JP3900736B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that forms a color image.
[0002]
[Prior art]
An image formed using an image forming apparatus such as a color copying machine and a printer is formed not only on dedicated paper but also on plain paper and recycled paper. Conventionally, optimal conditions for image formation with high image quality have been studied for dedicated paper, and satisfactory image quality has been obtained for images formed on dedicated paper. Satisfactory image quality has not been obtained for paper and recycled paper. For example, because recycled paper has a dull color, there is a problem with the color reproducibility of images formed on recycled paper, and plain paper, especially plain paper used overseas, can have uneven images. There is a problem that it is easy. In particular, plain paper in the United States and Europe uses conifers as the raw material, and the fibers of the conifers are long and rigid, so that the density of the fibers in the produced plain paper can be reduced. When an image is formed on an image forming apparatus that employs an electrophotographic method on a paper with such fiber density, the electrical characteristics of the paper vary depending on the part of the paper due to the density of the paper fiber. However, the electrical characteristics are uneven. Due to the uneven electrical characteristics, the image formed on the paper is deteriorated. This image degradation is caused by the quality of the paper, but it is difficult to improve the quality of the paper itself. Therefore, in order to form a high-quality image regardless of the paper quality, it is necessary to devise the configuration of the image forming apparatus itself.
[0003]
[Problems to be solved by the invention]
As an example in which the configuration of the image forming apparatus itself is devised in order to improve the image quality, for example, in Japanese Patent Laid-Open No. 5-104754, an image forming apparatus employing an ink jet method is controlled by controlling an applied voltage. A method for controlling ink dots has been proposed, and Japanese Patent Application Laid-Open No. 5-220978 has focused on the fact that ink irregularities appear regularly, and there is a method for reading the irregularities and correcting them with a one-dimensional LUT. Although proposed, the methods of these publications have problems such as blurring and the image quality is likely to deteriorate.
[0004]
Even if the method used in the above-described inkjet image forming apparatus is applied to an electrophotographic image forming apparatus, unevenness in printing that occurs when toner is fixed on a sheet varies depending on the type of the sheet. It cannot be read and corrected. Further, in an electrophotographic image forming apparatus, it is conceivable to improve image quality by changing a bias and a transfer current during development, but it is difficult to control the bias and the transfer current.
[0005]
Japanese Patent Application Laid-Open No. 10-55085 proposes an image forming apparatus that smoothes toner at the time of paper fixing using transparent toner for the purpose of improving image quality. Therefore, there is a problem that costs are increased. Japanese Patent Application Laid-Open No. 9-69960 proposes an image forming apparatus that attempts to reproduce colors by controlling characteristic values. The method of controlling the value is unclear.
[0006]
SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus that is low in cost and can improve the image quality of an image formed on the paper regardless of the type of the paper.
[0007]
[Means for Solving the Problems]
The image forming apparatus of the present invention that achieves the above object is
Based on image signals corresponding to each of the four colors of cyan, magenta, yellow, and black, four toner images composed of these four colors of toner are formed, and these four toner images are finally formed on a predetermined sheet of paper. In an image forming apparatus that forms a color image on the paper by transferring and fixing to the paper,
(1) A formation sensor for detecting the texture of paper used for image formation
(2) According to the texture of the paper detected by the texture sensor, the replacement ratio of cyan, magenta, and yellow toner to black toner is obtained, and each of the three colors red, green, and blue is supported. A signal processing unit that inputs image signals to be processed and performs signal processing according to the replacement ratio on the input image signals to generate image signals corresponding to cyan, magenta, yellow, and black
(3) A toner image forming unit that forms toner images of respective colors based on image signals corresponding to four colors of cyan, magenta, yellow, and black generated by the signal processing unit.
It is provided with.
[0008]
Here, in the image forming apparatus of the present invention, it is preferable that the signal processing unit obtains a larger ratio as the replacement ratio as the texture detected by the texture sensor is smaller.
[0009]
Furthermore, in the image forming apparatus of the present invention, the signal processing unit obtains an average brightness of the color image formed on the paper based on the image signal, and together with the formation of the paper detected by the formation sensor. It is preferable that the substitution ratio is obtained based on the average brightness.
[0010]
Further, in the image forming apparatus of the present invention, the signal processing unit obtains an average brightness for each region when the color image formed on the paper is divided into a plurality of regions based on the image signal. It is preferable that the replacement ratio is obtained for each area based on the average brightness of each area together with the formation of the paper detected by the formation sensor.
[0011]
Here, in the image forming apparatus of the present invention, it is preferable that the signal processing unit obtains a larger ratio as the replacement ratio as the average lightness is lower.
[0012]
In the image forming apparatus of the present invention, the signal processing unit obtains a difference between the maximum value and the minimum value of the image signals corresponding to the three colors of red, green, and blue for each pixel, For pixels whose difference is within 20% of the value that can be taken by the image signal, a replacement ratio according to the texture of the paper detected by the texture sensor is obtained, and for pixels whose difference exceeds 20%, the texture is determined. It is preferable to obtain a replacement ratio according to the texture of the paper detected by the sensor and the difference between them.
[0013]
In the image forming apparatus of the present invention, the signal processing unit converts the input image signal corresponding to each of the three colors of red, green, and blue into a signal representing L * a * b * for each pixel. Then, the difference between the maximum value and the minimum value of the three values of L * a * b * for each pixel is obtained for each pixel, and the paper whose difference is within 20 is detected by the ground sensor. It is preferable that a replacement ratio corresponding to the texture is obtained, and a replacement ratio corresponding to the texture of the paper detected by the texture sensor and the difference is obtained for the pixels having the difference exceeding 20.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described.
[0015]
FIG. 1 is a diagram illustrating an embodiment of a printer that is an example of an image forming apparatus of the present invention.
[0016]
The printer 100 includes a photosensitive drum 4 inside. The photosensitive drum 4 is disposed so as to be rotatable in the direction of arrow A while passing through the transfer position T. Around the photosensitive drum 4, there are a cleaner 7 for cleaning the surface of the photosensitive drum 4, a laser scanner 6 for writing an electrostatic latent image on the photosensitive drum 4, and black (K) and cyan (C). , Four developing units 5K, 5C, 5M, and 5Y that store toners of magenta (M) and yellow (Y) are sequentially arranged in the arrow A direction. These four developing devices 5K, 5C, 5M, and 5Y develop the electrostatic latent image written on the photosensitive drum 4 with toner of each color, and form a toner image on the photosensitive drum 4.
[0017]
The printer 100 also includes a paper tray 1 that stores paper. A pickup roll 11 that feeds out the paper stored in the paper tray 1 is provided on the paper feeding side of the paper tray 1, and the paper fed out by the pickup roll 11 follows a path indicated by a broken line. It is conveyed to the winding position M.
[0018]
The printer 100 also includes a transfer drum 3 that winds and holds paper. The transfer drum 3 is disposed so as to be rotatable in the direction of the arrow B while passing through the winding position M and in contact with the photosensitive drum 4 at the transfer position T. The transfer drum 3 conveys the wound and held paper to the transfer position T, and transfers the toner image formed on the photosensitive drum 4 to the paper at the transfer position T. The printer 100 further includes a fixing device 9 that fixes the toner image transferred onto the paper to the paper, and a discharge tray 10 that discharges the paper on which the toner image is fixed.
[0019]
The printer 100 further includes a formation sensor 2 and a signal processing means 8. The formation sensor 2 detects the texture of the sheet fed by the pickup roll 11 before being conveyed to the winding position M. The signal processing means 8 is supplied from an external device 12 such as a personal computer. The image signals corresponding to each of the three colors of red (R), green (G), and blue (B) are input, and the input image signals are based on the texture detected by the formation sensor 2. Signal processing is performed to generate image signals corresponding to four colors of cyan, magenta, yellow, and black.
[0020]
Hereinafter, the manner in which the printer 100 configured as described above forms an image on a sheet will be described with reference to FIG.
[0021]
First, the paper stored in the paper tray 1 shown in FIG. 1 is fed out by the pick-up roll 11, conveyed along the path shown by the broken line, and passes through the formation sensor 2.
[0022]
The formation sensor 2 includes a white light source that emits white light to a sheet to be conveyed, and a CCD sensor (200 × 500 elements) that detects light transmitted through the white light source. The white light source of the formation sensor 2 emits white light when the paper passes through the formation sensor 2, and at this time, the CCD sensor detects the light transmitted through the paper, and the detected light A gray scale (64-color gradation) is measured. The formation sensor 2 takes a histogram for the measured gradation and calculates the formation FI using the following equation (1).
[0023]
Formation FI = peak value (frequency) / (number of classes of 100 degrees or more × 100) (1)
In this way, the sheet texture F1 is calculated, and a signal representing the calculated texture F1 is input to the signal processing means 8. Further, the sheet that has passed through the formation sensor 2 further moves along a path indicated by a broken line and is conveyed to the winding position M.
[0024]
FIG. 2 is a diagram showing a specific configuration of signal processing means provided in the printer shown in FIG.
[0025]
Image signals (R, G, B) corresponding to the three colors red, green, and blue, which are output from the external device 12 and passed through the image input unit 8a, are input to the pixel signal average value calculation unit 8b. The pixel signal average value calculation unit 8b outputs the input image signal (R, G, B) as it is to the input gradation correction unit 8c, and the input image signal (R, G, B). The average value Ave (R, G, B) of the pixel signals (R, G, B) constituting the is calculated. The image signal (R, G, B) input to the input gradation correction unit 8c is subjected to gradation correction, and the image signal (R ′, G ′, B ′) after the gradation correction is used as the color signal correction unit 8d. Is input. In this color signal correction unit 8d, the image signal (R ', G', B ') is converted into image signals (C, M, Y, K) corresponding to four colors of cyan, magenta, yellow, and black, respectively. A three-dimensional lookup table for conversion is stored. This three-dimensional lookup table includes R'G'B 'definition formulas and light source conversions (shown below (2) used for conversion from R'G'B' parameters to L * a * b * parameters. ) And the printer model used for conversion from the L * a * b * parameter to the CMYK parameter are stored as parameters. In the printer model, an image signal representing a patch is corrected by an output tone correction unit 8e described later, and a patch print state (for example, when the patch represented by the tone-corrected image signal is printed on a sheet) , The color of the patch, etc.), the conditions are set when the printing state is optimal.
[0026]
X = 0.4124 × R + 0.3576 × G + 0.1805 × B
Y = 0.2126 × R + 0.7152 × G + 0.0722 × B
Z = 0.0190 × R + 0.1192 × G + 0.9505 × B
L * = 116 × (Y / Yw) ^1/3 -16 (Y / Yw ≧ 0.008856)
L * = 903.29 × Y / Yw (Y / Yw <0.008856)
yy = (Y / Yw) ^1/3 (Y / Yw ≧ 0.008856)
yy = 7.787 × Y / Yw + 16/116 (Y / Yw <0.008856)
xx = (X / Xw) ^1/3 (X / Xw ≧ 0.008856)
xx = 7.787 × X / Xw + 16/116 (X / Xw <0.008856)
zz = (Z / Zw) ^1/3 (Z / Zw ≧ 0.008856)
zz = 7.787 × Z / Zw + 16/116 (Z / Zw <0.008856)
a * = 500 × (xx−yy)
b * = 200 × (yy−zz)
(2)
[0027]
In addition, the three-dimensional lookup table stored in the color signal correction unit 8d has a UCR (inking) amount D representing the replacement ratio of cyan, magenta, and yellow toner to black toner as a parameter. is doing. The UCR amount D is a value calculated based on a signal output from a color conversion parameter selection unit 8g described later. By calculating the UCR amount D, the K signal of the image signal (C, M, Y, K) is set. The UCR amount D is calculated using the following equation (3).
[0028]
UCR amount D = B (F1) · K (Ave) (3)
The color conversion parameter selection unit 8g outputs signals representing B (F1) and K (Ave) shown in Equation (3) to the color signal correction unit 8d, and the color signal correction unit 8d Using (3), the UCR amount D is calculated. The signals representing B (F1) and K (Ave) output from the color conversion parameter selector 8g to the color signal corrector 8d will be described in detail later.
[0029]
Further, as described above, the pixel signal average value calculation unit 8b is configured to output each pixel signal (R, G, B) constituting the image signal (R, G, B) input to the pixel signal average value calculation unit 8b. The average value Ave (R, G, B) is calculated. This average value Ave (R, G, B) is a value calculated by integrating the R signals, the G signals, and the B signals of each pixel signal (R, G, B), and dividing by the number of pixels. The calculated value is the average brightness of the image represented by the image signal (R, G, B), that is, the area when the color image formed on the paper is defined as one area as a whole. It is a value indicating the overall average brightness. The average pixel signal representing the calculated average value Ave (R, G, B) is input to the color conversion parameter selector 8g. The color conversion parameter selection unit 8g includes paper detected by the ground sensor 2 in addition to the average value pixel signal representing the average value Ave (R, G, B) calculated by the pixel signal average value calculation unit 8b. A ground signal representing the ground FI is input. The color conversion parameter selector 8g calculates the UCR reference amount B (F1) based on the value of the texture F1, and also uses the UCR coefficient K (Ave) based on the average value Ave (R, G, B). Is calculated. Signals representing the calculated B (F1) and K (Ave) are output to the color signal correction unit 8d, and the color signal correction unit 8d calculates the UCR amount D using (3).
[0030]
This UCR amount D is based on the average value Ave (R, G, B) to the UCR reference amount B (F1) calculated on the basis of the value of the texture F1, as shown in the equation (3). This is a value calculated by multiplying the calculated UCR coefficient K (Ave). That is, the UCR reference amount B corresponds to the UCR amount D when the average value Ave (R, G, B) is ignored. In this embodiment, the UCR reference amount B is corrected by the UCR coefficient K. The amount of UCR is D.
[0031]
Hereinafter, how the color conversion parameter selection unit 8g calculates the values of the UCR reference amount B (F1) and the UCR coefficient K (Ave) based on the input average pixel signal and the ground signal, respectively. Explain what they do.
[0032]
FIG. 3 is a graph showing the correspondence between the texture F1 and the UCR reference amount B, and FIG. 4 is a graph showing the correspondence between the average value Ave and the UCR coefficient K.
[0033]
The color conversion parameter selection unit 8g stores correspondences represented by the straight lines L1 and L2 shown in FIGS. The correspondences represented by the straight lines L1 and L2 are obtained in advance by experiments.
[0034]
The UCR reference amount B (F1) shown in FIG. 3 is expressed by equation (4).
[0035]
B (F1) = − 2.5 × F1 + 112.5 (4)
In an image forming apparatus that employs an electrophotographic system, such as the printer 100 of the present embodiment, generally, as the paper texture becomes smaller, the toner transferred to the paper tends to cause a transfer failure. Therefore, in the present embodiment, the correspondence relationship between the UCR reference amount B corresponding to the UCR amount D when the average value Ave (R, G, B) is ignored and the texture F1 is set to satisfy the equation (4). It is. If the correspondence relationship between the UCR reference amount B and the texture F1 is set in this way, the UCR reference amount B increases as the texture F1 decreases. That is, the smaller the texture F1, the higher the replacement ratio of cyan, magenta, and yellow toner to black toner. As a result, the amount of toner can be reduced and toner transfer failure is suppressed.
[0036]
The UCR coefficient K (Ave) shown in FIG. 4 is expressed by equations (5) and (6).
[0037]
K (Ave) = − (Ave−100) / 80 (Ave> 20) (5)
K (Ave) = 1.0 (0 ≦ <Ave ≦ 20) (6)
Generally, as the brightness of the image signal (R, G, B) becomes darker, the unevenness of the image printed on the paper is more conspicuous. Therefore, in the present embodiment, the correspondence relationship between the UCR coefficient K (Ave) used for correcting the UCR reference amount B (F1) and the average value Ave (R, G, B) is expressed by equations (5) and (6). It is set to satisfy. When the correspondence is set in this way, the UCR coefficient K (Ave) increases as the average value Ave (R, G, B) decreases. Accordingly, the smaller the average value Ave (R, G, B), the larger the UCR amount D calculated using the equation (3). That is, as the brightness of the image becomes darker, the replacement ratio of cyan, magenta, and yellow toner to black toner increases. As a result, the amount of toner can be reduced, and the unevenness of the image can be made inconspicuous.
[0038]
When the formation signal is input to the color conversion parameter selection unit 8g in which the correspondence relationship shown in FIGS. 3 and 4 is stored, the UCR reference amount B (corresponding to the formation F1 represented by the formation signal from the equation (4). F1) is calculated, and on the other hand, when the average value pixel signal is input, the UCR coefficient K corresponding to the average value Ave (R, G, B) represented by the average value pixel signal from the equations (5) and (6) (Ave) is calculated.
[0039]
When the UCR reference amount B (F1) and the UCR coefficient K (Ave) are calculated in this way, signals representing the UCR reference amount B (F1) and the UCR coefficient K (Ave) are sent to the color signal correction unit 8d. Entered. The color signal correction unit 8d calculates the UCR amount D based on the input signal.
[0040]
The color signal correction unit 8d sets the K signal using the calculated UCR amount D when converting the image signal (R ', G', B ') into the image signal (C, M, Y, K). is doing.
[0041]
Since it is difficult to have all UCR amounts as parameters in the three-dimensional lookup table, in this embodiment, the UCR amount is stored as a parameter in units of 10% in the three-dimensional lookup table. In the meantime, it is obtained by linear interpolation.
[0042]
As described above, when the image signal (R ′, G ′, B ′) input to the color signal correction unit 8d is converted into the image signal (C, M, Y, K), the image signal (C , M, Y, K) are input to the output tone correction unit 8e. The output tone correction unit 8e corrects the tone of the input image signal (C, M, Y, K). This correction is performed, for example, so that the gray balance becomes neutral or the color difference becomes constant. The image signals (C ′, M ′, Y ′, K ′) after being corrected by the output tone correction unit 8e are input to the image output unit 8f, and the image signals (C ′, M ′, Y ′, K). 1), the laser scanner 6 (see FIG. 1) first writes an electrostatic latent image corresponding to black (K) on the photosensitive drum 4, and the electrostatic latent image is developed by the developing device 5K. A black (K) toner image is formed. The black (K) toner image is conveyed to the transfer position T by the rotation of the photosensitive drum 4 in the direction of arrow A, and the black (K) toner image is formed on the paper held by the transfer drum 3 at the transfer position T. Is transcribed. Thereafter, the surface of the photosensitive drum 4 is cleaned by the cleaner 7 until the transfer drum 3 finishes one rotation cycle. Thereafter, an electrostatic latent image corresponding to cyan (C), magenta (M), and yellow (Y) is sequentially formed by the laser scanner 6 every rotation cycle of the transfer drum 31, and the surface of the photosensitive drum 4. In addition, cyan (C), magenta (M), and yellow (Y) toner images are sequentially formed, and these toner images are sequentially transferred onto a sheet held on the transfer drum 3.
[0043]
In this way, a superimposed toner image is formed on the paper held on the transfer drum 3 by toner images of four colors. The sheet on which the toner images of four colors are transferred is peeled off from the transfer drum 3, and the toner image is fixed by the fixing device 9 along the path of the broken line, and is discharged to the discharge tray 10.
[0044]
The printer 100 according to the present embodiment detects the texture of the paper by the texture sensor 2, calculates the UCR reference amount B based on the detected texture, and further represents the average color of the image formed on the paper. The UCR coefficient K is obtained by calculating the average pixel signal, and the UCR amount is calculated based on the UCR reference amount B and the UCR coefficient K. The UCR reference amount B is set so as to increase as the paper texture becomes smaller (so that the replacement ratio of toner with black increases) (see FIG. 3), and as expressed by the equation (3). The UCR amount D increases as the UCR reference amount B increases. Therefore, the UCR amount D is set to a larger value as the texture is smaller. In general, as the paper texture becomes smaller, the toner transferred to the paper tends to cause a transfer failure. However, in this embodiment, the smaller the paper texture, the smaller the amount of toner required for image formation. Transfer defects are suppressed, and image quality is improved.
[0045]
In the above-described Japanese Patent Application Laid-Open No. 10-55085, transparent toner is used to improve image quality. However, in this embodiment, transparent toner is unnecessary, and image quality can be improved at low cost. .
[0046]
By the way, in this embodiment, when the average color of the image is dark (Ave <20), the UCR coefficient K = 1 is set. On the other hand, when the average color of the image is light (Ave ≧ 20), The UCR coefficient K is set to a smaller value as Ave increases. Therefore, from equation (3), even if the texture is the same, the UCR amount D is set to a larger value as the average color of the image becomes darker. In general, the unevenness of the image is more noticeable as the average color of the image is darker, but the unevenness of the image can be made less noticeable by setting the UCR amount D to a larger value as the average color of the image is darker. The image quality is improved. In this embodiment, Ave representing the average brightness of the image is obtained based on the image signal (R, G, B). For example, the image signal (Y, M, C, K) Based on this, the average brightness of the image may be obtained. In this embodiment, the UCR amount D is set based on both the paper texture and the average color of the image. However, even if the UCR amount D is set only based on the paper texture. Therefore, it does not depart from the spirit of the present invention to improve the image quality of an image formed on a sheet at low cost regardless of the type of sheet.
[0047]
Further, in the present embodiment, the pixel signal average value calculation unit 8b uses the average value Ave (R, R) that represents the average brightness of the entire area when the color image formed on the paper is defined as one area as a whole. G, B) is calculated, and the UCR amount D is calculated based on the texture of the paper detected by the formation sensor 2 and the average brightness of the entire area. Based on this, the average brightness of each area when the color image formed on the sheet is divided into a plurality of areas is obtained, and the average of each area is detected along with the formation of the sheet detected by the formation sensor 2. The UCR amount may be obtained for each of these areas based on the brightness. In this way, the color image formed on the paper is divided into a plurality of areas, and the average brightness for each of these areas is obtained, so that there are areas with extremely different brightness in the image formed on the paper. However, the UCR amount D can be set according to the brightness of the image formed in each area, and the image quality can be improved for each area of the image formed on the paper.
[0048]
In the present embodiment, as described above, in the pixel signal average value calculation unit 8b, the average representing the average brightness of the entire area when the color image formed on the sheet is defined as one area as a whole. The value Ave (R, G, B) is calculated to calculate the UCR amount D. For example, the maximum value and the minimum value among the image signals corresponding to the three colors of red, green, and blue are further included. A difference from the value is obtained for each pixel, and for a pixel whose difference is within 20% of a value that can be taken by the image signal, a UCR amount corresponding to the texture of the paper detected by the formation sensor 2 is obtained. For pixels where the difference exceeds 20%, the texture of the paper detected by the texture sensor and the UCR amount corresponding to the difference may be obtained. Thus, by obtaining the brightness for each pixel of the color image formed on the paper, the UCR amount D can be set according to the brightness of each pixel, and the image quality can be further improved.
[0049]
In this embodiment, the printer is described for explaining the image forming apparatus of the present invention. However, the image forming apparatus of the present invention can be applied to, for example, a copying machine and a fax machine in addition to the printer. Is possible. In the case of a copying machine or FAX, the input signal of the three-dimensional lookup table is L * a * b *. Therefore, when obtaining the brightness for each pixel of the color image formed on the paper, the input image signal corresponding to each of the three colors of red, green, and blue is set to L * a * b * for each pixel. What is necessary is just to obtain | require the difference of the maximum value of the L * a * b * 3 value for every pixel, and the minimum value for every pixel by converting into the signal to represent. Here, the UCR amount corresponding to the texture of the paper detected by the formation sensor is obtained for pixels whose difference is within 20, and the texture of the paper detected by the texture sensor is obtained for pixels whose difference exceeds 20. When the UCR amount corresponding to the difference between the two and the difference is obtained, the image quality of the image formed on the paper can be further improved as in the printer.
[0050]
【The invention's effect】
As described above, according to the image forming apparatus of the present invention, the image quality of the image formed on the paper can be improved at low cost regardless of the paper type.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of a printer that is an example of an image forming apparatus of the present invention.
FIG. 2 is a diagram showing a specific configuration of signal processing means provided in the printer shown in FIG. 1;
FIG. 3 is a graph showing a correspondence relationship between the formation F1 and the UCR reference amount B;
4 is a graph showing a correspondence relationship between an average value Ave and a UCR coefficient K. FIG.
[Explanation of symbols]
1 Paper tray
2 Ground sensor
3 Transfer drum
4 Photosensitive drum
5K, 5C, 5M, 5Y Developer
6 Laser scanner
7 Cleaner
8 Signal processing means
8a Image input unit
8b Pixel signal average value calculator
8c Input tone correction unit
8d color signal correction unit
8e Output tone correction unit
8f Image output unit
8g color conversion parameter selection part
9 Fixing device
10 Discharge tray
11 Pickup roll
12 External equipment

Claims (3)

Based on image signals corresponding to each of the four colors of cyan, magenta, yellow, and black, four toner images composed of these four colors of toner are formed, and these four toner images are finally formed on a predetermined sheet of paper. In an image forming apparatus that forms a color image on the paper by transferring and fixing to the paper,
A formation sensor for detecting the formation of a sheet used to form the image,
The replacement ratio is determined so that the replacement ratio of the cyan, magenta, and yellow toners to the black toner becomes larger as the texture of the paper detected by the formation sensor becomes non-uniform . An image signal corresponding to each of the three colors of green and blue is input, and signal processing corresponding to the replacement ratio is performed on the input image signal to generate image signals corresponding to cyan, magenta, yellow, and black. A signal processor to generate;
An image forming system comprising: a toner image forming unit that forms toner images of respective colors based on image signals corresponding to four colors of cyan, magenta, yellow, and black generated by the signal processing unit. apparatus. The signal processing unit obtains an average brightness of a color image formed on a sheet based on the image signal, and the replacement ratio is larger as the formation of the sheet detected by the formation sensor is uneven. 2. The image forming apparatus according to claim 1, wherein the replacement ratio is calculated so that the replacement ratio becomes larger as the average brightness becomes lower. The signal processing unit obtains an average brightness for each region when the color image formed on the paper is divided into a plurality of regions based on the image signal, and detects the paper detected by the formation sensor. The replacement ratio is determined for each area so that the replacement ratio becomes larger as the formation is non-uniform, and the replacement ratio becomes higher as the average brightness of each area is lower. The image forming apparatus according to claim 1, wherein:

Images