JP4173452B2 - 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 for 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.

  Therefore, according to Patent Document 3, four series of outputs from a 4-channel output image sensor, that is, FE (odd number in the first half), FO (even number in the first half), LE (odd number in the second half), LO (second half). The data between the F and L series is adjusted by performing gamma (γ) correction as a correction process on the data after A / D conversion and shading correction for each of the even number of data) Yes.

JP-A-11-215298 JP 2002-158837 A JP 2002-218186 A

  FIG. 9 is a block diagram of a part of a conventional image reading apparatus showing this correction processing method. The CCD 101 is a four-channel output image sensor that outputs analog image signals for four channels of FE, FO, LE, and LO as described above in parallel, and FE, FO and LE, LO are paired with each other. The data is input to the corresponding analog processing circuits 102 and 103 configured by LSI. Then, after the respective data are amplified to a predetermined level under the automatic gain adjustment control (AGC) by the amplifiers in the analog processing circuits 102 and 103, the E series and the O series are time-series using a multiplexer or the like. The synthesis process and other necessary analog signal processes are performed in order. Thereafter, the analog image signals F and L in the first half and the second half are input to the A / D converters 104 and 105 to be converted into digital data, and further, shading correction circuits 106 and 107 each including a memory and an arithmetic element. The shading process is performed. Thereafter, these two series of digital data are supplied to a pixel rearrangement unit that combines the digital data into one time series signal, and is further output from the image reading apparatus through necessary image processing.

  Here, the amplification factor adjustment of the amplifiers in the analog processing circuits 102 and 103 is performed by recognizing the digital data level after A / D conversion by the A / D converters 104 and 105 by the arithmetic processing unit 108 and calculating the amplification factor. By doing so, it is configured to automatically adjust, that is, perform AGC control.

  Further, for one series of digital data, for example, L series digital data output from the A / D converter 107, the linearity characteristic is expressed as F series digital data output from the A / D converter 106. A γ correction table 109 is provided to match the linearity characteristics. Thereby, the output difference between the first half F side and the second half L side is amplified to a voltage value which is an amplifier in the analog processing circuits 102 and 103, and then A / D converted by the A / D converters 104 and 105, Further, after correction by the shading correction circuits 106 and 107, one of them is corrected by correction by the γ correction table 109.

  Incidentally, the difference between E / O (even / odd) and F / L (first half / second half) is caused by the signal processing circuit, but most is caused by variations in linearity characteristics of the CCD 101 output itself. Here, the “linearity characteristic” refers to the characteristic of the incident light amount of the CCD 101 versus the analog output (scanner output). The analog output is proportional to the light amount, and thus is basically linear. It may not be as shown. FIG. 10 shows a state in which there is a difference in linearity characteristics between the F series and the L series.

  Considering such a point, when the correction method disclosed in Patent Document 3 is considered, there is a problem that it is not possible to cope with a change in the CCD output value due to a change in the amount of light over time. This is because the amplifier used in the analog processing circuits 102 and 103 is an auto gain (AGC) amplifier, which automatically amplifies the CCD output value to a certain level regardless of the CCD output value. This is because the γ correction table 109 corrects the output value thus amplified after A / D conversion and shading correction. In other words, if the γ correction table 109 obtained under the initial 100% light amount condition is used after adjustment at the time of shipment from the factory, the case where the light source light amount deteriorates (decreases) to 50%, for example, can be handled. (It will be described in detail with reference to the drawings in the embodiment).

  An object of the present invention is to appropriately perform correction processing necessary for digital image data immediately after A / D conversion even when the light amount of a light source is reduced.

  More specifically, the linearity correction between each output series when using an image sensor that divides the output into two parts in the first half and the second half and outputs them may reduce the light amount of the light source. However, it is always possible to do it properly.

An image reading apparatus according to a first aspect of the present invention includes a light source that exposes a document surface, an image sensor that receives reflected light from the document surface and outputs an analog image signal corresponding to the amount of received light, and the analog image signal. An amplification factor variable amplifier that amplifies the analog image signal to a predetermined level, an A / D converter that converts the amplified analog image signal into digital image data, and a target linearity for the digital image data immediately after A / D conversion Correction means for performing linearity correction processing based on characteristics, and the correction means multiplies the digital image data immediately after A / D conversion by the reciprocal of the amplification factor of the amplifier as the digital image data. Thus , correction processing is performed using the calculated data value as an input .

  In the present invention and the following invention, “immediately after A / D conversion” means after A / D conversion but before image processing such as shading correction processing is performed on the digital image data. .

According to a second aspect of the invention, in the image reading apparatus according to claim 1, wherein said correcting means comprises a correction table for linearity correction.

According to a third aspect of the invention, in the image reading apparatus according to claim 2, wherein the correcting means, downstream of said correction table performs a conversion process corresponding to the amplification by the amplifier to the data value after the correction processing It has conversion means.

According to a fourth aspect of the present invention, in the image reading device according to any one of the first to third aspects, the image sensor is divided into a first half and a second half at the center in the main scanning direction, and the pixels of the sensor array. The output is distributed to the corresponding amplifiers.

According to a fifth aspect of the present invention, in the image reading device according to the fourth 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 amplifiers.

According to a sixth aspect of the present invention, in the image reading device according to any one of the first to fifth aspects, the image sensor is a color image sensor having a sensor section for each of RGB colors.

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 process of the correction unit is performed by either one of the two series of outputs of the first half and the second half. This is processing for correcting the other linearity characteristic using the linearity characteristic as a target linearity characteristic.

According to an eighth aspect of the present invention, in the image reading apparatus according to any one of the first to sixth aspects, the correction process of the correction unit is performed by using the first half and the second half with respect to a predetermined target linearity characteristic. This is a process of correcting each linearity characteristic output from the series.

According to a ninth aspect of the present invention, in the image reading device according to the second or third aspect , the gray scale is read by the image sensor while the amplification factor of the amplifier is set to a fixed magnification, and image data is acquired. And a means for calculating correction data based on the image data and the target linearity characteristic to create a correction table.

According to a tenth aspect of the present invention, in the image reading apparatus according to the ninth aspect , the means sets the fixed magnification to 1.

According to an eleventh aspect of the present invention, in the image reading apparatus according to the tenth aspect , the means includes means for increasing the amount of light received by the image sensor during the gray scale reading.

According to a twelfth aspect of the present invention, in the image reading apparatus according to the eleventh aspect , the increase in the amount of received light is due to the increase in the amount of light source.

According to a thirteenth aspect of the present invention, in the image reading device according to the eleventh aspect , the increase in the amount of received light is due to an increase in the accumulation time of the image sensor.

According to a fourteenth aspect of the present invention, there is provided an image forming apparatus comprising the image reading device according to any one of the first to thirteenth aspects for reading an image of a document, and forming an image on a recording medium based on the read image of the document. Do.

In the image reading method according to the fifteenth aspect, reflected light from the original surface exposed by the light source is received by the image sensor, an analog image signal corresponding to the amount of received light is output, and the analog image signal is variable in gain. The amplified analog image signal is converted to digital image data by an A / D converter, and the target linearity characteristic is used as a reference for the digital image data immediately after the A / D conversion. In the correction processing step, the digital image data immediately after A / D conversion is multiplied by the reciprocal of the amplification factor as the digital image data. Thus, correction processing is performed using the calculated data value as an input .

According to a sixteenth aspect of the present invention, in the image reading method according to the fifteenth aspect , a correction table for linearity correction processing is used in the correction processing step.

According to a seventeenth aspect of the present invention, in the image reading method according to the sixteenth aspect , in the correction processing step, after the linearity correction processing using the correction table, the data value after the correction processing is amplified by the amplifier. The corresponding conversion process was applied.

According to an eighteenth aspect of the present invention, in the image reading method according to any one of the fifteenth to seventeenth aspects, the image sensor is divided into two parts, a front half part and a rear half part, in the center in the main scanning direction. The output is distributed to the corresponding amplifiers.

According to a nineteenth aspect of the present invention, in the image reading method according to the eighteenth 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 amplifiers.

A twentieth aspect of the invention is the image reading method according to any one of the fifteenth to nineteenth aspects, wherein the image sensor is a color image sensor having a sensor unit for each of RGB colors.

According to a twenty- first aspect of the invention, in the image reading method according to any one of the fifteenth to twentieth aspects, the correction processing has one linearity characteristic of two series of outputs of the first half and the second half. This is processing for correcting the other linearity characteristic as the target linearity characteristic.

According to a twenty-second aspect of the present invention, in the image reading method according to any one of the fifteenth to twentieth aspects, the correction processing is output from two series of the first half and the second half with respect to a predetermined target linearity characteristic. It is the process which correct | amends each linearity characteristic to be performed.

According to the first and fifteenth aspects of the present invention, the data value corresponding to the level before amplification by the amplifier is used as the digital image data, and correction processing is performed according to a predetermined standard. In such a case, even if the digital image data itself immediately after A / D conversion has been subjected to amplification processing to a predetermined level by an amplifier, the data value used for the correction processing is the value before amplification that is not affected by such amplification processing. The data value corresponding to the level, that is, the data value corresponding to the level of the raw data from the image sensor, so that it is possible to perform proper proper correction processing considering light quantity fluctuations while corresponding to the output of the image sensor itself. Since such processing is performed immediately after A / D conversion, subsequent digital data processing such as shading correction is also optimized. Can.

Further , it is possible to appropriately perform correction processing so that the linearity characteristic of the image sensor output itself matches the target linearity characteristic.

Also, as a means for its, considering the amplification factor of the amplifier, since the set of data values to be corrected in accordance with the amplification factor, the implementation is clear, in addition, the reciprocal of the amplification factor By setting the data value to be corrected by multiplying, it is possible to provide a specific method for realizing it.

Further, according to the inventions of claims 2 and 16 , since the correction table is used for the correction processing, it can be easily realized. At this time, according to the inventions of claims 3 and 17 , since the conversion process corresponding to the amplification by the amplifier is performed on the data value after the correction process, the significance of the amplification by the amplifier is exhibited, and the influence of the level change is exerted. Unacceptable data can be obtained.

According to the inventions described in claims 4 , 5 , 18 , and 19 , linearity correction between each output series when using an image sensor of a type that is divided into two parts in the first half and the second half and distributed and output is performed. Even if the amount of light decreases, it can always be performed appropriately. In particular, as in the inventions of claims 6 and 20 , when applied to the case of a color image sensor having a sensor unit for each color of RGB, linearity correction is appropriately performed even when there is a difference in light quantity variation for each color. be able to. That is, in the case of a color image reading apparatus using a color image sensor, the light amount fluctuation (decrease) of the light source is not equal to each color, and the light quantity fluctuation of blue B in particular tends to be larger than the others, and appropriate linearity correction is performed. Otherwise, the hue changes and the gray balance is lost, but this can be dealt with by appropriate linearity correction.

According to the invention described in claims 7 , 8 , 21 , and 22 , it can be realized by applying the correction process to one series or both series.

According to the ninth and tenth aspects of the present invention, it is possible to easily and appropriately create a correction table for linearity correction processing that can be appropriately corrected even when the light source light quantity varies. That is, since the correction table is created under the same conditions (amplification factor is a fixed magnification, for example, 1 time) as when the data value corresponding to the level before amplification by the amplifier is used, it is made to correspond to the output of the image sensor itself. In addition, it is possible to perform original proper correction processing in consideration of light quantity fluctuations.

According to the invention described in claims 11 , 12 , and 13 , when the correction table is created, for example, if the amplification factor is fixed to 1 times, the signal level of the image sensor is small, so that an appropriate correction table is not obtained without full scale. Although there is a concern that it cannot be created, it is possible to create an appropriate correction table by making the output full scale by substantially increasing the amount of light received by the image sensor by increasing the light source light amount, increasing the accumulation time, etc. it can. In other words, it is possible to cope with the incident light quantity from 0 to saturation of the image sensor, and to create a correction table capable of linearity correction for all the light quantities.

According to the invention of claim 14 wherein is provided with the image reading apparatus of any one of claims 1 to 13, you can achieve the same effects as the invention of these claims 1 to 13, wherein . In particular, when using an image sensor that divides the output into two parts for the first half and the second half, the linearity correction between each output series is always appropriate even if the light quantity of the light source decreases. And an output image in which the difference in linearity is not noticeable between the first half and the second half can be obtained.

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

  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 board 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.

  FIG. 3 shows a block diagram of a part of the image reading apparatus of the present embodiment using such a CCD 10. FIG. 3 shows up to the shading correction process. The CCD 10 is a four-channel output image sensor that outputs analog image signals for four channels of FE, FO, LE, and LO as described above in parallel. FE, FO and LE, LO are paired with each other. The data is input to corresponding analog processing circuits 41 and 42 formed of LSI. Then, after each data is amplified to a predetermined level under the automatic gain adjustment control (AGC) by the amplifier in the analog processing circuits 41 and 42, the E series and the O series are time-series using a multiplexer or the like. The synthesis process and other necessary analog signal processes are performed in order. Thereafter, the analog image signals F and L in the first half and the second half are input to the A / D converters 43 and 44 to be converted into digital image data. Further, the shading correction circuit 45 including a memory and an arithmetic element, A shading process is performed by 46. Thereafter, these two series of digital data are provided to a pixel rearrangement unit that synthesizes the digital data into one time series signal, and is further output from the image reading apparatus 1 through necessary image processing (such as MTF correction processing). Is done.

  Here, the amplification factor adjustment of the amplifier in the analog processing circuits 41 and 42 is performed by recognizing the digital data level after A / D conversion by the A / D converters 43 and 44 by the arithmetic processing unit 47 and calculating the amplification factor. By doing so, it is configured to automatically adjust, that is, perform AGC control.

  Further, for one series of digital image data, for example, L series digital image data output from the A / D converter 44, the linearity characteristic thereof is the same as that of the F series output from the A / D converter 43. A γ correction table (correction table) 48 for adjusting the linearity characteristics of the digital image data as the target linearity characteristics is provided, and a multiplication / division circuit (conversion means) 49 is provided at the subsequent stage of the γ correction table 48. It has been. The γ correction table 48 and the multiplication / division circuit 49 constitute correction means. Here, the amplification factor (L amplification factor data) of the amplifier in the analog processing circuit 42 calculated by the arithmetic processing unit 47 is input to the γ correction table 48 and the multiplication / division circuit 49. The digital image data is subjected to data value conversion processing corresponding to the amplification factor. Schematically, for example, in the γ correction table 48, a data value obtained by multiplying digital image data immediately after A / D conversion by the A / D converter 44 by an inverse of the amplification factor is used for the γ correction table 48. As input data, the multiplication / division circuit 49 is configured to multiply the digital image data corrected by the γ correction table 48 by the amplification factor (or divide by the inverse of the amplification factor).

  Although not particularly shown, the digital system such as the γ correction table 48, the multiplication / division circuit 49, and the shading correction circuits 45 and 46 is connected to a CPU for controlling them, and the A / D converters 43 and 44 are connected. A CPU-connected timing control means is connected to the earlier analog system.

  In such a configuration, a difference from the conventional method shown in FIG. 9 will be described. First, as in the case of the present embodiment, the amplification factor adjustment of the amplifiers in the analog processing circuits 102 and 103 (41, 42) is performed as described above with the level of the digital image data after A / D conversion. Is automatically adjusted (AGC) when detected by the arithmetic processing unit 108 (47). Specifically, for example, every time the image reading apparatus is turned on, the white reference plate 12 that is also used for shading correction is read and corresponds to each FL and EO (ie, every FE, FO, LE, and LO). The analog voltage value of the reference (white) is adjusted to a constant value by changing the amplification factor of the amplifier. Actually, when the data after A / D conversion is, for example, 8 bits, the amplification factors are adjusted so that 240/255 is obtained when the white reference plate 12 having a reflectance of 90% is read.

  At this time, AGC is an auto gain, and the reference (white) level is adjusted to 240/255 regardless of the output value of the CCD 101 (10) itself, and is obtained here for all digital image data. It will be multiplied by the amplification factor. This is a very convenient method if there is no fluctuation in the incident light amount of the halogen lamp 4 or if the relationship between the incident light amount and the CCD output is completely linear. In addition, if there is a difference as shown in FIG. 10 (the same applies to FIG. 4A) in the linearity characteristics between the F series and the L series, there is a contradiction.

  For example, at the time of factory adjustment, the gray scale is read in a state where the halogen lamp 4 has no light amount deterioration (light amount 100%), and F-series and L-series linearity characteristics as shown in FIG. After creating a gamma correction table having characteristics as shown in FIG. 4B for adjusting the linearity characteristics of the L series to match the linearity characteristics of the series with the linearity characteristics of the series as the target linearity characteristics, the image reading apparatus is installed on the market. Consider a case where the light quantity of the halogen lamp 4 is reduced to 50% (= 1/2) due to deterioration over time during use. If the lamp light quantity is halved, the output value of the CCD 101 is also halved. Conventionally, the AGC function doubles the amplification factor of the amplifier, and the reference (white) is the same as when the light quantity is 100%. As a result of adjusting to a level of 240/255, all image data are uniformly amplified by a factor of 2, and after shading correction, an L-sequence image is created using a γ correction table created with a light quantity of 100%. The data is corrected. It is the processing of this part that contradicts. That is, when the CCD output is halved, the range up to 50% (= 1/2) of the incident light amount is shown in FIG. 4B in the γ correction table created with 100% light amount. In spite of the fact that correction must be performed, the process of doubling the amplification factor is not considered to be a decrease in the amount of incident light due to the process of doubling the amplification factor, and therefore an appropriate correction process according to the γ correction table cannot be performed. In some cases, the L-sequence linearity characteristics do not match the F-sequence linearity characteristics. That is, referring to FIG. 4A, since the white level at the light amount of 50% is regarded as the white level at the light amount of 100% by the amplification process, a data value different from the original data value is used. This is a correction process.

  In this respect, in the present embodiment, the data value corresponding to the level before amplification by the amplifier in the analog processing circuit 42 as the digital image data, that is, the data value set according to the amplification factor of the amplifier, here Linearity correction processing is performed by the γ correction table 48 using a data value obtained by multiplying the digital image data obtained from the A / D converter 44 by the reciprocal of the amplification factor of the amplifier. Referring to a schematic flowchart for reading a document image shown in FIG. 5, first, when a reading operation is performed with power-on (step S1), each analog image signal FE, FO, LE, output from the CCD 10 is displayed. LO is amplified to a predetermined level by an amplifier and then converted into digital image data by A / D converters 43 and 44. The amplification of the amplifiers in the analog processing circuits 41 and 42 according to the level of the digital image data at this time. The rate is automatically variably set by the arithmetic processing unit 47 (S2). The amplification factor of the amplifier in the analog processing circuit 42 in this case is also given to the γ correction table 48. Therefore, in the γ correction table 48, the digital image data output from the A / D converter 44 is multiplied by the reciprocal of the amplification factor of the amplifier given (or divided by the amplification factor) to obtain the γ correction. It is set as an input value for the table 48, and the data value is γ corrected using a γ correction table as shown in FIG. 4B (S3). For example, when the amplification factor of the amplifier is twice, the digital image data output from the A / D converter 44 is halved, and when the amplification factor is 0.75, the A / D converter 44 The output digital image data is multiplied by 3/4. That is, correction processing is performed by the γ correction table 48 using a data value corresponding to the level of raw data from the CCD 10. For example, when the amount of incident light is low as the light amount of the halogen lamp 4 decreases, for example, when the amount of incident light is 50%, linearity correction is performed using correction data within the range of the dotted line shown in FIG. Therefore, an appropriate correction process using the original data value is performed. In other words, it is possible to perform proper correction processing in consideration of fluctuations in light intensity while corresponding to the output of the CCD 10 itself. The digital image data corrected in this way by the γ correction table 48 is multiplied or divided again by the multiplication / division circuit 49 in consideration of the amplification factor (for example, when the amplification factor is two, the digital image data is halved, (S4) and undergoes a conversion process substantially equivalent to amplification by an amplifier, so that the truly corrected data is output to the shading correction circuit 46 side for use in subsequent image processing. The

  By the way, a method of creating the γ correction table 48 suitable for the implementation of the present embodiment before the factory shipment will be described with reference to a schematic flowchart shown in FIG. First, after the power is turned on, the amplification factor of the amplifiers in the analog processing circuits 41 and 42 is set to a fixed magnification, here 1 (S11). In such a setting state of the amplification factor, the CCD 10 performs several kinds of reflectance gray scale reading processing (S12), calculates the average value of each gray scale for the reading result, and calculates the L of each reflectance. A γ correction table as shown in FIG. 4B for adjusting the reading value of the series to the reading value of the F series is created (S13). Creation of such a γ correction table 48 is realized by the function of the creation means under CPU control. In the case of the γ correction table 48 created with the amplification factor of 1 in this way, the data value when the correction process is performed in the γ correction table 48 corresponds to the level before amplification, that is, the amplification factor of 1. Therefore, appropriate correction processing can be performed under the same conditions as when the table was created.

  By the way, since the signal level output from the CCD 10 is originally low, the signal is originally amplified under the AGC control by the amplifier, and the amplification factor of the amplifier is set to 1 for the creation of such a γ correction table 48. When the gray scale is read, the full scale is not reached and the γ correction table 48 may not be completed. Therefore, only when the γ correction table 48 is created, as shown in step S12 of FIG. 6, the light amount of the lamp is increased (although rarely, the light amount can be made larger than the initial state of factory adjustment), or As a result, by increasing the accumulation time of the CCD 10, if the amount of light received by the CCD 10 is increased, the image signal of the CCD 10 becomes full scale compatible (equivalent to 100% light quantity). For example, as shown in FIG. A γ correction table as shown is completed.

  In this embodiment, the γ correction table 48 and the multiplication / division circuit 49 are provided on the L series side so that the linearity characteristic of the L series data is matched with the linearity characteristic of the F series as the target linearity characteristic. Further, the γ correction table 48 and the multiplication / division circuit 49 may be provided on the F-sequence side so that the linearity characteristics of the F-sequence data are matched with the L-sequence linearity characteristics as the target linearity characteristics. Alternatively, the γ correction table 48 and the multiplication / division circuit 49 may be provided in both the F series and the L series so that the linearity characteristics of each data are matched with the target linearity characteristics set as ideal values.

  Although not specifically shown, the present embodiment is a color image reading apparatus 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 of RGB colors. If applied to, it is more effective. That is, in the case of a color image reading apparatus, a halogen lamp, a xenon lamp, or the like is used as the light source. Regardless of the light source, the B (blue) component changes to the R (red) component or G (green). It has the property of being extremely large compared to the ingredients. For example, FIG. 7 is a characteristic diagram showing how the amount of light of each color component deteriorates in the case of a xenon lamp. Here, as the light amount reduction, the reduction amount is calculated (average in the main scanning direction) based on the initial 0 min and 10 min output. In the case of such a color CCD, according to the conventional linearity correction method, it is impossible to cope with the light amount deterioration, and naturally, the contradiction for B becomes larger, and the difference between the F series and the L series differs for each RGB. , Gray balance will be lost. Such a phenomenon is less preferable than when RGB shifts to the same extent. In this regard, according to the present embodiment, since appropriate linearity correction can be performed in consideration of a decrease in the amount of light from the light source, the difference between the F series and the L series is not different for each RGB, and the gray balance is lost. Can avoid such problems.

  The image reading apparatus 1 as described above is used alone as an image scanner. For example, as shown in FIG. 8, the image reading apparatus 1, a printer engine 52, and a microcomputer that controls the whole are controlled. The present invention may be applied to a digital copying machine 51 or the like as an image forming apparatus including the unit 53.

  The configuration of the image reading apparatus 1 is as described above. The printer engine 52 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 53 controls the image reading device 1 and the printer engine 52 to read the document 2 with the image reading device 1 and form an image with the printer engine 52 based on the read image data.

  Therefore, according to the digital copying machine 51, 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.

1 is a schematic side view illustrating a configuration example of an image reading apparatus according to an 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 characteristic view which shows an example of FL difference, and an example of a correction table. 6 is a schematic flowchart showing an example of operation during normal document reading. It is a schematic flowchart which shows the operation example at the time of correction table preparation. FIG. 6 is a characteristic diagram showing light amount deterioration of RGB color components in the case of a xenon lamp. It is a schematic front view which shows the example of application to a digital copying machine. It is a block diagram which shows the example of a structure of the front stage part of the conventional image reading apparatus. It is a characteristic view which shows an example of FL difference.

Explanation of symbols

4 Light source 10 Image sensor 41, 42 Amplifier 43, 44 A / D converter 48 Correction table 49 Conversion means 48, 49 Correction means

Claims (22)

A light source for exposing the document surface;
An image sensor that receives reflected light from the document surface and outputs an analog image signal corresponding to the amount of light received;
An amplifier with variable gain for amplifying the analog image signal to a predetermined level;
An A / D converter for converting the amplified analog image signal into digital image data;
Correction means for performing linearity correction processing with reference to target linearity characteristics on the digital image data immediately after A / D conversion;
With
The correction means performs a correction process using as input the data value calculated by multiplying the digital image data immediately after A / D conversion by the inverse of the amplification factor of the amplifier as the digital image data. . Said correction means has a correction table for the linearity correction processing, the image reading apparatus according to claim 1. The image reading apparatus according to claim 2 , wherein the correction unit includes a conversion unit that performs a conversion process corresponding to the amplification by the amplifier on the data value after the correction process, subsequent to the correction table. The image sensor is divided into two and the first half and the second half portion at the center of the main scanning direction sorting output to the amplifier, each corresponding to a pixel output of the sensor array, any one of claims 1 to 3 Image reading apparatus. 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 distributed and output to the corresponding amplifiers, The image reading apparatus according to claim 4 . The image sensor is a color image sensor having a sensor unit for each of RGB colors, the image reading apparatus of any one of claims 1 to 5. Wherein the correction process of the correction means, of the output of the two series of the second half portion and the front half portion, a process of correcting the other linearity one of linearity as a target linearity characteristic, claims 1 to 6 The image reading apparatus according to any one of the above. Wherein the correction process of the correction means is a process of correcting the linearity characteristic of each output from the two series of the second half portion and the front half portion with respect to a predetermined target linearity characteristic, any one of claims 1 to 6 An image reading apparatus according to claim 1. In a state where the amplification factor of the amplifier is set to a fixed magnification, the image sensor reads the gray scale to acquire image data, calculates correction data based on the acquired image data and target linearity characteristics, and calculates a correction table. and means for creating an image reading apparatus according to claim 2 or 3 wherein. The image reading apparatus according to claim 9 , wherein the unit sets a fixed magnification to one. The image reading apparatus according to claim 10 , wherein the means includes means for increasing the amount of light received by the image sensor when reading the gray scale. The image reading apparatus according to claim 11 , wherein the increase in the amount of received light is due to an increase in the amount of light from the light source. The image reading apparatus according to claim 11 , wherein the increase in the amount of received light is due to an increase in accumulation time of the image sensor. Comprising an image reading apparatus according to any one of claims 1 to 13 reading an image of a document, an image forming apparatus for forming an image on a recording medium based on the image of the read document. The reflected light from the document surface exposed by the light source is received by the image sensor, an analog image signal corresponding to the received light amount is output, and the analog image signal is amplified to a predetermined level by an amplifier having a variable amplification factor and amplified. The analog image signal is converted into digital image data by an A / D converter, and the digital image data immediately after the A / D conversion is subjected to linearity correction processing based on a target linearity characteristic. A method,
In the correction processing step, the digital image data is subjected to correction processing using as input the data value calculated by multiplying the digital image data immediately after A / D conversion by the inverse of the amplification factor of the amplifier . Image reading method. The image reading method according to claim 15 , wherein a correction table for linearity correction processing is used in the correction processing step. The image reading method according to claim 16 , wherein in the correction processing step, after linearity correction processing using the correction table, conversion processing corresponding to amplification by the amplifier is performed on the data value after the correction processing. . 18. The image sensor according to any one of claims 15 to 17 , 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 amplifiers. Image 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 distributed and output to the corresponding amplifiers, The image reading method according to claim 18 . The image sensor is a color image sensor having a sensor unit for each of RGB colors, the image reading method of any one of claims 15 to 19. The correction process, among the outputs of the two series of the second half portion and the front half portion, a process of correcting the other linearity one of linearity as a target linearity characteristic, one of claims 15 to 20 one The image reading method described. The correction process according to any one of claims 15 to 20 , wherein the correction process is a process of correcting each linearity characteristic output from the two series of the first half and the second half with respect to a predetermined target linearity characteristic. Image reading method.

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