JP2004212577A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is improved in print (density) variations which cannot be removed by only corrections of quantities of light. <P>SOLUTION: A printer that prints print images of the same print pattern by using an optical writing head obtains three types of print images printed using three values for correcting quantities of light, that is, a reference correction value, the reference correction value +n, and the reference correction value-n. The printer converts the print images to respective density data, and calculates amounts of changes in density data by using corresponding density data converted. Based upon the amounts of changes in the density data, the printer then calculates an amount of correction. Thus, the problem is solved by using the printer. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for correcting an output image so as to reduce printing (density) unevenness.
[0002]
[Prior art]
As a method of improving printing unevenness in a printing device using an optical writing device, the light energy unique to the recording element is measured in advance, and the current control is performed so that the variation width of the entire printing element is within a certain range, or the light emission time is used. The method of controlling is widely known.
[0003]
In addition, a print pattern for density correction is printed once on printing paper, the print pattern is read by a scanner, and a correction table is created using only one of the three most sensitive data of RGB, and the correction table is used. There is also a method of improving the printing unevenness by using the method (for example, Patent Document 1).
[0004]
Further, head shading data, which is information relating to print unevenness correction, is obtained in advance for each of the ejection ports 1 to i (i is a positive integer) of the head of the printing apparatus, and when processing data for each pixel, First, the ejection ports forming the pixel are associated with each other, and based on the head shading data of the associated ejection ports, a γ table is selected from a plurality of γ tables prepared in advance according to the ejection characteristics. There is also a method of performing density conversion using a table and finally obtaining drive data for each ejection port of the head, thereby reducing printing unevenness due to variation in ejection characteristics of ink ejection ports in the head (for example, Patent Document 2.).
[0005]
[Patent Document 1]
JP-A-11-309880 (pages 1-7, FIG. 1-13)
[Patent Document 2]
JP-A-10-795 (pages 1-24, FIG. 1-37)
[0006]
[Problems to be solved by the invention]
A method for improving printing unevenness in a conventional printing device using an optical writing device measures in advance light energy that differs for each printing element, and the variation amount of each printing element is within a certain range with respect to the average value of the entire printing element. In this manner, the light energy of each element is made uniform by a method such as current control or light emission time control using a value for adjusting the characteristics of each recording element (hereinafter, referred to as a “light amount correction value”), so that the print density can be reduced. Leveling. This improvement has been performed by the light amount correction control shown in FIG.
[0007]
FIG. 12 is a block diagram of light amount correction control in a conventional printing apparatus. The VIDEO signal is input to the image processing control circuit 106, and each element of the optical writing device 101 such as an LED head emits light based on the VIDEO signal. At this time, the CPU 103 reads the light amount correction value 2 stored in the storage device and develops the light amount correction value in the correction RAM 104 in order to correct the variation in light of the optical writing device 101. Then, based on the dot position information 105 indicating which element of the optical writing device 101 is emitting light (the dot position information 105 is stored in the storage device) and the light amount correction value developed in the correction RAM 104, the optical writing device By adjusting the light emission time and current for each element 101, the light energy of each element was made uniform, and the variation in light of the optical writing device 101 was corrected.
[0008]
However, even if the light energy is equalized, it is possible to improve the resolution limit of light quantity correction, uneven light collection of the optical light collecting lens, and uneven printing caused by the image forming process such as photoreceptor (drum) and toner development. There was a problem that it could not.
Further, in the conventional method, for example, streak-like unevenness occurring in an adjacent portion of a recording element assembly such as an LED chip cannot be improved. To improve this, readjustment of a light amount correction value based on a printing result is performed. In such a method, there is also a problem that the degree of effect changes with an excess or deficiency of the light amount correction value adjustment amount or a change in the print pattern.
[0009]
In view of the above problems, the present invention provides an image forming apparatus in which printing (density) unevenness which cannot be dealt with only by light amount correction is improved.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided an image forming apparatus for printing a print image of the same print pattern using an optical writing unit, wherein the printing is performed by using a reference correction value that is a reference correction value. Acquiring means for acquiring a printed image on which a pattern is printed, one or more printed images on which a printed pattern is printed using a correction value having a difference from the correction value by a predetermined value, and each of the obtained prints Conversion means for converting an image into each density data, density change amount calculation means for calculating a density change amount based on each density data converted by the conversion means, and a correction value based on the density change amount. And a correction value calculating means for calculating the correction value.
[0011]
With this configuration, the final correction value is calculated from the density data based on the printing result, so that the optical writing device itself forms printing unevenness, photoreceptor (drum), toner development, transfer, and fixing. There is an effect that printing unevenness caused by a process can be improved.
[0012]
According to another aspect of the present invention, the density change amount calculating means calculates a density change amount obtained in the case of the minimum resolution of the light amount correction value. This can be achieved by providing an image forming apparatus.
With this configuration, the final correction value is calculated from the density data based on the printing result, so that the optical writing device itself forms printing unevenness, photoreceptor (drum), toner development, transfer, and fixing. There is an effect that printing unevenness caused by a process can be improved.
[0013]
According to the third aspect of the present invention, the correction value calculating means calculates a first additional correction value for compensating the reference correction value, based on the density change amount calculating means. An upper limit value is set for the first additional correction value, a second additional correction value is calculated by dividing the first additional correction value by the upper limit value, and the second additional correction value is calculated. The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus is added to the reference correction value.
[0014]
With this configuration, the final correction value is calculated from the density data based on the printing result, so that the optical writing device itself forms printing unevenness, photoreceptor (drum), toner development, transfer, and fixing. There is an effect that printing unevenness caused by a process can be improved.
[0015]
According to a fourth aspect of the present invention, there is provided an image forming apparatus for printing using an optical writing unit, wherein the obtaining unit obtains a printed image printed using a reference correction value that is a reference correction value. Converting means for converting the obtained print image into density data; and first moving average calculating means for calculating a moving average of density values of a predetermined range of the obtained print image based on the density data. Based on the density data, a second moving average calculating means for calculating a moving average of density values in a range narrower than a predetermined range of the first moving average calculating means, and the first moving average calculating means. A correction range calculating unit that calculates a correction range of a density value for each pixel of the acquired print image; and a pixel position corresponding to a density value calculated by the first moving average calculation unit that is not included in the correction range. An image forming apparatus comprising: a pixel position obtaining unit that obtains a pixel position; and a correction value calculating unit that calculates a correction value for the pixel position based on the pixel position obtained by the pixel position obtaining unit. Can be achieved by:
[0016]
With this configuration, when a correction target portion is extracted, a moving average in a certain range is compared with a moving average in a sufficiently narrow range, and a non-correction area (dead zone) is provided for the moving average in a certain range. Thus, there is an advantage that it is possible to correct only the portion where the printing unevenness is emphasized.
[0017]
According to a fifth aspect of the present invention, in the image forming apparatus, the image forming apparatus further includes: a correction position information storage unit that stores correction position information that is information on a pixel position to be corrected; Calculating a first average value which is an average of density values of a predetermined number of consecutive pixels including predetermined pixels of the printed image, and averaging a predetermined number of consecutive pixels including pixels adjacent to the predetermined pixel; Is calculated, the first average value is compared with the second average value, and correction is performed to correct the pixel at the pixel position based on the comparison result and the correction position information. The image forming apparatus according to any one of claims 1, 2, 3, and 4, further comprising a position correcting unit.
[0018]
With this configuration, even if the correction resolution is a fixed amount of the minimum value, the correction resolution can be reduced pseudo by changing the number of correction dots, and more flexible according to the degree of printing unevenness. Correction becomes possible. That is, it is possible to reduce a sudden change in density due to the correction and to make a gradual change in density.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
As a first embodiment, in an image forming apparatus, printing is performed by using a correction value obtained by calculating and correcting a density data correction value obtained from a printing result to a correction value of a recording element as a final correction value. (Density) unevenness can be improved. Further, a print pattern for detecting print density unevenness can be performed by an ON / OFF pattern for each dot of the optical writing device. Further, the density unevenness correction method is performed for each gradation value of the image forming apparatus, and is selectively used according to the gradation value to be printed. Further, the same correction method is performed a plurality of times. In addition, correction methods having different processing methods are used in combination.
[0020]
As a second embodiment, in the image forming apparatus, a non-correction area (dead zone) is provided for extracting a density unevenness correction portion. The extraction of the density unevenness correction portion is determined from a comparison result of moving average values of two different ranges with respect to the density data. In addition, extraction of the density unevenness correction portion is performed based on a comparison result between a moving average value of a certain range in which a non-correction area is provided for density data and a moving average value of a certain range in which a different non-correction area is not provided. Do.
[0021]
As a third embodiment, when the image forming apparatus performs a combination of correction methods having different processing methods, the second correction is performed based on the correction value obtained at the first time and the correction amount is used as the correction resolution. Is the minimum value of
As a fourth embodiment, in the image forming apparatus, the extraction of the density unevenness correction portion is performed for a plurality of printing elements as one block and an arbitrary printing element among them. In the image forming apparatus, the density unevenness correction portion is extracted by using a plurality of recording elements as one block and selecting and using a correction portion pattern prepared in advance according to the density unevenness.
[0022]
In the fifth embodiment, in the image forming apparatus, when density data is detected, a reference value having a uniform density is arranged, thereby canceling an error of the density detection apparatus.
Now, each embodiment will be described in detail below.
<First embodiment>
(Example 1)
In this embodiment, printing is performed once using a reference correction value, the density of the printed portion is read by a CCD (Charge Coupled Devices), and the density of the read density data is determined. I am going to do the correction.
[0023]
FIG. 1 is a block diagram of light amount correction control of the image forming apparatus according to the present embodiment. The VIDEO signal is input to the image processing control circuit 10, and each element of the optical writing device 1 such as an LED head emits light based on the VIDEO signal. At this time, the CPU 4 reads the reference light amount correction value 2 stored in the storage device in advance, and develops the light amount correction value (reference) 2 in the correction RAM 6.
[0024]
Then, from the dot position information 9 indicating which element of the optical writing device 1 is emitting light (the dot position information 9 is stored in the storage device) and the light amount correction value (reference) developed in the correction RAM 6, The light emission time and the flowing current are adjusted for each element of the optical writing device 1 and printing is performed by the optical writing device 1. At this time, the target to be printed may be the surface of the conveyor belt of the printer or printing paper. The printed print pattern is, for example, as shown in FIG. FIG. 2 will be described later.
[0025]
After printing, the printed portion is read by the CCD sensor 5. The CCD sensor 5 is a scanner or the like. The scanner may be built in the printer, or may be a separate device that can be attached to the printer. In this embodiment, a line sensor is used as the CCD sensor 5.
[0026]
When a print pattern is read by the CCD sensor 5, it is stored as density data 8 in a storage device. Then, based on the density data 8, an amount of correction for the correction amount used for the above-described printing is generated, and the amount of correction (correction amount) is developed in the correction data RAM.
[0027]
The arithmetic unit 3 calculates a more accurate correction value by calculating a light amount correction value (reference) of the correction RAM 6 and a correction amount of the correction data RAM 7, and actually performs printing using the correction value.
FIG. 2 shows a print pattern for each gradation value as an example. The printing pattern is an ON / OFF pattern for each dot corresponding to the recording density of the optical writing device. This print pattern may be printed for each gradation value.
[0028]
FIG. 3 is a diagram illustrating a flow of the correction processing in the present embodiment. First, with respect to all the recording element data of the conventional light amount correction values, the light amount correction value −n (n is a positive integer and the shift width of the light amount correction value), the light amount correction value ± 0, and the light amount correction value + n Printing is performed using the three light quantity correction values. Here, n is the maximum / minimum value of 1 ≦ n ≦ light quantity correction range. In contrast to the light amount correction value ± n, the conventional light amount correction value is an increase / decrease amount ± 0, and the conventional light amount correction value (± 0) and the printing result obtained using this correction value are Treat as a reference for correction.
[0029]
First, a reference correction value (± 0) is set in the correction RAM 6 (Step S1; hereinafter, the step is abbreviated as “S”). Next, printing is performed using the reference correction value (± 0) according to the control mechanism described with reference to FIG. 1, and the printed image is read (collected) by the CCD sensor 5 (S2).
[0030]
Next, after setting the reference correction value + n in the correction data RAM 7 (S3), printing is performed according to the control mechanism described with reference to FIG. 1, and the printed image is read (collected) by the CCD sensor 5 (S4).
Next, after setting the reference correction value -n in the correction data RAM 7 (S5), printing is performed according to the control mechanism described in FIG. 1, and the printed image is read (collected) by the CCD sensor 5 (S6).
[0031]
Next, density data conversion is performed (S7). The print density of each dot in the main scanning direction of the optical writing device for each image is measured from the print result using the above three light amount correction values (light amount correction value -n, light amount correction value ± 0, light amount correction value + n). . For measuring the print density, it is preferable to use a CCD sensor 5 having a recording density at least twice the recording density of the optical writing device 1 or more.
[0032]
The density data thus obtained is data of 1200 pixels when the recording density of the optical writing device 1 is 600 dpi. In order to make the data of 1200 pixels correspond to each dot of the optical writing device 1, an averaging process for every two pixels is performed. To obtain data of 600 pixels.
[0033]
Note that a scanner in which an optical system is added to the CCD sensor 5 or a contact-type image sensor that does not require an optical system may be used as the density measuring device. FIG. 4 shows the density data of each dot of the optical writing device 1 thus obtained.
FIG. 4A shows the density of the density data for each dot of the print image. FIG. 4B is a diagram illustrating a correction portion based on FIG. 4A and a correction amount thereof. FIG. 4A shows an example in which the density data has 256 levels of a white level “0” and a black level “255”. In FIG. 4A, point A indicates that the measured value is larger than other parts and the density is higher. The point B indicates that the density is lower than the other portions.
[0034]
In FIG. 4 (b), point A corresponds to point A in FIG. 4 (a), and since the density is high at point A in FIG. 4 (a), the correction amount needs to be minus (-). It is shown that. In FIG. 4B, point B corresponds to point B in FIG. 4A, and since the density is low at point B in FIG. 4A, the correction amount needs to be plus (+). It indicates that there is.
[0035]
Next, if there is an excess or deficiency in the reading result of the CCD sensor 5 with respect to the number of dots of the optical writing device 1, the total number of dots of the optical writing device 1 is divided by (the amount of excess or deficiency ± 1) and divided. The excess / deficiency amount is adjusted by applying / deleting the density data of the previous dot to the portion (S8).
[0036]
Next, the average value (AVE0) is calculated from the densities of all the dots of the print image (print image with the light intensity correction value ± 0) collected in S2 (S9).
Next, a reference image density change rate, that is, a change rate (Dk) of each dot with respect to the average value AVE0 (k is a number representing a dot position) is calculated by Expression 1 (S10).
[0037]
Dk = (density value of each dot−AVE0) / AVE0 × 100 (%) Equation 1
Next, the average value (AVE1) is calculated from the density change rate at the minimum resolution, that is, the density of all dots of the print image (the print image of the light amount correction value + n) collected in S4, and the print image ( The average value (AVE2) is calculated from the densities of all the dots of the light amount correction value -n (the print image of the light amount correction value -n), and the density change amounts + D and -D obtained at the minimum resolution of the light amount correction value are calculated by Expression 2 (S11). ).
[0038]
+ D = AVE1 / n, -D = AVE2 / n Equation 2
Next, an additional correction amount ΔH of each dot is calculated from Expressions 3 and 4 according to the sign of Dk (S12). When Dk is a positive sign,
ΔH = Dk / −D Equation 3
When Dk is a negative sign,
ΔH = Dk / + D Equation 4
The additional correction amount ΔH is obtained from Expressions 3 and 4. As described above, the reference light amount correction value is data for adjusting the characteristics of each recording element in advance so that the light energy is within a certain range. Therefore, when the additional correction amount due to ΔH is large, the light energy may exceed a certain range by the reference correction value. In this case, the opposite effect is obtained for the improvement of the printing unevenness.
[0039]
Therefore, an upper limit value △ Hmax is provided so that △ H does not become a certain value or more (S13), and △ H obtained by Expressions 3 and 4 is compressed to an upper limit value by Expression 5 (S14).
ΔHk = ΔH / ΔHmax Equation 5
The correction amount ΔHk thus obtained is added to the reference correction value to obtain the final light amount correction value of each dot (S15), and the correction is actually performed using this value, and printing is performed on the printing paper.
[0040]
If the printing apparatus has a gradation control function, the above-described correction method may be performed for each gradation value.
As described above, by calculating the final correction value from the density data based on the printing result, the printing caused by the image forming process such as the printing unevenness by the optical writing device itself, the photoconductor (drum), the toner development, the transfer, and the fixing. There is an effect that unevenness can be improved.
(Example 2)
In the first embodiment, the number of correction amount calculations for the reference correction value is set to one. However, the light amount correction value obtained by the execution of the first embodiment is set as a new reference correction value, and the correction value calculation is repeated a plurality of times. May be. Thereby, the accuracy of the correction can be improved.
<Second embodiment>
(Example 1)
In this embodiment, the light amount correction value is calculated using two moving averages. Here, the moving average generally means that when data changes rapidly and it is difficult to grasp the temporal trend of the entire data, the average value of a certain number of data is continuously obtained, and the trend of the overall data change is calculated. Is to be analyzed. In this embodiment, the outline of the light amount correction control is the same as that described with reference to FIG.
[0041]
FIG. 5 is a diagram illustrating a flow of the correction processing in the present embodiment. Printing using the conventional light amount correction value is performed (S20). That is, printing is performed by correcting the light amount using only the light amount correction value (reference). As the printing pattern, a printing pattern as shown in FIG. 2 or a uniform halftone dot pattern may be used. The printing result is converted into density data for each dot of the optical writing device by the method described in Example 1 of the first embodiment (processing in S7) (S21).
[0042]
Next, from the obtained density data, a moving average Cave in a certain range of the dots of the print image is calculated (S23), and a moving average Nave in a range sufficiently narrower than the Cave is calculated (S24), and Equation 6 is established. Nave is extracted as a correction target. Here, if the shift width of Cave is a positive integer (or real number) m,
Cave-m% ≦ Nave ≦ Cave + m% Formula 6
FIG. 6A shows a moving average of density data for each dot of a print image. The horizontal axis indicates the dot position in the print image, and the vertical axis indicates the density of each dot (the upper direction indicates higher density and the lower direction indicates lower density). In the figure, the density data that has not been moving averaged is represented by 20, and the moving average Nave for every 13 dots is represented by 21. Further, a moving average Cave for each 129 dots is obtained, and ± m% of the Cave (m = 1 in this embodiment) is obtained and expressed as 22 and 23 (Cave is located at an intermediate position between 22 and 23). However, if this Cave is illustrated, FIG. 6 is omitted because it becomes complicated).
[0043]
At this time, the range from Cave-m% to Cave + m% (the range between 22 and 23 in FIG. 6A) is set as a non-correction area (dead zone) (S25), and the moving average Nave not included in this range is used. The represented portion is set as a correction target, and this portion is extracted (S26).
[0044]
FIG. 6B shows only the range in which the moving average Nave does not satisfy the expression 6 (the moving average Nave 21 protruding from the range between 22 and 23 in FIG. 6A) is extracted. The horizontal axis in the figure represents the dot position in the print image, and corresponds to the horizontal axis in FIG. The vertical axis in the figure represents the correction amount. The vertical axis in FIG. 6A and the vertical axis in FIG. 6B have the same relationship as the vertical axis in FIG. 4A and the vertical axis in FIG. 4B. At this time, looking at the correction amount, the absolute value of the correction amount is equal at all correction points, and is equal to one scale in FIG. This one scale is the minimum value of the correction resolution.
[0045]
The correction amount for only the minimum value of the correction resolution is added to the reference correction value for the correction location extracted in this manner (S27). That is, if the correction amount of the extracted dot is minus, one scale (minimum value of correction resolution) is subtracted from the reference correction amount, and if it is plus, one scale (minimum value of correction resolution) is added to the reference correction amount. to add.
[0046]
Then, the value obtained in S27 is used as a final correction value (S28), the correction is actually performed using this value, and printing is performed on a printing paper.
As described above, in the present embodiment, when extracting a correction target portion, the moving average in a certain range is compared with the moving average in a sufficiently narrow range, and a non-correction area (dead zone) is provided for the moving average in a certain range. Thus, there is an advantage that it is possible to correct only the portion where the printing unevenness is emphasized.
(Example 2)
In the first embodiment, the correction amount for the extracted correction part is set to the minimum value of the correction resolution. However, the correction amount may be calculated from the density change at the minimum correction resolution of each dot by the method described in the first embodiment. .
<Third embodiment>
(Example 1)
This example is a combination of Example 1 of the first embodiment and Example 1 of the second embodiment, and performs two corrections. Now, description will be given with reference to FIG.
[0047]
FIG. 7 is a diagram illustrating a flow of the correction processing in the present embodiment. In the first correction (S30), the processes in S31 to S45 are performed, and the first correction is completed (S46). At this time, the processing of S31 to S45 respectively corresponds to the processing of S1 to S15 in FIG. 3, and performs the same processing.
[0048]
Next, in the second correction (S47), the correction value acquired in S45 is set as a light amount correction value (S48), and the processing of S49 to S57 is performed. At this time, the processing of S49 to S57 corresponds to the processing of S20 to S28 in FIG. 5, respectively, and performs the same processing.
[0049]
The above processing will be further described. The first correction method calculates a correction value by the method described in the first embodiment. According to the correction method described in the first embodiment, a dither pattern generated by a screen angle or a controller is used in order to use a printing pattern for turning on / off a recording element for each dot according to the recording density of an optical writing device. Can be corrected without being affected by the above. The correction value thus obtained is used as a reference correction value for the second correction to be performed next, and correction is performed by the correction method described in the second embodiment.
[0050]
According to the correction method described in the second embodiment, a non-correction area (dead zone) is set at the time of correction point extraction, and the correction amount is set to only the minimum value of the correction resolution, so that the first correction can be performed. It is possible to improve only the remaining print unevenness without impairing the obtained print unevenness improvement effect.
[0051]
As described above, the accuracy of correction can be improved by combining the two types of correction methods.
(Example 2)
In the first embodiment, two types of correction methods are combined, but a plurality of types of correction methods may be combined. Further, the combined correction method may be repeated a plurality of times.
[0052]
As described above, when the printing unevenness is improved, the improvement effect is improved every time the number of corrections is repeated.
<Fourth embodiment>
(Example 1)
The minimum value of the correction resolution when calculating the correction amount according to the density data of each dot of the optical writing device is the minimum resolution value of the light amount correction value of the optical writing device. Even if the correction is performed, the correction amount may be inappropriate depending on the printing unevenness. This is because, even if the correction amount is the minimum unit, if the area is intensively arranged, the density of the image looks visually emphasized.
[0053]
Therefore, it is necessary to perform correction by thinning out, instead of performing all corrections for each calculated dot. Thinning refers to, for example, correcting one dot in one block (correction of 1/5 = 20%) from five dots as one block to correcting all five dots in one block (5/5 = The correction pattern is selected and used by comparing the data up to 100% correction) with the density data of the surrounding blocks.
[0054]
FIG. 8 is a block diagram of the light amount correction control of the image forming apparatus according to the present embodiment, in which a correction portion pattern 11 is added to the light amount correction control block diagram of FIG. The correction location pattern 11 is stored in the storage device and is used to perform correction sparsely. For example, if there are five consecutive dots to be corrected, not all of the five dots are corrected, but three dots at intervals of one dot are corrected, that is, correction is performed in a tooth-like manner.
[0055]
FIG. 9 is a diagram illustrating a flow of the correction processing in the present embodiment. The processes in S60 to S73 correspond to the processes in S1 to S14 in FIG. 3 and perform the same processes.
Next, when a certain dot is set as a target dot, an average density of five dots is calculated by adding the dot itself and two dots on the left and right of the dot (S74). Next, the average density of five dots on the left and right of the target dot is calculated (S75).
[0056]
The difference between the average density acquired in S74 and the average density acquired in S75 is determined (S76). In this embodiment, the average density difference is determined in five stages of A, B, C, D, and E, and there is no difference in the average density in the determination result A, and the difference is determined as B, C, D, and E are obtained. Becomes larger. Next, from the correction pattern shown in FIG. 10, only the dots corresponding to the determination result obtained in S76 are corrected (S77).
[0057]
FIG. 10 shows a correction pattern corresponding to the determination results (A, B, C, D, E) acquired in S76. This correction pattern is stored in the correction location pattern 11. In the table, “「 ”indicates a dot to be corrected, and“ × ”indicates a dot not to be corrected. In the figure, a positive integer k indicates a dot position. If the density determination result in S76 is A, there is no density difference, so only k dots are corrected. If the density determination result in S76 is B, k-1 dots and k + 1 dots are corrected. If the density determination result in S76 is C, k-1 dots, k dots, and k + 1 dots are corrected. If the density determination result in S76 is D, k-2 dots, k dots, k + 1 dots, and k + 2 dots are corrected. If the density determination result in S76 is D, k-2 dots and k to k + 2 dots are corrected. If the density determination result in S76 is E, all five dots from k-2 dots to k + 2 dots are corrected.
[0058]
Next, the correction process (thinning process) is actually performed in accordance with the correction pattern of S77 (S78), and the correction value of the selected (“「 ”) dot after the thinning is the final correction value (S79). .
The correction pattern shown in FIG. 10 is an example. Therefore, the density determination result is not limited to five levels, and may be, for example, three levels or ten levels. Further, the correction pattern can take not only the pattern shown in FIG. 10 but also any combination.
[0059]
As described above, even if the correction resolution is the fixed amount of the minimum value, the correction resolution can be artificially reduced by changing the number of correction dots, and more flexible correction according to the degree of print unevenness becomes possible. . That is, it is possible to reduce a sudden change in density due to the correction and to make a gradual change in density.
(Example 2)
Example 1 can be used in combination with the first embodiment, the second embodiment, and the third embodiment. That is, when correction is performed using the final correction value calculated in each of the first embodiments, it can be used to prevent overcorrection.
<Fifth embodiment>
(Example 1)
When a print result is converted into density data, a CCD sensor is used. However, in the constant density region, noise of the CCD sensor cannot be ignored, and the accuracy of the converted density data deteriorates. That is, in the present embodiment, if a non-uniform image (including noise) is obtained as a result of reading a uniform image, the noise is attributed to the CCD sensor and is removed. Therefore, the present embodiment proposes a method for improving this.
[0060]
FIG. 11 is a diagram illustrating a flow of the correction processing in the present embodiment. First, an image or a density chart or the like (hereinafter, referred to as a reference density image) serving as a reference of the density arranged over the entire reading area is set (S80). Next, a correction value is set (S81). As the correction value here, a reference correction value is set as in the first embodiment. Next, the reference density image is read at the same time when the print result is read by the CCD sensor (S82).
[0061]
Next, when the reading result is converted into fineness data, the density fluctuation of the reference image is first set to 0, and the CCD sensor offset amount is defined so that the fluctuation amount becomes 0 at the fluctuation point (S83). Next, at the time of density conversion of the print result, the CCD sensor offset amount is added to obtain final density data (S84, S85).
[0062]
S86 to S93, which are subsequent processes, correspond to the processes of S8 to S15 in FIG. 3 and perform the same processes.
It should be noted that the reference density image is configured so that use or non-use can be selected according to the print density, and may be used at all times.
[0063]
As described above, the noise caused by the CCD sensor can be corrected.
(Example 2)
Example 1 can be used in combination with the first embodiment, the second embodiment, the third embodiment, and the fourth embodiment. That is, the noise caused by the CCD sensor can be corrected together with the correction of the first embodiment, the second embodiment, the third embodiment, or the fourth embodiment. Thereby, the accuracy of the correction can be further improved.
[0064]
【The invention's effect】
As described above, according to the present invention, since the final correction value is calculated from the density data based on the printing result, the operations such as the printing unevenness, the photoreceptor (drum), the toner development, the transfer, and the fixing by the optical writing device itself are performed. There is an effect that printing unevenness caused by an image process can be improved.
[0065]
In addition, when extracting a correction target portion, a moving average in a certain range is compared with a moving average in a sufficiently narrow range, and a non-correction area (dead zone) is provided for the moving average in a certain range. There is an advantage that only the emphasized part can be corrected.
Further, even if the correction resolution is a fixed amount of the minimum value, the correction resolution can be artificially reduced by changing the number of correction dots, and more flexible correction according to the degree of print unevenness becomes possible. That is, it is possible to reduce a sudden change in density due to the correction and to make a gradual change in density.
[Brief description of the drawings]
FIG. 1 is a block diagram of light amount correction control according to a first embodiment.
FIG. 2 is a diagram illustrating a print pattern for each gradation value according to the first embodiment.
FIG. 3 is a diagram illustrating a flow of a correction process according to the first embodiment.
FIG. 4A illustrates the density of density data in dots of a print image according to the first embodiment. FIG. 4B is a diagram illustrating a correction portion based on FIG. 4A and a correction amount thereof.
FIG. 5 is a diagram illustrating a flow of a correction process according to the second embodiment.
FIG. 6A illustrates a moving average of density data in dots of a print image according to the first embodiment. FIG. 6B is a diagram in which only the moving average Nave 21 protruding from the range between 22 and 23 in FIG. 6A is extracted as a correction point, and the extracted correction point and the correction amount are shown. .
FIG. 7 is a diagram illustrating a flow of a correction process according to the third embodiment.
FIG. 8 is a block diagram of light amount correction control according to a fourth embodiment.
FIG. 9 is a diagram illustrating a flow of a correction process according to a fourth embodiment.
FIG. 10 is a diagram illustrating a correction pattern according to a fourth embodiment.
FIG. 11 is a diagram illustrating a flow of a correction process according to a fifth embodiment.
FIG. 12 is a block diagram of light amount correction control in a conventional printing apparatus.
[Explanation of symbols]
1 Optical writing device
2 Light intensity correction value (reference)
3 arithmetic unit
4 CPU
5 CCD sensor
6 Correction RAM
7 Correction data RAM
8 Concentration data
9 dot position information
10. Image processing control circuit
11 Correction location pattern
20 Concentration data without moving average
21 Moving Average Nave
22 Moving average Cave + 1%
23 Moving Average Cave-1%
101 Optical writing device
102 Light intensity correction value
103 CPU
104 Correction RAM
105 dot position information
106 Image processing control circuit

Claims (5)

In an image forming apparatus that prints a print image of the same print pattern using optical writing means,
A print image in which the print pattern is printed using a reference correction value that is a reference correction value, and one or more print images in which a print pattern is printed using a correction value having a predetermined value difference from the correction value Acquisition means for acquiring
Conversion means for converting each of the acquired print images to each density data,
Density change amount calculation means for calculating a density change amount based on each density data converted by the conversion means,
Correction value calculating means for calculating a correction value based on the density change amount,
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the density change amount calculation unit calculates a density change amount obtained when the light amount correction value has the minimum resolution. The correction value calculation means calculates a first additional correction value for compensating the reference correction value based on the density change amount calculation means, and sets an upper limit value for the first additional correction value. And calculating a second additional correction value by dividing the first additional correction value by the upper limit value, and adding the second additional correction value to the reference correction value. Or the image forming apparatus according to 2. In an image forming apparatus that prints using optical writing means, obtaining means for obtaining a printed image printed using a reference correction value that is a reference correction value,
Conversion means for converting the obtained print image to density data,
First moving average calculating means for calculating a moving average of density values in a predetermined range of the acquired print image based on the density data;
Second moving average calculating means for calculating a moving average of density values in a range narrower than a predetermined range of the first moving average calculating means from the density data;
Correction range calculation means for calculating a correction range of a density value for each pixel of the acquired print image based on the first moving average calculation means;
A pixel position acquisition unit that acquires a pixel position for a density value calculated by the first moving average calculation unit that is not included in the correction range;
A correction value calculating unit that calculates a correction value for the pixel position based on the pixel position acquired by the pixel position acquiring unit;
An image forming apparatus comprising: The image forming apparatus further includes a correction position information storage unit that stores correction position information that is information on a pixel position to be corrected,
Calculating a first average value which is an average of density values of a predetermined number of continuous pixels including predetermined pixels of the obtained print image, and calculating a predetermined number of continuous pixels including pixels adjacent to the predetermined pixel Is calculated, a second average value is calculated, the first average value is compared with the second average value, and a pixel at the pixel position is corrected based on the comparison result and the correction position information. Correction position correcting means for performing
The image forming apparatus according to claim 1, further comprising:

Images