KR100510120B1 - Apparatus and method for obtaining gamma characteristic curve of image sensor - Google Patents

Abstract

The present invention includes a photoelectric conversion unit for forming an incident light incident from the light source during the optical accumulation time to an optical image through photoelectric conversion; An analog / digital converter configured to analog-to-digital convert the output voltage of the photoelectric converter; In order to obtain a gamma characteristic curve for the photoelectric conversion unit, the pixel gray scale value and the optical accumulation time increase from a minimum gray scale value determined by a predetermined number of bits per pixel to a maximum gray scale value while maintaining a linear proportional relationship. An optical accumulation time controller configured to generate a line clock signal; And a gamma table storage unit using a gamma table storage unit for storing a output of the analog / digital converter as the line clock signal is applied to obtain a gamma table having an incident light amount of the photoelectric converter and an output voltage of the photoelectric converter as a coordinate axis. An apparatus and method for obtaining characteristic curves.

According to the present invention, in order to obtain a gamma characteristic curve for an image sensor having a high quantization resolution using a gamma test pattern having a low quantization resolution, a high reliability gamma is adjusted by adjusting the exposure time of the image sensor to incident light in proportion to the amount of light. There is an advantage that the characteristic curve can be easily obtained.

Description

Apparatus and method for obtaining gamma characteristic curve of image sensor

The present invention relates to an apparatus and method for obtaining a gamma characteristic curve of an image sensor, and more particularly, to obtain a gamma characteristic curve for an image sensor having a high quantization resolution by using a gamma test pattern having a low quantization resolution. Apparatus and method for acquiring the gamma characteristic curve of the visual image sensor that can easily obtain a high reliability gamma characteristic curve by adjusting the exposure time of the image sensor in proportion to the amount of light ).

The rapid development of the semiconductor industry has made it easier to manipulate information, and the acquisition and use of this information has become essential for the maximization of value creation among individuals, companies, society and countries. If you get a lot of information scattered around the world faster than others, you can improve your work efficiency and productivity. The means for acquiring the information is important for obtaining the information we want in a timely manner through the process of acquiring and processing the information. In the past, when technology did not evolve, there were only a few ways to get information, but in recent years it has been possible to obtain information in a variety of ways.

With the advent of the multimedia era, people have been able to manipulate video and audio information at will, and they want to use high quality information more quickly throughout their lives. Among them, the human desire for image information has reached the level of producing, processing, and storing directly, not just watching TV or video. In addition, in communication, technology has been developed toward adding images in the existing voice-oriented manner, and the need for an image input tool is increasing. CCD coupled sensor (Charge Coupled Device Image sensor) has been evaluated as a device of good image quality among the image input tools developed to date.

In general, an image sensor refers to a photoelectric conversion sensor such as a charge coupled device (CCD) or a contact image sensor (CIS), and may also be referred to as a charge coupling device or a charge imaging device.

Systems that use image sensors include video cameras such as TV cameras, camcorders, and unmanned surveillance cameras, as well as digital still cameras (DSCs) and black and white / color scanners. Systems such as digital copier, facsimile, multi-function peripheral (MFP), and the like.

In particular, among such systems, an image scanning device such as a black-and-white / color scanner, which is popular with affinity, is used for scanning (i.e., reading) printed text, photographs, memos or letters in the form of human hands. The most common means are essential components such as multifunction devices, document translators, computers for CAD (Computer Aided Design), facsimiles, character recognizers, and digital copiers, where the operating characteristics of the image sensor are the decisive factors that determine the performance of the system. It is becoming.

The CCD image sensor can be largely divided into a two-dimensional CCD image sensor and a linear one-dimensional CCD image sensor. The criteria for this classification are to obtain image information two-dimensionally at a time. It depends on whether you acquire in one dimension. The two-dimensional CCD image sensor can be divided into a frame transfer CCD, an interline transfer CCD, and a frame interline transfer CCD according to a transmission method. have.

CCD image sensors handle analog signals and their driving is a device that uses a digital clock, while at the same time a very unique device whose input signal is light.

In general, an image sensor performs various correction processes by employing various signal processing techniques to match image reproduction characteristics with human viewing characteristics. A typical correction process is a gradation correction process. Gradation correction matches the linearity of the gradient between the optical density of the original image and the optical density of the reproduced image on the coordinates of the optical density of the original and the optical density of the reproduced image in order to match the gray scale reproduction characteristics with the human viewing characteristics. It is to control to have. This slope is referred to as a tone reproduction curve, or often a gamma characteristic curve. In order to have desirable gradation reproduction characteristics, it is necessary to perform gamma correction that gives linearity to the gamma characteristic curve, that is, gamma correction has become a typical example of gradation correction.

FIG. 1A is a plan view illustrating an arrangement of an image sensor and a light source of a general scanner, and FIG. 1B is a configuration diagram illustrating an example of obtaining a gamma table by optical effects of a light source and an image sensor on an input sheet.

In general, a light emitting diode (LED) is used as a light source of a scanner. As shown in FIG. 1A, light incident on an input paper from a light source is reflected by an opposite image sensor to obtain an optical density on the input paper. Can be.

The gamma characteristic curve acquisition method of the image sensor according to the prior art typically scans a gamma test pattern (e.g., input paper, etc.) having 16 kinds of brightness (ie, 16 gradations), and thus the brightness value (optical density) of the resulting image. We estimate the gamma characteristic curve corresponding to 16 gray levels by measuring.

However, in recent scanners and copiers, since the quantized bit rate of the input image is 8 bits or more, it is necessary to use a gamma test pattern having a brightness value of 256 gradations or more. However, it is almost impossible to make such a gamma test pattern. .

Accordingly, the present invention has been made to solve such a problem, and in order to obtain a gamma characteristic curve for an image sensor having a high quantization resolution using a gamma test pattern having a low quantization resolution, an exposure time of the image sensor with respect to incident light It is an object of the present invention to provide an apparatus and method for obtaining a gamma characteristic curve of an image sensor that can easily obtain a high reliability gamma characteristic curve by adjusting the proportional to the amount of light.

In order to achieve the above object, the present invention includes a photoelectric conversion unit for imaging the incident light incident from the light source during the optical accumulation time to the optical image through photoelectric conversion; An analog / digital converter configured to analog-to-digital convert the output voltage of the photoelectric converter; In order to obtain a gamma characteristic curve for the photoelectric conversion unit, the pixel gray scale value and the optical accumulation time increase from a minimum gray scale value determined by a predetermined number of bits per pixel to a maximum gray scale value while maintaining a linear proportional relationship. An optical accumulation time controller configured to generate a line clock signal; And a gamma table storage unit which obtains a gamma table having an incident light amount of the photoelectric conversion unit and an output voltage of the photoelectric conversion unit as coordinate axes by storing the output of the analog / digital conversion unit as the line clock signal is applied.

Hereinafter, a preferred embodiment of a gamma characteristic curve acquisition device of an image sensor according to the present invention will be described with reference to the accompanying drawings.

Figure 2 is a block diagram showing a preferred embodiment of the gamma characteristic curve acquisition device of the image sensor according to the present invention.

As shown in FIG. 2, in the preferred embodiment of the apparatus for acquiring a gamma characteristic curve of the image sensor according to the present invention, the photoelectric conversion unit 100 is configured to form incident light incident from a light source during an optical accumulation time into an optical image through photoelectric conversion. Wow;

An analog / digital converter 110 for converting the output of the photoelectric converter 10 into an analog / digital converter;

In order to obtain a gamma characteristic curve of the photoelectric conversion unit 100, the pixel gray scale value and the optical accumulation time maintained from the lowest gray scale value determined by a predetermined number of bits per pixel and the maximum gray scale value maintain a linear proportional relationship. An optical accumulation time control unit 120 generating a line clock signal controlling to increase while increasing; And

As the line clock signal is applied, the gamma table storage unit 130 stores the output of the analog / digital converter 110 to obtain a gamma table having an incident light amount of the photoelectric converter and an output voltage of the photoelectric converter as coordinate axes. ), Including

Hereinafter, the operation of the preferred embodiment of the gamma characteristic curve acquisition device of the image sensor according to the present invention configured as described above will be described in detail with reference to the accompanying drawings.

First, the present invention assumes the following assumptions. The amount of light accumulated in the photoelectric conversion unit 100 is equal to the amount of light accumulated for 1 second for 1 second and that for 2 seconds of light for 2 seconds. The amount of light accumulated in the photoelectric conversion unit 100 is proportionally controlled by adjusting the time of induction to the photoelectric conversion unit 100, that is, the time that the light source is turned on, with a constant light source, instead of measuring the output value by inputting the measured value. To adjust the gamma table. As is well known, such a hypothesis is a theory accepted in the field of image processing, and thus, further detailed description will be avoided here.

In addition, in implementing the present invention, in order to effectively control the incident light accumulation time of an image sensor such as a CCD or a CIS, the pixel gray scale value from the lowest gray scale value determined by the predetermined number of bits per pixel to the maximum gray scale value and The frequency of the system clock is doubled by dividing the system clock applied to the system so that the optical accumulation time increases while maintaining the linear proportional relationship, and uses the doubled clock as the line clock signal of the image sensor.

First, the photoelectric conversion unit 100 forms incident light incident from a light source during an optical accumulation time into an optical image through photoelectric conversion. The photoelectric conversion unit 100 of the present invention is the same as the photoelectric conversion unit of a general image sensor and may use other image sensors.

3 is a block diagram illustrating the photoelectric conversion unit 100 of the present invention.

As shown in FIG. 1, the photoelectric conversion unit 100 of the present invention includes a photoelectric conversion element unit 101, a charge transfer unit 102, and a signal detection unit 103.

The photoelectric conversion element unit 101 is an element that accumulates charges proportional to incident light, and absorbs light to generate electrons. The photoconductor, photo diode, photo gate, etc. Three types of unit devices are available.

The charge transfer unit 102 serves to transfer charges generated in the photoelectric conversion element unit 101 to the signal detection unit 103. In this case, the charge wells are dynamically moved to realize charge transfer.

The signal detector 103 is a device for detecting signal charge at the end of the charge transfer unit 102. Image information received by the photoelectric conversion element unit 101 using a method of detecting a current from a normal charge and a method of detecting a voltage. Is finally converted to an electrical signal and exported to the outside world. Most CCD image sensors follow the above-described configuration, and there are various kinds of image sensors in which each configuration is slightly modified.

Meanwhile, the analog-to-digital converter 110 according to the present invention converts the output of the photoelectric converter 10 into analog-to-digital converter. In general, the photoelectric converter 100 converts an accumulated charge amount corresponding to each pixel into a voltage. As a result of outputting a digital signal having a predetermined number of bits per second (bpp) through the sampling process, the quantization process, and the encoding process, the output voltage is input.

Except for the special case in the general video signal processing field, 8 bits are used as the number of bits per pixel. Accordingly, the analog / digital converter 110 of the present invention also uses 8-bit analog / digital conversion. / digital conversion) is preferred.

In addition, the optical accumulation time controller 120 may include a pixel gray scale value from a minimum gray scale value determined by a predetermined number of bits per pixel to obtain a gamma characteristic curve of the photoelectric conversion unit 100. A line clock signal is generated to control the optical accumulation time to increase while maintaining a linear proportional relationship.

Thereafter, the gamma table storage unit 130 stores the output of the analog / digital converter 110 as the line clock signal is applied, thereby adjusting the incident light amount of the photoelectric converter 100 and the output voltage of the photoelectric converter. Acquire a gamma table of coordinate axes.

Here, the first embodiment of the optical accumulation time control unit 120 includes: a division setting unit 121 for setting a division multiple to divide a system clock; Downwards to load the frequency divider from the frequency division setting unit and receive the system clock as an operation clock to down-count the system clock by the frequency multiple to generate a carry according to an overflow. A counter 122;

A first up counter (123) for receiving a carry of the down counter (122) as an operation clock and counting up to output a first up counting value; A second up counter (124) for receiving the line clock signal as an operation clock and counting up to output a second up counting value; When the first up counting value and the second up counting value are the same, the line clock signal is generated to generate a write command signal (Write) of the gamma table storage unit 130 and the first up counter 123. It is composed of an equivalent comparator 125 which provides a clear input and an operation clock of the second up counter 124.

Preferably, the frequency division setting unit 121 may operate to set a frequency division multiple of 10 bits or 8 bits, and the downward counter 122 may be a 10 bit or 8 bit retractable down counter (10 bit or 8 bit loadable down counter). In addition, the first up counter 123 and the second up counter 124 are 8-bit up counters, respectively, and the equivalent comparator 125 is an 8-bit equivalent to compare 8-bit data. It is preferable that it is a comparison part.

First, when the frequency divider setting unit 121 sets a frequency division multiple for dividing the system clock SYSTEM CLK through a unit time register, the down counter 122 may have a data stage DATA. Load the frequency division multiplex from the frequency division setting unit 121 and receive the system clock SYSTEM CLK as the operation clock CLK, and count down the system clock by the frequency multiple to overflow the system clock. Generate a carry according to OVF).

For example, when the system clock is 25 MHz (that is, the period of the system clock is 40 nsec.), And the frequency division setting unit 121 operates with 10 bits, the values input to the frequency division setting unit 121 are 1, 2 and 2 respectively. When, 3,4 ....., the output of the down counter 122 has a period of 40 nsec, 80 nsec, 90 nsec, 120 nsec ....., respectively.

The first up counter 123 receives the carry of the down counter 122 as an operation clock CLK, counts up to output the first up counting value CountD1, and outputs the second up counter 124. ) Receives the line clock signal LINE CLK as an operation clock CLK and counts up to output the second up counting value CountD2.

The equivalent comparison unit 125 generates the line clock signal when the first up counting value and the second up counting value are the same to generate the write command signal of the gamma table storage unit 130 and the first. A clear input of the up counter 123 and an operation clock of the second up counter 124 are provided.

For example, the first up counter 123 and the second up counter 124 may be configured as 8-bit up counters, respectively, and the equivalent comparator 125 may compare 8-bit data. The understanding of the present invention will be improved by describing an example of configuring the bit equivalent comparator.

First, when the frequency division setting unit 121 sets the frequency division multiple to determine how much the system clock is divided, the down counter 122 loads the frequency division multiple from the frequency division setting unit 121 to divide the system clock. After counting down by the frequency division multiple times, by generating a carry to determine the operating clock of the first up counter (123). For example, when the first up counter 123 operates in 8 bits, counting is possible from 0 to 255.

At this time, the carry of the down counter 122 is input to the operation clock of the first up counter 123 and is re-inputted into its own load LOAD, thereby dispensing the division setting unit 121 through the data terminal DATA. Reload the multiples. Here, it is well known that if the frequency division multiple value is not changed, the period in which the carry-down of the downward counter 122 is generated is constant, whereas if the frequency division multiple value of the frequency division setting unit 121 is changed, it is changed accordingly.

Meanwhile, as the second up counter 124 counts a line clock signal, the first up counter 123 and the second up counter 124 perform an interlocking operation through mutual feedback. In other words, the equivalent comparison unit 125 compares and determines whether the first up counting value CountD1 and the second up counting value CountD2 are equal to each other, and generates a line clock signal if the same is equal to the gamma table. In addition to being applied as the write command signal of the storage unit 130, it is provided as a clear input of the first up counter 123 and an operation clock of the second up counter 124.

Therefore, when the first upper counter 123 counts the carry of the down counter 122 only to the second up counting value CountD2 of the second up counter 124, the equivalent comparator 125 determines one line clock signal. As the output of the analog-to-digital converter 110 is recorded in the gamma table storage unit 130, the second up counting value of the 8-bit second up counter 124 is increased by one, and the 8-bit first value is increased. As the upward counter 122 is cleared, if such an operation is repeated, the gamma table of 256 levels can be effectively generated from 0 to 255.

4 is a block diagram illustrating a second embodiment of the optical accumulation time controller 120 according to the present invention.

The second embodiment of the optical accumulation time controller 120 maintains a linear proportional relationship between the pixel gray scale value and the optical gray scale time from the lowest gray scale value determined by a predetermined number of bits per pixel to the maximum gray scale value. A division setting unit 121a for setting a division multiple for dividing the system clock so as to increase;

The division multiplexing unit 121a loads the division multiples, receives the system clock as an operation clock, and counts down the system clock by the division multiples to carry a carry according to an overflow. And a down counter 122b output as the line clock signal.

In this case, when the division setting unit 121a wants to acquire a gamma characteristic of 256 steps, the division setting unit 121a may operate to set the division multiple of 8 bits, and the down counter 122b may be an 8 bit loadable down counter. down counter).

In the first embodiment of the optical accumulation time controller 120, the multiplier of the frequency division setting unit 121a is removed while the first upward counter 123, the second upward counter 124, and the equivalent comparison unit 125 are removed. The optical accumulation time control unit 120 of the present invention can be implemented through another configuration example by controlling the optical accumulation time of 256 steps by varying from 0 to 255 in 256 steps.

In other words, the division setting unit 121a may adjust the system clock to increase the pixel gray scale value and the optical accumulation time from the lowest gray scale value determined by the preset number of bits per pixel to the maximum gray scale value while maintaining a linear proportional relationship. Sets the multiplier to dispense.

Accordingly, the down counter 122b loads the frequency division multiplex from the frequency division setting unit, receives the system clock as an operation clock, and counts down the system clock down by the frequency division multiplexing to overflow. The carry is output as the line clock signal.

At this time, the carry of the down counter 122b is inputted as a line clock signal and is re-inputted into its own load LOAD, thereby loading another division multiple of the division setting unit 121a through the data terminal DATA. The line clock signal corresponding to the pixel gray value may be repeatedly generated.

Of course, it is well known that the frequency division multiple value of the frequency division setting unit 122a is not maintained at a constant value but is sequentially changed in the range from the lowest gray value determined by the preset number of bits per pixel to the maximum gray value.

According to the second embodiment, there is a disadvantage in that the generation time of the line clock signal depends on the system clock, but there is an advantage in that the implementation circuit can be simply configured while achieving the intended purpose of the present invention.

5 is a timing diagram of generating a line clock signal corresponding to each pixel value, and FIG. 6 is a waveform diagram illustrating a gamma characteristic curve obtained by using an incident light amount of a photoelectric converter and an output voltage of the photoelectric converter as coordinate axes. to be.

As shown in FIG. 5, it can be seen that the generation time of the line clock signal is delayed twice as each pixel value increases. That is, this means a point in time at which the output of the analog / digital converter 110 is stored in the gamma table storage 130. Often, the gamma table storage unit 130 may be configured as a static random access memory (SRAM), which has been described above because a write command is applied at the same time as the generation of the line clock signal.

By controlling the optical accumulation time by the operation as described above, a gamma characteristic curve as shown in FIG. 6 can be obtained, and gamma correction is performed to give linearity to the system based on the obtained gamma characteristic curve.

In other words, storing 256 analog / digital conversion values in memory (i.e. gamma table storage) yields the gamma curves of image sensors such as CCD and CIS used in this experiment. It is well known that gamma properties are not available at once for all cells of a CCD or CIS consisting of more than a thousand unit cells. That is, in order to investigate gamma characteristics of all cells, it is necessary to repeat as many as the number of cells. However, it is inefficient to investigate gamma characteristics of all cells. Therefore, a user extracts only a few samples at random. You can also check.

Hereinafter, a preferred embodiment of the gamma characteristic curve acquisition method of the image sensor according to the present invention will be described with reference to FIG. 7.

7 is a flowchart illustrating a preferred embodiment of a method for obtaining a gamma characteristic curve of an image sensor according to the present invention.

According to a preferred embodiment of the method for acquiring a gamma characteristic curve of an image sensor according to the present invention, as shown in FIG. 7, an image sensor forms an incident light incident from a light source during an optical accumulation time into an optical image through photoelectric conversion ( S100);

Analog-to-digital conversion of the output of the image sensor (S200);

In order to obtain a gamma characteristic curve of the image sensor, the pixel gray scale value and the optical accumulation time of the lowest gray scale value determined by a predetermined number of bits per pixel and the maximum gray scale value are increased while maintaining a linear proportional relationship. Generating a line clock signal (S300);

And storing the analog / digital converted output as the line clock signal is applied, thereby obtaining a gamma table having an incident light amount of the image sensor and an output voltage of the image sensor as coordinate axes (S400).

Here, as the number of bits per pixel is preferably 8 bits, the lowest gray value is 0 and the maximum gray value is 255. Also, the image sensor refers to a general image acquisition means such as a CCD image sensor or a CIS image sensor.

Hereinafter, a preferred embodiment of the gamma characteristic curve acquisition method of the image sensor according to the present invention will be described with reference to FIG. 7.

First, in step S100, the image sensor forms an incident light incident from the light source during the optical accumulation time into an optical image through photoelectric conversion.

In step S200, the output of the image sensor is analog-to-digital converted, and in step S300, in order to obtain a gamma characteristic curve of the image sensor, the lowest gray value determined by the predetermined number of bits per pixel for the maximum gray value is obtained. A line clock signal is generated to control the pixel gray value and the optical accumulation time to increase while maintaining a linear proportional relationship.

In operation S400, as the line clock signal is applied, the analog / digital converted output is stored, thereby obtaining a gamma table having an incident light amount of the image sensor and an output voltage of the image sensor as coordinate axes.

As described above, in the present invention, the amount of light accumulated in the image sensor is zero when the amount of light accumulated for 1 second is equal to the amount accumulated for 1 second and the amount of light accumulated for 2 seconds is equal to 0. Instead of measuring the output value by inputting lux to 256 lux, the gamma is controlled by proportionally adjusting the amount of light accumulated in the image sensor by adjusting the time when the light is turned on with a certain light source, that is, when the light source is turned on. You want to create a table. According to the present invention as described above, even in the absence of a separate test pattern, such as the gamma test pattern, 256 gray levels intended in the present invention by stepwise adjusting the optical accumulation time irradiated to the image sensor using the same light source Gamma characteristic curves having a range can be easily obtained.

Terminologies used herein are terms defined in consideration of functions in the present invention, which may vary according to the intention or customs of those skilled in the art, and the definitions should be based on the contents throughout the present application. will be.

In addition, since the present invention has been described through the preferred embodiment of the present invention, in view of the technical difficulty aspects of the present invention, those having ordinary skill in the art can easily be different from another embodiment of the present invention. Since modifications may be made, it is obvious that both the embodiments and modifications cited in the above description belong to the claims of the present invention.

As described in detail above, the photoelectric conversion unit for forming the incident light incident from the light source during the optical accumulation time to the optical image through the photoelectric conversion; An analog / digital converter configured to analog-to-digital convert the output voltage of the photoelectric converter; In order to obtain a gamma characteristic curve for the photoelectric conversion unit, the pixel gray scale value and the optical accumulation time increase from a minimum gray scale value determined by a predetermined number of bits per pixel to a maximum gray scale value while maintaining a linear proportional relationship. An optical accumulation time controller configured to generate a line clock signal; And a gamma table storage unit for storing a output of the analog / digital converter as the line clock signal is applied to obtain a gamma table having an incident light amount of the photoelectric converter and an output voltage of the photoelectric converter as a coordinate axis. According to an apparatus and method for obtaining a gamma characteristic curve of an image sensor, in order to obtain a gamma characteristic curve for an image sensor having a high quantization resolution by using a gamma test pattern having a low quantization resolution, the exposure time of the image sensor with respect to incident light is converted into an amount of light. By adjusting the ratio, there is an advantage in that a high reliability gamma characteristic curve can be easily obtained.

1A is a plan view showing an arrangement of an image sensor and a light source of a typical scanner;

1B is a configuration diagram showing an example of acquiring a gamma table by an optical action of a light source and an image sensor on an input sheet;

Figure 2 is a block diagram showing a preferred embodiment of the gamma characteristic curve acquisition device of the image sensor according to the present invention,

3 is a block diagram showing a photoelectric conversion unit of the present invention;

4 is a block diagram showing a second embodiment of an optical accumulation time controller according to the present invention;

5 is a timing diagram for generating a line clock signal corresponding to each pixel value;

6 is a waveform diagram illustrating a gamma characteristic curve obtained by using an incident light amount of a photoelectric converter and an output voltage of the photoelectric converter as coordinate axes;

7 is a flowchart illustrating a preferred embodiment of a method for obtaining a gamma characteristic curve of an image sensor according to the present invention.

<Explanation of symbols for the main parts of the drawings>

100: photoelectric conversion unit 101: photoelectric conversion element

102: charge transfer unit 103: signal detection unit

110: analog / digital conversion unit 120: optical accumulation time control unit

121: frequency division setting unit 122: down counter

123: first upward counter 124: second upward counter

125: equivalent comparison unit 130: gamma table storage unit

Claims (8)

A photoelectric conversion unit configured to form incident light incident from the light source during the optical accumulation time into an optical image through photoelectric conversion; An analog / digital converter configured to analog-to-digital convert the output voltage of the photoelectric converter; In order to obtain a gamma characteristic curve for the photoelectric conversion unit, the pixel gray scale value and the optical accumulation time increase from a minimum gray scale value determined by a predetermined number of bits per pixel to a maximum gray scale value while maintaining a linear proportional relationship. An optical accumulation time controller configured to generate a line clock signal; And And a gamma table storage unit configured to obtain a gamma table having an incident light amount of the photoelectric conversion unit and an output voltage of the photoelectric conversion unit as coordinate axes by storing the output of the analog / digital conversion unit as the line clock signal is applied. Gamma characteristic curve acquisition device of the image sensor. The apparatus of claim 1, wherein the number of bits per pixel is 8 bits. The method of claim 1, wherein the optical accumulation time control unit, A division setting unit for setting a division multiple to divide a system clock; Downwards to load the frequency divider from the frequency division setting unit and receive the system clock as an operation clock to down-count the system clock by the frequency multiple to generate a carry according to an overflow. A down counter; A first up counter that receives the carry of the down counter as an operation clock and counts up to output a first up counting value; A second up counter that receives the line clock signal as an operation clock and counts up a number to output a second up count value; And When the first up counting value and the second up counting value are the same, the line clock signal is generated to generate a write command signal of the gamma table storage unit, a clear input of the first up counter, and the second up count. Apparatus for obtaining a gamma characteristic curve of an image sensor, characterized in that it comprises an equivalent comparator provided as an operation clock of the up counter. 4. The apparatus of claim 3, wherein the first up counter and the second up counter operate with 8 bits. The method of claim 1, wherein the optical accumulation time control unit, Setting a division multiple for dividing the system clock to increase the pixel gray scale value from the lowest gray scale value determined by a predetermined number of bits per pixel to the maximum gray scale value while maintaining the linear accumulation time linearly. Dispensing setting unit; And Load the frequency division multiplex from the frequency division setting unit and receive the system clock as an operation clock and down count the system clock by the frequency division multiplex to carry a carry according to an overflow. Gamma characteristic curve acquisition device of the image sensor, characterized in that it comprises a down counter (122b; outputted as a signal). A photoelectric conversion step of the image sensor imaging an incident light incident from the light source during the optical accumulation time into an optical image through photoelectric conversion; Analog-to-digital conversion of the output of the image sensor; In order to obtain a gamma characteristic curve of the image sensor, the pixel gray scale value and the optical accumulation time of the lowest gray scale value determined by a predetermined number of bits per pixel and the maximum gray scale value are increased while maintaining a linear proportional relationship. Generating a line clock signal; And Acquiring a gamma table having the incident light amount of the image sensor and the output voltage of the image sensor as coordinate axes by storing the analog / digital converted output as the line clock signal is applied. How to obtain gamma characteristic curve of. The method of claim 6, wherein the number of bits per pixel is 8 bits. The method of claim 6, wherein the image sensor is one of a charge coupled device (CCD) and a contact image sensor (CIS).