JPH1169162A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image that is not influenced by the change of a dark output level which results from the change of accumulation time by performing dark output compensation of image data from an image sensor based on data for dark output compensation which is stored in a storing means in accordance with accumulation time. SOLUTION: Image data from an image sensor is undergone dark output compensation based on data from dark output compensation which is stored in a storing means in accordance with accumulation time that is set as a prescribed accumulation time in the process of original reading. In this device, a dark compensation level data storing part 25 preliminarily stores three dark level data. A dark level compensating part 24 switches an access area of the part 25 to a storage area of dark level data which corresponds to the accumulation time that is set by an accumulation time setting signal from a CPU among the three dark level data, reads it and compensates a dark output component of image data that is inputted from an A/D converter 23.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image reading apparatus, and more particularly, to obtaining image data by photoelectrically converting reflected light from a document by an image sensor for a predetermined storage time, and performing the predetermined storage time in a plurality of steps. The present invention relates to an image reading device that can be set to a device.

[0002]

2. Description of the Related Art In an image reading apparatus such as a scanner apparatus or an apparatus including an image reading apparatus as a configuration such as a facsimile apparatus or a copying machine, distortion of the photoelectric conversion characteristic of an image sensor in the main scanning direction is corrected. This is an important factor in achieving faithful image reproduction.

In general, the distortion of the photoelectric conversion characteristics of an image sensor is such that each photoelectric conversion element (pixel) constituting the image sensor, which should ideally be at a constant level, outputs an incident light of a constant intensity. Signal level (bright output) due to variation in each pixel and the signal level output from each photoelectric conversion element (pixel) constituting the image sensor which should ideally be a no signal in the absence of incident light (Dark output)
There are two types of distortion: distortion due to the offset varying for each pixel.

[0004] In the bright output, only the relative distortion of each pixel is mainly a problem, whereas in the dark output, a certain amount of offset is generated for all pixels, In that both the relative distortions of each pixel are problematic.

[0005] A contact image sensor (actual size sensor), which has been increasingly used as an image sensor in recent years, is a CC sensor.
Since the output level in darkness is higher than that in D, not only the distortion correction of the bright output level but also the distortion correction of the dark output level is important.

The distortion correction of the dark output level is performed by dark level correction,
This is called dark output correction or offset correction, and is output from the image sensor when the light source is turned off or when light is blocked.
The dark output correction data for the lines is stored in pixel units, and when reading the original, the dark output correction data is obtained from the line-based image data obtained by photoelectrically converting the reflected light from the original by the image sensor. This is a process for obtaining net image data derived from the intensity of the reflected light from the document by subtracting the application data for each pixel. With respect to the original image data after the dark output correction, distortion correction (shading correction) of the light output level can be correctly performed.

There are various factors, such as a change in photoelectric conversion characteristics due to a change in ambient temperature and a change with time in the photoelectric conversion characteristics, as factors that cause the dark output level distortion in the image sensor. Is fixed, it is not possible to cope with the fluctuation of the distortion characteristic of the dark output level for each reading operation performed after a certain time. Therefore, conventionally, every time a reading operation is performed, before the reading of the document image is started,
Alternatively, it has been common practice to collect the dark output correction data during the reading of a document image to cope with fluctuations in the dark output level distortion characteristics.

As a technique for coping with a change in the distortion characteristic of the dark output level due to an environmental change such as an ambient temperature, an image reading apparatus such as an "image reading apparatus" disclosed in Japanese Patent Laid-Open No. 2-63378 is used. The signal level corresponding to the light-shielded pixel output from the means is held, and the image signal output from the reading means by image reading is corrected based on the held signal level. There is an image in which an image can be read with an appropriate density gradation.

However, according to the above-mentioned known technique, a pixel in a certain specified area among all the pixels constituting the image sensor is set as a light-shielded pixel, and the signal level from the light-shielded pixel is set to the darkness of all the pixels constituting the image sensor. Since the output level is considered to be representative, it is not possible to correct the variation between the dark output level of the light-shielded pixel and the dark output level of the effective pixel for actually reading an image. In particular, in a general contact sensor in which one sensor line is formed by connecting a plurality of sensor chips, even if the variation in the dark output level between pixels in the same chip is relatively small,
A large difference in the dark output level between the chips cannot be completely corrected by the above-mentioned known technique.

In order to accurately correct the dark output level that varies between effective pixels by the above-described known technique, all the effective pixels for one line of the image sensor must be shielded from light to collect dark output level data. However, it is physically impossible to shield the effective pixels from light during the reading operation. Therefore, in order to absorb the variation of the dark output between the effective pixels, a method of collecting the dark level data of all the effective pixel sections before the start of the reading operation has to be taken.

On the other hand, in a conventional image reading apparatus, in order to obtain the best image data as possible, control is performed to change the accumulation time of the image sensor in accordance with a set reading mode such as a read line density. is there. Specifically, for example, the settable read line densities are 3.85 lines / mm, 7.7 lines / mm, and 15.4 lines / mm.
Assuming that one original can be read in a fixed time regardless of the reading line density, the time required to read one main scanning line is inversely proportional to the reading line density. Therefore, by increasing the accumulation time of the image sensor in proportion to the time required to read one main scan line, the level of the image signal output from the image sensor becomes higher, and the noise is relatively reduced and the S / S Image data with a high N ratio can be obtained.

As described above, the longer the accumulation time, the higher the level of the image signal, but at the same time, the higher the dark output level. That is, the dark output level varies with the ambient temperature,
It changes not only with time but also with the accumulation time of the image sensor. In other words, the dark output level is composed of a component that depends on the accumulation time and a component that does not depend on the accumulation time, such as a change in ambient temperature or a change with time.

Therefore, unlike the case where the component depending on the fluctuation of the ambient temperature or the change over time of the dark output level is collected only once before the start of the reading operation, it hardly changes during the reading operation. If the reading linear density is changed by the user during the reading operation, the component that depends on the accumulation time and changes accordingly changes greatly during the reading operation.

The change due to the change in the accumulation time of the dark output level, which is a combination of the component dependent on the accumulation time and the component not dependent on the accumulation time, is caused by the change in the accumulation time, the change in the image signal level from the image sensor. For converting the image signal from the image sensor into digital data
Even if the gain is switched by a gain switching circuit disposed before the A / D converter in order to normalize the image signal level input to the / D converter to be substantially constant, the gain cannot be canceled. .

This will be described schematically with reference to FIG.

FIG. 1A shows a dark output level of a specific pixel among the pixels constituting the image sensor, and the dark output level includes a component B substantially proportional to the accumulation time, Is composed of the uncorrelated component A.

In FIGS. 3A, 3B, and 3C, the dark output level shown on the left is the dark output level output from the image sensor, and the dark output level shown on the right is the image output level. It is output from the sensor and the analog gain is adjusted for normalization.

FIG. 1A shows a dark output level at a reference accumulation time L. The dark output level output from the image sensor is composed of a component A independent of the accumulation time and a component B proportional to the accumulation time. This is the level of (A + B) added. The dark output level after the analog gain is adjusted by the gain of 1 is (A + B).

FIG. 1B shows a dark output level at an accumulation time 2L twice as long as the reference accumulation time L. The dark output level output from the image sensor includes the component A independent of the accumulation time and the accumulation time. A component 2B proportional to time is added (A +
2B). The dark output level after the analog gain has been adjusted by a gain of 1/2 is (A / 2 +
B).

FIG. 3C shows a half of the reference accumulation time L.
The dark output level at the double accumulation time L / 2 is shown. The dark output level output from the image sensor is obtained by adding the component A independent of the accumulation time and the component B / 2 proportional to the accumulation time (A + B / 2). ) Level. The dark output level after the analog gain is adjusted by the gain 2 is (2A
+ B).

As described above, the dark output level output from the image sensor changes in accordance with the change in the accumulation time, and even if the gain of the dark output level output from the image sensor is adjusted, it depends on the accumulation time. A change in the dark output level, which is a combination of the component that does not depend on the component and the component that does not depend on the component, cannot be offset.

For this reason, when the user sets a plurality of originals to be read in the image reading apparatus and performs image reading, the setting of the reading line density is changed at a page break during the reading of the original, and the change is made in accordance with the change. Therefore, when the accumulation time is changed, it is necessary to collect dark output correction data every time in order to accurately correct the dark output level.

On the other hand, during the reading operation, the light source for illuminating the original is not repeatedly turned on and off every time one original is read, but is continuously turned on throughout the reading of a plurality of originals to reduce the original reading throughput. It is common to raise it.

[0024]

Therefore, the light source is turned off when dark output correction data is collected during reading because the accumulation time of the image sensor has been changed in accordance with the change in the setting of the reading linear density. In addition, since it is necessary to secure a stable period of the output level of the image sensor in accordance with the change of the accumulation time, the throughput of document reading is reduced. On the other hand, even if the storage time is changed during the reading operation, if the dark output correction is performed using the dark output correction data collected before the start of the reading operation, the dark output after the storage time is changed during the reading operation will be described. There is a problem in that the level cannot be accurately corrected, which may cause insufficient reproduction or excessive reproduction of the high density portion.

The present invention has been made in view of the above circumstances, and does not collect the dark output correction data each time the dark output level of the image sensor changes due to a change in the storage time setting. It is another object of the present invention to provide an image reading apparatus capable of obtaining an image which is not affected by a change in a dark output level caused by a change in setting of an accumulation time.

[0026]

According to a first aspect of the present invention, there is provided an image reading apparatus for obtaining image data by photoelectrically converting reflected light from a document by an image sensor for a predetermined accumulation time. In the image reading apparatus capable of setting the predetermined accumulation time in a plurality of stages, a storage unit in which dark output correction data respectively corresponding to a plurality of stages of accumulation times that can be set as the predetermined accumulation time are stored in advance,
During document reading, correction for dark output correction of image data from the image sensor based on dark output correction data stored in the storage means corresponding to the storage time set as the predetermined storage time Means.

According to a second aspect of the present invention, there is provided an image reading apparatus which obtains image data by photoelectrically converting reflected light from a document by a predetermined storage time by an image sensor, and wherein the predetermined storage time can be set in a plurality of stages. In the reading device, storage means for storing dark output correction data respectively corresponding to a plurality of stages of accumulation times which can be set as the predetermined accumulation time, and at the start of document reading, the plurality of stages of accumulation times are sequentially A correction data collection unit that sets the predetermined accumulation time, collects dark output correction data corresponding to each of the set accumulation times, and stores the data in the storage unit; Image data from the image sensor based on the dark output correction data stored in the storage means corresponding to the storage time set as Characterized by comprising a correction means for dark output corrected.

According to a third aspect of the present invention, there is provided an image reading apparatus which obtains image data by photoelectrically converting reflected light from a document by an image sensor for a predetermined storage time, and which can set the predetermined storage time in a plurality of stages. In the reading device, a storage unit that stores in advance gamma correction tables respectively corresponding to a plurality of stages of storage times that can be set as the predetermined storage time, and a storage unit that is set as the predetermined storage time during document reading. Correction means for gamma-correcting image data from the image sensor based on a gamma correction table stored in the storage means corresponding to time.

According to a fourth aspect of the present invention, there is provided an image reading apparatus which obtains image data by photoelectrically converting reflected light from a document by an image sensor for a predetermined storage time, and wherein the predetermined storage time can be set in a plurality of stages. A reading unit that stores in advance a threshold pattern corresponding to each of a plurality of stages of accumulation times that can be set as the predetermined accumulation time, and an accumulation unit that is set as the predetermined accumulation time during document reading. Processing means for performing gradation processing on image data from the image sensor according to a threshold pattern stored in the storage means in response to time.

[0030]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described in detail.

FIG. 1 shows a block configuration of an image reading apparatus 1 according to an embodiment of the present invention.

In FIG. 1, an image reading apparatus 1 includes an image reading section 2, an image processing section 3, an image recording section 4, a mechanism control section 5,
CPU 6, ROM 7, RAM 8, operation display unit 9, and
It is constituted by a system bus 10.

Here, the image reading section 2 has 3.85 lines / m.
m, 7.7 lines / mm or 15.4 lines / mm for reading an original image at a reading line density of 1 to obtain image data. The image processing unit 3 performs image processing described below on image data obtained by the image reading unit 2.

The image recording section 4 records the image data read by the image reading section 2 and processed by the image processing section 3 on a recording sheet in accordance with the linear density. The output form of the image data read by the image reading section 2 and processed by the image processing section 3 in the image reading apparatus 1 is not limited to the form of recording on the recording paper by the image recording section 4 but may be stored as a file or facsimile. It can be transmitted as a message or transferred to a higher-level device via an interface. The present invention is not limited by the output form of the obtained image data.

The mechanism control unit 5 separates and conveys the document read by the image reading unit 2, sub-scans and discharges the original, and separates and conveys the recording paper on which image data is recorded by the image recording unit 4. And controls the entire mechanism of the image reading apparatus 1.

The CPU 6 controls each part of the apparatus according to the control program stored in the ROM 7 while using the RAM 8 as a work area. As described above, the ROM 7 is a read-only memory that stores a control program for the CPU 6 to control each unit of the apparatus. The RAM 8 is a random access memory used as a work area of the CPU 6 as described above. RAM
Reference numeral 8 is backed up by a backup circuit (not shown), and its stored contents are retained even when the power of the apparatus is cut off.

The operation display unit 9 is provided with various keys such as a start key for instructing the start of a copying operation for recording image data read by the image reading unit 2 by the image recording unit 4. And a display such as a liquid crystal display device, and displays the operating state of the device to be notified to the user and various messages. The system bus 10 is used for exchanging data between the above-described units.

FIG. 2 shows the internal configuration of the image reading unit 2.

Referring to FIG. 1, an image sensor 21 is an image sensor such as a contact image sensor or a CCD image sensor, and is illuminated by a light source (not shown). This is for obtaining an image signal by performing photoelectric conversion in units.
The image sensor 21 includes a line sync signal generation unit 28
The line sync signal is input from the
Reads the original image one main scanning line at a time in synchronization with the line sync signal,
The image signal is output in synchronization with the driving clock from. Therefore, the time required for the image sensor 21 to read the original image for one main scanning line by photoelectric conversion, that is, the accumulation time, and the cycle of the line sync signal are in a proportional relationship. The image signal output from the image sensor 21 includes an accumulation time, an ambient temperature,
Dark output component which depends on the change over time of the characteristics of the above.

The image reading apparatus 1 can set the accumulation time of the image sensor 21 in three stages, and the setting can be changed by a user's setting operation from the operation display unit 9.

More specifically, keys are provided on the operation display section 9 in correspondence with the indications of "large characters", "ordinary characters" and "small characters". When the content of the document to be read by the image reading apparatus 1 is a fine character, the user presses the key corresponding to the “normal character”. In this case, the key corresponding to the "large character" is pressed, and if the character is relatively small, the key corresponding to the "small character" is pressed.

On the other hand, as shown in FIG. 3, the reading "large character", "ordinary character" and "small character" correspond to reading line density, accumulation time, analog gain, and accumulation time setting signal, respectively. doing. In other words, "ordinary characters"
A reading line density of 7.7 lines / mm, an accumulation time L, an analog gain of 1, and an accumulation time setting signal 01 correspond to “large characters”, a reading line density of 3.85 lines / mm, an accumulation time of 2 L, and an analog gain. 1/2, accumulation time setting signal 00 corresponds,
“Small characters” include a reading line density of 15.4 lines / mm, an accumulation time L / 2, an analog gain of 2, and an accumulation time setting signal 10
Is supported.

When any one of the keys corresponding to the "large character", "ordinary character" and "small character" is pressed by the operation display unit 9, the CPU 6 corresponds to the pressed key. An accumulation time setting signal is output to the image reading unit 2 and the image processing unit 3.

The accumulation time setting signal output to the image reading unit 2 is, as shown in FIG.
8, the gain switching circuit 22 and the dark level correction unit 24.

The line sync signal generation section 28 generates a line sync signal having a cycle corresponding to the storage time corresponding to the input storage time setting signal as shown in FIG.

The image signal output from the image sensor 21 that photoelectrically converts the reflected light from the original image in the storage time according to the storage time setting signal is input to the gain switching circuit 22. The gain switching circuit 22 adjusts the gain of the input image signal with an analog gain inversely proportional to the storage time corresponding to the input storage time setting signal as shown in FIG. Thereby, the image sensor 2 proportional to the accumulation time
The level of the image signal from the A / D converter 23 is
The input voltage range is normalized to a certain level that can be used effectively.

The gain switching circuit 22 is not essential to the present invention, but is included in the configuration of the image reading section 2 as a general component of the image reading apparatus. Note that the gain switching circuit 2
2, the fluctuation according to the accumulation time of the dark output including the component depending on the accumulation time included in the image signal from the image sensor 21 cannot be canceled by the gain adjustment according to the set accumulation time. Is as already described with reference to FIG. When the gain switching circuit 22 is not provided, the fluctuation of the dark output including the component depending on the accumulation time according to the accumulation time cannot be canceled out.
5 has already been described.

The image signal whose level has been normalized by the gain switching circuit 22 is converted into an analog signal by the A / D converter 23.
The digital image data is converted into digital image data and input to the dark level correction unit 24.

The dark level correction unit 24 includes an A / D converter 23
The dark level data is stored in the dark level data storage unit 25 in correspondence with each pixel constituting the image data of the line unit input from, and the dark level of each pixel is subtracted from the pixel value of each pixel. Then, the dark output component included in the input image data is removed.

The image data whose dark level has been corrected by the dark level corrector 24 is input to the shading corrector 26. The shading correction unit 26 includes the dark level correction unit 2
The reference white level data storage unit 27 stores the reference white level data previously read and collected in the reference white level data storage unit 27 corresponding to each pixel constituting the line-by-line image data input from the input unit 4. By subtracting the reference white level of each pixel from the pixel value of, the white level distortion including the light source distortion included in the input image data is corrected.

The image data read by the image reading unit 2 and subjected to the basic correction processing is input to the image processing unit 3 via the system bus 10.

FIG. 4 shows the internal configuration of the image processing unit 3.

In the figure, image data input from the image reading unit 2 is first input to the scaling unit 31.
The scaling unit 31 converts the main scanning size of the input image data into a predetermined size and inputs the converted data to the MTF correction unit 32. The MTF correction unit 32 performs MTF correction, which is an enhancement process for correcting the blur of the image data due to the quantization, on the input image data, and inputs the image data to the gamma correction unit 33.

The gamma correction section 33 performs gamma correction on the input image data so as to convert the density gradient of the image data proportional to the reflectance of the original into density proportional. The gamma correction can be realized by replacing the level of the input image data with the corresponding conversion level. A gamma correction table corresponding to the correspondence table is stored in the gamma correction table storage unit 34 in advance. Gamma correction unit 3
3 performs gamma correction on the input image data by reading data from the gamma correction table storage unit 34 using the level of the input image data as a read address.

The image data output from the gamma correction section 33 is input to a gradation processing section 34. The gradation processing unit 35
The input image data is subjected to gradation processing into data having a predetermined bit width. The gradation processing in this case is processing for converting the read image data into a gradation number (bit width) suitable for the purpose of use of the read image data, specifically, the facsimile processing. This is a binarization process of converting the image into one bit of black and white using a certain threshold value as in an apparatus.

The image data finally output from the gradation processing unit 35 is recorded and output by the image recording unit 4. The gamma correction unit 33 and the gradation processing unit 3 of the image processing unit 3
5 includes a gain switching circuit 22, a dark level correction unit 24, and a line sync signal generation unit 28 of the image reading unit 2;
The accumulation time setting signal from the PU 6 is input.

Next, the image reading apparatus 1 according to this embodiment
Will be described in order of the first to fourth embodiments. 2 and 4, the accumulation time setting signal from the CPU 6 is output from the gain switching circuit 22, the dark level correction unit 24,
Although it is illustrated as being commonly input to the line sync signal generation unit 28, the gamma correction unit 33, and the gradation processing unit 35, in fact, in all of the first to fourth embodiments, the accumulation time setting signal is Only the gain switching circuit 22 and the line sync signal generation unit 28 are input.
Alternatively, in the second embodiment, the accumulation time setting signal is input to the dark level correction unit 24 in addition to the gain switching circuit 22 and the line sync signal generation unit 28, and in the third embodiment, the gain switching circuit 22 and the line sync signal The storage time setting signal is input not only to the generation unit 28 but also to the gamma correction unit 33. In the fourth embodiment, the storage time setting signal is set not only to the gain switching circuit 22 and the line sync signal generation unit 28 but also to the gradation processing unit 35. A signal is input.

First, the first embodiment will be described.

In the first embodiment, as shown in FIG. 5, three dark level data A, B and C are stored in advance in the dark correction level data storage unit 25. As shown in FIG. 6, the dark level data A corresponds to the accumulation time L, the dark level data B corresponds to the accumulation time L / 2, and the dark level data C corresponds to the accumulation time 2L, as shown in FIG. doing. The dark level data corresponding to each accumulation time can be obtained by collecting in advance the dark output actually output from the image sensor 21 in each accumulation time.

The dark level correction section 24 switches the access area of the dark level data storage section 25 to a storage area of dark level data corresponding to the accumulation time set by the accumulation time setting signal from the CPU 6 and reads out the data. D converter 2
3 corrects the dark output component of the image data input from the input unit 3.

However, the dark level data storage unit 25 stores
Rather than remembering all the dark level data,
The dark level data storage unit 25 stores one (for one line)
The three dark level data A, B, and C are stored in the RAM 8 as a storage capacity that can store only the dark level data, and the CPU 8 stores one of the three dark level data in accordance with the set accumulation time. One of them may be loaded into the dark level data storage unit 25.

Next, an image reading processing procedure according to the first embodiment performed in the image reading apparatus 1 will be described with reference to FIG.

In the figure, the CPU 6 operates as the image reading unit 2.
It is monitored whether a document to be read has been set (Judgment 1).
01 (No loop), when a document is set (decision 1)
01 (Yes), it is monitored that the start key of the operation display unit 6 for instructing the start of the document reading is pressed (No loop of the judgment 102), and when it is pressed (the judgment 102).
Yes) confirms the currently set accumulation time (process 103). That is, it is checked whether the key of the operation display unit 9 corresponding to any of the displays “large characters”, “normal characters”, and “small characters” shown in FIG. Check.

Then, an accumulation time setting signal corresponding to the accumulation time confirmed in processing 103 is output (processing 104).
In the first embodiment, the accumulation time setting signal is input to the gain switching circuit 22, the dark level correction unit 24, and the line sync signal generation unit 28 of the image reading unit 2. The cycle of the line sync signal supplied to 21 is set to a cycle proportional to the set accumulation time, and the gain of the gain switching circuit 22 is set to a gain inversely proportional to the set accumulation time. Then, as shown in FIG. 6, the dark level correction unit 24 corresponds to the set accumulation time of the dark level data A, B, or C stored in the dark level data storage unit 25 as shown in FIG. The dark level data to be referred to at the time of dark level correction.

After the process 104, the reference white level data for shading correction by the shading correction unit 26 is sampled and stored (process 105). That is, the image data obtained by turning on the light source for document illumination and reading the reference white image is stored in the reference white level data storage unit 27.

Then, while monitoring whether there is a change in the setting of the accumulation time, the copying process is performed until the copying process is completed (No in decision 106, No loop in process 108 and decision 109). In the copying process (process 108) in this case, the image signal from the image sensor 21 for reading the document to be sub-scanned by the mechanism control unit 5 is normalized by the gain switching circuit 22, and the digital image data is converted by the A / D converter 23. To
The dark level correction unit 24 performs dark level correction using dark level data corresponding to the set accumulation time, performs shading correction using the reference white level data sampled in the process 105 by the shading correction unit 26, and changes the image processing unit 3. The image data that has been subjected to the scaling processing in the doubling processing unit 31, the MTF correction in the MTF correction unit 32, the gamma correction in the gamma correction unit 33, and the gradation processing in the gradation processing unit 35 are line-by-line This is a process of recording and outputting on recording paper by the recording unit 4.

If the setting of the storage time is changed during that time (Yes in decision 106), that is, while the original is being read,
When the user desires to change the reading line density and presses a key of the operation display unit 9 corresponding to one of the displays “large characters”, “normal characters”, and “small characters” shown in FIG. If the depressed key is different from the one corresponding to the read linear density set up to then, the corresponding accumulation time setting signal is output as shown in FIG. 3 (process 107). Thus, the accumulation time setting signal is input to the gain switching circuit 22, the dark level correction unit 24, and the line sync signal generation unit 28 of the image reading unit 2 as in the case of the process 104, and the dark level correction unit 24 Is
As the dark output level data that can optimally correct the dark output level of the image sensor 21 in the storage time that has been changed in the setting, the dark level stored in the dark level data storage unit 25 as shown in FIG. Level data A, B
Or, select the corresponding one of C.

Thus, even if the storage time is changed during reading of the document, the dark output level of the image sensor 21 in the changed storage time can be optimally corrected without recollecting the dark output level data. It is possible to obtain an image that is not affected by a change in the dark output level due to a change in the setting of the accumulation time without lowering the reading throughput.

Next, a second embodiment will be described.

In the second embodiment, as shown in FIG. 5, the storage capacity of the dark correction level data storage unit 25 is three dark level data A, B, and C (for three lines). Capacity. As in the case of the first embodiment, the dark level data A corresponds to the accumulation time L, the dark level data B corresponds to the accumulation time L / 2, and Dark level data C
Corresponds to the accumulation time 2L.

The dark level correction section 24 switches the access area of the dark level data storage section 25 to a storage area of the dark level data corresponding to the accumulation time set by the accumulation time setting signal from the CPU 6 and reads out the data. D converter 2
3 corrects the dark output component of the image data input from the input unit 3.
However, instead of storing all three dark level data in the dark level data storage unit 25, the dark level data storage unit 25 has a storage capacity that can store only one (one line) dark level data. , The three dark level data A, B, and C are stored in the RAM 8, and the CPU 8 loads one of the three dark level data into the dark level data storage unit 25 according to the set accumulation time. It may be.

In the above-described first embodiment, the dark level data A, B, and C corresponding to each accumulation time stored in the dark level data storage unit 25 are stored in the dark level data actually output from the image sensor 21 in each accumulation time. Although the output is obtained by collecting the output in advance, in the second embodiment, the dark level data at each accumulation time is collected each time before the image reading is started.

An image reading process performed by the image reading apparatus 1 according to the second embodiment will be described with reference to FIG.

In the same figure, the CPU 6 is the image reading unit 2
It is monitored whether a document to be read has been set (Judgment 2).
01 (No loop), when a document is set (decision 2)
01 (Yes), it is monitored that the start key of the operation display unit 6 instructing the start of the document reading is pressed (No loop of the determination 202), and when it is pressed (the determination 202).
Yes) sets the accumulation time to 2L (analog gain ２) by outputting the accumulation time setting signal “00” to the line sync signal generation unit 28 and the gain switching circuit 22.
Then, the dark output output from the image sensor 21 and gain-adjusted by the gain switching circuit 22 is sampled by the A / D converter 23 to obtain digital dark level data. The obtained dark level data is stored as dark level data C in the dark level data storage unit 25 (process 205).

Further, by outputting the accumulation time setting signal “01” to the line sync signal generation unit 28 and the gain switching circuit 22, the accumulation time is set to L (analog gain 1) (processing 206), and The dark output output from the sensor 21 and gain-adjusted by the gain switching circuit 22 is sampled by the A / D converter 23 to obtain digital dark level data, and the sampled dark level data is converted to dark level data. A is stored in the dark level data storage unit 25 (Step 208).

The accumulation time is set to L / 2 (analog gain 2) by outputting the accumulation time setting signal "10" to the line sync signal generation unit 28 and the gain switching circuit 22 (processing 209). The A / D converter 23 samples the dark output output from the image sensor 21 and the gain of which has been adjusted by the gain switching circuit 22.
Digital dark level data is obtained, and the sampled dark level data is stored as dark level data B in the dark level data storage unit 25 (process 211).

As a result, not only the component that depends on the accumulation time of the dark output of the image sensor 21 but also the dark level that includes the component of the dark output that depends on the variation of the ambient temperature and the aging of the characteristics of the image sensor 21 is obtained. Data can be obtained for each accumulation time before the reading of the original begins.

Next, the CPU 6 checks the currently set accumulation time (step 212). That is, it is checked whether the key of the operation display unit 9 corresponding to any of the displays “large characters”, “normal characters”, and “small characters” shown in FIG. Check.

Then, an accumulation time setting signal corresponding to the accumulation time confirmed in step 212 is output (step 213).
In the second embodiment, the accumulation time setting signal is input to the gain switching circuit 22, the dark level correction unit 24, and the line sync signal generation unit 28 of the image reading unit 2. The cycle of the line sync signal supplied to 21 is set to a cycle proportional to the set accumulation time, and the gain of the gain switching circuit 22 is set to a gain inversely proportional to the set accumulation time. Then, as shown in FIG. 6, the dark level correction unit 24 corresponds to the set accumulation time of the dark level data A, B, or C stored in the dark level data storage unit 25 as shown in FIG. The dark level data to be referred to at the time of dark level correction.

After the process 213, the reference white level data for shading correction by the shading correction unit 26 is sampled and stored (process 214). That is, the image data obtained by turning on the light source for document illumination and reading the reference white image is stored in the reference white level data storage unit 27.

Then, while monitoring whether there is a change in the accumulation time setting, the copying process is performed until the copying process is completed (No in decision 215, No in process 217, and No in decision 218). In the copying process (process 217) in this case, the image signal from the image sensor 21 for reading the sub-scanned document by the mechanism control unit 5 is normalized by the gain switching circuit 22, and the digital image data is converted by the A / D converter 23. To
The dark level correction unit 24 performs dark level correction using the dark level data corresponding to the set accumulation time, performs shading correction using the reference white level data sampled in the process 214 by the shading correction unit 26, and changes the image processing unit 3. The image data that has been subjected to the scaling processing in the doubling processing unit 31, the MTF correction in the MTF correction unit 32, the gamma correction in the gamma correction unit 33, and the gradation processing in the gradation processing unit 35 are line-by-line This is a process of outputting to recording paper in the recording unit 4.

If the setting of the storage time is changed during that time (Yes in decision 215), that is, while the original is being read,
When the user desires to change the reading line density and presses a key of the operation display unit 9 corresponding to one of the displays “large characters”, “normal characters”, and “small characters” shown in FIG. If the depressed key is different from the key corresponding to the read linear density set up to then, the corresponding accumulation time setting signal is output as shown in FIG. 3 (process 216). As a result, the accumulation time setting signal is input to the gain switching circuit 22, the dark level correction unit 24, and the line sync signal generation unit 28 of the image reading unit 2 in the same manner as in the process 213. Is
As the dark output level data that can optimally correct the dark output level of the image sensor 21 in the storage time that has been changed in the setting, the dark level stored in the dark level data storage unit 25 as shown in FIG. Level data A, B
Or, select the corresponding one of C.

As a result, even when the storage time is changed during reading of the document, the dark output level of the image sensor 21 in the changed storage time can be optimally corrected without recollecting the dark output level data. It is possible to obtain an image that is not affected by a change in the dark output level due to a change in the setting of the accumulation time without lowering the reading throughput.

Next, a third embodiment will be described.

In the third embodiment, as described above,
The gamma correction unit 3 of the image processing unit 3 in addition to the gain switching circuit 22 and the line sync signal generation unit 28 of the image reading unit 2
3, an accumulation time setting signal is also input. As shown in FIG. 9, three gamma correction tables A, B, and C are stored in the gamma correction table storage unit 34 in advance. In each of these correction tables, as shown in FIG. 10, the correction table A corresponds to the accumulation time L, the correction table B corresponds to the accumulation time L / 2, and the correction table C
Corresponds to the accumulation time 2L.

The gamma correction section 33 switches the access area of the gamma correction table storage section 34 to a storage area of the correction table corresponding to the accumulation time set by the accumulation time setting signal from the CPU 6 and reads out the MTF correction section 3.
2 performs gamma correction on the image data input from step 2. However, instead of storing all the three correction tables in the gamma correction table storage unit 34, the gamma correction table storage unit 34 has three correction tables in the RAM 8 with a storage capacity enough to store only one correction table. The tables A, B, and C may be stored, and the CPU 8 may load one of the three correction tables into the gamma correction table storage unit 34 according to the storage time to be set.

With the above configuration, the image reading apparatus 1 according to the third embodiment performs the same image reading processing procedure as that of the first embodiment shown in FIG. However, in the procedure shown in the figure,
The accumulation time setting signal output by the CPU 6 in the processing 104 and the processing 107 is input to the gain switching circuit 22 and the line sync signal generation unit 28 of the image reading unit 2 and the gamma correction unit 33 of the image processing unit 3 as described above. Is done.

That is, the gamma correction unit 33 performs processing 104
In step 107, gamma correction is performed by selectively referring to one of the correction tables A, B, and C according to the accumulation time setting signal input from the CPU 6. In parallel with the gamma correction by the gamma correction unit 33, the dark level data storage unit 25 in which the dark level data in the reference accumulation time L is stored in advance is stored in the dark level correction unit 24.
May be used to correct the dark level. In this case, there is an advantage that the dark output component can be removed from the image data read in the reference accumulation time L.

FIG. 11 shows characteristic examples of the correction tables A, B and C. Referring to the correction table A corresponding to the accumulation time L in the figure, the dark output included in the image signal output from the image sensor 21 and gain-adjusted by the gain switching circuit 22 at the gain 1 during the accumulation time L Is A + B as shown in FIG.

Therefore, the correction table A is stored in the storage time L
In which the dark output of the image data can be optimally corrected, that is, 6 in the range from 0 (white) to 63 (black) in the gradation value of the image data.
Assuming that the density is expressed in four stages, the correspondence between the pre-conversion density (read address) and the post-conversion density (read data) is set so that the high density side of the pre-conversion density (read address) is further converted to the higher density side to some extent. Set.

Here, assuming that the gamma correction table referred to by the gamma correction section 33 is fixed to the correction table A irrespective of the set accumulation time, the accumulation time 2L is shown in FIG. As described above, the dark output level becomes A / 2 + B, which is smaller than the level A + B in the case of the accumulation time L shown in FIG. 15A, and the high density side of the pre-conversion density (read address) of the image data is excessive. Then, the image data is further converted to a higher density side, and the image data after the conversion becomes dark.

Therefore, in the third embodiment, when the accumulation time is 2 L, the density (read address) of the image data before conversion (read address) is smaller than the correction table A for the accumulation time L as shown in FIG. The gamma correction unit 33 refers to the correction table C in which the correspondence between the density before conversion (read address) and the density after conversion (read data) is set so that the high density side is converted to the low density side.

If the gamma correction table referred to by the gamma correction section 33 is fixed to the correction table A regardless of the set storage time, the storage time L / 2
In FIG. 15C, as shown in FIG. 15C, the dark output level becomes 2A + B, and the accumulation time L shown in FIG.
In this case, the level becomes larger than the level A + B, and the conversion of the pre-conversion density (read address) of the image data from the high-density side to the high-density side is insufficient, so that the converted image data becomes too bright.

Therefore, in the third embodiment, when the accumulation time is L / 2, as shown in FIG.
Between the pre-conversion density (read address) and the post-conversion density (read data) such that the higher density side of the pre-conversion density (read address) of the image data is converted to the higher density side than the correction table A for Correction table B in which
The gamma correction unit 33 refers to this.

As a result, even if the storage time is changed while reading the original, the dark output level data of the image sensor 21 at the changed storage time can be applied to the obtained image without re-collecting the dark output level data. Can be optimally corrected at the stage of gamma correction, and it is possible to obtain an image that is not affected by a change in the dark output level due to a change in the storage time setting without lowering the throughput of document reading.

Next, a fourth embodiment will be described.

In the fourth embodiment, as described above,
In addition to the gain switching circuit 22 and the line sync signal generation unit 28 of the image reading unit 2, the gradation processing unit 35 of the image processing unit 3
Also, an accumulation time setting signal is input. 12, three threshold patterns A, B and C are stored in advance in the threshold pattern storage unit 36. In each of these patterns, as shown in FIG. 13, pattern A corresponds to accumulation time L, pattern B corresponds to accumulation time L / 2, and pattern C corresponds to accumulation time 2L.

The gradation processing section 35 switches the access area of the threshold pattern storage section 36 to a storage area of a pattern corresponding to the accumulation time set by the accumulation time setting signal from the CPU 6 and reads out the data. Pseudo intermediate processing is performed on the image data input from 33 by binarization based on comparison with each threshold value of the threshold value pattern. However, instead of storing all three threshold patterns in the threshold pattern storage unit 36, the threshold pattern storage unit 36 has a storage capacity enough to store only one threshold pattern. The three threshold patterns A, B, and C are stored in the RAM 8 and the CPU 8 stores one of the three threshold patterns in the threshold pattern storage unit 36 in accordance with the set accumulation time. You may make it load.

With the above configuration, the image reading apparatus 1 according to the fourth embodiment performs the same image reading processing procedure as the first embodiment shown in FIG. However, in the procedure shown in the figure,
The accumulation time setting signal output by the CPU 6 in the processing 104 and the processing 107 is transmitted to the gain switching circuit 22 and the line sync signal generation unit 28 of the image reading unit 2 and the gradation processing unit 35 of the image processing unit 3 as described above. Is entered.

That is, the gradation processing section 35 performs the gradation processing selectively referring to any one of the patterns A, B and C according to the accumulation time setting signal input from the CPU 6 in the processing 104 and the processing 107. Do. Note that, in parallel with the gradation processing by the gradation processing unit 35, the reference accumulation time L
The dark level correction section 24 may refer to the dark level data storage section 25 in which the dark level data stored in advance has been stored in advance to correct the dark level. Image data
There is an advantage that the dark output component can be removed from the source.

FIG. 14 shows an example of each of the threshold patterns A, B and C. In the figure, considering a pattern A corresponding to an accumulation time L as a reference, in the accumulation time L, a dark output included in an image signal output from the image sensor 21 and adjusted by a gain of 1 in the gain switching circuit 22 is included. The level is A +, as shown in FIG.
B.

Therefore, the pattern A can be used to optimally perform pseudo halftone processing on image data including the dark output level during the accumulation time L, that is, 64 patterns from 0 (white) to 63 (black). It is set so that the average of the threshold values constituting the 4 × 4 threshold pattern A is about half of the maximum value of the gradation value, as expressed in stages.

Here, assuming that the threshold pattern referred to by the gradation processing section 35 is fixed to the pattern A regardless of the set accumulation time, the accumulation pattern shown in FIG. As shown in FIG.
2 + B, which is smaller than the level A + B in the case of the accumulation time L shown in FIG. 15A, and the gradation value of the image data before the binarization processing is converted into a black pixel after the binarization processing. Opportunities increase, and the converted image data becomes dark.

Therefore, in the fourth embodiment, when the accumulation time is 2 L, as shown in FIG. 14, each threshold is larger by 2 than the threshold pattern A for the accumulation time L. The gradation processing unit 35 refers to the threshold value pattern C.

If the threshold pattern referred to by the gradation processing unit 35 is fixed to the correction table A regardless of the set accumulation time, the accumulation pattern shown in FIG. As shown in FIG. 15C, the dark output level becomes 2A + B, and the accumulation time L shown in FIG.
In this case, the level becomes larger than the level A + B, and the tone value before the binarization processing of the image data is converted into white pixels after the binarization processing, and the converted image data becomes whitish. .

Therefore, in the fourth embodiment, when the accumulation time is L / 2, as shown in FIG.
The tone processing unit 35 refers to a threshold pattern B in which each threshold is smaller by two than the threshold pattern A for use.

As a result, even if the storage time is changed during the reading of the original, the dark output level of the image sensor 21 in the changed storage time is affected on the obtained image without re-collecting the dark output level data. Can be optimally corrected at the stage of gradation processing, and an image which is not affected by a change in the dark output level due to a change in the storage time setting can be obtained without lowering the original reading throughput. In the fourth embodiment, the gradation processing unit 3
5, the case where the gradation processing is performed by the pseudo halftone processing of binarizing the multi-gradation image by the threshold value pattern has been described as an example. However, the present invention is not limited thereto.
A similar response is possible.

In the embodiment described above,
The accumulation time of the image sensor 21 is 3 of 2L, L, L / 2.
Although the case where the stage can be set has been described as an example, the present invention is not limited to this, and is similarly applicable to a case where the accumulation time can be set in two stages or four or more stages.

[0109]

According to the first aspect of the present invention, dark output correction data respectively corresponding to a plurality of stages of accumulation times that can be set as the predetermined accumulation time are obtained and stored in advance and stored. In the meantime, during document reading, image data from the image sensor is dark-output based on dark output correction data stored in the storage means corresponding to the storage time set as the predetermined storage time. In order to make corrections, when the dark output level of the image sensor changes due to a change in the storage time during document reading, it is not necessary to turn off the light source for document illumination and re-collect the dark output correction data each time. The dark output included in the image data output from the image sensor in the photoelectric conversion in the storage time after the setting change can be corrected with the optimum dark output correction data.
For this reason, it is possible to obtain an image that is not affected by a change in the dark output level caused by a change in the storage time setting without lowering the document reading throughput.

According to the second aspect of the present invention, at the time of starting document reading, the storage times of the plurality of stages are sequentially set as the predetermined storage times, and the dark output correction data corresponding to each of the set storage times is set. Is collected and stored in the storage means, and during document reading, based on the dark output correction data stored in the storage means corresponding to the storage time set as the predetermined storage time. In order to correct the dark output of the image data from the image sensor, when the dark output level of the image sensor changes due to a change in the accumulation time during reading of the document, the light source for document illumination is turned off and darkened each time. Even if the output correction data is not collected again, the dark output included in the image data output from the image sensor by the photoelectric conversion in the storage time after the setting change is changed to the optimum dark output. It can be corrected by the force correction data. For this reason, it is possible to obtain an image that is not affected by a change in the dark output level caused by a change in the storage time setting without lowering the document reading throughput. Further, since the dark output correction data respectively corresponding to the plurality of stages of accumulation time are collected each time the document reading is started, the image sensor of the image sensor due to a change in the ambient temperature and a change in the characteristics of the image sensor with the passage of time. The effect that the change of the dark output level can be accurately corrected is obtained.

According to the third aspect of the present invention, gamma correction tables respectively corresponding to a plurality of stages of accumulation times that can be set as the predetermined accumulation time are stored in advance, and during the reading of the original, the predetermined gamma correction tables are stored. Since the image data from the image sensor is gamma-corrected based on the gamma correction table stored in the storage means corresponding to the storage time set as the storage time, the storage time is changed during document reading. When the dark output level of the image sensor changes, the light source for document illumination is turned off each time and the dark output correction data is not collected again. The influence of the dark output included in the image data output from the image sensor on the obtained image data can be offset. For this reason, it is possible to obtain an image that is not affected by a change in the dark output level caused by a change in the storage time setting without lowering the document reading throughput.

According to the fourth aspect of the present invention, threshold patterns respectively corresponding to a plurality of stages of accumulation times that can be set as the predetermined accumulation time are stored in advance, and during the reading of the document, the predetermined threshold patterns are stored. Since the image data from the image sensor is subjected to gradation processing according to the threshold pattern stored in the storage means corresponding to the storage time set as the storage time, the storage time is changed during document reading. When the dark output level of the image sensor changes, the light source for manuscript illumination is turned off each time and the dark output correction data is not collected again. The influence of the dark output included in the image data output from the sensor on the obtained gradation image data can be offset. for that reason,
An effect is obtained in which it is possible to obtain a gradation image which is not affected by a change in the dark output level due to a change in the setting of the accumulation time, without lowering the throughput of document reading.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a block configuration of an image reading apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an internal configuration of an image reading unit.

FIG. 3 is a diagram showing a correspondence between each accumulation time, a read linear density, and the like.

FIG. 4 is a diagram showing an internal configuration of an image processing unit 3;

FIG. 5 is a diagram illustrating storage contents of a dark level data storage unit according to the first and second embodiments.

FIG. 6 is a diagram showing a correspondence between each accumulation time and dark level data.

FIG. 7 is a flowchart illustrating an image reading processing procedure according to the first, third, and fourth embodiments.

FIG. 8 is a flowchart illustrating an image reading processing procedure according to the second embodiment.

FIG. 9 is a diagram illustrating storage contents of a gamma correction table storage unit according to the third embodiment.

FIG. 10 is a diagram showing a correspondence between each accumulation time and a correction table.

FIG. 11 is a diagram illustrating a gamma characteristic example of each correction table.

FIG. 12 is a diagram showing stored contents of a threshold pattern storage unit in the fourth embodiment.

FIG. 13 is a diagram showing a correspondence between each accumulation time and a threshold pattern.

FIG. 14 is a diagram showing an example of each threshold pattern.

FIG. 15 is a diagram showing a comparison of dark output levels corresponding to respective accumulation times.

[Explanation of symbols]

 Reference Signs List 1 image reading device 2 image reading unit 3 image processing unit 4 image recording unit 5 mechanism control unit 6 CPU 7 ROM 8 RAM 9 operation display unit 10 system bus 21 image sensor 22 gain switching circuit 23 A / D converter 24 dark level correction Unit 25 dark level data storage unit 26 shading correction unit 27 reference white level data storage unit 28 line sync signal generation unit 29 sensor drive clock generation unit 31 scaling processing unit 32 MTF correction unit 33 gamma correction unit 34 gamma correction table storage unit 35 Gradation processing unit 36 Threshold pattern storage unit

Claims (4)

[Claims] 1. An image reading apparatus in which reflected light from a document is photoelectrically converted by an image sensor for a predetermined storage time to obtain image data, and wherein the predetermined storage time can be set in a plurality of stages. Storage means for preliminarily storing dark output correction data respectively corresponding to a plurality of accumulation times that can be set as time, and the storage corresponding to the accumulation time set as the predetermined accumulation time during document reading. An image reading device comprising: a correction unit configured to perform a dark output correction on the image data from the image sensor based on the dark output correction data stored in the unit. 2. An image reading apparatus in which reflected light from a document is photoelectrically converted by an image sensor for a predetermined storage time to obtain image data, and wherein the predetermined storage time can be set in a plurality of stages. Storage means for storing dark output correction data respectively corresponding to a plurality of accumulation times which can be set as time, and at the start of document reading, the plurality of accumulation times are sequentially set as the predetermined accumulation time. A correction data collection unit that collects dark output correction data corresponding to each of the set storage times and stores the data in the storage unit. Correction means for correcting the dark output of the image data from the image sensor based on the dark output correction data correspondingly stored in the storage means; Image reading apparatus characterized by comprising. 3. An image reading apparatus in which reflected light from a document is photoelectrically converted by an image sensor for a predetermined storage time to obtain image data, and wherein the predetermined storage time can be set in a plurality of stages. Storage means for storing in advance gamma correction tables respectively corresponding to a plurality of stages of storage times which can be set as time, and storage means corresponding to the storage time set as the predetermined storage time during document reading An image reading apparatus comprising: a correction unit configured to perform gamma correction on image data from the image sensor based on a gamma correction table stored in the image reading apparatus. 4. An image reading apparatus in which reflected light from a document is photoelectrically converted by an image sensor for a predetermined storage time to obtain image data, and wherein the predetermined storage time can be set in a plurality of stages. Storage means in which threshold patterns respectively corresponding to a plurality of stages of accumulation times that can be set as time are stored in advance, and the storage means corresponding to the accumulation time set as the predetermined accumulation time during document reading. Processing means for performing gradation processing on image data from the image sensor according to a threshold pattern stored in the image reading apparatus.