JP2012191278A - Image processing apparatus and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus which suppresses irregular color by correcting gamma characteristics by noticing difference in the gamma characteristics on a chip basis.SOLUTION: The image processing apparatus for an image reading apparatus composed of plural image sensor chips for converting light applied onto and reflected by a document, to an electric signal comprises: gamma characteristic detection means 4 and 6 which detect gamma characteristics on the chip basis of the image sensor chip; and correction means 5 and 7 which correct the respective detected gamma characteristics on the chip basis, thereby suppressing the irregular color in the chip basis.

Description

  The present invention relates to an image processing apparatus and an image processing method, and more particularly to an image processing method using an image reading apparatus configured by using a plurality of image sensor chips that irradiate a document with light and convert the reflected light into an electrical signal. Is.

  As a method for reading a document in an image reading apparatus, a method is generally used in which light from a light source is irradiated onto a document, and reflected light from the document is received by an image sensor and converted into an electrical signal.

  Recently, for the purpose of reducing the size of the apparatus, a so-called CIS (Contact Image Sensor) that reads an image with a linear sensor using an LED (Light Emitting Diode) as a light source has become widespread.

  As such an image sensor in the CIS, a so-called multi-chip type image sensor array is widely used which includes a plurality of sensor chips in which photoelectric conversion sensors (corresponding to image pixels) are arranged in a straight line.

  In such a multi-chip CIS, since the characteristics are different for each chip, color unevenness occurs at the chip width when a document is read. In extreme cases, the read image data has a striped pattern. Will occur.

  Therefore, referring to Patent Documents 1 and 2, when adjusting the saturation, a conversion process for reducing the saturation only for the low-saturation image signal is performed, so that the chip width of the CIS of the multi-chip system can be reduced. Techniques for suppressing color unevenness generated in units have been proposed.

JP 2010-183396 A JP 2010-154152 A

  However, in the techniques of the above-mentioned Patent Documents 1 and 2, as described above, the color unevenness is suppressed by reducing the saturation, but the color reproducibility is sacrificed by decreasing the saturation. There is a problem.

  Note that it is generally known to suppress variations in sensor chip characteristics by creating shading correction data using a white plate or the like and performing shading correction of read data before reading a document. However, if the γ characteristics between chips differ greatly, there is a problem in that color unevenness occurs in units of chip width in a halftone.

  Accordingly, the present invention focuses on the difference in γ characteristics in units of chips, and corrects the γ characteristics, thereby suppressing color unevenness without sacrificing color reproducibility and an image. It aims to provide a processing method.

An image processing apparatus according to the present invention includes:
An image processing apparatus in an image reading apparatus configured by using a plurality of image sensor chips that irradiate light on a document and convert reflected light into an electrical signal,
Gamma characteristic detection means for detecting gamma characteristics of the image sensor chip in units of chips;
Correction means for suppressing color unevenness in chip units by correcting the detected gamma characteristics in chip units.

An image processing method according to the present invention includes:
An image processing method in an image reading apparatus configured by using a plurality of image sensor chips that irradiate a document with light and convert the reflected light into an electrical signal,
A gamma characteristic detection step of detecting a gamma characteristic of the image sensor chip in units of chips;
And correcting the detected gamma characteristics in units of chips to correct color unevenness in units of chips.

  According to the present invention, the γ characteristic for each chip is calculated, and this is inversely converted and corrected to suppress the color unevenness. Therefore, the simple configuration and without sacrificing the color reproducibility. There is an effect that uneven color can be suppressed.

It is a block diagram which shows one embodiment of this invention. It is a flowchart which shows operation | movement of one embodiment of this invention. It is a figure which shows the example of the gamma characteristic of a certain chip | tip obtained by one Embodiment of this invention, and its correction characteristic. It is a block diagram which shows other embodiment of this invention. It is a flowchart which shows the operation | movement of other embodiment of this invention. It is a block diagram which shows other embodiment of this invention.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic functional block diagram of an embodiment of the present invention. Referring to FIG. 1, an embodiment of the present invention includes an image processing unit 1, an uneven color suppression unit 2, a multi-chip CIS 3, and a shading correction data acquisition unit 8. Yes.

  The color unevenness suppression unit 2 includes an LED lighting time adjustment unit 4, a γ inverse conversion unit 5, a γ calculation unit 6, and a conversion table 7. The LED lighting time adjustment unit 4 has a function of adjusting the LED lighting time of the CIS 3 when calculating γ. The γ calculation unit 6 has a function of calculating γ based on the CIS3 output at this time. The conversion table 7 is a table in which inverse conversion values of each γ value are stored in advance according to the characteristics of the CIS 3.

  The γ inverse conversion unit 5 refers to the conversion table 7 based on the calculation result of the γ calculation unit 6, converts the document read data, and linearizes the characteristics of the gradation and the CIS output value (see FIG. 3). It has the function to do. The image processing unit 1 performs generally known image processing such as shading correction and background removal.

  The shading correction data acquisition unit 8 has a function of acquiring light correction data and dark correction data required when the γ calculation unit 6 calculates γ.

  FIG. 2 is a flowchart showing the γ calculation operation in the embodiment of the present invention shown in FIG. 1, and in particular, is a flowchart of the γ calculation process performed by the LED lighting time adjustment unit 4 and the γ calculation unit 6. FIG. 3 is a graph showing the calculated γ characteristic (dotted line) of a certain chip and the characteristic (solid line) when the γ characteristic is inversely converted to make the γ characteristic linear.

  The operation of this embodiment will be described with reference to FIG. First, the LED lighting time adjustment unit 4 sets the LED lighting time to 90% (step S1), and reads the output of the CIS 3 at that time (step S2).

  It is assumed that the LED lighting time at the time when the shading correction data acquisition unit 8 acquires the bright correction data of the shading correction data is 100%. Next, the LED lighting time adjustment unit 4 sets the LED lighting time to 30% (step S3), and reads the output of the CIS 3 at that time (step S4).

  Using these two data and the dark correction data acquired by the shading correction data acquisition unit 8, the γ calculation unit 6 performs the γ calculation shown in step S5.

That is,
(CIS output at 90%-dark correction data) / (CIS output at 30%-dark correction data) (1)
Is calculated. In S5, “90% CIS output” is expressed as “90% data”, and “30% CIS output” is expressed as “30% data”. It shall be.

The meaning of the above formula (1) will be described below. Γ of the γ characteristic of each chip of CIS3 can be represented by the following equation (2) in a pseudo manner.
(Y−c) = a * (x to the γ power) (2)
Here, y is a CIS output, x is an original color, a is a proportionality constant, and c is dark correction data.

Now, when the LED lighting time is 90% (corresponding to 90% of the gradation of the image), 90% data which is the CIS output is y1, the original color is x1, and 30% (30 of the gradation of the image). 30% data, which is the CIS output when the original color is x2,
γ = {log (y1−c) −log (y2−c)} / {log (x1) −log (x2)} = log {(y1−c) / (y2−c)} / log {x1 / x2 } …… (3)
It becomes.

  In this equation (3), x1 / x2 = 90% data / 30% data, which is known, so that (y1-c) / (y2-c) can be used to calculate γ. Therefore, the above equation (1) is calculated.

  If the CIS3 is composed of 10 chips and each of these chips has 200 pixels, the processing of the above steps S1 to S5 is performed simultaneously on all the pixels of all the chips. .

  Therefore, the γ averaging process is performed on a chip basis (step S6). That is, since it is necessary to average the variation in γ of each pixel in one chip, the averaging process in step S6 is performed. Furthermore, there may be a large variation in γ with another chip (for example, γ of the first chip is 1.1 and that of the second chip is 1.2, etc.). Therefore, each chip is associated with γ.

  Thereafter, the γ characteristic (dotted line in FIG. 3) calculated and detected for each chip is inversely converted using the conversion table 7 in the γ despreading unit 5 and converted into a linear characteristic (solid line in FIG. 3). It is done.

  In the above description, the LED lighting time corresponding to the gradation is set to two points of 90% and 30%. However, for example, two points of data of 80% and 20% may be used. Here, if two points of data near 100% or near 0% are used, the γ characteristic cannot be calculated. Because there is γ in which 0% is gradation 0 and 100% is gradation 255, in this case, a curve (characteristic) between them cannot be calculated. On the other hand, when data near the center of about 50% is used, an error occurs with respect to γ near 100% or near 0%.

  Therefore, the predetermined first gradation within the range of about 90% to about 60% of the gradation of each pixel of the image and the predetermined second floor within the range of about 40% to about 10% of the gradation. It is preferable to detect chip output data corresponding to each of the furniture and perform γ calculation using these two data. By doing so, it is possible to calculate γ simply by using two points of chip output data, thus enabling high-speed processing.

  Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 4, the same parts as those in FIG. The uneven color suppression unit 2 in this example includes an LED current adjustment unit 9, a γ inverse conversion unit 5, a γ calculation unit 6, and a conversion table 7. The other configuration is the same as the configuration of FIG. 1 in the previous embodiment.

  In the present embodiment, an LED current adjustment unit 9 is used instead of the LED lighting time adjustment unit 4 in FIG. 1, and the LED current unit adjustment unit 9 adjusts the current of the LED. Yes. In the previous embodiment, for example, the lighting time was adjusted to obtain a chip output corresponding to two gradations of 90% and 30% for γ calculation. By adjusting the drive current, a chip output corresponding to two gradations of 90% and 30% for calculating γ is obtained.

  With reference to FIG. 5, the operation of γ calculation in the present embodiment will be described. First, the LED current adjustment unit 9 performs 90% LED current setting (step S11), and reads the CIS3 output at that time (step S12). It is assumed that the LED current when acquiring bright correction data of shading correction data is 100%.

  Next, the LED current adjustment unit 9 performs 30% LED current setting (step S13), and reads the CIS3 output at that time (step S14). Using the two pieces of data thus obtained and the dark correction data acquired by the shading correction data acquisition unit 8, the calculation according to the equation shown in step S15 is performed to calculate γ.

  It is obvious that the equation for calculating γ shown in step S15 in this case is as described above. Then, γ is averaged and associated with each chip in units of chips (step S16).

  At the time of reading the document, the γ inverse conversion unit 5 performs conversion of each chip using the conversion table 7 to make the characteristic linear as shown by the solid line in FIG.

  Still another embodiment of the present invention will be described with reference to FIG. Referring to FIG. 6, the shading correction unit 10 is provided inside the color unevenness suppression unit 2 shown in FIG. 4. Of course, the same configuration is possible in FIG. 1.

  In the example of FIGS. 1 and 4, the shading correction is performed inside the image processing unit 1. However, in this example, the shading correction is performed first, and the γ inverse conversion process taking this into consideration. By performing the above, the characteristics are made linear.

  It is obvious that the operation procedure in each of the above embodiments can be configured to be stored in advance in a recording medium as a program and read and executed by a computer.

  A part or all of the above-described embodiment can be described as follows in addition to the description in the claims, but is not limited to the following description.

[Appendix 1]
An image processing apparatus according to any one of claims 1 to 5 in the claims,
An image processing apparatus, wherein the light irradiation time or light intensity is controlled in order to obtain a chip output corresponding to the first and second gradations.

[Appendix 2]
An image processing method according to any one of claims 6 to 10 in the claims,
An image processing method, wherein the light irradiation time or the light intensity is controlled in order to obtain a chip output corresponding to the first and second gradations.

[Appendix 3]
A program that causes a computer to read and execute an image processing method in an image reading apparatus configured by using a plurality of image sensor chips that irradiate light on a document and convert reflected light into electrical signals,
Processing for detecting gamma characteristics of the image sensor chip in units of chips;
And a process of suppressing color unevenness in chip units by correcting the detected gamma characteristics in chip units.

1 Image processing unit 2 Color unevenness suppression unit 3 CIS
4 LED lighting time adjustment unit 5 γ inverse conversion unit 6 γ calculation unit 7 conversion table 8 shading correction data acquisition unit 9 LED current adjustment unit 10 shading correction unit

Claims (10)

An image processing apparatus in an image reading apparatus configured by using a plurality of image sensor chips that irradiate light on a document and convert reflected light into an electrical signal,
Gamma characteristic detection means for detecting gamma characteristics of the image sensor chip in units of chips;
An image processing apparatus comprising: correction means for suppressing color unevenness in units of chips by correcting the detected gamma characteristics in units of chips.   In each of the chips, the gamma characteristic detection means includes a predetermined first gradation degree of 90% to 60% of the gradation degree of each pixel of the image, and 40% to 10% of the gradation degree. A calculating means for detecting a chip output corresponding to each predetermined second gradation and calculating a gamma characteristic for each chip based on the chip outputs corresponding to the first and second gradations; The image processing apparatus according to claim 1. The calculation means has a chip output corresponding to the first and second gradations as y1 and y2, respectively, and dark correction data as c in a pixel.
(Y1-c) / (y2-c)
The image processing apparatus according to claim 2, wherein the gamma characteristic of the pixel is calculated by using.   4. The image processing according to claim 2, wherein the correction unit averages the gamma characteristics obtained for all the pixels in each of the chips and uses the average as the gamma characteristics of the chip. apparatus.   The image processing apparatus according to claim 1, wherein the correction unit corrects the gamma characteristic of the chip unit by using a characteristic opposite to the characteristic. An image processing method in an image reading apparatus configured by using a plurality of image sensor chips that irradiate a document with light and convert the reflected light into an electrical signal,
A gamma characteristic detection step of detecting a gamma characteristic of the image sensor chip in units of chips;
An image processing method comprising: a correction step of suppressing color unevenness in units of chips by correcting the detected gamma characteristics in units of chips.   In the gamma characteristic detection step, in each of the chips, a predetermined first gradation degree of 90% to 60% of the gradation degree of each pixel of the image, and 40% to 10% of the gradation degree A calculation step of detecting a chip output corresponding to each predetermined second gradation and calculating a gamma characteristic for each chip based on the chip outputs corresponding to the first and second gradations; The image processing method according to claim 6. In the calculation step, when a chip output corresponding to the first and second gradation levels is set to y1 and y2 and dark correction data is set to c in a certain pixel,
(Y1-c) / (y2-c)
The image processing method according to claim 7, wherein the gamma characteristic of the pixel is calculated using.   9. The image processing according to claim 7, wherein the correcting step averages the gamma characteristics obtained for all the pixels in each of the chips and uses the average as the gamma characteristics of the chip. Method.   The image processing method according to claim 6, wherein the correcting step corrects the gamma characteristic of the chip unit using a characteristic opposite to the characteristic.

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