JP2002051229A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color image forming device capable of performing gradation correction for minimizing a color tone change by performing gradation correcting operation to a signal, which is the main component of a color among RGB signals, and changing the sub-component signal of the color corresponding to the change quantity of the main component signal of the color so as not to change the color tone. SOLUTION: An input gradation correcting part 52 for performing the gradation correction corresponding to the taste of a user has a gradation correction setting means and an input gradation correction operating means. The input gradation correction operating means is composed of a main component selecting means for selecting the signal to become the main component of the color among RGB signals, a gradation correction operating means for main signal component and an arithmetic means for sub-component signal. Then, converting processing, which is to be performed by the input gradation correction operating means for picture quality control, from a main component signal X to X', is performed by using a look-up table previously stored in a memory or the like. The converting processing from a sub-component signal Y to Y' is arithmetically processed by the arithmetic means corresponding to the change quantity of the main component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus which digitally performs image processing and correction processing on image information and uses the processed image information for copying.

[0002]

2. Description of the Related Art In order to digitally process color image information to obtain an output of a copying machine or the like, a color original must be R
(Red) G (green) and B (yellow) are separated and read, and color correction is required. When the color reproduction range of the output image matches the color reproduction range of the input image, or when the color reproduction range of the output image is larger than the color reproduction range of the input image, the input image can be output as it is. In color correction, a document image is compressed and output.

Recently, a color digital copying machine or the like is equipped with a contrast adjustment processing function or the like in order to preferably bring the original image close to the original image or to change the original image according to the user's preference. Gradation correction can be easily performed. For example, Japanese Patent Laying-Open No. 9-112284 discloses such a contrast adjustment processing device.

[0004]

However, in the case of performing the contrast adjustment, uniform arithmetic processing is performed on the RGB signals, so that a tone change is caused at the same time as the gradation correction is performed.
In addition, since the contrast adjustment processing is performed using a certain existing look-up table, arithmetic processing, or the like, it is not always possible to reflect the user's preference.

Therefore, in the present invention, a gradation correction calculation process is performed on a signal that is a main component of a color among RGB signals, and a main component of a color is not changed on a sub-component signal of a color so that the color tone does not change. It is an object of the present invention to provide a color image forming apparatus capable of performing tone correction by changing the signal in accordance with the amount of change of the signal and minimizing a change in color.

The present invention has other objects as follows. That is, it is desired that the look-up table can be set using a memory area that can be written by the user in addition to the existing look-up table. That is, it is desirable that gradation correction can be performed as desired by the user. If the look-up table is displayed on the liquid crystal operation panel and can be checked again, it is more preferable that setting errors can be prevented.

[0007] Further, as an auxiliary function of creating the look-up table, a look-up operation is performed by changing the gradation of an area in an image designated by a user by executing a pre-scan or by removing a background. If an up table can be created, the user can easily output an image as desired without having to create the lookup table by himself.

The look-up tables created by these creation assisting functions are subjected to gradation correction arithmetic processing on the press-scan image, and if the image can be confirmed on the liquid crystal operation panel, the desired look-up table can be obtained. It is possible to easily confirm whether or not an uptable has been created.

[0009]

According to the present invention, means for solving the above-mentioned problems are constituted as follows.

(1) In a color image forming apparatus for color-adjusting and outputting RGB signals from a color input image device such as a scanner, the color image is subjected to gradation correction according to the user's preference. An input tone correction unit is provided, the input tone correction unit includes a tone correction setting unit and an input tone correction operation unit, and the input tone correction operation unit is configured to output a main color component of the RGB signal. It is characterized by comprising principal component selecting means for selecting a signal to be a component, gradation correction calculating means for the main component signal, and calculating means for the sub component signal.

According to this configuration, when performing the gradation correction, the main component signal and the sub-component signal of the color are executed by different arithmetic processing, so that the change in the color tone can be suppressed even if the gradation correction is performed. Becomes

(2) The conversion process from the main component signal X to X ', which is performed by the input tone correction calculation means for image quality adjustment, uses a look-up table stored in a memory or the like in advance. The conversion process from the sub-component signal Y to Y ′ is performed by the calculation means in accordance with the amount of change of the main component.

According to this configuration, since a look-up table is used for color gradation correction, there is no need to perform complicated arithmetic processing, and the processing speed and circuit scale can be reduced.

(3) In the conversion processing of the main component signal from X to X 'performed by the input gradation correction calculating means for image quality adjustment, the look-up is performed so that the user can adjust the image quality as desired. The up table is stored in a rewritable memory.

According to this configuration, since the user himself creates the look-up table, the user can perform the desired tone correction without preparing many existing tone corrections γ.

(4) The user can confirm the look-up table used in the conversion processing of the main component signal from the X signal to the X 'signal, which is performed by the input gradation correction calculation means for image quality adjustment. Is displayed on a liquid crystal operation panel.

According to this configuration, it is possible to confirm the gradation correction γ and the preview image processed by the gradation correction γ on the liquid crystal operation panel, so that an operation error can be prevented.

(5) When creating the look-up table, the user can preliminarily designate the area and the degree of gradation of the image portion whose gradation is to be corrected, and pre-scan so that the gradation of the area can be adjusted. Preferably, the look-up table can be created by arithmetic processing.

According to this configuration, by using the tone correction γ creation function, tone correction as desired by the user can be easily performed.

(6) When the look-up table is created, the size of the area of the image part whose gradation is to be corrected is mainly selectable according to the user's request.

According to this configuration, by using the tone correction γ creation function, tone correction as desired by the user can be easily performed.

(7) At the time of creating the look-up table, the look-up table is created by reading a base by a press key and performing an arithmetic processing so as to remove the base.

According to this configuration, the user can select the tone correction γ
By using the creation function, gradation correction for removing the background can be easily and accurately performed.

(8) When the background is read by the press scan, a histogram is created for each density section, and when the value of the histogram exceeds a predetermined threshold, the standard deviation before and after the peak of the histogram is obtained. According to the arithmetic processing to completely remove the base,
It is characterized in that the lookup table is created.

According to this configuration, the user can select the tone correction γ
By using the creation function, gradation correction for removing the background can be easily and accurately performed.

(9) The process of converting the main component signal from X to X 'for image adjustment according to claim 3 and the arithmetic process for background removal according to claim 7 are performed together. Thus, the lookup table can be created.

According to this configuration, since the user's favorite image adjustment and the background removal can be combined, the gradation correction as desired by the user can be easily performed.

(10) The look-up table is created by performing the arithmetic processing for adjusting the gradation according to claim 5 and the arithmetic processing for removing the background according to claim 7 together. Is possible.

According to this configuration, it is possible to combine the tone correction desired by the user with the background removal, so that the tone correction desired by the user can be easily performed.

(11) The arithmetic processing for adjusting the gradation according to the fifth aspect, the arithmetic processing for removing the background according to the seventh aspect, or for creating the look-up table according to the ninth aspect When the calculation processing and the press-can be performed, after the creation of the lookup table,
The pre-scanned image is subjected to arithmetic processing for tone correction by the tone correction arithmetic means, so that the processed image can be confirmed on a liquid crystal operation panel.

According to this configuration, it is possible to confirm the gradation correction γ and the preview image processed by the gradation correction γ on the liquid crystal operation panel, so that an operation error can be prevented.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus according to an embodiment of the present invention will be specifically described with reference to the drawings. FIG. 1 is a cross-sectional view illustrating a configuration of a digital color image forming apparatus. A document table 111 and an operation unit (not shown) are provided on the upper surface of the image forming apparatus main body 1, and an image input device 110 and an image output device 210 are provided inside the image forming apparatus main body 1.

The upper surface of the original table 111 is supported so as to be openable and closable with respect to the original table 111, and has a predetermined positional relationship with respect to the original table 111 surface.
ADF: Reversing Automatic D
document feeder 112 is mounted.

Further, the automatic two-sided automatic document feeder 112
First, the original is conveyed so that one side of the original faces the image input device 110 at a predetermined position on the original platen 111, and after the image reading on this one side is completed, the other side is moved to the predetermined position on the original platen 111. The document is inverted so that the document faces the image input device 110 at the position.
To be conveyed toward.

The automatic two-sided automatic document feeder 112
After both sides of the image have been read for one document, the document is discharged, and a double-sided conveyance operation is performed for the next document. The above-described operation of conveying the document and reversing the front and back is controlled in relation to the operation of the entire image forming apparatus.

The image input device 110 is arranged below the document table 111 for reading an image of a document conveyed onto the document table 111 by the automatic duplex document feeder 112. The image input device 110 includes original scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the original table 111.
, An optical lens 115, and a CCD as a photoelectric conversion element
(Charge Coupled Device) line sensor 116.

The original scanning bodies 113 and 114 are composed of a first scanning unit 113 and a second scanning unit 114. The first scanning unit 114 has an exposure lamp for exposing the surface of the document image and a first mirror for deflecting a reflected light image from the document in a predetermined direction. It reciprocates in parallel at a predetermined scanning speed while maintaining the distance.

The second scanning unit 114 further deflects the reflected light image from the document deflected by the first mirror of the first scanning unit 113 in a predetermined direction.
And a third mirror, and the first scanning unit 113
And reciprocate in parallel while maintaining a constant speed relationship. The optical lens 115 reduces the reflected light image from the document deflected by the third mirror of the second scanning unit, and forms the reduced light image at a predetermined position on the CCD line sensor 116.

The CCD line sensor 116 photoelectrically converts the formed light image sequentially and outputs it as an electric signal. The CCD line sensor 116 reads a black-and-white image or a color image, and outputs R (red), G (green), and B (blue).
This is a three-line color CCD capable of outputting line data color-separated into each color component. The document image information converted into an electric signal by the CCD line sensor 116 is further transferred to an image processing device (shown in FIGS. 2 and 3), which will be described later, and subjected to predetermined image data processing.

Next, the configuration of the image output device 210 and the configuration of each unit related to the image output device 210 will be described.

Below the image output device 210, there is provided a paper feed mechanism 211 for separating the sheets (recording media) P stored in the paper tray one by one and supplying the separated sheets P toward the image output device 210. ing. The sheets P separated and supplied one by one are conveyed to the image output device 210 with the timing controlled by a pair of registration rollers 212 disposed in front of the image output device 210. Further, the sheet P on which an image is formed on one side is re-supplied and conveyed to the image output device 210 in synchronization with the image forming timing of the image output device 210.

Below the image output device 210, a transfer and transport belt mechanism 213 is disposed. A transfer light lamp,
A first mirror for deflecting a reflected light image from the document in a predetermined direction, and reciprocating in parallel at a predetermined scanning speed while maintaining a constant distance with respect to the lower surface of the document table 111; . The second scanning unit 114 further deflects the reflected light image from the document deflected by the first mirror of the first scanning unit 113 in a predetermined direction.
And a third mirror, and the first scanning unit 113
And reciprocate in parallel while maintaining a constant speed relationship.

The optical lens 115 reduces the reflected light image from the document deflected by the third mirror of the second scanning unit, and forms the reduced light image at a predetermined position on the CCD line sensor 116. The CCD line sensor 116 sequentially photoelectrically converts the formed light image and outputs it as an electric signal.

The CCD line sensor 116 reads a black-and-white image or a color image, and outputs R (red), G (green), B
This is a three-line color CCD that can output line data that is color-separated into each color component of (blue). This CC
The document image information converted into an electric signal by the D line sensor 116 is further transferred to an image processing device (shown in FIGS. 2 and 3), which will be described later, and subjected to predetermined image data processing.

Next, the configuration of the image output device 210 and the configuration of each unit related to the image output device 210 will be described. Below the image output device 210, a sheet feeding mechanism 21 that separates sheets (recording media) P stacked and accommodated in a sheet tray one by one and supplies the separated sheets P toward the image output device 210
1 is provided. The sheets P separated and supplied one by one are conveyed to the image output device 210 with the timing controlled by a pair of registration rollers 212 disposed in front of the image output device 210. Further, the sheet p on which an image is formed on one side is re-supplied and conveyed to the image output device 210 in synchronization with the image forming timing of the image output device 210.

Below the image output device 210, a transfer and transport belt mechanism 213 is disposed. The transfer / transport belt mechanism 213 is provided between the drive roller 214 and the driven roller 215 to extend substantially in parallel with the transfer / transport belt 2.
The sheet P is electrostatically attracted to the sheet 16 and transported. Then, in the vicinity of the lower side of the transfer conveyance belt 216,
A pattern image detection unit is provided.

Further, a fixing device 217 for fixing the toner image transferred and formed on the sheet p on the sheet p is provided downstream of the transfer / conveyance belt mechanism 213 in the sheet conveyance path.
Is arranged. The sheet P passing through the nip between the pair of fixing rollers of the fixing device 217 passes through a conveyance direction switching gate 218, and is discharged by a discharge roller 219 to a discharge tray 22 attached to the outer wall of the image forming apparatus main body 1.
Drained above zero.

The switching gate 218 is connected to the sheet P after fixing.
Is selectively switched between a path for discharging the sheet P to the image forming apparatus main body 1 and a path for re-supplying the sheet P toward the image output device 210. The sheet P whose transport direction has been switched again toward the image output device 210 by the switching gate 218 is turned upside down via the switchback transport path 221 and then supplied again to the image output device 210.

The first image forming unit Pa and the second image forming unit Pb are located above the transfer belt 216 in the image output device 210 and close to the transfer belt 216.
A third image forming unit Pc and a fourth image forming unit Pd
Are arranged in order from the upstream side of the paper transport path.

The transfer conveying belt 216 is driven by a driving roller 214.
Is driven in the direction indicated by arrow Z in FIG.
As described above, the sheet P that is fed through the sheet feeding mechanism 211 is carried, and the sheet P is sequentially conveyed to the image forming units Pa to Pd.

Each of the image forming units Pa to Pd has substantially the same configuration. Each image forming unit Pa / Pb / Pc /
Pd includes photosensitive drums 222a, 222b, 222c, and 222d that are driven to rotate in the direction of arrow F shown in FIG.

Around the photosensitive drums 222a to 222d, chargers 223a, 223b, 223c and 2 for uniformly charging the photosensitive drums 222a to 222d, respectively.
23d, and developing devices 224a and 224a for developing the electrostatic latent images formed on the photosensitive drums 222a to 222d, respectively.
24b, 224c, 224d, and transfer members 225a, 225b, 225c, 225d for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper p.
Cleaning devices 226a, 226b, 226 for removing toner remaining on photoconductor drums 222a to 222d
c.226d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.

Each of the photosensitive drums 222a to 222d
Above the laser beam scanner unit 227a
227b, 227c, and 227d are provided respectively. Laser beam scanner units 227a-22
7d is a semiconductor laser device (not shown) for emitting light modulated according to image data, polygon mirrors (deflecting devices) 240a to 240d for deflecting a laser beam from the semiconductor laser device in the main scanning direction, F8 lenses 241a to 241d and mirrors 242a to 242 for forming the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d.
242d, 243a to 243d, and the like.

The laser beam scanner 227a receives a pixel signal corresponding to the black component image of the color original image, the laser beam scanner 227b receives a pixel signal corresponding to the cyan component image of the color original image, and the laser beam scanner 227c. Is a pixel signal corresponding to the image of the magenta color component of the color original image, and the pixel signal corresponding to the image of the yellow color component of the color original image is input to the laser beam scanner 227d.

As a result, an electrostatic latent image corresponding to the color-converted document image information is formed on each of the photosensitive drums 222a to 222d. The developing device 224a receives the black toner, the developing device 224b receives the cyan toner, the developing device 224c receives the magenta toner, and the developing device 224c.
24d contains yellow toner respectively, and the electrostatic latent images on the photosensitive drums 222a to 222d are:
The image is developed with the toner of each color. As a result, the image output device 210 reproduces the document image information as a toner image of each color.

Further, the first image forming unit Pa and the paper feed mechanism 2
11 is provided with a paper suction charger 228, which charges the surface of the transfer / transport belt 216 and transfers the paper P supplied from the paper feed mechanism 211.
Transports the image from the first image forming station Pa to the fourth image forming station Pd without being shifted onto the transfer / transport belt 216 without fail.

On the other hand, the fourth image portion Pd and the fixing device 217
The static eliminator 22 is provided almost directly above the drive roller 214.
9 are provided. This static eliminator has a conveyor belt 216.
An alternating current is applied to separate the paper P electrostatically attracted to the transfer conveyance belt 216 from the transfer belt 216.

In the digital color image forming apparatus having the above-mentioned structure, cut sheet-shaped paper is used as the paper P. When the paper P is sent out of the paper feed cassette and supplied into the guide of the paper feed path of the paper feed mechanism 211,
The leading end of the sheet P is detected by a sensor (not shown), and is temporarily stopped by a pair of registration rollers 212 based on a detection signal output from the sensor.

The paper P is stored in each of the image forming sections Pa to Pd.
At this time, the sheet is fed onto the transfer / transport belt 216 rotating in the direction of arrow Z in FIG. At this time, the transfer / transport belt 216 is attached to the attraction charger 22 as described above.
8, the sheet p is stably conveyed and supplied while passing through the image forming units Pa to Pd. In each of the image forming units Pa to Pd, a toner image of each color is formed, and is superposed on the support surface of the sheet P conveyed by being electrostatically attracted and conveyed by the transfer conveyance belt 216.

When the transfer of the image by the fourth image forming portion Pd is completed, the paper P is sequentially separated from the transfer / conveying belt 216 by the discharging device 229 from the leading end thereof, and is guided to the fixing device 217. . Finally, the paper P on which the toner image has been fixed is discharged onto a paper discharge tray 220 from a paper discharge port (not shown).

In the above description, the laser beam is scanned and exposed by the laser beam scanner units 227a to 227d, thereby performing optical writing on the photosensitive member. However, instead of the laser beam scanner unit, a writing optical system (LED: Light Em) including a light emitting diode array and an imaging lens array is used.
(itting diode head) may be used. L
The ED head is smaller in size than the laser beam scanner unit, and has no moving parts and is silent.
Therefore, it can be suitably used in a tandem-type digital color image forming apparatus or the like that requires a plurality of optical writing units.

FIG. 2 shows the configuration of the control unit of the image processing apparatus. The CPU 44 has an image data input unit 50, an image processing unit 60, and an image data output unit 4 via an image data bus.
2, the memory 43, the image editing unit 45, and the communication interface 47 are connected. The image data input unit 50
Is provided with a shading correction unit 51 and an input gradation correction (processing) unit 52. The image processing unit 60 includes an input processing unit 61, a color correction unit 62, an image area separation processing unit 63, a black generation /
A base removing unit 64, a spatial filter processing unit 65, and a tone reproduction processing unit 66 are provided.

With such a configuration, the image data input unit 50, the image processing unit 60, the image data output unit 42, the memory 43, the image editing unit 45, the IR interface 46, and the communication interface 47 are totally controlled by the CPU 44. In the image input device 110, a reflected light image from a document placed on a document table 111 is read as an RGB analog signal by a CCD line sensor 116, and is converted into a digital signal by an A / D (analog / digital) converter. Is converted. Then, the shading correction unit 51
, A shading correction for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image input apparatus 110 is performed.

Next, the input tone correction (processing) section 52
At the same time as adjusting the color balance of the GB reflectance signal, an input tone correction process for converting the GB reflectance signal into a signal such as a density signal that is easy to handle by the image processing system is performed. The signal subjected to the input gradation correction processing is converted into RGB signals corresponding to the three primary colors in the input processing unit 61 via the CPU 44 and then converted into CMY signals corresponding to the three primary colors. For realization, a color correction process for removing color turbidity based on the spectral characteristics of the CMY color materials including unnecessary absorption components is performed.

The black generation / background removing unit 64 subtracts the black signal for generating a black (K) signal from the three CMY color signals after color correction and the K signal obtained by the black generation from the original CMY signal. Under-color removal processing for generating a new CMY signal is performed, and the CMY three-color signal is converted into a CMYK four-color signal.

Next, the obtained image signal is subjected to a spatial filter processing by a digital filter in a spatial filter processing section 65, and the spatial frequency characteristic is corrected to prevent the output image from being blurred or grainy deterioration. It is processed as follows. Then, (after the print data is input from the communication interface 47), the output tone correction unit 66 performs an output tone correction process of converting a signal such as a density signal into a dot area ratio which is a characteristic value of the image forming apparatus. The tone reproduction processing unit 6
In step 7, a tone reproduction process (halftone generation process) for finally dividing the image into pixels and performing processing so that each tone can be reproduced is performed.

After the above-described color correction processing, in order to enhance the reproducibility of black characters or color characters, especially in a mixed document of characters and photographs, the image area separation processing section 63 executes black characters (including color characters in some cases). In the image region extracted as, the enhancement amount of the high frequency in the sharpness enhancement processing in the spatial filter processing unit 65 is increased.

At the same time, in the halftone generation processing, binarization or multi-value processing on a high-resolution screen suitable for high-frequency reproduction is selected. On the other hand, the area determined as a photograph by the image area separation processing section 63 is subjected to low-pass filtering processing for removing an input halftone dot component in the spatial filtering processing section 65. At the same time, in the halftone generation processing, binarization or multi-value processing is performed on a screen that emphasizes tone reproducibility. The image data subjected to each of the above-described processes is temporarily stored in the memory 43, read out at a predetermined timing, and input to the image output device 210.

It should be noted that image data is input to the IR interface 46 from an external image input device such as a digital camera, a digital video camera, or a portable terminal without passing through a cable. Image data is input to the communication interface 47 from a personal computer or a facsimile (not shown) via a cable, a network cable, or the like. That is, the communication interface 47 functions as a printer interface and a fax interface.

The image processing section 60 also performs predetermined image processing on the image data input from the interfaces 46 and 47. However, interfaces 46 and 4
If the image data input from 7 is a CMY signal, the processing in the input processing unit 61 is not performed. Also,
The image editing unit 45 performs an editing process on the image data stored in the memory 43 using the editing content set by operating the operation panel. Although not shown, the above-described image processing unit 60 is provided with an identification pattern adding unit (for example, connected to the tone reproduction processing unit 67) so that the characteristics of the input image data are not impaired and the visibility is improved. Alternatively, predetermined identification information may be added to the image data as a yellow (Y) image having a low image quality.

Next, the gradation correction processing performed by the input gradation correction (processing) section 52 will be described. The input tone correction (processing) section 52 is provided with tone correction setting means and input tone correction calculating means, and the input tone correction calculating means converts a signal which is a main component of a color among the RGB signals. It comprises principal component selecting means for selection, tone correction calculating means for the main component signal, and calculating means for the sub component signal.

When the user selects the gradation correction key on the liquid crystal operation panel, the RGB signals read by the image input device 110 are subjected to input gradation correction (processing) such as shading correction as shown in FIG. ) Section 52, where it selects which of the RGB signals is the color principal component signal, and then processes the color principal component signal using a lookup table or the like stored in advance in memory. Tone correction calculation processing is executed, and for color sub-component processing, calculation processing corresponding to the amount of change in the main component signal is executed. After that, the R'G'B 'signal undergoes the same color correction, black generation, background removal processing, area separation processing, spatial filter processing, output gradation correction processing, and gradation reproduction processing (halftone generation) as in the normal copy. Is output.

On the other hand, in the case of normal copying (when gradation correction processing is not performed), the RGB signals read by the image input device 110 are subjected to processing such as shading correction and the like, and then input to the input gradation correction (processing) section 52. Color correction, black generation, background removal processing, area separation processing, spatial filter processing, output gradation correction processing,
A tone reproduction process (halftone generation) is performed and output.

First, the operation principle of the input gradation correction operation means will be described. The signals read from the image input device 110 are R: 105, G: 225, B: 24
In the case of 0, the RGB signal is 255 for white and 0 for black, so the main color component signal is the smallest R signal of the RGB signals. The R signal is converted into an R ′ signal 85 by the look-up table of FIG.
The signal is processed by the following equation.

(255-F ′) = (255-F) × (2
55-S ') / (255-S) F': Color sub-component signal after gradation correction calculation processing F: Color sub-component signal before gradation correction calculation processing S ': After gradation correction calculation processing Color principal component signal S: Color principal component signal before gradation correction calculation processing <Before gradation correction processing><After gradation correction processing of the present invention> R signal: 105 (C: 150) R 'signal: 85 (C ′: 170) G signal: 225 (M: 30) → G ′ signal: 221 (M ′: 34) B signal: 240 (Y: 15) B ′ signal: 238 (Y ′: 17) The G signal is converted to a B ′ signal 238 by the G ′ signal 221. The RGB signals read by the image input device 110 are sequentially converted into R′G′B ′ signals to perform gradation correction. On the other hand, in the case of the conventional gradation correction processing, all the RGB signals are processed by the look-up table of FIG. 4 in order to perform the same processing on the RGB signals. The signal read from the image input device is R: 105,
In the case of G: 225, B: 240, the R signal 105 becomes the R 'signal 85, the G signal 225 becomes the G' signal 240, and the B signal 2
40 is converted to a B 'signal 255, and since the mixing ratio of the RGB signals changes, it can be seen that a color change occurs simultaneously with the gradation correction.

<Before floor correction processing><After conventional gradation correction processing> R signal: 105 (C: 150) R 'signal: 85 (C': 170) G signal: 225 (M: 30) → G 'Signal: 240 (M': 15) B signal: 240 (Y: 15) B 'signal: 255 (Y': 0) On the other hand, in the input tone correction calculation processing of the present invention, R
Since the gradation correction is performed without changing the mixing ratio of the GB signals, the change in the color tone can be suppressed.

In the above description, when the X signal, which is the main component of the color, is converted into the X ′ signal during the gradation correction calculation processing, the conversion is performed using the look-up table stored in the memory 43 in advance. It is also possible.
In addition to the existing look-up table stored in the memory 43, a rewritable memory is provided so that the look-up table can be set according to the user's preference.

When the user sets the look-up table, a value of 0 to 255 is read from the 17-point read value (0, 16, 32, 48, 64,..., 255) of each scanner using the numeric keypad. The setting can be made, and the user can confirm what setting value is input to the reading value of the scanner by a graph on the liquid crystal operation panel. The user can check the input tone correction γ in the graph on the liquid crystal panel and input a set value for the read value of each scanner, so that a setting error or the like can be prevented. Initial setting is the reading value of each scanner 0, 16, 32, 48, 64, ‥‥‥,
255, 0, 16, 32, 48, 64,
.., 255 are set.

However, when a general user wants to perform tone correction, it is necessary to raise the reproducibility by setting the tone of a certain part of the image or to remove the sense of gap by removing the tone of the certain part of the image. For example, it is very difficult to know which density area of the read value of the scanner corresponds to the gradation to be corrected. Therefore, an input gradation correction γ creation function is provided so that the user can easily perform desired gradation correction.

In the input tone correction .gamma. Creation function, a histogram of the density distribution of the designated area is preliminarily obtained by the press key in order to perform the tone correction of the area designated by the user in the image. The user sets the designated area by inputting the X coordinate and the Y coordinate of the upper right point, the upper left point, and the lower right point of the area to be corrected.
At this time, since the values of the X coordinate and the Y coordinate are determined using the scale attached to the document table 111, the designated area can be set from the local area to the area of the copy original large. After the execution of the prescan, only the main component signals of the colors are selected from the RGB signals, and the density distribution of the designated area is converted into a histogram. The density histogram represents the number of pixels for each of the 256 levels of density, and the one shown in FIG. 5 is created. In this density histogram, density areas a and b exceeding a certain number of pixels are defined as density areas of the area designated by the user. The number of pixels serving as a threshold value (threshold value) is obtained by the following equation based on the number of pixels in the designated area.

The number of pixels of the threshold value = the threshold value when the A4 size is specified * (the number of pixels of the specified area / the number of pixels of the A4 size) When the density area of the specified area is ab, the input floor of ab The tone correction γ can be calculated by the following equation.

X ′ = α * X + (a + b) (1−α) / 2
Where b ≦ X ≦ a, where X: signal value before gradation correction processing X ′: signal value after gradation correction processing α: gradation correction coefficient for the designated area α> 1 gradation correction γ When α <1, the gradation correction γ falls asleep b: Density area of the designated area The input gradation correction γ other than a and b (outside the density area of the designated area) passes through the origin and the point of 255 and a The input gradation correction γ and the curve are stored for the density gradations 〜b (the density area of the designated area). After the user sets the area for which gradation correction is to be performed and the gradation correction degree, when the user presses the execution button, the pre-scan is executed, and the gradation correction γ is calculated in consideration of the gradation correction of the designated area. At this time, when the confirm button is pressed, the image obtained by actually performing the input tone correction calculation processing on the pre-scan image together with the calculated input tone correction γ can be confirmed on the liquid crystal operation panel.

In the case of background removal as well, a pre-scan is executed in advance, counting is performed only when all of the RGB signals of the pixel are 240 or more, and a histogram of a density distribution of 240 or more is obtained. These are when the density region of the base is set to 240 or more. The density histogram represents the number of pixels for each density for each RGB signal, and the one shown in FIG. 6 is created.

When the number of pixels having densities 240 to 255 exceeds the threshold value, it is determined that background removal should be executed, and the average value c and standard deviation d of the densities in the density regions 240 to 255 are calculated. The obtained background removal density is the point of (cd). The above processing is performed for each of the RGB signals to obtain the background removal density point, and the RGB signal having the largest background is set as the background removal density point of the input tone correction γ.

When the background removal is performed together with the gradation correction of the user-specified area, the input gradation correction γ can be calculated by the above-described formula for the density areas a and b of the specified area. The input tone correction γ other than 〜b (outside the density area of the designated area) rises from the origin, stores the curve with the input tone correction γ of ab (the density area of the designated area), and is made at the background removal density point. The Rukoto. At this time, when the confirmation button is pressed, the image obtained by actually performing the input gradation correction arithmetic processing on the pre-scan image together with the calculated input gradation correction γ can be confirmed on the liquid crystal operation panel.

When the user actually performs the gradation correction, first, when the gradation correction button on the liquid crystal operation panel is selected,
A contrast setting key, a user setting key, and a user setting auxiliary function key are displayed, and one of the setting keys is selected according to the user's preference. Here, when the user selects the contrast setting key, setting keys from minus 4 to plus 4 are displayed so that the contrast can be adjusted in 9 steps.

The minus 4 displayed here has the weakest contrast. The closer to 0, the less the contrast becomes weaker. At 0, there is no change in contrast. Plus 4 has the strongest contrast, and the closer to 0, the smaller the degree of contrast strength. The increment of the setting key here is a uniform change.

On the other hand, when the user setting key is selected, 17
The value read by each scanner at point (0, 16, 3)
2, 48, 64,..., 255) can be set and input by the user himself using the numeric keypad. At this time, when the confirmation button is pressed, it is possible to confirm what set value has been input for the read value of the scanner by the input gradation correction γ on the liquid crystal operation panel.

Also, the user can set the value of the lookup table and simultaneously select the background removal key. When both are set and the execution button is pressed, the press key is executed, and the value set by the user and the background removal are considered. Then, the input gradation correction γ is recalculated. When the confirm button is pressed, an image obtained by actually performing input tone correction calculation processing on the pre-scan image together with the recalculated input tone correction γ can be confirmed on the liquid crystal operation panel.

When the user setting auxiliary function key is selected,
An area for which gradation correction is desired and a setting key for how to perform gradation correction of the area are displayed. The area is designated by inputting the X and Y coordinates of the upper right point, the upper left point, and the lower right point of the image to be designated. The gradation correction of this area can be adjusted in seven stages, and setting keys from plus 3 to minus 3 are displayed.

In the minus 3 displayed here, the gradient of the gradation correction γ is the steepest (gradation correction coefficient α <1). As it approaches 0, the gradient of the gradation correction γ approaches 45 degrees. The gradient of the gradation correction γ is 45 degrees (gradation correction coefficient α =
1). In the case of plus 3, the gradient of the gradation correction γ is the most steep (gradation correction coefficient α> 1). As it approaches 0, the gradient of the gradation correction γ approaches 45 degrees. The increment of the setting key here is a uniform change.

After the user sets the area to be corrected and the degree of the gradation correction, the user can simultaneously select the background removal key. When both are set, the user presses the execution button to execute the press key to execute the gradation correction of the designated area. At the same time, the gradation correction γ is calculated in consideration of the background removal. At this time, when the confirmation button is pressed, the image obtained by actually performing the input gradation correction arithmetic processing on the pre-scan image together with the calculated input gradation correction γ can be confirmed on the liquid crystal operation panel.

In the above description, a color digital copying machine using an electrophotographic process has been described as an example. However, the present invention is not limited to the above example, and information can be input from an image input means and a predetermined The present invention is also applicable to an image forming apparatus that performs image processing and outputs the result, for example, an image forming apparatus using an inkjet recording method or a sublimation recording method.

[0094]

The present invention configured as described above has the following effects.

According to the first aspect, when performing the gradation correction, the main component signal and the sub-component signal of the color are executed by different arithmetic processings. It becomes possible.

According to the second aspect, since the lookup table is used for color gradation correction, there is no need to perform complicated arithmetic processing, the processing speed and the circuit scale can be reduced, and the usability is improved. And the size of the device can be reduced.

According to the third aspect, since the user himself creates the look-up table, the user can execute the desired tone correction without preparing a large number of existing tone corrections γ.

According to the fourth aspect, it is possible to confirm the gradation correction γ and the preview image processed by the gradation correction γ on the liquid crystal operation panel, so that an operation error can be prevented.

According to the fifth aspect, by using the tone correction γ creation function, the tone can be easily corrected as desired by the user.

According to the sixth aspect, by using the tone correction γ creation function, the tone can be easily corrected as desired by the user.

According to claim 7, the user can select the tone correction γ.
By using the creation function, it is possible to easily and accurately perform gradation correction for removing the background.

According to the eighth aspect, the user can select the tone correction γ.
By using the creation function, it is possible to easily and accurately perform gradation correction for removing the background.

According to the ninth aspect, it is possible to combine the user's favorite tone correction and the background removal, so that the tone correction as desired by the user can be easily performed.

According to the tenth aspect, it is possible to confirm the gradation correction γ and the preview image processed by the gradation correction γ on the liquid crystal operation panel, so that an operation error can be prevented.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a color image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram of the control system.

FIG. 3 is an explanatory diagram of the gradation correction process.

FIG. 4 is a diagram showing an example of a look-up table used for the gradation correction calculation means.

FIG. 5 is a diagram showing an example of a density histogram of an area designated by the user.

FIG. 6 is a diagram illustrating an example of a density histogram in a background density region of each of the RGB signals.

[Explanation of symbols]

 52-input tone correction unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H04N 1/46 H04N 1/46 Z (72) Inventor Toshihiro Kaneda 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term within Sharp Corporation (reference) 2C262 AA04 AA24 AA26 AB13 AB17 AC04 AC08 BA05 BA09 BB03 BC01 EA02 FA14 GA19 5B057 AA11 BA02 BA24 BA25 BA26 BA30 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CC01 CE11 DC18 CH17 DA08 5C077 LL16 LL17 MM20 MP08 NN04 PP15 PP25 PP32 PP33 PP57 PP68 PQ08 PQ19 PQ23 SS05 SS07 TT06 5C079 HB01 JA04 LA12 LA21 LA31 MA05 MA11 MA17 NA05 NA09 NA19 NA27 NA29

Claims (11)

[Claims] 1. A color image forming apparatus for adjusting the color of an RGB signal from a color input image device such as a scanner and outputting the same, wherein an input for performing tone correction on the color image according to a user's preference. A gradation correction unit is provided, the input gradation correction unit includes a gradation correction setting unit and an input gradation correction calculation unit, and the input gradation correction calculation unit includes: A color image forming apparatus comprising: a main component selection unit for selecting a signal; a tone correction calculation unit for a main component signal; and a calculation unit for a subcomponent signal. 2. The conversion process from the main component signal X to X ′, which is performed by the input tone correction calculation means for image quality adjustment, uses a look-up table stored in a memory or the like in advance. 2. The color image forming apparatus according to claim 1, wherein the conversion process from the sub-component signal Y to Y 'is performed by the calculation unit in accordance with the amount of change of the main component. 3. In the conversion processing of the main component signal from X to X 'performed by the input gradation correction calculation means for image quality adjustment, the look-up is performed so that the user can adjust the image quality as desired. 3. The color image forming apparatus according to claim 2, wherein the table is stored in a rewritable memory. 4. A lookup table used in a conversion process of a main component signal from an X signal to an X ′ signal, which is performed by the input tone correction calculation means for image quality adjustment, so that a user can confirm the lookup table. 4. The color image forming apparatus according to claim 2, wherein the image is displayed on a liquid crystal operation panel. 5. When creating the look-up table,
The lookup table can be created by arithmetic processing so that the user can specify in advance the area and the degree of gradation of the image part to be corrected, and pre-scan, so that the gradation of the area can be adjusted. The color image forming apparatus according to claim 2, wherein 6. When creating the look-up table,
Mainly, the size of the area of the image part you want to
The image forming apparatus according to claim 5, wherein the image forming apparatus can be selected according to a user's request. 7. When creating the look-up table,
7. The color image forming apparatus according to claim 2, wherein the look-up table is created by reading a base by a press key and performing an arithmetic processing to remove the base. 8. When a background is read by a press scan, a histogram is created for each density section, and when a value of the histogram exceeds a predetermined threshold, a standard deviation before and after a peak of the histogram is obtained. 8. The color image forming apparatus according to claim 7, wherein the look-up table is created by performing arithmetic processing so as to completely remove the base. 9. A conversion process of converting a main component signal from X to X 'for adjusting an image according to claim 3 and an arithmetic process for removing a background according to claim 7 together. A color image forming apparatus capable of creating the look-up table. 10. A look-up table is created by performing the arithmetic processing for adjusting the gradation according to claim 5 and the arithmetic processing for removing the background according to claim 7. A color image forming apparatus characterized in that it is possible. 11. An arithmetic processing for adjusting a gradation according to claim 5, an arithmetic processing for removing a background according to claim 7, or an arithmetic processing for creating a look-up table according to claim 9. In the case where the arithmetic processing and the press-scan have been executed, after completing the creation of the look-up table, the pre-scanned image is subjected to the arithmetic processing for tone correction by the tone correction arithmetic means, A color image forming apparatus characterized in that a processed image can be confirmed on a liquid crystal operation panel.