of the present invention, in the image forming apparatus according to the eleventh aspect , the linearity correction data is generated and set when the apparatus is started and when process adjustment of the printer engine is executed.

In the image reading method according to the fourteenth aspect of the invention, optical image information is received by an image sensor, an analog image signal corresponding to the amount of received light is output, and the analog image signal is converted into digital image data by an A / D converter. An image reading method, wherein the driving frequency of the image sensor is lower than the first frequency, the analog signal output from the image sensor, and the optical image information. Is changed to a linear second frequency, and the output level of the digital image data obtained when the driving frequency of the image sensor is the first frequency, the driving frequency of the image sensor is set to the second frequency. wherein correcting the linearity correction data to which the associated so that the output level of the digital image data obtained when the frequency of And a step of setting the stage, a step of correcting the digital image data converted by the read from the document at the document image reading said A / D converter to the correct data by linearity correction data of the correction means.

According to a fifteenth aspect of the present invention, in the image reading method according to the fourteenth aspect , the image sensor is divided into a first half and a second half at the center in the main scanning direction to respectively correspond to the pixel outputs of the sensor array. Sort output to the A / D converter.

According to a sixteenth aspect of the present invention, in the image reading method according to the fifteenth aspect , the image sensor includes a sensor array in which each of the first half and the second half is further divided into an even pixel portion and an odd pixel portion. Are alternately distributed and output to the corresponding A / D converters.

According to a seventeenth aspect of the present invention, in the image reading method according to the fifteenth or sixteenth aspect , the image sensor is a color image sensor having a sensor section for each of RGB colors.

According to an eighteenth aspect of the present invention, in the image reading method according to the fifteenth or sixteenth aspect , in the correction step, the digital image data is corrected for each path output from each A / D converter.

According to a nineteenth aspect of the present invention, in the image reading method according to the sixteenth aspect , in the correction step, the even-numbered pixel portion and the odd-numbered pixel portion that are output from the A / D converters in the first half portion and the second half portion. The digital image data is corrected for each path synthesized in time series.

According to a twentieth aspect of the present invention, in the image reading method according to any one of the fourteenth to nineteenth aspects, the correction step corrects the digital image data before shading correction.

According to a twenty- first aspect of the present invention, in the image reading method according to the twentieth aspect , the correction step corrects the digital image data after an offset level correction process.

According to a twenty-second aspect of the present invention, in the image reading method according to any one of the fourteenth to twenty- first aspects, a lookup correction table in which linearity correction data is set is used in the correction step.

A twenty- third aspect of the present invention is the image reading method according to any one of the fourteenth to twenty-second aspects, wherein the linearity correction data generation / setting operation is performed when the apparatus is activated.

According to the first and fourteenth aspects of the present invention, the drive condition of the image sensor can be changed, and linearity correction data that associates digital image data before and after the change obtained by changing the drive condition is set in the correction means. In the correction means, the digital image data is corrected to appropriate data using the linearity correction data. Therefore, even when digital image data whose linearity is impaired under certain driving conditions is output, By correcting using linearity correction data based on digital image data with good linearity under conditions, an output result with good linearity can be obtained, and as a result, it is related to reading methods such as the first half / second half split method. Therefore, a normal read output result can be obtained. For this purpose, it is sufficient to change the driving conditions of the image sensor, and this can be realized without requiring a correction document or a copy print image as in Patent Document 1.

According to the invention described in claims 2, 3, 4, 15 , 16 , and 17, even when using an image sensor of a type that is divided into two parts for the first half and the second half and outputs the divided linearity, Since correction can be performed properly, there is basically no step between the systems, and clean read image data can be obtained.

According to the fifth and eighteenth aspects of the present invention, since linearity correction of digital image data is performed for each path output from the A / D converter, the read data can be optimized for each path. According to the sixth and nineteenth aspects of the invention, in the case of a so-called four-channel image sensor, correction processing is performed in two systems of the first half and the second half, so that the configuration of the correction means is further improved. It can be simplified.

According to the inventions of claims 7 and 20 , since the linearity correction process is performed before the shading correction, the shading correction process can be performed using appropriate data, and the shading correction process can be optimized. it can.

According to the invention of claim 8, 21 wherein, since the performing linearity correction processing after the offset level correction processing, without being affected by the offset level, it is possible to further optimize the linearity correction processing .

Further, according to the ninth and twenty-second aspects of the present invention, the lookup correction table is used for the linearity correction processing, and therefore, it can be easily realized.

According to the tenth and twenty-third aspect of the present invention, since the linearity correction data is generated and set every time the apparatus is started up, even if there is a change in the image sensor output characteristics due to some factors over time, Linearity correction data that can be dealt with can be generated and set, and a reading operation with good linearity characteristics can be performed even when viewed over time.

According to the eleventh aspect of the present invention, since the image reading apparatus according to the first to tenth aspects is provided, the image forming operation can be performed based on the read image data having good linearity characteristics, and a clean image can be obtained. Can do.

According to the inventions according to claims 12 and 13, since the linearity correction data is generated and set using the process adjustment execution time for the printer engine, a unique time for the correction data generation processing is set. Can be processed efficiently.

  The best mode for carrying out the present invention will be described with reference to the drawings.

[First embodiment]
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a longitudinal side view showing an overall configuration of an image reading apparatus 1 according to the present embodiment. As shown in FIG. 1, the image reading apparatus 1 is of a flat bed type, and includes a contact glass 3 on which a document 2 is placed, a halogen lamp (light source) 4 for exposing the document 2, and a first reflection mirror 5. A first carriage 6 comprising: a second carriage 9 comprising a second reflecting mirror 7 and a third reflecting mirror 8; a CCD linear image sensor 10 (hereinafter simply referred to as CCD 10) that is an image sensor; A white reference plate 12 for shading correction, and a stepping motor 14 for driving the first carriage 6 and the second carriage 9. The CCD 10 is provided on the sensor substrate 13. The halogen lamp 4, the first, second and third reflection mirrors 5, 7, 8 and the lens unit 11 constitute a scanning optical system.

  The halogen lamp 4 irradiates light at a certain angle with respect to the reading surface of the white reference plate 12 or the contact glass 3, and the light reflected by the white reference plate 12 or the original 2 is the first, second and third reflecting mirrors. The light enters the CCD 10 via 5, 7, 8 and the lens unit 11. The CCD 10 outputs a voltage corresponding to the amount of incident light as an analog image signal. The first and second carriages 6, 9 are moved in the sub-scanning direction while the distance between the reading surface of the document 2 and the CCD 10 is kept constant by driving the stepping motor 14, and the document 2 is exposed and scanned.

  In this embodiment, a 4-channel output image sensor (FL CCD) as shown in FIG. 2 is used as the CCD 10. FIG. 2 is a block diagram showing an internal configuration example of such a FL CCD 10. In FIG. 2, reference numeral 21 denotes a photodiode array (light receiving pixel array) in which a number of pixels that actually receive the reflected light from the document surface in the CCD 10 are arranged in a line. Reference numerals 22 to 25 denote shift gate registers for separating charges accumulated in each pixel of the photodiode array 21 into odd (ODD) pixels and even (EVEN) pixels and sequentially reading them in different directions. Shift gates 26 and 27 are interposed between the diode array 21. Reference numerals 29 to 32 denote output amplifiers for converting electric charges read from the shift gate registers 22 to 25 into voltage signals and outputting them.

  With such a configuration, the shift gate registers 22 to 25 of the CCD 10 according to the present embodiment allow the charge accumulated in each pixel of the photodiode array 21 to be in the first half (First) and second half with the center in the main scanning direction as a boundary. (Last) is divided into two parts on the left and right sides, and each is divided into ODD / EVEN alternately and read. More specifically, the first half pixel is output sequentially from the first pixel on the first half side, and the second half pixel is output sequentially from the last pixel on the second half side.

  In FIG. 2, a signal SH is a charge shift pulse, and controls shift gates 26 and 27 for simultaneously shifting charges accumulated in the photodiode array 21 to the shift gate registers 22 to 25. Signals φ1 and φ2 are charge transfer pulses for driving the shift gate registers 22 to 25. Charges shifted from the photodiode array 21 to the shift gate registers 22 to 25 at the same time by the charge shift pulse SH are Each pixel is sequentially moved by one pixel in the direction of the output amplifiers 29 to 32 at the ends of the shift gate registers 22 to 25. As a result, four series of analog image signals as shown in FO, FE, LO, and LE are output.

  A schematic block diagram of a part of the image reading apparatus of the present embodiment using such a CCD 10 is shown in FIG. FIG. 3 shows processing up to the image processing means. The CCD 10 is a four-channel output image sensor that outputs analog image signals for the four channels FE, FO, LE, and LO as described above in parallel, and each of the FE, FO, LE, and LO is configured by an LSI. Input to corresponding AFEs (analog front-end processors) 31a to 31d that perform analog processing. Then, after predetermined analog processing is performed by the AFEs 31a to 31d, they are input to A / DC (A / D converters) 32a to 32d and converted into digital image data, respectively. Then, the correction process is performed by the linearity correction means 33, which is a particularly characteristic feature of the present embodiment. Thereafter, these two series of digital image data are combined into one time-series data, and further passed through normal image processing means 34 for performing necessary image processing (such as MTF correction processing), from the image reading apparatus 1. Is output. In this case, the operation timing and the like are controlled by a timing signal from the timing generation unit 35.

  The configuration example shown in FIG. 3 will be further described with reference to FIG. 4 showing the details. The AFE 31a includes a sample hold circuit (S / H1) 41a, a variable gain amplifier (AMP1) 42a, a reference level adjustment circuit (BK1) 43a, and a buffer amplifier (buffer 1) 44a. The same applies to the other AFEs 31b to 31d. Analog image signals FE, FO, LE, and LO output from the CCD 10 are converted into digital image data Dfe, Dfo, Dle, and Dlo by the A / DCs 32a to 32d after passing through the AFEs 31a to 31d. The image is output as an image output through the processing means 34. The CPU 36 is connected to the linearity correction unit 33 and the timing generation unit 35, and adjusts the reference level, adjusts the gains of the variable gain amplifiers 42a to 42d, sets linearity correction data for the linearity correction unit 33 described later, and the like. The light source lighting device 37 is a voltage supply source for lighting the light source 4.

  The CCD 10 is supplied with the drive clock S1 output from the timing generation means 35, and outputs voltages (FE, FO, LE, LO) substantially proportional to the amount of received light as analog image signals. Here, the drive clock S1 drives the analog shift gate registers 23, 22, 25, and 24, which is a clock for transferring charges from the photodiode array 21 shown in FIG. 2 to the analog shift gate registers 23, 22, 25, and 24. The clocks Φ1, Φ2, etc. are indicated.

  The sample and hold circuits (S / H1 to 4) 41a to 41d sample and hold the output voltages (FE, FO, LE, and LO) according to the clock S2, and remove unnecessary high frequency components included in the image signal. The variable gain amplifiers (AMP1 to 4) 42a to 42d amplify the outputs of the sample hold circuits (S / H1 to 4) 41a to 41d with the gain indicated by the voltage signal S5.

  The reference level (black level) adjustment circuits (BK1 to 4) 43a to 43d clamp the outputs of the variable gain amplifiers (AMP1 to 4) 42a to 42d in the period indicated by the timing signal S3, and are instructed by the voltage signal S6. Add an offset level. The A / D converters (A / DC1 to 4) 32a to 32d convert the input analog image signal into digital image data at the timing of the clock S4.

  The timing generation unit 35 generates a clock under the conditions instructed by the CPU 36 and interfaces with a D / A converter (D / AC) 38. Here, the conditions instructed by the CPU 36 are a clock frequency, a phase between clocks, and the like.

  The light source lighting device 37 turns on the light source 4 by the lamp lighting signal S7 and the lamp clock S8 from the timing generation means 35 (see FIG. 7). In the state where the lamp clock S8 is input and the lamp lighting signal S7 is in the low level period, the light source lighting device 37 applies a voltage to the lamp 4 at a period based on the lamp clock S8 to light it. Further, when the lamp lighting signal S7 is in the high level period, the periodic voltage is not applied to the lamp 4 and is turned off.

  The linearity correction means 33 has a function of storing linearity correction data created based on data obtained by changing the drive frequency as a drive condition of the CCD 10, and the memory stored when the original image is actually read. It has a function of correcting digital data Dfe, Dfo, Dle, and Dlo using linearity correction data. The timing for storing the linearity correction data is performed every time the image reading apparatus 1 is activated, for example, when the power is turned on or when the energy saving mode is exited.

  Next, a detailed configuration example of the linearity correcting unit 33 will be described with reference to a block diagram shown in FIG. The linearity correction means 33 of this embodiment includes a black level subtraction circuit 51, a black level detection circuit 52, a linearity correction circuit 53, a shading calculation circuit 54, a shading data generation circuit 55, a peak data detection circuit 56, and a sequence conversion circuit 57. . Of these, except for the order conversion circuit 57, the others are individually provided for FE, FO, LE, and LO for each path of the digital image data Dfe, Dfo, Dle, and Dlo.

  First, digital image data Dfe, Dfo, Dle, and Dlo digitized by A / D converters (A / DC1 to 4) 32 a to 32 d are input to a black level detection circuit 52 and a black level subtraction circuit 51.

  The black level detection circuit 52 is a circuit that detects an offset (black) level added to an image signal, and detects each path through which digital image data Dfe, Dfo, Dle, and Dlo are transmitted. As the offset level, the value of the OPB pixel (several consecutively light-shielded pixels) of the CCD 10 is taken in as long as the “black level detection range” signal shown in the timing chart of FIG. Ask. This calculation may be a simple average or a multiple addition average. The obtained offset level is stored in the register as Bkfe, Bkfo, Bkle, Bklo. This process is periodically performed while the “black level detection range” signal is H.

  The black level subtraction circuit 51 subtracts the corresponding offset levels Bkfe, Bkfo, Bkle, Bklo obtained by the black level detection circuit 52 from each pixel of the input digital image data Dfe, Dfo, Dle, Dlo. It is.

  The linearity correction circuit 53 has a correction conversion circuit corresponding to each path of the digital image data Dfe1, Dfo1, Dle1, and Dlo1, and corrects the corrected values when black-subtracted data Dfe1, Dfo1, Dle1, and Dlo1 are input. Obtained and output as appropriate data Dfe2, Dfo2, Dle2, Dlo2. The relation between the input data Dfe1, Dfo1, Dle1, and Dlo1 and the appropriate data Dfe2, Dfo2, Dle2, and Dlo2 that are corrected and output is a configuration that the CPU 36 can set in the linearity correction circuit 53.

  The shading data generation circuit 55 is a predetermined period for reading the white reference plate 12 in the sub-scanning direction, and a period in which the “shading data generation range” signal shown in the timing chart of FIG. The average values of the linearity corrected image data Dfe2, Dfo2, Dle2, and Dlo2 are obtained for each pixel and stored in an internal memory. This calculation may be a simple average or a multiple addition average.

  The peak data detection circuit 56 obtains peak data during the period when the “shading data generation range” signal is H for each series of image data Dfe2, Dfo2, Dle2, and Dlo2 whose linearity has been corrected, and stores them in the register as Pkfe, Pkfo, Pkle, and Pklo. Store.

  The shading calculation circuit 54 calculates the corrected digital image data Dfe2, Dfo2, Dle2, and Dlo2 as the shading data SDfe, SDfo, SDle, and SDlo when reading the document. Since the shading calculation itself is well-known, description is omitted.

  The order conversion circuit 57 has a function of rearranging the data Dfe3, Dfo3, Dle3, and Dlo3 subjected to the shading operation into one data string. That is, whether the image data of the four systems of the even number pixel of the first half reading, the odd number pixel of the first half reading, the even number pixel of the second half reading, and the odd number pixel of the second half reading are read out in a dot-sequential manner from the left. Sort as follows. This may be the order from the right.

  Next, the operation of the image reading apparatus 1 of the present embodiment will be described with reference to FIGS.

  In the present embodiment, an attempt is made to obtain characteristics with excellent linearity by changing the reading conditions. Here, an example is considered in which the characteristics actually obtained are converted into characteristics close to ideal by changing the drive frequency of the CCD 10. In this case, it is said that the driving frequency of the CCD 10 is mainly changed. In addition, a clock for handling data such as a sample hold clock, an A / DC sampling clock, etc. is used for changing the driving frequency of the CCD 10. It shall be changed at the same rate.

  First, when the CCD drive frequency during normal reading is set to the high-speed drive frequency f1 (MHz), linear output characteristics with respect to the amount of received light cannot be obtained as in the case where data is sampled at point B in FIG. Think of a case. Here, when the CCD drive frequency is changed to the low-speed drive frequency f2 (MHz) where f1> f2, the output period of the CCD 10 becomes longer, so that the output converges to a certain value. Further, since the sampling position is also shifted backward, the output of the CCD 10 converged to a certain value can be obtained sufficiently stably. That is, appropriate data (correct value) can be acquired. However, reading at a driving frequency f2 slower than the driving frequency f1 during normal reading deteriorates the performance of the image reading apparatus 1 in terms of productivity. Therefore, before the actual reading operation, the data obtained at the drive frequency f1 is associated with the data obtained at the drive frequency f2.

  However, when performing this association, if the input conditions are different, the output range will be different. Therefore, even when the drive frequency is changed, the received light amount within one main scanning time must be the same.

  Therefore, the driving of the light source 4 will be described with reference to FIG. The light source lighting device 37 receives a lamp clock and a lamp lighting signal. In the case of the present embodiment, the lamp is turned on when the lamp lighting signal S7 is at a low level and the lamp is turned off at a high level while the lamp clock is input. More specifically, when the lamp lighting signal S7 is at a low level, discharge occurs in the light source 4 in synchronization with the edge of the lamp clock, and it strikes the phosphor inside the lamp and emits light. Since the lamp lighting signal is managed by a clock inside the timing generating means 35, very fine time management is possible. In FIG. 7, when the CCD driving frequency = f1, the main lighting time is 100%, 75%, 50%, 25%, and when the CCD driving frequency = f2 (where f1> f2), one main The timing example in which the amount of received light within the scanning time is the same as f1 is shown (the lamp clock in FIG. 7 is for f1, and in the case of f2, the time of this lamp clock is also changed). Such stepwise change of the lighting time of the light source 4 corresponds to means for stepwise changing the optical image information input to the CCD 10, and may be changed more finely stepwise.

  FIG. 8 is a flowchart showing “correction data creation” in which linearity correction data is set in the linearity correction circuit 53 based on data obtained by changing the drive frequency of the CCD 10 in the present embodiment.

  First, as the processing of step S1, the CCD drive frequency is set to f1, the initial gains of the variable gain amplifiers (AMP1 to AMP4) 42a to 42d (S5 in FIG. 4), and the initial value of the offset level (S6 in FIG. 4). Etc. are set. The light source 4 is turned on under condition 1 (100% on) shown in FIG. At this time, the CPU 36 sets linearity correction data in the memory of the linearity correction circuit 53 such that the corrected output values Dfe2, Dfo2, Dle2, and Dlo2 are the same as the input values Dfe1, Dfo1, Dle1, and Dlo1. .

Next, in step S2, the CPU 36 reads the peak values Pkfe, Pkfo, Pkle, Pklo of each system from the peak data detection circuit 56, and obtains the maximum value: Pk1 among them. The peak values Pkfe, Pkfo, Pkle, and Pklo of these systems are the data (Dfe2, Dfo2, Dle2, Dlo2) that have passed through the black level subtraction circuit 51 and the linearity correction circuit 53.
= (Dfe1, Dfo1, Dle1, Dlo1)
= (Dfe, Dfo, Dle, Dlo)-(Bkfe, Bkfo, Bkle, Bklo)
It is a value obtained based on.

  In steps S3 and S4, similarly to the case of step S2, the CCD drive frequency is changed to f2, and the maximum value: Pk2 is obtained.

  In steps S5, S6, and S7, Pk1 and Pk2 are compared, and black level adjustment and gain adjustment are executed under the condition that the larger data is obtained. In the black level adjustment, the CPU 36 reads the black levels Bkfe, Bkfo, Bkle, Bkl from the black level detection circuit 52, and supplies them to the reference level (black level) adjustment circuits (BK1 to 4) 43a to 43d so that they become target values. On the other hand, by resetting the voltage signal S6, the black level (Bkfe, Bkfo, Bkle, Bklo) is set to the target value.

  For gain adjustment, the CPU 36 reads the peak levels Pkfe, Pkfo, Pkle, and Pklo from the peak data detection circuit 56, and outputs the voltage signal S5 to the variable gain amplifiers (AMP1 to AMP4) 42a to 42d so that they become target values. By resetting, the black level (Bkfe, Pkfo, Pkle, Pklo) = target value is set.

  In steps S8 and S9, the CCD drive frequency is set to f2, and average data is obtained for each of the conditions 5 to 8 in FIG.

  Specifically, the CPU 36 reads a predetermined number of data at the center of the image (including the boundary between the first half reading and the second half reading) in the main scanning direction of the outputs SDfe, SDfo, SDle, SDlo of the shading data generation circuit 55, The average value is obtained as Avefe2, Avefo2, Avel2, and Avelo2. The result is stored in memory.

  In steps S10 and S11, the CCD drive frequency is set to f1, and average data is obtained for each of the conditions 1 to 4 in FIG. Specifically, the CPU 36 reads a predetermined number of data at the center of the image (including the boundary between the first half reading and the second half reading) in the main scanning direction of the outputs SDfe, SDfo, SDle, SDlo of the shading data generation circuit 55, Average values Avefe1, Avefo1, Avel1, and Avelo1 are obtained by calculation. The result is stored in memory.

  In step S12, the CPU 36 obtains a relational expression between them for each system based on the data obtained in steps S9 and S11.

  In step S13, the CPU 36 inputs a value to the memory in the linearity correction circuit 53 based on the relational expression obtained in step S12.

  Specifically, the linearity correction circuit 53 has a correction table configuration in the form of a look-up table (LUT), and the CPU 36 regards the output value of the CCD drive frequency f1 as the address of the LUT and reads the address at the CCD drive frequency f2. In this case, the associated values Lnfe, Lnfo, Lnle, and Lnlo are stored.

  Here, FIG. 9 is a graph showing the output values in the case of the CCD drive frequencies f1 and f2 obtained in steps S9 and S11. The horizontal axis represents the amount of incident light, and the vertical axis represents the obtained output value. An example in which the output value is linear = appropriate data (correct value) with respect to the incident light amount at the slow CCD drive frequency f2, whereas the output value increases excessively with respect to the increase in the incident light amount at the high speed drive frequency f1. Is shown. In the case of this example, the contents of the lookup table of the linearity correction circuit 53 are as shown in FIG. These look-up tables are individually provided for each path of FE, FO, LE, and LO. That is, the table is used to correct the data Dfe1, Dfo1, Dle1, and Dlo1 when the driving frequency is f1 to the appropriate data Dfe2, Dfo2, Dle2, and Dlo2 when the driving frequency is f2. Since this lookup table acquires data only under four lighting conditions of 100%, 75%, 50%, and 25%, the data between them is calculated by data interpolation processing.

  Here, in the present embodiment, such correction data creation processing (setting to the linearity correction circuit 53) is performed when the image reading apparatus 1 is activated (for example, when the power is turned on), as shown in FIG. (S21), and thereafter, when it is necessary to read a document (Y in S22), a document reading operation is performed (S23).

  The document reading operation will be described with reference to a schematic flowchart shown in FIG. First, in step S31, the black level subtraction circuit 51 subtracts the offset levels Bkfe, Bkfo, Bkle, Bklo of the black level detection circuit 52 from the digitally converted image data Dfe, Dfo, Dle, Dlo. Note that “*” in FIG. 12 indicates e or o.

  Next, in step S32, data correction processing 53 is performed on the data Dfe1, Dfo1, Dle1, and Dlo1 subjected to black subtraction in accordance with a lookup table as shown in FIG. 10, for example, so that Dfe2, Dfo2 , Dle2, and Dlo2.

  In step S33, the corrected appropriate data Dfe2, DDfo2, Dle2, and Dlo2 are output to the shading arithmetic circuit 54 to perform a shading correction process (in this embodiment, since it is 8-bit data, 255 is used. )

  Further, in step S34, the data input in parallel to the four systems to the linearity correction means 33 is serially rearranged and output by the order conversion circuit 57.

  Therefore, according to the present embodiment, it is possible to change the drive condition of the CCD 10, for example, the drive frequency, and the linearity correction data obtained by associating the digital image data before and after the change obtained by changing the drive condition is converted into the linearity correction circuit. 53, the linearity correction circuit 53 uses this linearity correction data to correct the digital image data to appropriate data. Therefore, even when digital image data whose linearity is impaired under certain driving conditions is output. By performing correction using linearity correction data based on digital image data with good linearity under other driving conditions, an output result with good linearity can be obtained. As a result, as in this embodiment, the CCD 10 can obtain a normal read output result regardless of the reading method such as the first half / second half divided method. For this purpose, it is only necessary to change the driving conditions of the CCD 10 to execute the reading operation, and this can be realized without requiring a correction document or a copy print image as in Patent Document 1. In particular, even in the case of using an FL type CCD that divides and outputs in the first half and the latter half as in the present embodiment, the linearity correction of each output system can be performed properly. In addition, there is no difference in level between the systems, particularly between the first half and the second half, and clean read image data can be obtained.

  Further, as specific processing, linearity correction of digital image data is performed for each path output from the A / D converters 32a to 32d, so that read data can be optimized for each path. Furthermore, since the linearity correction process is performed before the shading correction by the shading calculation circuit 54, the shading correction process can be performed using appropriate data, and the shading correction process can be optimized. Similarly, since the linearity correction processing is performed after the offset level correction processing by the black level subtraction circuit 51, the linearity correction processing can be further optimized without being affected by the offset level.

  In the present embodiment, since the linearity correction circuit 53 uses the lookup correction table for the linearity correction processing, it can be easily realized.

  Further, in this embodiment, since the linearity correction data is generated and set every time the image reading apparatus 1 is started up, it is possible to cope with the case where the image sensor output characteristics fluctuate due to some factors over time. The obtained linearity correction data can be generated and set, and a reading operation with good linearity characteristics can be performed even when viewed over time.

[Second Embodiment]
A second embodiment of the present invention will be described with reference to FIGS. The same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted (the same applies to the following embodiments).

  FIG. 13 is a block diagram illustrating a configuration example of the linearity correction unit 33 according to the present embodiment. Basically, the configuration is the same as that shown in FIG. 5, but in this embodiment, an EO synthesis circuit 58 is added after the black level subtraction circuit 51. The EO synthesizing circuit 58 synthesizes the digital image data Dfe1 and Dfo1 into one time series and outputs it as Dfeo, and synthesizes the digital image data Dle1 and Dlo1 into one time series and outputs it as Dleo. That is, the EO synthesis circuit 58 outputs two systems of digital image data Dfeo and Dleo divided into two parts, the first half and the second half, and the linearity correction circuit 53 and the shading calculation circuit 54 are associated with this. The shading data generation circuit 55 is also provided with two systems for FE / FO sharing and LE / LO sharing.

  FIG. 14 is a schematic flowchart showing an example of processing for creating linearity correction data based on data obtained by changing the CCD drive frequency and setting it in the linearity correction circuit 53 in the case of the configuration of the present embodiment. Basically, the processing example shown in FIG. 8 is applied. However, the major difference from the case of FIG. 8 is that the signals (Dfe1 and Dfo1) sequentially output from the first half of the CCD 10 are made one system, and the latter half of the CCD 10 is used. That is, the signals (Dle1 and Dlo1) sequentially output from the unit are processed as one system. As a result, the average in step S9 ′ is the average of Aveeo2 and Aveleo2, the average in step S11 ′ is the average of Aveeo1 and Aveeo1, and the relational expression obtained in step S12 is the relationship between Aveeo2 and Aveeo1. These are two correction data relating to the relation, Avelo2 and Aveleo1. The CPU 36 stores and sets in the linearity correction circuit 53 correction data for signals (Dfe1 and Dfo1) output in order from the first half of the CCD 10, and signals (Dle1 and Dlo1) output in order from the second half of the CCD 10. Correction data.

  Therefore, in the case of this embodiment, the same operation and effect as in the case of the first embodiment can be obtained, and in the case of the FL type CCD, correction processing is collectively performed in two systems of the first half and the second half. Therefore, the configuration of the correction means can be further simplified.

[Third embodiment]
A third embodiment of the present invention will be described with reference to FIGS. In this embodiment, instead of using the image reading apparatus 1 alone as described above, for example, as shown in FIG. 15, the image reading apparatus 1, the printer engine 62, a microcomputer for controlling the whole, and the like. An application example to a digital copying machine 61 or the like as an image forming apparatus provided with a control unit 63 composed of

  The configuration of the image reading apparatus 1 is as described above. The printer engine 62 forms an image on a recording medium such as paper, and the printing method is an electrophotographic method, an inkjet method, a sublimation type thermal transfer method, a silver salt photographic method, a direct thermal recording method, a melting method. Various known methods such as a mold thermal transfer method can be used. The control unit 63 controls the image reading device 1 and the printer engine 62, reads the document 2 with the image reading device 1, and forms an image with the printer 62 based on the read image data.

  Therefore, according to the digital copying machine 61, it is possible to form an image in which the linearity difference is not noticeable between the F series and the L series when the FL CCD is used.

  Here, in the image forming apparatus as in the present embodiment, in general, process conditions around the photoconductor and other conditions are set with respect to the printer engine 62 at power-on or at a predetermined timing prior to the image forming operation. A process adjustment operation is performed. Therefore, in the case of the present embodiment, as shown in FIG. 16, during the process adjustment operation on the printer engine 62 side (Y in S24), the linearity correction data is obtained by changing the driving condition (driving frequency) of the CCD 10. If the correction data generation process that is generated and stored and set in the linearity correction circuit 53 is performed (S25), the correction data generation process does not require a unique time and can be processed efficiently.

  Alternatively, as shown in the schematic flowchart of FIG. 17, after the correction data creation process is performed when the image reading apparatus 1 is started up (S21), the process adjustment on the printer engine 62 side is performed (Y in S24). Then, correction data creation processing may be performed (S25). According to this, even after activation, more appropriate correction data can be created and used for more appropriate linearity correction processing every time process adjustment is executed.

  Although not shown in particular, in each of the above-described embodiments, a color image using a color CCD (color image sensor) in which the CCD 10 as shown in FIG. 2 is integrally arranged as a sensor chip for each color of RGB. The same can be applied to the reading apparatus.

1 is a schematic side view illustrating a configuration example of an image reading apparatus according to a first embodiment of the present invention. It is a block diagram which shows the internal structural example of FL type CCD. 2 is a block diagram illustrating a configuration example of a part of the preceding stage of the image reading apparatus. FIG. It is a block diagram shown in more detail. It is a block diagram which shows the detailed structural example of a linearity correction | amendment means. It is a timing chart which shows the operation example for black level detection and shading data generation. It is a timing chart which shows the example of a condition in the case of changing the drive frequency of CCD, and its operation example. It is a schematic flowchart which shows the example of correction data creation processing. It is a characteristic figure of incident light quantity-output value at the time of drive frequency f1 and f2. It is explanatory drawing which shows the example of a characteristic of the lookup table. It is a schematic flowchart for demonstrating the time of correction data creation. It is a schematic flowchart which shows the example of a process control in the linearity correction | amendment means at the time of original reading. It is a block diagram which shows the detailed structural example of the linearity correction | amendment means of 2nd embodiment of this invention. It is a schematic flowchart for demonstrating the time of the correction data creation. It is a schematic front view which shows the digital copying machine of 3rd embodiment of this invention. It is a schematic flowchart for demonstrating the time of the correction data creation. It is a schematic flowchart for demonstrating the time of other correction data creation. It is explanatory drawing which shows the example of sampling output timing of CCD.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image reader 4 Light source 10 Image sensor 32 A / D converter 53 Correction means

Claims (23)

An image sensor that receives optical image information and outputs an analog image signal corresponding to the received light amount; and
An A / D converter for converting the analog image signal into digital image data;
Correction means for correcting the converted digital image data into appropriate data by linearity correction data;
The drive frequency of the image sensor is changed to a first frequency and a second frequency that is slower than the first frequency and the relationship between the analog signal output from the image sensor and the optical image information is linear. Means,
The output of the digital image data obtained when the output level of the digital image data obtained when the driving frequency of the image sensor and said first frequency is a second frequency the drive frequency of the image sensor Means for setting the linearity correction data associated to be level to the correction means;
An image reading apparatus comprising:   2. The image according to claim 1, wherein the image sensor is divided into a first half and a second half at the center in the main scanning direction, and outputs the pixel outputs of the sensor array to the corresponding A / D converters. Reader.   In the image sensor, each of the first half and the second half is further divided into an even-numbered pixel portion and an odd-numbered pixel portion, and the pixel outputs of the sensor array are alternately supplied to the corresponding A / D converters. The image reading apparatus according to claim 2, wherein the image reading apparatus performs sorting output.   The image reading apparatus according to claim 1, wherein the image sensor is a color image sensor having a sensor unit for each of RGB colors.   The image reading apparatus according to claim 2, wherein the correction unit corrects the digital image data for each path output from each of the A / D converters.   The correction means corrects the digital image data for each path output from each A / D converter and in which the even-numbered pixel portion and the odd-numbered pixel portion are synthesized in time series in the first half and the second half. The image reading apparatus according to claim 3.   The image reading apparatus according to claim 1, wherein the correction unit corrects the digital image data before shading correction.   The image reading apparatus according to claim 7, wherein the correction unit corrects the digital image data after an offset level correction process.   The image reading apparatus according to claim 1, wherein the correction unit includes a lookup correction table in which linearity correction data is set. The linearity generating and setting operation of the correction data is performed upon startup of the apparatus, the image reading apparatus of any one of claims 1 to 9. An image reading apparatus according to any one of claims 1 to 10 , which reads an image of a document;
A printer engine that forms an image on a recording medium based on the read image of the document;
An image forming apparatus comprising: The image forming apparatus according to claim 11 , wherein the linearity correction data generation / setting operation is performed when process adjustment of the printer engine is executed. The image forming apparatus according to claim 11 , wherein the linearity correction data generation / setting operation is performed when the apparatus is activated and when process adjustment of the printer engine is performed. An image reading method in which optical image information is received by an image sensor, an analog image signal corresponding to the received light amount is output, and the analog image signal is converted into digital image data by an A / D converter,
The drive frequency of the image sensor is changed to a first frequency and a second frequency that is slower than the first frequency and the relationship between the analog signal output from the image sensor and the optical image information is linear. Process,
The output of the digital image data obtained when the output level of the digital image data obtained when the driving frequency of the image sensor and said first frequency is a second frequency the drive frequency of the image sensor Setting the linearity correction data associated to be level to the correction means;
Correcting the digital image data read from the original and read by the A / D converter at the time of reading the original image into appropriate data using the linearity correction data of the correction unit;
An image reading method comprising: 15. The image according to claim 14 , wherein the image sensor is divided into a first half part and a second half part in the center of the main scanning direction, and outputs the pixel outputs of the sensor array to the corresponding A / D converters. Reading method. In the image sensor, each of the first half and the second half is further divided into an even-numbered pixel portion and an odd-numbered pixel portion, and the pixel outputs of the sensor array are alternately supplied to the corresponding A / D converters. The image reading method according to claim 15 , wherein the output is distributed. The image reading method according to claim 15 or 16 , wherein the image sensor is a color image sensor having a sensor unit for each of RGB colors. The image reading method according to claim 15 or 16 , wherein, in the correction step, the digital image data is corrected for each path output from each of the A / D converters. In the correction step, the digital image data is corrected for each path output from each A / D converter and in which the even-numbered pixel portion and the odd-numbered pixel portion are synthesized in time series in the first half and the second half. The image reading method according to claim 16 . Wherein the correction step corrects the digital image data prior to shading correction, any one image reading method according to claims 14 to 19. 21. The image reading method according to claim 20 , wherein the correction step corrects the digital image data after an offset level correction process. The image reading method according to any one of claims 14 to 21 , wherein in the correction step, a lookup correction table in which linearity correction data is set is used. The generating and setting operation of the linearity correction data is performed upon startup of the apparatus, an image reading method as claimed in any one of claims 14 to 22.

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