JPH04347972A - Contact type image sensor - Google Patents

Abstract

PURPOSE:To provide a contact type image sensor capable of performing the sufficient shading correction even if the capacity of memory is reduced. CONSTITUTION:A picture reading element is selected from each block and the bright output is stored as the data for the shading correction in a ROM 10. Based on this, the shading correction is performed for the picture signal from all the picture reading elements within the same block. The method for selecting the picture reading element applying the data for the shading correction is arbitrary. The data of the bright output of these picture reading elements is preliminarily stored in the ROM 10 and is read at the time of the execution of the shading correction.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contact type image sensor used as an image reading device such as a small facsimile or a handy scanner.

0002

2. Description of the Related Art Among image sensors, a contact type image sensor can read a document without using a reduction optical system, so the optical path length is short, and the device can be miniaturized. Therefore, in recent years, they have been widely used as image reading devices such as small facsimiles, handy scanners, and barcode readers.

The image reading element of an image sensor generally consists of a photodiode and a blocking diode, whose cathodes are connected front to front, or whose anodes are connected back to back. The photodiode photoelectrically converts light reflected by the original and stores charges corresponding to image information, and the blocking diode serves as a switching element that takes out the charges accumulated in the photodiode. An image sensor is constructed by arranging a large number of image reading elements including photodiodes and blocking diodes in the main scanning direction corresponding to the width of one line. For example, if 8 elements are provided per 1 mm, A4
In the case of size data, 1728 image reading elements are required per line.

[0004] When a large number of image reading elements are arranged in the main scanning direction in this way, the amount of light incident on the image sensor changes due to large variations in the amount of light from the LEDs used as light sources. Furthermore, the gain of the image reading element is not uniform throughout the main scanning direction. Therefore, the output of the image sensor when reading pure white paper, so-called bright output, becomes non-uniform depending on the position in the main scanning direction. Although such a problem is not so much of a problem in an image sensor that performs binarization processing, it becomes a big problem when multi-value processing is performed to perform gray scale processing such as 64 gradations.

In order to correct such non-uniformity of bright output, shading correction has been conventionally performed. FIG. 6 is a circuit diagram of a circuit that performs shading correction of this bright output. In the figure, ROM (read only)
The memory 54 is a storage element in which bright output correction data of all the image reading elements in the main scanning direction is stored in advance. A conventional image sensor serially outputs an image signal from an image reading element, and correspondingly outputs an image signal from an image reading element as shown in FIG.
An image signal serially output from an image reading element is supplied to an input terminal 50 of the image reading element. On the other hand, the input terminal 52 is supplied with a read address of a ROM 54 in which shading correction data for the bright output of the image reading element is stored. The order in which the image signals are supplied to the terminal 50 corresponds to the order in which the image reading elements are arranged in the main scanning direction.
The address signal of the ROM 54 supplied to the terminal 52 can be generated in increments of one.

The bright output shading correction data thus read out is converted into an analog signal by the DA converter 56 and then supplied to one terminal of the comparator 58. This comparator normalizes the voltage level by using data from the ROM 54 as a clamp input (reference input). That is, if the data to be output is 4 bits, the clamp input voltage is set to the maximum value, the ground potential is set to the minimum value, and the voltage between them is quantized in 16 steps. Then, the voltage supplied from the input terminal 50 is made to correspond to the closest value among these 16 levels of voltage, and is output as a digital value. In this way, digital image data that has undergone shading correction for each image reading element is obtained from the terminal 60.

FIG. 7 shows a RAM in place of the ROM 54 in FIG.
This is an example using (random access memory) 62. When using an image sensor in a scanner, the white level may change depending on the quality of the paper being scanned. Even in such a case, it is necessary to perform shading correction for bright output every time reading is performed. That is, before reading the image, the ground portion is scanned to capture bright output data, shading correction data is created based on it, and is stored in the RAM 62. After that, shading correction is performed in the same manner as in the case of FIG.

[0008]

By the way, conventional image sensors store shading correction data for all image reading elements arranged in the main scanning direction.
I am using this to perform shading correction, so
A large capacity memory is required, thus increasing costs.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a contact type image sensor that can reduce the memory capacity and perform sufficient shading correction. be.

0010

[Means for Solving the Problems] To achieve the above object, the present invention divides a plurality of image reading elements linearly arranged in the main scanning direction into a predetermined number of blocks, and each block is divided into blocks. In a contact image sensor that reads image information by connecting the image reading elements in a matrix, a memory means for storing one or more bright output levels for each block, and data stored in the memory means. The apparatus is characterized by comprising a correction means for correcting image data from all image reading elements included in the block using the correction means.

In order to achieve the above object, the present invention divides a plurality of image reading elements linearly arranged in the main scanning direction into a predetermined number of blocks, and reads the image using each block as a unit. In a contact image sensor that reads image information by connecting elements in a matrix, a memory means for storing one bright output level for each of a plurality of blocks, and a plurality of bright output levels are stored using data stored in the memory means. The apparatus is characterized by comprising a correction means for correcting image data from all image reading elements included in the block.

0012

[Operation] When the inventors investigated the change in bright output of the image sensor in the main scanning direction, it was found that the change was continuous and did not change much. In particular, the higher the linear density of the image reading elements of the image sensor, the brighter output can be considered to be approximately the same for several consecutive image reading elements. Therefore, it is possible to use the shading correction data of any one of several consecutive image reading elements to perform shading correction of neighboring image reading elements.

[0013] Accordingly, the present invention has the above-mentioned configuration, so that, for example, one of the image reading elements included in one block is
The bright output level of one image reading element is used for shading correction of the image reading elements of the entire block. Therefore, the number of image reading elements belonging to one block is 32.
In an image sensor in which eight image reading elements are provided per 1 mm, a bright output for shading correction is taken out every 4 mm, making it possible to perform practically sufficient shading correction. Also, in the above example,
The amount of memory is reduced to 1/32 compared to the conventional one, and the required memory address is also reduced to 1/32 of the conventional one. Note that, among the image reading elements included in one block, the number of image reading elements that extract bright output for shading correction may be plural.

[0014] Furthermore, a configuration may be adopted in which a bright output is extracted from one image reading element for each of a plurality of blocks, for example, every two or three blocks. This allows the memory capacity to be further reduced compared to the conventional one.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram of the first embodiment of the present invention, FIG. 2 is a circuit diagram of the entire contact type image sensor connected in a matrix, FIG. 3 is a graph showing changes in bright output, and FIG.
is a more detailed circuit diagram of the comparator, and FIG. 5 is a circuit diagram of a second embodiment of the present invention.

The contact image sensor shown in FIG. 2 includes input circuits A1 to A54, photoelectric conversion circuits (blocks) B1 to B54 each having 32 channels, and output circuits C1 to B54.
C32, and the output circuits C1 to C32
Thirty-two lines L1 to L32 are provided corresponding to the number of lines L1 to L32. Input circuits A1 to A54 and photoelectric conversion circuit B1
- B54 are provided in total, 54 each. One photoelectric conversion circuit includes 32 sets of image reading elements corresponding to 32 channels. This set of image reading elements is formed by connecting the cathodes of a photodiode and a blocking diode front to front as described above. Note that the anodes of the photodiode and blocking diode can be connected back-to-back by changing the polarity of the applied pulse.

The arrangement of each photoelectric conversion circuit in FIG. 2 corresponds to the actual arrangement in the main scanning direction when used in a handy scanner, for example, and the photoelectric conversion circuits B1 to B54 are arranged in order from left to right. There is. First input circuit A1
Drive pulses are simultaneously supplied from the photoelectric conversion circuit B1 to the 32 blocking diodes in the photoelectric conversion circuit B1. At this time, output image signals corresponding to the charges accumulated in the 32 photodiodes in the photoelectric conversion circuit B1 are obtained from each of the output circuits C1 to C32. By sequentially and continuously performing operations similar to those described above for all 54 blocks, an image signal for one line in the main scanning direction is obtained.

In this embodiment, each of the 54 photoelectric conversion circuits is provided with 32 image reading elements.
The total number of image reading elements is 1728. These are arranged in the main scanning direction at a rate of 8 pieces per 1 mm, and are designed to make it possible to read A4 size images. When the length in the main scanning direction increases in this way, the bright output of each image reading element, that is, the output when reading pure white paper, is no longer uniform and varies depending on the location as shown in FIG. 3.

However, as shown in FIG. 3, the change in bright output is continuous, and when viewed microscopically, it can be seen that the bright output of a plurality of consecutive image reading elements can be considered to be approximately equal. Therefore, in this embodiment, one image reading element is selected from each block, its bright output is stored in the memory as shading correction data, and based on this, the image signals of all the image reading elements in the same block are shaded. to correct. The image reading element that takes the shading correction data can be selected in any way, but in this embodiment, for convenience, the first image reading element of each block, that is, the 1st, 33rd, 65th, and 65th image reading elements from the left in FIG.
..., the 1697th image reading element. The bright output data of these image reading elements is stored in the ROM 10 in FIG.
memorize it in advance.

FIG. 1 shows an actual shading correction circuit in this embodiment. Input terminal O1
.about.O32 are supplied with image signals in parallel from the output circuits C1 to C32 of FIG. Among these, the signals inputted to O1 include, in addition to the image signal, an address signal of the ROM 10 in which data to be read out for shading correction is stored. For example, if the image signal supplied to O1 to O32 is from the first block, the address signal of the ROM address where the bright output data of the leftmost image reading element in FIG. Supplied to O1. If the image signal is from the second block, the address signal of the ROM address in which the bright output data of the 33rd image reading element from the left in FIG. 2 is stored is supplied to O1 together with the image signal. below,
The same is true. Therefore, the ROM required in this embodiment
10 addresses is 54, which is significantly reduced compared to the conventional 1728 addresses.

[0021] Shading correction data is stored in ROM10.
This data is converted into an analog signal in the DA converter 12, and then sent to the comparators H1 to H
32. FIG. 4 is a more detailed circuit diagram of this comparator H. The shading correction data from the ROM 10 is supplied to the +ref terminal of the comparator H as a clamp input or a reference signal. On the other hand, −ref
A ground level signal is always supplied to the terminal.

This comparator H is a kind of AD converter. That is, the voltage level is normalized with the +ref input as the maximum value and the -ref input as the minimum value, and in the case of a 4-bit output, for example, the voltage between these is quantized in 16 steps. Then, the voltages supplied to O1 to O32 are made to correspond to the closest value among these 16 levels of voltage, and are output as digital values. Therefore, shading correction for one block is executed in parallel, and corrected data for one block is obtained at the same time.

FIG. 5 is a circuit diagram of a second embodiment of the present invention. In this case, the data supplied to the terminals O1 to O32 are first converted into digital signals in the respective AD converters I1 to I32. Among these, the signals supplied to O1 include, in addition to the image signal, an address signal of the ROM 10 in which data to be read out for shading correction is stored, as in the case of FIG. ROM
The digital data read from 10 is sent to comparator J1.
~J32. Here, comparators J1 to J32 are digital comparators, and each of these comparators is O1 to O
32 and converted into digital signals by the AD converters I1 to I32, the data from the ROM 10 is compared with the data, and a predetermined correction is made and output.

In the embodiments so far, each block has been described as having one image reading element that takes out the bright output for shading correction, but when more precise correction is required, or when the bright output changes in the main scanning direction, If the shading is severe, shading correction may be performed by extracting bright outputs for shading correction from a plurality of image reading elements spaced at appropriate intervals within each block. Conversely, if the change in bright output is small, one image reading element may be selected for every two or three blocks to extract bright output for shading correction.

Further, in the embodiment of the present invention, a case has been described in which a ROM is used as a storage means, but a RAM can also be used as a storage means, similar to the conventional circuit shown in FIG. Furthermore, in the embodiment of the present invention shown in FIGS. 1 and 5, the digital signal after shading correction is output in parallel, but it is possible to easily convert it to serial output by using a shift register or the like as necessary. Needless to say.

[0026]

Effects of the Invention As explained above, according to the present invention, the memory capacity can be reduced while maintaining practical shading correction accuracy, so a contact image sensor is provided that enables significant cost reduction. can be provided.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a shading correction circuit of a contact type image sensor according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of the entire image sensor connected in a matrix.

FIG. 3 is a graph showing changes in bright output of image reading elements arranged in the main scanning direction.

FIG. 4 is a more detailed circuit diagram of the comparator shown in FIG. 1;

FIG. 5 is a circuit diagram of a shading correction circuit of a contact type image sensor according to a second embodiment of the present invention.

FIG. 6 is a circuit diagram of a shading correction circuit of a conventional contact type image sensor.

FIG. 7 is a circuit diagram of another shading correction circuit of a conventional contact type image sensor.

[Explanation of symbols]

10 ROM 12 DA converter A1 ~ A54 Input circuit B1 ~ B54 Photoelectric conversion circuit C1 ~ C32 Output circuit H1 ~ H32 Comparator I1 ~ I32 AD converter

Claims (2)

[Claims] 1. A plurality of image reading elements linearly arranged in the main scanning direction are divided into a predetermined number of blocks, and the image reading elements are connected in a matrix using each block as a unit, and image information is transmitted. In a contact type image sensor for reading, there is a storage means for storing one or more bright output levels for each block, and data stored in the storage means is used to read information from all image reading elements included in the block. A contact image sensor comprising: a correction means for correcting image data. 2. A plurality of image reading elements linearly arranged in the main scanning direction are divided into a predetermined number of blocks, and the image reading elements are connected in a matrix using each block as a unit, so that image information is transmitted. In a contact type image sensor for reading, there is a storage means for storing one bright output level for each of the plurality of blocks, and data stored in the storage means is used to read from all image reading elements included in the plurality of blocks. A contact image sensor comprising: a correction means for correcting image data of.