JP3291964B2 - Image recording apparatus and recording method in image recording apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus used for a copying machine, a printer and the like, and a method for generating a discrete curve suitable for the image recording apparatus.

[0002]

[Prior art]

(Correction of Image Data Using Correction Table) Conventionally, an electrophotographic color image recording apparatus has been used in a copying machine, a printer, or the like. In such an image recording apparatus, since the density characteristics fluctuate with respect to the voltage and temperature rise of each part, it is generally necessary to correct the density characteristics of the input image data and supply it to the image recording apparatus in order to obtain desired density characteristics. It is a target. That is, when the power is turned on or every time a predetermined number of sheets are output, a plurality of toner patches corresponding to a predetermined density are generated in the image carrier of the image recording apparatus.

Next, the density of the toner patch is measured by a sensor, and a difference between the measured density and a most desirable density (hereinafter referred to as an image reference density) is obtained, and a correction table is created based on the difference. You. Thereafter, the density of the input image data is corrected based on the correction table, and an image is output based on the corrected density (hereinafter, referred to as output image density) (Japanese Patent Application Laid-Open Nos. 5-33667 and 5-33667). 014728, etc.).

(Curve generation) Conventionally, when generating an outline font or the like of a printer, what is called a Bezier curve is used. The outline will be described with reference to FIG. First, vectors of "3" points on a plane are represented by Z ₁ , Z ₂ ,
And the Z _3. Here, a vector Z (t) represented by the following equation (1) is assumed.

[0005]

(Equation 3)

[0006] Now, the locus of the vector Z (t) in the case of changing the variable t in the range of "0 ≦ t ≦ 1" becomes a curve (Z ₁ ~Z ₃₎ shown in FIG. This curve has a straight line (Z ₁ → Z ₂ ) and a straight line (Z ₂ ) at both end points Z ₁ and Z ₃ .
→ Touch Z ₃ ). This curve is called a Bezier curve, and is used for smoothing an angular line.

[0007]

By the way, in the above-mentioned conventional image recording apparatus, a correction table is generated so that the output image density matches the image reference density as much as possible. However, according to studies made by the present inventors, such a correction method may not always be appropriate.
In other words, when there is a limit value lower than the maximum image reference density in the high density area of the output image density, there is no gradation in the area above the limit value. As a result, there is a problem that a pseudo contour occurs in the output image.

On the other hand, the above-described Bezier curve is generated using a variable t as a parameter. That is, “0 ≦ t ≦
The variable t is changed by Δt in the range of “1”, thereby obtaining a discrete value of the vector Z (t). But,
In some cases, the curve on the xy plane should be expressed with the variable x as a parameter. For example, let us assume a value y (the value y is a function of the value x) corresponding to each sampling point using a discrete value sampled on the x-axis at a predetermined value Δx interval as a parameter. When these values y are changed by a Bezier curve, it is necessary to determine the changed values corresponding to the original discrete values on the x-axis.

However, with respect to the variation Δt of the variable t, x
The amount of change on the axis is not uniquely determined. Therefore, in the conventional method of calculating a Bezier curve, after obtaining a sampling point of the curve using the variable t as a parameter, x
It was necessary to determine the value y for each sampling interval Δx on the axis. That is, such a process required extra calculation time.

The present invention has been made in view of the above circumstances, and has as its first object to provide an image recording apparatus capable of effectively suppressing false contours. It is a second object of the present invention to provide a discrete curve generation method which is suitable for this image recording apparatus and has a short calculation time.

[0011]

According to a first aspect of the present invention, there is provided an image processing apparatus, comprising: an input image density based on test image data and an image output by the test image data; A correction table generating means for generating a correction table for defining a corresponding output image density; and a saturation input image corresponding to the saturation point when the output image density corresponding to the input image density has a saturation point in the correction table. The curve processing is performed by performing a predetermined calculation using output image density values respectively corresponding to a first input image density higher than the density by a predetermined value and a second input image density lower by a predetermined value. Table correction means for correcting the correction table so that the output image density between the first and second input image densities changes smoothly, and the corrected correction table Based on, characterized by comprising a density correction means for correcting the density characteristics of the input image data.

According to a second aspect of the present invention, there is provided a correction table for defining an output image density corresponding to an input image density based on test image data and an image output by the test image data. And, if a saturation point exists in the output image density corresponding to the input image image density in the correction table, a first input image higher by a predetermined value than the saturation input image density corresponding to the saturation point. The curve processing between the first and second input image densities is performed by performing a predetermined calculation using a value of the output image density corresponding to the density and a second input image density lower by a predetermined value. Correcting the correction table so that the output image density changes smoothly; and correcting the density characteristics of the input image data based on the corrected correction table. And having a step.

[0013]

[0014]

[0015]

According to the first aspect of the present invention, if a saturation point exists in the output image density corresponding to the input image density in the correction table, the saturation input image density corresponding to the saturation point is a predetermined value. The first and second input images are subjected to a curve processing for performing a predetermined operation using output image density values respectively corresponding to a high first input image density and a second input image density lower by a predetermined value. By correcting the correction table so that the output image density changes smoothly between the densities, and correcting the density characteristics of the input image data based on the corrected correction table, the density of the input image data becomes the saturation point. , The gradation characteristics can be provided.

According to a second aspect of the present invention, when the saturation point is present in the output image density corresponding to the input image density in the correction table, the method is applied to the image recording apparatus. Curve processing for performing a predetermined calculation using output image density values respectively corresponding to a first input image density that is higher by a predetermined value than a saturated input image density and a second input image density that is lower by a predetermined value. By the first
And correcting the correction table so that the output image density changes smoothly between the second input image density and the density characteristics of the input image data based on the corrected correction table. Even when the data density exceeds the saturation point, it is possible to impart gradation characteristics.

[0017]

[0018]

[0019]

【Example】

A. Configuration of the Embodiment A copying machine according to an embodiment of the present invention will be described below with reference to FIG. In the figure, reference numeral 9 denotes a transfer material carrier, which conveys a transfer material (paper) 15 conveyed from a transfer material conveyance roll 14 to the left in the figure. Reference numeral 1 denotes a K-color engine for attaching a K-color toner to the surface of the transfer material carrier 9 or the surface of the transfer material 15. Reference numerals 2, 3, and 4 denote a Y color engine, an M color engine, and a C color engine, which are arranged along the transfer material carrier 9 and have a color corresponding to the surface of the transfer material carrier 9 or the surface of the transfer material 15, respectively. Apply toner.

Reference numeral 10 denotes a density detector, which is a transfer material carrier 9
, And a light receiving unit 10-2 for receiving light passing through the transfer material carrier 9, and a toner patch attached to the surface of the transfer material carrier 9. The concentration of is measured. 11 is a peeling corotron,
The transfer material 15 on the transfer material carrier 9 is peeled off. The peeled transfer material 15 is transported to a fixing device (not shown), and the toner on the transfer material 15 is fixed here. Reference numeral 12 denotes a transfer material carrier static elimination corotron, which removes electricity from the transfer material carrier 9.
Reference numeral 13 denotes a transfer material carrier cleaner, which scrapes off toner remaining on the surface of the transfer material carrier 9.

Next, reference numeral 30 denotes a scanner, which reads a document image and outputs the content as uncorrected image data.
Reference numeral 31 denotes a gradation correction circuit which stores an image data correction table corresponding to the image densities before and after correction, corrects the density of the image data before correction based on the image data correction table, and converts the result to the corrected image data. Output as data. 3
Reference numeral 2 denotes a laser exposure device that controls the exposure time of the laser diodes of the engines 1 to 4 based on the corrected image data.

Reference numeral 34 denotes a control circuit, which creates the above-described image data correction table based on the density detection signal output from the light receiving section 10-2 of the density detector 10 and writes it in the gradation correction circuit 31. Further, the control circuit 34 outputs a toner patch creation command signal when the power of the copying machine is turned on and every predetermined number of copies. Reference numeral 33 denotes a toner patch generation circuit, which receives “4.
Test image data is output to the laser exposure device 32 so that the transfer material carrier 9 generates a toner patch of “color × 12 gradations”. FIG. 2 shows an example of the toner patch 16 obtained as a result.

Next, the structure of the light emitting section 10-1 is shown in FIG. The light emitting unit 10-1 is formed in a long shape along the main scanning direction, and provided with light emitting elements 20-1K to 20-1C corresponding to positions facing the center of each color toner patch. The light receiving unit 10-2 is formed symmetrically with respect to the light emitting unit 10-1, and the optical sensors 20-2K to 20-2C are provided at positions facing the light emitting elements 20-1K to 20-1C. .

B. Operation of embodiment B-1. Next, the operation of this embodiment will be described. First, when the power of the copying machine is turned on, a main routine shown in FIG. 4 is started. In the figure, when the processing proceeds to step SP1, a toner patch creation command signal is output from the control circuit 34 to the toner patch generation circuit 33, and the toner patch generation circuit 33 supplies the test image data to the laser exposure device 32. Accordingly, the toner patches 16 as shown in FIG. 2 are formed on the transfer material carrier 9 by the engines 1 to 4.

Next, when the process proceeds to step SP2, the densities of these toner patches are read by the density detector 10 and supplied to the control circuit 34 as a density detection signal.
Here, since the number of toner patches is "12" for each color, "12" density points are obtained for each color. Next, when the process proceeds to step SP3, spline interpolation is performed on the density point of "12", and the density point number becomes "25".
6 "gradation.

Next, when the processing proceeds to step SP4, an image data correction table is created based on the image density with the expanded density points. The details of this process will be described later. Next, when the process proceeds to step SP5, the created image data correction table is transferred to the gradation correction circuit 31. Next, when the process proceeds to step SP6, the contents of the original placed on the scanner 30 are read, and the image data before correction is supplied to the gradation correction circuit 31.

In the gradation correction circuit 31, the density correction of the input image data is performed based on the image data correction table transferred earlier, and the result is supplied to the laser exposure device 32 as corrected image data. You. Thus, the laser diodes of the engines 1 to 4 are driven by the laser exposure device 32 based on the corrected image data of the engines 1 to 4, and an image is formed on the transfer material 15.

Next, when the process proceeds to step SP7, it is determined whether or not a predetermined number of image outputs have been performed after step SP4 was executed last. If the determination is "NO", the process returns to step SP6, and an image is output to the next transfer material 15. If the process proceeds to step SP7 after such process has been repeated the predetermined number of times, “YES” is determined here, and the process proceeds to step S7.
Return to P1. As a result, the toner patch 16 is formed again on the transfer material carrier 9, and the content of the image data correction table is updated. Thereafter, similarly, every time a predetermined number of copies are made, a toner patch 16 is formed, and based on this, the contents of the image data correction table are updated.

B-2. Details of Processing for Creating Image Data Correction Table Next, details of processing for creating an image data correction table in step SP4 will be described. First, step S
In P4, a subroutine shown in FIG. 5 is called. In the figure, when the process proceeds to step SP11, a table called "simple correction table" is created.

Here, the simple correction table is created such that the output image density obtained through the correction table matches the image reference density as much as possible. An example is shown in FIG. In the figure, A is an input image density characteristic, which is formed by density points that have been expanded to "256" gradations in step SP3. B is an image reference density.

The simple correction table C is, as described above, a density C_IN of the input image data according to the table.
Is converted to a table value (density C_OUT), the result (density characteristic D) is set so as to match the image reference density B as much as possible. Note that the simple correction table C is the same as the correction table used in the conventional image recording apparatus. However, if the simple correction table C is set as the image data correction table, the following problem occurs.

In this embodiment, the density of the image data is set to "25".
6 ”, the upper limit of the density C_OUT is“ 25 ”.
5 ". And the simple correction table C is (C_IN =
180), it is saturated at “255”, and the density corresponding to this value becomes the maximum density. That is, the output image density has a limit value lower than the maximum image reference density. Therefore, the corrected image data has no gradation in an area equal to or larger than the limit value. As a result, a pseudo contour occurs in the output image.

In an electrophotographic image recording apparatus,
When the exposure width of the laser diode is gradually increased from "0", the image density initially becomes extremely low, but the output image density rapidly increases at a certain exposure width (reproduction start point). Since the simple correction table C is generated corresponding to such characteristics, a sharp change is seen in the low density area (area F). However, the reproduction start point fluctuates due to a slight change in temperature or the like. After such a change has occurred, the contents of the simple correction table C become extremely inappropriate, and the gradation characteristics in the low density area are greatly disturbed.

Therefore, in steps SP12 and SP13, the simple correction table C is modified so that the high-density area and the low-density area change "smoothly", and the modified correction table (image data correction table) is changed. To perform density correction. First, in step SP12, in the simple correction table C, the density C_OUT is set to “25”.
Points away from "5" are searched. This point is the density C_IN (D)
And

Next, a density C_IN (E) higher than the density C_IN (D) by a predetermined value (curved range width e) and a density C_IN (F) lower than the density C_IN (D) by a curve range width e. Is required. Then, in the range from the density C_IN (E) to the density C_IN (F), the correction table is converted into a curve. The details of the curve forming process will be described in detail.

First, in the graph of FIG.
C_IN) is the x-axis, the vertical axis (concentration C_OUT) is the y-axis, and the density C_I
N (E), C_IN (D ) and C_IN coordinates of points on a simple correction table C corresponding to _{(F) (x 1, y} 1), (x 2, y 2) and (x _3, y ₃₎ And Here, each of the density C_IN (E) and the density C_IN (F) is larger than the density C_IN (D) by the curve range width e.
Because it ’s just

[0037]

(Equation 8) Always holds.

In the curve forming process, values y corresponding to a plurality of variables i (variables x) are obtained based on the following equation (3).

(Equation 9)

Here, the variable i is expressed as “x ₂ − | x ₁ −x ₂ |
≦ i ≦ x ₂ + | x ₂ −x ₃ | ”, the increment is incremented by Δi (Δi = 1 in this embodiment). Accompanying this, the variable j is incremented by Δj (Δ
j = Δi / (x ₃ −x ₁ )). Thereby, y corresponding to the range of “x ₂ − | x ₁ −x ₂ | ≦ i ≦ x ₂ + | x ₂ −x ₃ |” is obtained.

Referring back to FIG. 5, when the process proceeds to step SP13, a point in the simple correction table C where the density C_OUT departs from "0" is searched. This point is referred to as a density concentration C_IN (A). Next, a density C_IN (B) higher than the density C_IN (A) by a predetermined value (curved range width b), and a density C_IN (C) lower than the density C_IN (A) by the curve range width b. Is required. Then, curve processing of the correction table is performed in the range of the density C_IN (B) to the density C_IN (C). The details of the curve forming process are the same as those in step SP12. 8 to 14 show the result of coding equation (3) in C language.

As described above, in steps SP12 and SP13, the discrete value y was obtained in the high density area and the low density area. In the range where the value y is obtained,
The image data correction table in this embodiment is obtained by replacing the density C_OUT of the simple correction table C with the value y. The image data correction table obtained in this way is indicated by "G" in FIG. The density characteristic obtained by the image data correction table G is indicated by "H".

C. Effects of Embodiment First, effects in a low-density area of an output image will be examined. The simple correction table C is created so that the density characteristic D matches the image reference density B as much as possible, whereas the image data correction table G of the present embodiment is deformed to be “smooth” in the low density area. Have been.

Therefore, when the image quality of the low density area of the first transfer material 15 is compared after the correction table is created, the image using the simple correction table C (conventional type) of this embodiment is compared. It is thought to be slightly higher than the one. However, assuming that the reproduction start point or the like fluctuates due to a slight change in temperature or the like, the present embodiment can output a stable image because the image data correction table G that changes smoothly is used.

Next, the effect in the high density area of the output image will be examined. As described above, the simple correction table C is created so that the density characteristic D matches the image reference density B as much as possible, whereas the image data correction table G of the present embodiment is “smooth” in the high density area.
Has been transformed to become.

Therefore, as for the gradation characteristics of the output image, the conventional one using the simple correction table C is excellent as long as the density C_IN of the input image data is equal to or lower than the saturation point E. However, according to the present embodiment, even when the density C_IN of the input image data exceeds the saturation point E, gradation characteristics can be provided, and the occurrence of false contours and the like can be effectively suppressed. Become.

Further, in this embodiment, since the value y is obtained based on the equation (3), a constant increment Δ
It becomes possible to directly determine the value y for each i. This makes it possible to perform the calculation for obtaining the image data correction table at high speed.

D. Modifications The present invention is not limited to the above-described embodiments, and various modifications are possible, for example, as follows. In step SP3 of the above embodiment, spline interpolation was used to expand the density point of “12” to “256” gradations. However, the interpolation method is not limited to spline interpolation. May be used. Further, the density point of “256” gradation may be obtained by least square approximation instead of interpolation.

In the above embodiment, the equation (3) was used to obtain the image data correction table G by transforming the simple correction table C into “smooth”. The present invention is not limited to this, and an arc or elliptic equation may be used.

On the other hand, in the above embodiment, equation (3) was used to obtain the image data correction table.
(3) may be used for other purposes. That is, the expression (3) can be used for various types of applications in which a discrete curve y (x) on the xy plane is obtained using the variable x discrete at regular intervals as a parameter.

[0050]

As described above, according to the configuration of the first aspect, the correction table is modified so that the output image density changes smoothly with respect to the input image density in a range including at least the saturation input image density. Therefore, the pseudo contour can be suppressed.

In the method according to the second aspect, x
Since the increment Δi on the axis can be made constant, the value y can be directly obtained according to the sampling interval on the x axis, and a discrete curve can be generated in a very short time. .

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment.

FIG. 2 is an explanatory diagram of a toner patch 16;

FIG. 3 is a diagram showing a configuration of a concentration detector 10;

FIG. 4 is a flowchart of a main routine of one embodiment.

FIG. 5 is a flowchart of a subroutine of one embodiment.

FIG. 6 is an operation explanatory diagram of one embodiment.

FIG. 7 is an explanatory diagram of a conventional Bezier curve.

FIG. 8 is a C language program list of one embodiment.

FIG. 9 is a C language program list of one embodiment.

FIG. 10 is a C language program list of one embodiment.

FIG. 11 is a C language program list of one embodiment.

FIG. 12 is a C language program list of one embodiment.

FIG. 13 is a C language program list of one embodiment.

FIG. 14 is a C language program list of one embodiment.

[Explanation of symbols]

31 gradation correction circuit (density correction means) 34 control circuit (correction table generation means, table generation means)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (2)

(57) [Claims] 1. A on the basis of the output image by the test image data and the test image data, a correction table generating means for generating a correction table defining the output image density corresponding to the input image density, the correction Output corresponding to the input image density in the table
If there is a saturation point in the image density, correspond to this saturation point
Input which is higher than the saturated input image density by a predetermined value.
Image density and a second input image density lower by a predetermined value.
Performs a predetermined operation using the corresponding output image density value
The first and second input image densities are obtained by a curve processing.
The output image density changes smoothly during
Sea urchin wherein the table correction means for correcting a correction table, on the basis of the correction table is corrected, the image recording apparatus characterized by comprising a density correction means for correcting the density characteristics of the input image data. 2. The test image data and the test image data.
To the input image density based on the image output by
Generate a correction table that defines the corresponding output image density
And an output corresponding to the input image density in the correction table.
If there is a saturation point in the image density, correspond to this saturation point
Input which is higher than the saturated input image density by a predetermined value.
Image density and a second input image density lower by a predetermined value.
Performs a predetermined operation using the corresponding output image density value
The first and second input image densities are obtained by a curve processing.
The output image density changes smoothly during
Correcting the correction table, and input image data based on the corrected correction table.
Correcting the density characteristic of the data in the image recording apparatus.
Law.