JPH09252389A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inhibit processing of succeeding image forming with signals corrected by abnormal data when correction data stored in a RAM are the abnormal data. SOLUTION: A RAM 5 stores correction data used by a dark state output correction circuit 3 and a shading correction circuit 4. Then dispersion in an output signal from each pixel of an image sensor is corrected by the dark state output correction circuit 3 or the like. In this case, whether or not the voltage of the backup battery 6 of the RAM 5 satisfies the data storage voltage of the RAM 5 is detected by a voltage detection circuit 8 and when the voltage is less than the data storage voltage and a system power supply is started after that, a changeover device 9 is thrown to the position of outputting a signal given to the dark state output correction circuit 3 or the like. Thus, the succeeding signal processing by the signals corrected by abnormal data is not conducted.

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 which does not deteriorate more than the image quality before correction even when correction data for correcting deterioration of image quality caused by an image sensor or the like is not correct data.

[0002]

2. Description of the Related Art Conventionally, in an image reading apparatus, a document is irradiated with light, and the reflected light is condensed on an image sensor composed of a plurality of pixels by an imaging lens or the like, and photoelectric conversion is performed by the image sensor. The original information is read by.

However, in such an image reading apparatus, due to factors such as the light amount distribution of the light source, the aberration of the image forming lens, the sensitivity distribution of the image sensor, etc. (hereinafter, this is referred to as a cause peculiar to the apparatus), the original having a uniform density is used. However, there is a problem in that the output signal from each pixel varies even when reading the.

Therefore, a white original is read in advance, data obtained by performing a predetermined data process on a signal output from the image sensor at that time is stored in a memory as correction data, and is actually read when the image is read. The output signal from the image sensor is corrected based on the correction data.

There is an image reading apparatus that can read such correction data only at the time of shipment from the factory due to its configuration.
In such an apparatus, a white original is read at the time of shipment, and the correction data obtained by this is stored in a ROM (Japanese Patent Laid-Open No. 6-58242).
No. 3-97059), or stored in a RAM using a battery as a backup power source.

[0006]

However, in order to store the correction data in the ROM, a circuit for storing the correction data is required separately, which causes a cost increase.

RA backed up by a battery
When the correction data is stored in M, it does not require a special circuit as in the case of ROM, which can increase the cost, but the data can be retained when the backup battery is exhausted or fails. Since it disappears, there was a problem described below.

That is, since data cannot be retained due to insufficient battery power, the data stored in such RAM is different from the correction data (hereinafter referred to as abnormal data). Therefore, when the correction is performed based on the abnormal data read from the RAM, the variation in the signal from each pixel is increased and the image quality is further deteriorated as compared with the case where the correction is not performed.

Further, the MTF (Modulation) is applied to the signal corrected based on the abnormal data as described above.
When emphasis correction such as transfer function correction is performed, the variation of the output signal from the image sensor is emphasized to the contrary, which causes a problem that lines such as characters are cut or crushed.

Therefore, the present invention provides an image reading apparatus in which the deterioration of the image quality is prevented more than the deterioration of the image quality due to the peculiar cause of the apparatus even when the voltage of the backup battery becomes lower than the data holding voltage of RAM. To aim.

[0011]

In order to solve the above problems, the invention according to claim 1 is directed to an image sensor that receives reflected light from a document and performs photoelectric conversion, and a variation in output signal from the image sensor. First correcting means for correcting,
An image reading apparatus having a storage unit for storing correction data used by the first correction unit, a detection unit for detecting whether or not the correction data is correctly stored in the storage unit, and a correction of the storage unit. A switch that outputs a signal from the first correction means if the data is correct, and outputs a signal to be input to the first correction means if the correction data in the storage means is incorrect; It is characterized by having.

According to a second aspect of the present invention, an image sensor that receives reflected light from a document and performs photoelectric conversion, a first correction unit that corrects variations in output signals from the image sensor, and the first correction unit are provided. In the image reading apparatus having a storage unit for storing the correction data used by the first correction unit, a detection unit for detecting whether the correction data is correctly stored in the storage unit, and the first correction unit. If the correction data of the second correction means for performing the enhancement correction on the signal of No. 2 and the storage means are correct, the signal from the second correction means is output, and the correction data of the storage means is incorrect. In this case, a switching device for outputting a signal input to the first correction means is included.

According to a third aspect of the present invention, an image sensor for receiving reflected light from a document and performing photoelectric conversion, a first correction means for correcting variations in output signals from the image sensor, and the first correction means. In the image reading apparatus having a storage unit for storing the correction data used in the first correction unit, the detection unit for detecting whether or not the correction data is correctly stored in the storage unit and the correction data in the storage unit are If it is correct, a signal from the first correction means is output, and if the correction data is not correct in the storage means, a switch that outputs a signal to be input to the first correction means; A second method of performing enhancement correction on the signal from the switch, and changing the correction formula according to whether the correction data is correctly stored in the storage means.
And a correcting means of.

[0014]

FIG. 1 shows a first embodiment of the present invention.
It will be described based on. In the figure, 1 is a line type image sensor composed of a plurality of pixels, which outputs an analog image signal by receiving reflected light from a document and photoelectrically converting it. An A / D converter 2 converts an analog image signal from the image sensor 1 into a multivalued digital image signal.

Reference numeral 3 is a dark output correction circuit, and 4 is a shading correction circuit, which constitute a first correction means and correct variations in the signal output from each pixel of the image sensor 1 due to various factors. ing.

Reference numeral 5 denotes a RAM which stores dark output correction data which is correction data when the dark output correction circuit 3 corrects and shading correction data which is correction data when the shading correction circuit 4 corrects. There is. These correction data are written at the time of factory shipment, and only read after the shipment.

Reference numeral 6 denotes a battery, which supplies power so that the RAM 5 can hold data when a system power supply (power supply for the image reading apparatus) (not shown) is stopped. Reference numeral 7 denotes a power supply switching device that switches the power supply so that the RAM 5 is supplied with power from the system power supply when the system power supply is operating and the power is supplied from the battery 6 to the RAM 5 when the system power supply is stopped. There is.

Reference numeral 8 is a voltage detection circuit which is a detection means and detects whether or not the voltage of the battery 6 is equal to or higher than the data holding voltage of the RAM 5. Reference numeral 9 denotes a switch, which switches a signal input to a comparator 11, which will be described later, according to the detection result of the voltage detection circuit 8. The normal comparator 11 includes a shading correction circuit 4
Although the output signal from the A / D converter 2 is input, when the system power supply is started in the state where the battery 6 is equal to or lower than the data holding voltage of the RAM 5, the multilevel digital signal from the A / D converter 2 is directly input to the comparator 11. I am switching to do so.

Reference numeral 10 is a threshold value generation circuit, which generates a threshold value and outputs it to the comparator 11. Then, the comparator 11 compares the magnitude of the multi-valued digital signal with the threshold value from the threshold value generation circuit 10 to convert it into a binary digital image signal and outputs it.

Next, the procedure of the correction process in the image reading apparatus having the above configuration will be described. At factory shipment, the dark output correction data and the shading correction data are stored in the RAM 5 backed up by the battery 6.

The dark output correction data is correction data for correcting variations in the signals output from the respective pixels of the image sensor 1 when the light source is turned off (in the dark state) and the document is read.

For data acquisition, a reference white original is read in a dark state, and a signal output from each pixel at that time is subjected to predetermined data processing such as A / D conversion. Vdi) is obtained.

The shading correction data is correction data for correcting the variation of the signal output from each pixel of the image sensor 1 when the light source is turned on (lighting state) and the document is read.

For data acquisition, a white original serving as a reference is read in a lighted state, and a multi-valued digital signal output-corrected in the dark is set to Wwi for the signal from each pixel at that time,
With this peak value as Vwp, the shading correction data (Vsi) is obtained by performing the arithmetic processing represented by Vsi = Vwi / Vwp.

In this way, each correction data is stored in the RAM 5 and shipped from the factory, and after the factory shipment, an image is formed by the following procedure. The original image is read, and the analog image signal output from the image sensor 1 at that time is A / D.
It is converted into a multi-valued digital image signal by the converter 2.

The variations in the output signal from the image sensor 1 are caused by the light intensity distribution of the light source for illuminating the original and the lens such as an image forming lens for forming the reflected light from the original on the image sensor 1 as described above. However, the dark-time output correction circuit 3 corrects the sensitivity variation of the pixels of the image sensor 1.

As a correction method, for example, dark output correction data (Vdi) stored in the RAM 5 is used, and multiple output signals from the A / D converter 2 are output corresponding to the output signals of the respective pixels when the document is read. With the value digital signal as Voi, the corrected signal (V1i) is output by performing arithmetic processing using the correction formula represented by V1i = Voi-Vdi.

As described above, the variation in the sensitivity of the pixel can be corrected by the dark output correction, but the luminous intensity distribution of the document illuminating light source,
The variation due to the aberration of the imaging lens cannot be corrected by the dark output correction. Therefore, in order to correct the variations due to such factors, the shading correction circuit 4 performs correction.

As a correction method, the shading correction data (Vsi) stored in the RAM 5 is used for the output signal (V1i) from the dark-time output correction circuit 3, and is expressed as V2i = V1i / Vsi. A signal (V2i) that has been subjected to arithmetic processing using a correction formula and corrected is output.

The multi-valued digital signal thus dark-time output-corrected and shading-corrected is compared in magnitude with the threshold value from the threshold value generation circuit 10 in the comparator 11,
The binary digital image signal is output for subsequent signal processing.

By the way, when the system power supply operates when the voltage of the battery 6 is lower than the data holding voltage of the RAM 5, that is, when the data stored in the RAM 5 is abnormal data different from the correction data, the RAM 5 is stored in the RAM 5. Power is supplied from the system power supply, so R
The abnormal data existing in AM5 is held by the system power supply, and the subsequent correction processing is corrected based on the abnormal data.

Therefore, when the voltage of the battery 6 is detected by the voltage detection circuit 8 and the system power supply is started after the voltage becomes equal to or lower than the data holding voltage of the RAM 5, the switching device 9 causes the A / D converter 2 to operate. The signals are switched so that the multi-valued digital signal from 1 is directly output to the comparator 11.

That is, when the voltage of the battery 6 becomes lower than the data holding voltage and the data stored in the RAM 5 becomes abnormal data, the signal corrected by the dark output correction circuit 3 and the shading correction circuit 4 is output. Instead of inputting to the comparator 11, the signal from the A / D converter 2 is directly input to the comparator 11 and converted into a binary digital image signal. As a result, it becomes possible to avoid signal processing such as subsequent image processing by using the corrected signal that has been subjected to dark output correction and shading correction due to abnormal data, and the image quality of the image formed is a device-specific cause. The image quality will not be deteriorated more than the deterioration of the image quality.

In the above description, the voltage of the battery 6 is detected to determine whether or not the data stored in the RAM 5 is normal data. However, specific data is written in a predetermined address of the RAM 5 and Whether or not the specific data is correct may be detected when the system power supply is started, and the switch 9 may be controlled according to the detection result.

Next, a second embodiment of the present invention will be described with reference to FIG. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

The image reading apparatus according to the present embodiment is provided with the MTF correction circuit 12 as the second correction means between the shading correction circuit 4 and the switch 9. If the resolving power of the imaging lens that forms the reflected light from the document on the image sensor 1 is low, lines and characters may be blurred or crushed when an image is formed. Therefore, the MTF correction circuit 12 performs emphasis correction. There is.

However, when the voltage of the battery 6 becomes equal to or lower than the data holding voltage of the RAM 5, if the MTF correction is performed on the dark output corrected signal and the shading corrected signal based on the abnormal data stored in the RAM 5, On the contrary, the variation of the signal from the image sensor is emphasized, which rather deteriorates the image quality.

Then, when the voltage of the battery 6 becomes equal to or lower than the data holding voltage of the RAM 5 and the system power supply is activated thereafter, the signal corrected by the dark output correction circuit 3, the shading correction circuit 4 and the MTF correction circuit 12 is output. Is not input to the comparator 11, but the multilevel digital signal from the A / D converter 2 is directly input to the comparator 11.

As an MTF correction method, for example, FIG.
A method of correcting the signal of the target pixel E by using the signals of the peripheral pixels B, D, F, and H can be applied by considering a minimal area including the target pixel E as shown in FIG. At this time, the corrected signal E ′ of the target pixel E is given by a correction equation such as E ′ = 3E− (B + D + F + H) / 2 or E ′ = 5E− (B + D + F + H).

As described above, even when the voltage of the battery 6 becomes equal to or lower than the data holding voltage of the RAM 5 and the abnormal data is stored in the RAM 5, the signal for which the dark output correction is performed based on the abnormal data is performed. Even if the MTF correction is performed on the A / D, the corrected signal is not output to the comparator 11 and the A / D
Since the signal from the converter 2 is directly output to the comparator 11, it is possible to prevent the deterioration of the image quality due to the device-specific cause.

Next, a third embodiment of the present invention will be described with reference to FIG. The same components as those in the first and second embodiments are designated by the same reference numerals and the description thereof will be omitted.

The image reading apparatus according to the present embodiment is the same as the second embodiment of the second invention, and is M as a second correction means.
Although it has the TF correction circuit 13, the MTF correction circuit 13
Is provided between the switch 9 and the comparator 11.

As described in the embodiment of the second invention, since the correction by the MTF correction circuit 13 is not the correction performed based on the data stored in the RAM 5,
It is possible to perform correction even if the voltage of the battery 6 has dropped.

However, when the MTF correction is performed on the signal on which the shading correction or the like is performed,
Since the signals to be corrected are different from the case where the MTF correction is performed on the signals from (1) to (4), it is necessary to perform the correction adapted to each.

Therefore, in the MTF correction circuit 13, when the voltage of the battery 6 becomes equal to or lower than the data holding voltage of the RAM 5 and the system power supply is subsequently activated, the voltage is set so that the correction formula is changed under this condition. A signal is input from the detection circuit 8.

That is, when the voltage of the battery 6 satisfies the data holding voltage of the RAM 5, the same correction as described in the second embodiment is performed.

On the other hand, when the voltage of the battery 6 does not satisfy the data holding voltage of the RAM 5, the signals of the peripheral pixels B and H are used for the minimum area including the target pixel E as shown in FIG. A method of correcting the signal of the pixel of interest E is possible. At this time, the corrected signal E ′ of the target pixel E is corrected by a correction equation such as E ′ = 2E− (B + H) / 2 or E ′ = 3E− (B + H).

As described above, even if the data stored in the RAM 5 is abnormal data, it becomes possible to perform an appropriate MTF correction.

[0049]

As described above, according to the first aspect of the present invention, the detection means detects whether the data stored in the storage means is correct correction data, and the switching unit stores the data based on the detection result. When it is determined that the correction data is correctly stored in the means, a signal from the first correction means is output, and when it is determined that the correction data is not correctly stored in the storage means, the first Since the signal input to the correction means is output, the variation in the signal output from each pixel of the image sensor is not emphasized. Therefore, the image quality is not deteriorated more than the deterioration of the image quality based on the cause peculiar to the apparatus.

According to the invention of claim 2, the first aspect
Even if the second correction means for performing the enhancement correction on the signal output from the correction means is included, if the first correction means does not perform correction based on the correct correction data, the switching is performed. Since the input unit inputs the input signal of the first correction unit to the comparator, the variation in the signal output from each pixel of the image sensor is not emphasized. Therefore, the image quality is not deteriorated more than the deterioration of the image quality based on the cause peculiar to the apparatus.

According to the third aspect of the invention, since the second correction means for performing the enhancement correction on the signal output from the switching device is provided, it is determined whether correct data is stored in the storage means. In spite of this, the enhancement correction can be performed, and the correction formula is changed depending on whether or not the correction data stored in the storage means is correct, so that it is possible to always perform the correction in the optimum state. Therefore, the image quality is not deteriorated more than the deterioration of the image quality based on the cause peculiar to the apparatus.

[Brief description of drawings]

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

FIG. 2 is a main block diagram of an image reading apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a correction method of an MTF correction circuit used in FIG.

FIG. 4 is a main block diagram of an image reading apparatus according to a third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image sensor 2 A / D converter 3 Dark output correction circuit (first correction means) 4 Shading correction circuit (first correction means) 5 RAM (storage means) 6 Battery 7 Power supply switching circuit 8 Voltage detection circuit ( Detecting means) 9 Switching device 10 Comparator 11 Threshold value generating circuit

Claims (3)

[Claims] 1. An image sensor that receives reflected light from a document and photoelectrically converts it, a first correction unit that corrects variations in output signals from the image sensor, and a first correction unit. In an image reading apparatus having a storage means for storing correction data, a detection means for detecting whether or not the correction data is correctly stored in the storage means, and the correction data in the storage means are correct, 1
An image reading apparatus, which outputs a signal from the correction means and outputs a signal to be input to the first correction means when the correction data in the storage means is incorrect. . 2. An image sensor for receiving photoelectrically reflected light from a document to perform photoelectric conversion, a first correction means for correcting variations in an output signal from the image sensor, and a first correction means. In an image reading apparatus having a storage unit for storing correction data, a detection unit for detecting whether or not the correction data is correctly stored in the storage unit, and an enhancement correction for a signal from the first correction unit. And a second correction unit that performs the correction data stored in the storage unit if the correction data is correct.
An image reading apparatus, which outputs a signal from the correction means and outputs a signal to be input to the first correction means when the correction data in the storage means is incorrect. . 3. An image sensor for receiving reflected light from a document and performing photoelectric conversion, a first correction means for correcting variations in an output signal from the image sensor, and a first correction means. In an image reading apparatus having a storage means for storing correction data, a detection means for detecting whether or not the correction data is correctly stored in the storage means, and the correction data in the storage means are correct, 1
A switch for outputting a signal from the correction means and outputting a signal to be input to the first correction means when the correction data is not correct in the storage means, and a signal from the switch. An image reading apparatus comprising: a second correction unit that performs enhancement correction and changes a correction formula according to whether the correction data is correctly stored in the storage unit.