JP2008288970A - Image forming apparatus and gamma correcting program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent unsuitable gamma correction processing caused by noise etc., in an image forming apparatus by accurately acquiring actual gradation characteristics and performing interpolation processing corresponding to the gradation characteristics. <P>SOLUTION: The image forming apparatus 10 which has intrinsic gamma characteristics and performs density control over an output image on the basis of the gamma characteristics has a gamma correction unit 300 comprising: a sensor unit 330 which measures the lightness of a patch image; and a processing unit 310 which arranges sample points indicating measured lightness in the decreasing or increasing order of gradation values, tries to detect an inflection point section or a straight line section among respective sample point sections, and approximately acquires a series of gradation characteristics by changing interpolation methods for sample points according to cases that an inflection point section is detected, a straight line section is detected, and neither of the inflection point section and the straight line point section is detected to correct the gamma characteristics on the basis of the gradation characteristics. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that performs printing output and image output using toner, such as a printer, a facsimile machine, and a copying machine, and in particular, sets an output value such as toner density to an optimum value according to an input tone value. Therefore, the present invention relates to an image forming apparatus having a gamma characteristic correction function and a gamma correction program thereof.

2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer, an image signal is generated by image processing based on input print data, and an image having an appropriate gradation is obtained by adjusting toner density based on the image signal. Print output.
In such an image forming apparatus, so-called gamma characteristics (density gradation characteristics) are corrected in order to match the image signal with the actually printed toner density.
Such a gamma characteristic is linear, that is, ideally, the toner density increases as the gradation becomes higher. However, since there is actually a variation in each apparatus, the initial stage after the completion of the apparatus. In the setting stage, the gamma characteristic is linearly corrected for each apparatus and is initially set.

However, in individual image forming apparatuses, due to secular change due to use or the like, the toner density attached to the photoconductor may deviate from the initially set gamma characteristic at the time of print output.
Therefore, in the conventional image forming apparatus, for example, when the deviation of the gamma characteristic from the linearity exceeds the threshold value, the initial gamma characteristic is corrected to set the actual toner density to an appropriate value. Thus, so-called gamma correction is performed (see Patent Document 1).

In such a gamma correction process in an image forming apparatus, generally, first, in accordance with a patch image for correction, toner is attached to a photosensitive member, and the toner density of the patch image is measured by a sensor, and based on the measured value. The actual gamma characteristic is corrected.
Here, since the patch image contains a lot of noise, it is necessary to repeat the measurement several times or increase the number of sample patch images, and then obtain the average value of the measurement data to determine the noise level. It is necessary to reduce the impact.
However, if measurement is repeated or the number of patch images is increased, it takes extra time to generate and measure patch images, leading to a reduction in processing speed.
For this reason, in practice, the density of a patch image with a sample point of an arbitrary number of points (for example, 8 points) is measured, and interpolation processing such as increasing points for these sample points is performed a plurality of times. A method of acquiring the entire gamma characteristic by developing in gradation is employed.

Specifically, as shown in FIG. 14, when obtaining gamma characteristics from eight sample points, a method of performing interpolation processing while paying attention to four consecutive sample points is employed.
For example, an equation for each straight line with line segments S1S2, S2S3, and S3S4 as L1, L2, and L3 is obtained, and the Y value (density value) for the X-axis value (gradation value) x1 is obtained. Let N1, N2, and N3.
Then, an interpolation point is obtained by performing a weighting process on N1, N2, and N3. The weighting process is calculated by a predetermined calculation formula (α · N1 + β · N2 + γ · N3) based on a preset weight ratio {α, β, γ}, or according to a distance ratio between N1, N2, and N3. It can be calculated each time.

Japanese Patent Laying-Open No. 2005-062357

However, in the above-described interpolation processing method, each interpolation point is calculated by a simple moving average process. Therefore, it is effective when the characteristics show a monotonous change, but the device's elementary characteristics and noise In the case where a sudden change in gradation characteristics occurs due to superposition, an appropriate interpolation point cannot be obtained.
For example, when sample points S _{0 to} S ₇ arranged as shown in FIG. 15 are to be subjected to interpolation processing, according to the conventional interpolation method, the interpolation points in each line segment section are arranged as X _{0 to} X ₆ . The _However, S 1 to S Taking the example of the interpolation point _{X 1} in _two sections, the line segment _S 0 _S 1 corresponding to the X-coordinate of the midpoint of a line segment _{S 1 S 2, S 1 S} 2, S 2 S 3 The value of the interpolation point can be obtained by the average value of the upper points N1, N2, and N3. However, since N3 is located extremely far from N2, it becomes an inappropriate arrangement deviating from the original characteristics. _Further, the same applies to the interpolation point _{X 6} in S 6 to S ₇ sections.
As described above, when the coordinates of N1 and N3 are far away from the coordinates of N2, the interpolation interpolation point coordinates can be calculated by simply taking the average value as in the conventional case, or the weighting set in a fixed manner. When the interpolation interpolation point coordinates are calculated based on the ratio, a so-called overshoot occurs and the current gamma characteristic cannot be accurately recognized, and as a result, accurate correction processing cannot be performed.

  The present invention has been proposed in order to solve the problems of the conventional techniques as described above. By accurately acquiring actual gradation characteristics and performing appropriate interpolation processing according to the characteristics, An object of the present invention is to provide an image forming apparatus and a gamma correction program that prevent inappropriate gamma correction processing due to noise and other characteristic irregularities.

In order to achieve the above object, an image forming apparatus according to the present invention has an inherent gamma characteristic and performs density control on an output image based on the gamma characteristic. Patch image forming means for forming a patch image corresponding to a plurality of gradation values on a predetermined medium, measurement means for measuring the density or brightness of each of the formed patch images, and the measured density value or brightness value. Sample point arrangement means for arranging the sample points to be displayed in descending order or ascending order of the gradation values; inflection point section detection means for detecting a predetermined inflection point section from each section of the arranged sample points; Straight line section detecting means for detecting a predetermined straight section from the sections of the sample points arranged, interpolation processing means for performing interpolation processing by adding and / or deleting sample points, and the interpolation processing And a characteristic correction unit that corrects the gamma characteristic based on the acquired gradation characteristic, and the interpolation processing unit is arranged continuously. in four sample points S _n to the interval of S _{n + 3,} when a predetermined inflection point interval is detected, the sample points S _n S n _{+ 1} S n _{+ 2} consisting triangle centroid and the sample point S _n The center of gravity of the triangle consisting of ₊₁ S _{n + 2} S _{n + 3} is added as a new sample point, and sample points S _{n + 1} and S _{n + 2} are deleted, and a predetermined straight line section is detected within the section. If the midpoint of the line segment S _{n + 1} S _{n + 2} is added as a new sample point, and the inflection point section and the straight section are not detected in the section, the sample point S _n , the center of gravity of a triangle consisting of S n _{+ 1} and the line segment S _n S _{n + 1} and the intersection of the line segment S _{n + 2} S _{n + 3} There a structure to perform interpolation processing by adding a valley sample points.

Specifically, as described in claim 2, wherein the inflection point interval detection means, in the four sample points S _n to S _{n + 3} which are placed sequentially section line S _n S rotation of the rotational direction of the _{n + 1} to the line segment S _{n + 1} S n _{+ 2} on the basis, the line segment S _{n + 2} S _{n + 3} relative to the line segment S _{n + 1} S n _{+ 2} When the directions are different, the presence of a predetermined inflection point section in the section of sample points _{Sn to} Sn _{+ 3} is detected.
Further, as described in claim 3, wherein the inflection point interval detection means, in the four sample points S _n to S _{n + 3} which are positioned contiguous intervals, the line segment S _n S n _{+ 1} The sign of the slope of the line segment S _{n + 1} S _{n + 2} is obtained, and the slope between the line segment S _{n + 1} S _{n + 2} and the line segment S _{n + 2} S _{n + 3} is obtained. seeking the sign when taking the difference, if positive and negative of the two codes are the same for both, configured to detect the presence of a predetermined inflection point interval at the sample point S _n to the interval of S _{n + 3} It can also be.
Further, according to a fourth aspect of the present invention, the straight line section detecting means includes sample points S _n , S _{n + 1,} and four sample points S _{n to} S _{n + 3} arranged in succession. When S _{n + 2} is arranged on the same straight line, or when the sample points S _{n + 1} , S _{n + 2} and S _{n + 3} are arranged on the same straight line, the sample points S _{n to} S _{n +} A configuration in which the presence of a predetermined straight section in the _three sections can be detected.

According to the image forming apparatus of the present invention having such a configuration, first, a predetermined patch image is formed on a medium, and then the brightness is measured. Sample points are extracted and placed on predetermined coordinates. Then, by interpolating new sample points with respect to these sample points, characteristics corresponding to all gradations can be acquired.
As a result, it is possible to accurately grasp the elementary characteristics of the density gradation actually held by the apparatus, and it is possible to connect to an accurate gamma correction process or calibration process.
In particular, according to the image forming apparatus of the present invention, attention is paid to four consecutive sample points according to the gradation value, and usually the gamma characteristic is adjusted by interpolating the center of gravity of the triangle formed according to a predetermined algorithm. However, when a characteristic section such as a so-called inflection point section or a straight section is included between these sample points, the gamma characteristic is adjusted by another interpolation method.

Specifically, usually, the sample point S _n, the center of gravity of a triangle consisting of S n _{+ 1} and the line segment S _n S _{n + 1} and the intersection of the line segment S _{n + 2} S _{n + 3} as a new sample point In the case of having an inflection point section, that is, the rotation direction to the line segment S _{n + 1} S _{n + 2} with respect to the predetermined line segment S _n Sn _{n + 1} , and the line segment S _{n + 1} S _{n + 2} when the rotation direction of the line segment S _{n + 2} S _{n + 3} on the basis differ the sample points _{S n S n + 1 S n} + 2 centroid and samples of a triangle consisting of The center of gravity of the triangle composed of the points S _{n + 1} S _{n + 2} S _{n + 3} is added as a new sample point, and the sample points S _{n + 1} and S _{n + 2} are deleted.
Similarly, when it has a predetermined straight section, that is, when sample points _Sn , _{Sn + 1} and _{Sn + 2} are arranged on the same straight line, or sample points _{Sn + 1} , _{Sn + 2} And S _{n + 3} are arranged on the same straight line, the midpoint of the line segment S _{n + 1} S _{n + 2} is added as a new sample point.

As a result, according to the present invention, it is possible to more accurately grasp the elementary characteristics actually held by the apparatus without being affected by characteristic changes due to noise or the like, and to realize an accurate gamma correction process.
Furthermore, by performing these processes periodically, it is possible to ensure the balance of density gradations in the initially set gamma characteristics while corresponding to the output characteristics that have changed over time, and to perform the calibration process effectively. You can also.

The image forming apparatus of the present invention, as described in claim 5, wherein the interpolation processing means among a certain number of sample points is measured, the low sample points the least gray scale value when the S _n Virtual sample points S _n-1 and S _n-2 that are equal to the density value of S _n and have a lower gradation value are provided in stages, so that S _n-2 through S _{n + 1} and S _n-1 through S _n The interpolation processing is performed in the _{n + 2} section.
The image forming apparatus of the present invention, as described in claim 6, wherein the interpolation processing means among a certain number of sample points is measured, the higher sample points most gradation value when the S _n , the S concentration value of _n equally, the gradation value is higher virtual sampling points S _{n + 1} and S _{n + 2} provided stepwise S _n-2 to S _{n + 1} and S _n-1 to S The interpolation processing is performed in the _{n + 2} section.

According to the image forming apparatus of the present invention having such a configuration, virtual sample points are arranged in the vicinity of the end points of the initially arranged sample points, and interpolation processing of the neighboring sections is performed.
For this reason, the interpolation process can be uniformly performed like the other sample point sections without requiring any special interpolation process for the end points.
Therefore, it is possible to efficiently grasp the entire characteristics, and as a result, it is possible to improve the processing efficiency of gamma correction and calibration.

  According to a seventh aspect of the present invention, there is provided a gamma correction program relating to output density control of an image forming apparatus that has a unique gamma characteristic and outputs image data based on the gamma characteristic. The computer constituting the image forming apparatus measures patch image forming means for forming patch images corresponding to a plurality of gradation values on a predetermined medium, and measures the density or brightness of each formed patch image. Measuring means for measuring, sample point arranging means for arranging the sample points indicating the measured density value or lightness value in descending or ascending order of the gradation values, and predetermined inflection point sections among the sections of the arranged sample points An inflection point section detecting means for detecting a straight line section detecting means for detecting a predetermined straight section from each section of the arranged sample points, addition of sample points and / or Interpolation processing means for performing interpolation processing by deletion, characteristic acquisition means for acquiring a series of gradation characteristics through the interpolation processing, and characteristic correction means for correcting the gamma characteristics based on the acquired gradation characteristics And when the inflection point section is detected from among the sections of the arranged sample points, the inflection point section is detected, the inflection point, the straight line is detected. This is a program for functioning as means for adding and / or deleting predetermined sample points according to each of the sections when none of the sections is detected.

Thus, the present invention can also be realized as a program.
Thus, the present invention can be realized by installing the program in various image forming apparatuses such as a printer, a facsimile machine, and a copying machine, and can be provided as a gamma correction program excellent in versatility and expandability. .

  As described above, according to the image forming apparatus of the present invention, an actual density gradation characteristic can be easily and accurately grasped regardless of whether noise, an end point, or other characteristic changes, and an accurate gamma can be obtained. Correction processing and calibration processing can be effectively performed.

Hereinafter, preferred embodiments of an image forming apparatus and a gamma correction program of the present invention will be described with reference to the drawings.
Here, the image forming apparatus according to the present invention described below is realized by processing, means, and functions executed by a computer according to instructions of a program (software). The program sends a command to each component of the computer to perform predetermined processing and functions as shown below. That is, each process / means in the image forming apparatus of the present embodiment is realized by specific means in which a program and a computer cooperate.
Note that all or part of the program is provided by, for example, a magnetic disk, optical disk, semiconductor memory, or any other computer-readable recording medium, and the program read from the recording medium is installed in the computer and executed. The The program can also be loaded and executed directly on a computer through a communication line without using a recording medium.

An image forming apparatus according to an embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the image forming apparatus 10 according to the present embodiment includes, for example, a printer, and specifically includes an image forming unit 100, a control unit 200, and a gamma correction unit 300.

For example, the image forming unit 100 generates image data based on print data input from an external host computer, and prints out the image data.
The image forming unit 100 prints and outputs a patch image based on the gamma correction patch image data input from the gamma correction unit 300, and constitutes a patch image forming unit of the present invention. Yes.

The control unit 200 controls the image forming unit 100 to perform print output based on the input print data.
At that time, the control unit 200 controls the image forming unit 100 based on the gamma characteristic that is initially set or corrected by the gamma correction unit 300, and corresponds to an image having multiple gradations, for example, 256 gradations. Appropriate printing output is performed by appropriately adjusting the toner density.
Here, the operations of the control unit 200 and the gamma correction unit 300 are controlled by a program that operates on a computer.

The gamma correction unit 300 is configured to perform gamma correction at the initial setting, periodically, or when the deviation of the gamma characteristic from the linearity exceeds a threshold value. It is composed.
Specifically, the gamma correction unit 300 includes a processing unit 310, a storage unit 320, and a sensor unit 330, as shown in FIG.

The storage unit 320 registers gamma correction patch image data and can be used as a work memory.
The sensor unit 330 detects the brightness of the patch image formed on the photosensitive drum of the image forming unit 100 when the image forming unit 100 prints out the patch image data for gamma correction. The measuring means according to the present invention is configured.

The processing unit 310 reads the patch image data for gamma correction from the storage unit 320 and sends it to the image forming unit 100 at the time of gamma correction. As a result, the image forming unit 100 can print out a patch image for gamma correction.
The processing unit 310 performs gamma correction based on the detection signal (brightness value) from the sensor unit 330 as described below, and sends the corrected gamma characteristic to the control unit 200.

Hereinafter, the procedure of gamma correction processing in the image forming apparatus 10 according to the present embodiment will be described in detail.
FIG. 3 is a flowchart showing a first-stage gamma correction processing procedure in the image forming apparatus 10 according to the present embodiment, and FIG. 4 is a flowchart showing the second-stage gamma correction processing procedure.
As shown in FIG. 3, first, in the image forming apparatus 10, the image forming unit 100 forms a predetermined patch image as a sample (step S1), and the sensor unit 330 measures the brightness of the image (step S2). ).

Specifically, patch images (sample points) corresponding to a plurality of gradation values (color values) are formed on the photoreceptor or the paper surface, and the brightness at each sample point is measured.
When the whole gradation is set to 256 gradations, it is preferable in terms of processing efficiency that the sample points are discretely arranged with a relatively small number such as 8 points, 17 points, and 33 points.
In addition, by arranging the measurement values of these sample points on the orthogonal coordinates composed of the lightness value (for example, the Y axis) and the gradation value (for example, the X axis), the actual values are arranged in descending or increasing order of the gradation values. An outline of the gamma characteristic can be acquired (sample point arrangement means of the present invention).

Next, the processing unit 310 of the gamma correction unit 300 performs preprocessing of steps S3 to S5 as preparation for interpolation processing corresponding to core processing.
As preprocessing, first, end point processing A is performed (step S3).
By performing the end point processing A, interpolation processing similar to that for other sample point sections (interpolation interpolation A, interpolation interpolation B, interpolation interpolation C) is performed without requiring special interpolation processing in the vicinity section of the end points. Is possible.
This is because the interpolation processing according to the present embodiment requires four consecutive sample points, and processing cannot be performed on the minimum side and the maximum side of the sample points as they are. Specifically, as shown in FIG. Processing for setting sample points (Sa, Sb, Sc, Sd) is performed.

More specifically, as shown in FIG. 6, when attention is paid to the arranged sample points S _{0 to} S ₇ , auxiliary data S ₋₂ , S ₋₁ , S as virtual sample points outside the section of the sample points. by adding _8, S _9, relates to the interpolation processing in the terminal point near the sample point interval _{(S -2 ~S 1, S -1} ~S 2, S 5 ~S 8 and S ₆ ~S _9), It is possible to apply the same algorithm as that for other sections including non-end points.
The virtual sample point is set to the same value as the brightness (Y coordinate) of the end point sample point, and the gradation value (X coordinate) is arranged at a ratio of about 5 to 10% with respect to the input range of the sample image. It is desirable.

As the next preprocessing, an inflection point section is detected as shown in FIG. 3 (step S4).
If the conventional interpolation processing method is applied to the inflection point section, an overshoot occurs, resulting in inconvenience. Further, the inflection point interval correction process cannot be performed by the monotonous change interval interpolation method (interpolation interpolation C described later) of the present embodiment described later.
Therefore, in this embodiment, such an inflection point interval is detected in advance by detecting a change in the rotation direction of an angle formed by two consecutive intervals or using a second derivative for all sample points. (Inflection point section detecting means according to the present invention).
When a predetermined inflection point section is detected, a process of interpolation A described later is performed (see step S7 in FIG. 3).

Here, a method for detecting the inflection point section (inflection point section detecting means according to the present invention) will be described in detail.
First, a method for detecting an inflection point section will be described by paying attention to a change in the rotation direction of an angle formed by two continuous sections.
Specifically, for each section (three sections) composed of two adjacent sample points of four consecutive sample points, it is observed whether the angles formed by the adjacent sections are continuously in the same direction. If the directions are the same, there is no inflection point in the middle two-point interval of four consecutive points, and if the directions are different, it can be determined that the inflection point exists in that interval.
For example, paying attention to the sections S _{2 to} S ₅ in the sample points shown in FIG. 7, the rotation direction to the line segment S ₃ S ₄ with reference to the line segment S ₂ S ₃ is defined as a plus direction (clockwise). Then, the rotation direction from the line segment S ₃ S ₄ to the line segment S ₄ S ₅ is a negative direction (counterclockwise), and it can be determined that an inflection point exists between S _{3 and} S ₄ .

In addition, a method for detecting an inflection point using second-order differentiation, that is, a method for detecting an inflection point by observing a code change in a continuous section will be described.
Specifically, the sign of the slope when taking the difference of the slope in the two sections composed of the three points before the four consecutive points is obtained, and further, in the two sections composed of the three points after the four consecutive points If the sign of the slope is taken, the sign of the sign is obtained. If the sign of these two signs is the same, the inflection point does not exist in that section, and if the sign is reversed, the inflection point exists. judge.

Then, as the final preprocessing, the amount of noise is detected (step S5).
If the measurement value of the sample value performed in step S2 includes a large amount of noise, accurate characteristics cannot be grasped and subsequent correction processing is adversely affected. For example, the detected noise amount is a predetermined threshold value. If the value exceeds, control such as stopping the processing itself is performed.

Next, the processing unit 310 performs an interpolation process that is a core process (steps S6 to S10).
First, it is confirmed by the above-described inflection point section detection means whether or not a predetermined inflection point is included in the target section (step S6).
Specifically, referring to the determination at the previous step S4, if there is an inflection point section (step S6: YES), the process of interpolation A is performed as an interpolation processing means (step S7).

Here, the process of the interpolation A will be described with reference to FIG.
FIG. 8A is a typical example having an inflection point between the line segments S _{n + 1} S _{n + 2} , and FIG. 8B is a diagram showing the characteristic after the interpolation processing.
As shown in FIG. 8A, the interpolation A is an intermediate line segment (line segment S _n ) for four consecutive sample points (S _n , S _{n + 1} , S _{n + 2} , S _{n + 3} ). _{When an} inflection point is detected at ₊₁ S _{n + 2} ), as shown in FIG. 8 (b), the center of gravity G _{n + 1 of the} triangle formed by the sample points S _n S _{n + 1} S _{n + 2} and A process of increasing the center of gravity G _{n + 2} of the triangle formed by the sample points S _{n + 1} S _{n + 2} S _{n + 3} as an interpolation point and deleting the sample points S _{n + 1} and S _{n + 2} Do.
This is particularly effective when there are many inflection point sections as in the example shown in FIG. In the case of this example, the so-called monotonous change section is only the line segment S ₅ S ₆ , and all other line segment sections have inflection points.

As a result of step S6, when it is determined that the predetermined inflection point is not included in the target section (step S6: NO), next, whether or not the predetermined straight section exists in the same section by the straight section detecting means. Is determined (step S8).
Specifically, as shown in FIG. 10, the straight section detection means is configured such that, among the four consecutive sample points, the last three points are arranged on a straight line or the first three points are arranged on a straight line. Then, it is determined that the intermediate line segment is a predetermined straight line section.
As a result, when it is determined that the predetermined straight section exists in the target section (S8: YES), the process of interpolation B is performed as an interpolation processing means (step S9).

Interpolation B is the last three points (S _{n + 1} , S _{n + 2} , S _{n + 3} ) among four consecutive points (S _n , S _{n + 1} , S _{n + 2} , S _{n + 3} ). ) Are arranged on a straight line (FIG. 10A), and the first three points (S _n , S _{n + 1} , S _{n + 2} ) are arranged on a straight line (FIG. 10B). In any case, a process of increasing the midpoint C _{n + 1} of the intermediate line segment (line segment S _{n + 1} S _{n + 2} ) as an interpolation point is performed.
As a result, it is possible to appropriately perform the interpolation process for a section that is not a so-called monotonous change section but does not correspond to the inflection point section.

On the other hand, as a result of step S8, when it is determined that the predetermined straight section does not exist in the target section (step S8: NO), processing of interpolation C is performed as an interpolation processing means (step S10).
The interpolation C is to perform an interpolation process in a so-called monotonous change section that does not correspond to a predetermined inflection point section or a straight section.
Specifically, as shown in FIG. 11, the sample point 4 consecutive points _{(S n, S n + 1} , S n + 2, S n + 3), a top section line S _n S n _{+ 1} to obtain the intersection C _{n + 1} of the extension line to S _{n + 1} is the extension and tail section in the direction of the line segment _{S n + 2 S n + 3} S n + 2 directions, triangle S _{n + 1} S _{n + 2} C _{n + 1} The center of gravity G _{n + 1} is increased as an interpolation point.
The center of gravity G _{n + 1} is the point where the midline of the triangle S _{n + 1} S _{n + 2} C _{n + 1} intersects, that is, the midpoint MA _{n + 1} and S _{n + of the} line segment S _{n + 1} C _{n + 1.} It is no straight line of _two Prefecture, line S _{n + 2} C _{n + 1} of the midpoint MB n _{+ 1} and to not linearly consists S _{n + 1} Tokyo, line S _{n + 1} S _{n + 2} of the middle point MC _n It is represented by the intersection of any two straight lines among the straight lines composed of ₊₁ and C _{n + 1} .

FIG. 12 shows an example in which many monotonous change intervals are included. In this example, the intersection C _{n + 1} takes C _{0 to} C ₂ and C _{4 to} C ₆ , and the non-monotonic change interval is , Only the section of the line segment S ₃ S ₄ .
In this regard, in the interpolation method in the conventional technology, as shown in FIG. 13, to take an average value of N1 and N2 and N3, the interpolation point X ₁ is smooth gradation curve becomes the arrangement projecting from the characteristic However, according to the interpolation C of this embodiment, such inconvenience does not occur.
As described above, by performing control that selects and executes each interpolation processing unit according to the situation, it is possible to accurately acquire the actual gamma characteristics regardless of the presence or absence of noise and other characteristics changes. It becomes.

Next, the processing unit 310 performs post-processing as post-processing by steps S11 to S14 as illustrated in FIG.
In this post-processing, first, the number of sample points increased by interpolation (A, B, and C) is counted, or the number of interpolation interpolations is counted (step S11). It is determined whether or not the number has been reached (step S12).
If the number of samples does not reach the predetermined value as a result of step S12 (step S12: NO), the processing from step S4 is repeated again.
On the other hand, if the number of samples has reached the predetermined value as a result of step S12 (step S12: YES), the interpolation interpolation D is performed (step S13).

The interpolation D is a process for switching to a method of increasing the number of sample points by simple interpolation calculation after the number of sample points is increased to such an extent that errors can be ignored even with simple linear ratio interpolation. In addition, a process for performing smoothing by a moving average process or the like may be added.
The interpolation D may be used only when reducing the load or improving the processing speed in the core processing. When the interpolation D is not performed, the interpolation A and the inner interpolation until the desired number of sample points is reached. Processing of interpolation B and interpolation C is performed.
Next, as end point processing B, auxiliary data for end point processing virtually added in step S3 and data between the auxiliary data are removed.

As described above, the actual gamma characteristics of the image forming apparatus 10 can be acquired approximately and in detail by the processing up to step S14 (characteristic acquisition means according to the present invention).
Finally, input / output characteristics, that is, inherent gamma characteristics preset in the apparatus are corrected (step S15).
It should be noted that the amount of toner ejection is controlled according to this gamma characteristic, and the density or brightness in the output image can be adjusted. Therefore, it is possible to bring the output characteristic of the apparatus closer to the ideal characteristic by correcting / updating the inherent gamma characteristic based on the actually recognized gamma characteristic.

Specifically, referring to the gamma characteristics expressed corresponding to all the gradations obtained up to step S14 (for example, 256 gradations), whether to correct the inherent gamma characteristics manually or automatically? The toner ejection amount and the like are controlled by updating a correction table prepared in advance.
The toner ejection amount adjusting means can be realized, for example, by changing the exposure amount (power or exposure time) for forming the latent image or changing the exposure area (number of dots, etc.). it can.

As described above, according to the image forming apparatus 10 (and the gamma correction program) of the present embodiment, after the image forming unit 100 forms a patch image for correction, the sensor unit 330 controls the brightness of the patch image. , And sample points for a plurality of gradations are selected by the processing unit 310 and arranged on the lightness-gradation coordinates.
Then, the processing unit 310 can effectively acquire the actual gamma characteristic by paying attention to each section obtained by the arrangement and applying an appropriate interpolation process.

Therefore, the actual gamma characteristic of the image forming apparatus 10 can be accurately and efficiently grasped, and can be effectively used in the gamma correction processing.
In addition, by performing calibration processing such as correcting the gamma characteristic when necessary or periodically, it becomes possible to maintain the ideal gamma characteristic continuously, and errors due to secular change and usage environment etc. It becomes possible to appropriately control the amount of toner ejected and the like.

The image forming apparatus and the gamma correction program of the present invention have been described with reference to the preferred embodiments. However, the image forming apparatus according to the present invention is not limited to the above-described embodiments, and the scope of the present invention. Needless to say, various modifications can be made.
For example, in the above-described embodiment, the case where a printer is used as an example of the image forming apparatus of the present invention has been described. However, the image forming apparatus to which the present invention can be applied is not limited to a printer, but is a facsimile machine, a copier, and a multifunction machine. Various apparatuses and devices that perform image forming processing such as the above may be used.

  The present invention can be suitably used for an image forming apparatus having a gamma correction function.

1 is a block diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration example of a gamma correction unit in the image forming apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating a previous-stage gamma correction processing procedure in the image forming apparatus according to the embodiment of the present disclosure. 6 is a flowchart showing a subsequent gamma correction processing procedure in the image forming apparatus according to the embodiment of the present disclosure. FIG. 5 is an explanatory diagram for explaining an outline of end point processing in preprocessing by the image forming apparatus according to the embodiment of the present disclosure; FIG. 6 is an explanatory diagram for explaining details of end point processing in preprocessing by the image forming apparatus according to the embodiment of the present disclosure. It is explanatory drawing for demonstrating the inflection point area determination in the pre-processing by the image forming apparatus which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the interpolation process (inflection point area) in the core process by the image forming apparatus which concerns on one Embodiment of this invention. FIG. 10 is a characteristic diagram illustrating an example in which many inflection point sections are included in the image forming apparatus according to the embodiment of the present disclosure. It is explanatory drawing for demonstrating the interpolation process (linear area) in the core process by the image forming apparatus which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the interpolation process (monotone change area) in the core process by the image forming apparatus which concerns on one Embodiment of this invention. FIG. 10 is a characteristic diagram illustrating an example in which many monotonous change sections are included in the image forming apparatus according to the embodiment of the present disclosure. It is explanatory drawing (Y axis is a lightness value) which shows the malfunction of the interpolation in the conventional gamma correction. It is explanatory drawing which shows the interpolation method in the gamma correction of the conventional image forming apparatus. It is explanatory drawing (Y-axis is a density value) which shows the malfunction of the interpolation in the conventional gamma correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 100 Image forming part 200 Control part 300 Gamma correction part 310 Processing part 320 Storage part 330 Sensor part

Claims (7)

In an image forming apparatus that has a unique gamma characteristic and performs density control on an output image based on the gamma characteristic.
Patch image forming means for forming a patch image corresponding to a plurality of gradation values on a predetermined medium;
Measuring means for measuring the density or brightness of each patch image formed;
Sample point arrangement means for arranging the sample points indicating the measured density value or lightness value in descending or ascending order of the gradation values;
Inflection point section detecting means for detecting a predetermined inflection point section from each section of the sample points arranged;
A straight line section detecting means for detecting a predetermined straight line section from each section of the arranged sample points;
Interpolation processing means for performing interpolation processing by adding and / or deleting sample points;
Characteristic acquisition means for acquiring a series of gradation characteristics through the interpolation process;
Characteristic correction means for correcting the gamma characteristic based on the acquired gradation characteristic,
The interpolation processing means includes
In four sample points S _n to the interval of S _{n + 3} which are arranged sequentially, when a predetermined inflection point interval is detected, the triangle consisting of the sample point S _n S n _{+ 1} S n _{+ 2} Add the center of gravity of the triangle consisting of the center of gravity and sample points S _{n + 1} S _{n + 2} S _{n + 3} as new sample points and delete the sample points S _{n + 1} and S _{n + 2} ,
If a predetermined straight line section is detected within the section, the midpoint of the line segment S _{n + 1} S _{n + 2} is added as a new sample point;
If the inflection point section and the straight section is not detected within the section, the sample point S _n, the S n _{+ 1} and the line segment S _n S _{n + 1} and the line segment S _{n + 2} S _{n + 3} An image forming apparatus that performs an interpolation process by newly adding a center of gravity of a triangle formed by an intersection as a sample point. The inflection point section detecting means is
The rotation direction to the line segment S _{n + 1} S _{n + 2} with respect to the line segment S _n S _{n + 1} within the section of four sample points S _{n to} S _{n + 3} arranged in succession; If the line segment direction of rotation of the S _{n + 1} S n _{+ 2} line relative to the S _{n + 2} S n _{+ 3} are different, predetermined inflection point in the interval of the sample points S _n to S _{n + 3} The image forming apparatus according to claim 1, wherein the presence of a section is detected. The inflection point section detecting means is
When the difference between the slopes of the line segment S _n S _{n + 1} and the line segment S _{n + 1} S _{n + 2} is obtained in the section of the four consecutively arranged sample points S _{n to} S _{n + 3} The sign of the sign is obtained, and the sign of the difference between the line segment S _{n + 1} S _{n + 2} and the line segment S _{n + 2} S _{n + 3} is obtained. _3. The image forming apparatus according to claim 1, wherein, when the same, the presence of a predetermined inflection point section in the section of the sample points _{Sn to} Sn _{+ 3} is detected. The straight section detection means includes
Sample points S _n , S _{n + 1} and S _{n + 2} are arranged on the same straight line within a section of four sample points S _{n to} S _{n + 3} arranged consecutively, or sample points In the case where S _{n + 1} , S _{n + 2} and S _{n + 3} are arranged on the same straight line, the presence of a predetermined straight line section in the section of sample points S _{n to} S _{n + 3} is detected. The image forming apparatus according to any one of claims 1 to 3. The interpolation processing means includes
Among a number of sample points is measured, the lowest sample point gradation value in case of the S _n, the S concentration value of _n equally, the gradation value is lower virtual sample point S _n-1 and S _5. The image forming apparatus according to claim _1, wherein _n-2 is provided in a stepwise manner and interpolation processing is performed in the sections of S _{n−2 to} S _{n + 1} and S _{n−1 to} S _{n + 2.} . The interpolation processing means includes
Among a number of sample points is measured, the highest sample point gradation value in case of the S _n, the S concentration value of _n equally, the gradation value is higher virtual sample point S _{n + 1} and S _6. The image forming apparatus according to claim 1, wherein _{n + 2} is provided in a stepwise manner to perform interpolation processing in the sections of S _{n−2 to} S _{n + 1} and S _{n−1 to} S _{n + 2.} . A gamma correction program related to output density control of an image forming apparatus that has inherent gamma characteristics and outputs image data based on the gamma characteristics,
A computer constituting the image forming apparatus;
Patch image forming means for forming a patch image corresponding to a plurality of gradation values on a predetermined medium;
Measuring means for measuring the density or brightness of each patch image formed;
Sample point arrangement means for arranging sample points indicating the measured density value or lightness value in descending or ascending order of the gradation values;
An inflection point section detecting means for detecting a predetermined inflection point section from each section of the sample points arranged;
A straight line detection means for detecting a predetermined straight line section from each of the sections of the arranged sample points;
Interpolation processing means for performing interpolation processing by adding and / or deleting sample points;
Characteristic acquisition means for acquiring a series of gradation characteristics through the interpolation processing;
Based on the acquired gradation characteristic, while functioning as a characteristic correction means for correcting the gamma characteristic,
It said interpolation means, in the four sample points within an interval of S _n or S _{n + 3} which are arranged in succession, when a predetermined inflection point interval is detected, the sample points S _n S n _{+ 1} S _{n The} triangle centroid of ₊₂ and the sample point S _{n + 1} S _{n + 2} S _{n + 3} are added as new sample points and the sample points S _{n + 1} and S _{n + 2} are deleted. When a predetermined straight line section is detected within the section, the midpoint of the line segment S _{n + 1} S _{n + 2} is added as a new sample point, and the inflection point section and the straight line section are added within the section. Add If is not detected, the sample point S _n, the center of gravity of a triangle consisting of S n _{+ 1} and the line segment S _n S _{n + 1} and the intersection of the line segment S _{n + 2} S _{n + 3} as a new sample point A gamma correction program for functioning as a means for performing interpolation processing.

Images