JP2004248095A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor capable of eliminating a background without requiring prescanning and without recognizing a highlight area of continuous tone as a background. <P>SOLUTION: An evaluation result, a determination result and a judgement result are inputted to a background determining circuit 314. Then, whether a pixel block is a background part or not is determined on the basis of these results. A background density storage circuit 316 stores the background density, a background candidate value and the determination result are inputted, and the stored background density is rewritten to the background candidate value in accordance with the determination result. A delay circuit 304 delays an inputted image signal for the size of the pixel block and outputs the delayed image signal to a background eliminating circuit 318, The background density 311 is also inputted to the background eliminating circuit, and the background eliminating circuit corrects and outputs the image signal in accordance with the background density. This correction controls conversion characteristic inclination so as to make an image signal value that is equal to detected background density to be fixed as shown in Fig. and performs correction by the conversion characteristic. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image processing apparatus that detects background density based on input image data and performs background removal in accordance with the background density, and more particularly, to a document reading mechanism such as an image scanner, a facsimile, and a digital copying machine. And an image processing apparatus having the same.
[0002]
[Prior art]
There are various types of originals handled by an image scanner, a facsimile, a digital copying machine, and the like, and the background density of the originals covers a wide range. On the other hand, if the output is performed while the background of the document is read, the image quality may be deteriorated as a whole. For this reason, in these apparatuses, background removal has been conventionally performed in which the background density of a document is uniquely detected and a portion having a background density or less is erased.
[0003]
[Patent Document 1] Japanese Patent No. 3134292
This document targets a document in which a plurality of independent background densities are mixed, such as a newspaper or a magazine cut and pasted on a white paper, and obtains the respective regions from the density histogram of the image data created by the prescan. In the main scan, the image to be processed is used to determine which of the detected background densities corresponds to the detected background density from the image data, and to perform the background removal processing according to the determined background density. A processing device is disclosed.
[Patent Document 2] JP-A-2002-94795
This document discloses a device that detects background density without performing pre-scanning and has means for storing background density, and calculates a difference between the background density of image data brighter than the stored background density and the background density for each line. An image processing apparatus that performs a background removal process while updating the background density of the next line based on the totaled difference and the stored background density, and updating the background density in a direction to darken at a fixed rate. Is disclosed.
[Patent Document 3] Japanese Patent Application Laid-Open No. 7-47952
This document discloses an image processing apparatus that detects a pixel that is not included in a pattern highlight area with a low density as a background pixel and performs background removal processing while updating the background density.
[Patent Document 4] JP-A-7-264409
This document discloses an image processing apparatus that performs background removal processing while maintaining the density of pixels detected as background by the image area separation unit as background density.
[0004]
[Problems to be solved by the invention]
By the way, variations in the background density in image data obtained by reading a document include two-dimensional variations in addition to those caused by the type of document. This means that the background density of the original document itself is not always uniform, the original document is bent, the floating of the original document due to saddle stitching such as a book original, the influence of flare caused by black solids around the document, and the reading This is due to mechanical variations of the mechanism, etc., and has a feature of continuously changing.
In recent years, there has been an increasing demand for higher image quality, especially for the highlight reproducibility of the image portion. However, since such a two-dimensional fluctuation of the background density could not be excluded, a sufficient response could not be achieved until now. I didn't.
For example, the technique disclosed in Japanese Patent Application Laid-Open No. H11-157572 has a problem that an original document cannot be processed at a high speed because of an extra operation called pre-scanning, and a plurality of independent background densities such as cut and pasted original documents exist. There is a drawback that the effect is exhibited only in such a case, and it cannot cope with a continuous change in the background density.
Further, the technique disclosed in Patent Document 2 updates the background density in units of lines, so that a strong directionality occurs and cannot respond to two-dimensional variations in the background density. There was a drawback that the response was poor because of updating.
[0005]
Further, in the technique disclosed in Patent Document 3, the detection of a picture highlight area is performed on the condition that a place where density fluctuation is large. This is because the printing halftone dot is targeted, and the highlight area of the continuous tone image cannot be detected. For this reason, there is a disadvantage that a highlight portion of a silver halide photograph or the like is recognized as a background and is removed.
Further, the technique disclosed in Patent Document 4 relies on an image area separation unit for recognition of a background portion. However, image area separation is originally performed because a filter processing such as edge enhancement or smoothing is performed on a necessary portion. It is a technology developed in Japan. For this reason, both have the drawback that the discrimination performance between the continuous tone region where smoothing is desirable and the background portion is low. In fact, also in this embodiment, the continuous tone area determination condition is based on the condition that there is a density change at an intermediate density, and in the same manner as described above, a highlight portion of a silver halide photograph or the like is recognized as a background and removed. There was a drawback that it would.
Accordingly, an object of the present invention is to provide an image processing apparatus which does not require a pre-scan, can follow two-dimensional fluctuations, and can perform background removal without recognizing a continuous tone highlight area as background. It is to be.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, a background density detecting unit that detects a background density of an image based on color image data including a plurality of color components, and the color image based on the background density detected by the background density detecting unit. A background density correction unit that corrects data, the background density detection unit includes a storage unit that stores the background density, and an image in each region when the main scanning direction is divided into a plurality of regions. Evaluation means for evaluating the flatness of data for each color component; extraction means for extracting a representative value of image data in an area where flatness is evaluated by the evaluation means; background density stored in the storage means; Comparing means for comparing a difference between the representative value extracted by the means with a predetermined threshold value; and a background density based on the background density stored in the storage means and the representative value extracted by the extracting means. Prediction means for predicting, the storage means stores the background density predicted by the prediction means in accordance with the evaluation result by the evaluation means and the comparison result by the comparison means, and the background density correction means The object is achieved by correcting color image data based on the background density predicted by the prediction means stored in the storage means.
According to a second aspect of the present invention, in the first aspect of the invention, the comparison by the comparing unit is performed for each color component extracted by the extracting unit.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a diagram schematically showing a mechanical section of a copying machine according to an embodiment of the present invention, and FIG. 2 is a diagram schematically showing an electrical section of the copying machine shown in FIG.
As shown in FIG. 1, the mechanism of the copying machine mainly includes a scanner unit 101 for reading a document and a printer unit 102 for recording an image on a recording sheet.
First, paying attention to the scanner unit 101, the document 103 is placed at a predetermined position on the platen 104, and is irradiated by the halogen lamps 105-1 and 105-2. The reflected light from the document 103 passes through a first mirror 106, a second mirror 107, a third mirror 108, and a lens 109, and forms an image on a CCD 110, which is a three-line color line image sensor. Photoelectric conversion is performed.
[0008]
Here, the halogen lamps 105-1 and 105-1 and the first mirror 106 are mounted on a first carriage (not shown), and the second mirror 107 and the third mirror 108 are mounted on a second carriage (not shown). The first and second carriages move from left to right at a speed ratio of 2: 1 by a carriage drive motor (not shown). Thus, the entire surface of the document placed on the platen 104 is scanned.
The image signal photoelectrically converted by the CCD 110 is subjected to various processes by an image processing unit 111 and the like, and then input to an LD (laser diode) (not shown) of the printer unit 102, where it is converted into a laser beam. Is done.
[0009]
Paying attention to the printer unit 102, the laser light emitted from the LD is reflected by the polygon mirror 112, passes through the fθ lens 113 and the fourth mirror 114, and is transferred to the photosensitive drum 115 rotating counterclockwise. An image is illuminated on the surface. Here, the polygon mirror 112 is fixed to the rotation axis of the polygon motor 116, and the polygon motor 116 rotates at a constant speed to rotate the polygon mirror 112. The rotation of the polygon mirror 112 causes the laser light to scan in a direction perpendicular to the rotational movement direction of the photosensitive drum 115, that is, in a direction along the drum axis.
The surface of the photosensitive drum 115 is charged in advance to a uniform positive potential by a charging charger 117 connected to a high voltage generator (not shown). When the laser beam is applied to the photosensitive drum 115, the charge on the surface flows to the equipment ground of the drum main body due to the photoconductive phenomenon and disappears.
Here, the LD with a light document density is weakly lit, and the LD with a high document density is strongly lit. As a result, an electrostatic latent image corresponding to the density of the document is formed on the surface of the photosensitive drum 115 by the main scanning by the polygon mirror 112 and the sub-scanning by the rotation of the photosensitive drum 115.
[0010]
The developing unit 118 has developing units K, C, M, and Y that respectively store black, cyan, magenta, and yellow positively charged toners, and any one of the developing units is selected.
The selected developing unit is biased to a predetermined positive potential by a high-voltage generator (not shown), develops the electrostatic latent image, and forms a toner image corresponding to the density of the document on the surface of the photosensitive drum 115.
The transfer belt 119 is biased to a predetermined negative potential by a high-voltage generator (not shown), and rotates clockwise at the same speed as the photosensitive drum 115. Further, while the photosensitive drum 115 and the transfer belt 119 approach each other, the toner image is attracted by the action of the bias and transferred to the surface of the transfer belt 119.
[0011]
The reading of the document, the formation of the electrostatic latent image, the formation of the toner image, and the transfer operation of the toner image are repeated a required number of times. That is, in the case of each mode of full color, original color, and registered color, the operation is performed four times, the developing units are selected in the order of K, C, M, and Y, and the formed toner images are aligned. They are superposed on the surface of the transfer belt 119. In the case of each of the black, cyan, magenta, and yellow modes, the operation is performed only once, and the developing units K, C, M, and Y are selected.
In each of the red, green, and blue modes, the operation is performed twice, and the developing units are selected in the order of M and Y, C and Y, and C and M, and the formed toner images are aligned. Is superimposed on the surface of the transfer belt 119.
[0012]
On the other hand, the recording papers 121-1 and 121-2 are stored in the paper feed cassettes 120-1 and 120-1, respectively, and one of the paper feed cassettes is selected. The recording paper 121-1 of the selected paper feed cassette, for example, the paper feed cassette 120-1 is fed out by the paper feeding operation of the paper feed roller 122-1 and reaches the registration rollers 123-1 and 123-1.
The registration rollers 123-1 and 123-2 are stopped at first, and start rotating at a predetermined timing in accordance with the position of the toner image on the rotating transfer belt 119, and send out the recording paper.
The transfer charger 124 is connected to a negative voltage generator (not shown), and the toner image on the transfer belt 119 is retransferred to the fed recording paper by the action of the transfer charger 124. When the toner image is re-transferred to the recording paper, the bias of the transfer belt 119 is released to promote the re-transfer.
[0013]
The recording paper on which the toner image has been retransferred is sent to the heat fixing units 125-1 and 125-2, where the toner image is fixed to the recording paper and discharged outside the apparatus.
The toner remaining on the surface of the photosensitive drum 115 after the transfer is removed by the cleaning unit 126, and the photosensitive drum 115 is prepared for the next operation. Further, even after the retransfer, the toner remaining on the surface of the transfer belt 119 is removed by the cleaning unit 127, and the transfer belt 119 is prepared for the next operation.
[0014]
Next, referring to FIG. 2, the electrical unit of the copying machine mainly includes an operation display for detecting and displaying inputs such as the scanner unit 101, image processing unit 111 and printer unit 102, and processing mode selection. The copier 202 is divided into a unit 201 and a system control unit 203 which communicates with a control circuit of each unit to control the overall operation of the copying machine 202.
The copier 202 is connected to a LAN (local area network) connection device 204, and is connected to another device such as a workstation 206 or a personal computer 207 connected to the LAN 205 via the LAN connection device 204. Input and output image signals.
[0015]
Paying attention to the scanner unit 101, the above-described CCD 110 separates the incident light into red, green, and blue, photoelectrically converts the incident light, and outputs three types of analog image signals to an A / D (analog / digital) conversion circuit 208. The A / D conversion circuit 208 converts the input image signals into digital signals, and corrects the unevenness in illumination of the originals of the halogen lamps 105-1 and 105-2 and the unevenness in the sensitivity of the light receiving elements in the CCD 110. Processing such as shading correction and correction for dark current is also performed.
The scanner control circuit 209 communicates with the system control unit 203 and controls the entire scanner unit 101. For example, it controls the operation of the A / D conversion circuit 208, the lighting control of the halogen lamps 105-1 and 105-2, and the rotation control of the carriage drive motor 210. The document size sensor 211 is a sensor that detects the size of a document placed on the platen 104, and outputs the detection result to the scanner control circuit 209.
[0016]
On the other hand, the image signal converted by the A / D conversion circuit 208 is input to the background removal circuit.
The background removal circuit detects the background density of the document based on the input image signal and performs correction according to the density. The corrected image signal is input to the γ conversion circuit 212.
The γ conversion circuit 212 is also connected to the LAN connection device 204, and performs gradation conversion of an image signal input from the A / D conversion circuit 208 or the LAN connection device 204 into an image signal proportional to density or the like. The signals are output to the separation circuit 213, the area control circuit 214, the delay circuit 230, and the filter circuit 215. Depending on the setting, the γ-conversion circuit 212 may perform gradation conversion on the image signal input from the A / D conversion circuit 208 and output it to the LAN connection device 204.
[0017]
The image area separation circuit 213 is a circuit that determines whether or not the image part being processed is a line drawing such as a character, and whether it is a monochrome image or a color image based on the input image signal. Is output to the filter circuit 215.
The region control circuit 214 is a circuit that stores the input image signal and generates a switching signal for performing different image processing for each partial region of the image, and outputs the generated switching signal to the delay circuit 230. I do.
The area control circuit 214 has a binarization circuit for binarizing the image signal from the γ conversion circuit, a dual-port image memory for storing the binarized image signal, and outputs the stored data as a switching signal. It comprises a dual-port area memory, a transmission circuit for transmitting image signals to the operation display unit 201, and the like.
[0018]
The image memory 602 and the area memory 604 can be accessed from an image processing control circuit 219 described later.
The filter circuit 215 is a circuit that subjects the image signal from the γ conversion circuit 212 to two-dimensional filter processing such as edge enhancement and smoothing, and outputs the result. These processes are controlled by the determination signal and the switching signal. For example, if the determination signal is a line image, edge enhancement is performed, and if the determination signal is a non-line image, a filter process of smoothing is performed.
In addition, the switching signal may perform edge enhancement or smoothing filter processing regardless of the determination signal.
[0019]
The color correction circuit 216 performs a color correction process for converting the image signal from the filter circuit 215 into a toner recording amount corresponding to the developing device selected as described above. This process is controlled by the determination signal and the switching signal. For example, the conversion signal is converted into a toner recording amount suitable for a full-color mode or a black mode in accordance with the switching signal. For example, the conversion may be performed such that the UCR (under color removal) rate is set to 100%, and the UCR rate is set to 70% for a non-line drawing or a color image.
Further, there may be a case where a filling process for outputting a fixed image signal value or a determination signal value in response to a switching signal, a color erasing process for erasing a specific color, and a color conversion process for changing a specific color to another color are performed.
[0020]
From the color correction circuit 216, one type of image signal converted to the toner recording amount, a determination signal, and a switching signal are output and input to the scaling circuit 217.
The scaling circuit 217 is a circuit that performs scaling processing for enlarging / reducing three types of signals from the color correction circuit 216 in the main scanning direction.
The scaling process for enlarging / reducing a document in the sub-scanning direction is performed by controlling the rotation of the carriage drive motor 210 described above.
[0021]
The gradation processing circuit 218 performs gamma correction processing for correcting recording characteristics (image signal vs. toner recording amount characteristics) of the printer unit 102 that fluctuates due to temperature, humidity, and the like, and one or several pixels in the main scanning direction and the sub-scanning direction. One or several pixels are defined as one unit, and gradation processing or the like for performing gradation expression with emphasis on resolution or gradation is performed. Here, the γ correction processing and the gradation processing are controlled by the above-described determination signal and the switching signal. For example, if the determination signal is a line drawing, the gradation processing that emphasizes the resolution is performed. Performed gradation processing. Further, since the above-described recording characteristics change depending on the type of gradation processing, different gamma correction processing is performed in conjunction with the gradation processing.
Further, a predetermined gradation process or a γ correction process may be performed by the switching signal regardless of the determination signal. Note that the gradation processing circuit 218 is also connected to the LAN connection device 204, and outputs the image signal subjected to the above processing or the image signal input from the LAN connection device 204. Further, depending on the setting, the gradation processing circuit 218 may output the processed image signal to the LAN connection device 204 in some cases.
[0022]
The image processing control circuit 219 communicates with the system control unit 203 and, in response to a request from the system control unit 203, the above-mentioned γ conversion circuit 212, image area separation circuit 213, area control circuit 214, delay circuit 230, The settings of the filter circuit 215, the color correction circuit 216, the scaling circuit 217, and the gradation processing circuit 218 are performed, and the entire image processing unit 111 is controlled.
On the other hand, the image signal output from the gradation processing circuit 218 is input to the LD control circuit 220 of the printer unit 102. The LD control circuit 220 drives the LD 221 by performing pulse width modulation, power modulation, and the like according to the input image signal, thereby adjusting the lighting intensity of the LD 221.
[0023]
The printer control circuit 222 communicates with the system control unit 203 and controls the entire printer unit 102. For example, the LD control circuit 220 is controlled to forcibly turn off the LD 221, the polygon motor 116, the motor 223 that drives the photosensitive drum 115 to rotate, the motor 224 that drives the transfer belt 119 to rotate, and the like. Control of the devices K, C, M and Y, output control for each load of the high-voltage power supply 225 (for example, charging charger 117, developing device, transfer belt 119, transfer charger 124, etc.), and heat fixing units 125-1 and 125-2. Perform temperature control and the like. The printer unit 102 has a paper size sensor 226 for detecting the size of the stored recording paper for each of the above-mentioned paper feed cassettes 120-1 and 120-2, and the detection result is sent to the printer control circuit 222. Has been output.
[0024]
The operation display unit 201 has a TPD (touch panel display) 227 in which a display unit that displays options and setting states of various modes, a read document image, and the like, and a detection unit that detects a pressed position of the display unit are integrated. , A keyboard 228 for inputting the number of copies, the start of copying, and the like, an operation display control circuit 229, and the like. The operation display control circuit 229 displays options in each mode on the TPD 227 to prompt a key input or the like, detects an input from the TPD 227 and the keyboard 228, displays a state set in the TPD 227, and performs system control. It communicates with the unit 203 to transmit an input result and the like.
An image signal of a read document or the like is transmitted via the above-described area control circuit 214 and stored in the TPD 227.
[0025]
Next, FIG. 3 is a diagram showing details of the above-described background removal circuit 318.
As shown in FIG. 3, an image signal 301 is an evaluation circuit 302 for evaluating the flatness of the image signal for each color component, and an extraction circuit for extracting a representative value of the image signal in the area where the flatness is evaluated for each color component. 303 and a delay circuit 304.
The evaluation circuit 302 evaluates the flatness of the image signal of the background portion of the document because the image signal shows a flat characteristic. The maximum value and the minimum value of are respectively detected, and these differences are compared with a predetermined threshold value.
[0026]
This detection / comparison is performed for each component of the image signal. When each difference is smaller than the threshold value determined for each component, the image signal is evaluated as flat, and the evaluation result 305 is output.
Also, the background portion of the document has a bright signal value while the image signal is flat. The extraction circuit 303 is a circuit for extracting the representative value of the image signal in the pixel block as described above. In the present embodiment, the extraction circuit 303 extracts the average of each component of the image signal in the pixel block as the representative value and outputs the result as the extraction result 306 I do.
The extraction result 306 is input to the first comparison circuit 307, the second comparison circuit 308, and the candidate value calculation circuit 309.
[0027]
The first comparison circuit 307 is a circuit for determining brightness, which is a characteristic of the background portion of the document, and compares the extraction result 306 with a predetermined threshold. This comparison is performed for each component of the extraction result 306. When each of the threshold values is larger than the threshold value determined for each component, it is determined that the image is bright, and a determination result 310 is output.
The detected background density 311 is also input to the second comparison circuit 308. The background density of an original varies depending on the type of paper used, and thus has a range.
On the other hand, a light image portion exists in a document, and in the case of a document having a low background density, the density of the light image portion may be brighter than the background density of a document having a high background density.
The second comparison circuit 308 is a circuit for detecting such a light image portion, and compares the extraction result 306 with the detected background density 311. This comparison is performed for each component. When the result obtained by subtracting the extraction result 306 from the background density 311 is larger than a predetermined threshold, the image is determined to be a light image portion, and the determination result 312 is output.
[0028]
The detected background density 311 is also input to the candidate value calculation circuit 309, and the candidate value calculation circuit 309 calculates a weighted average of both, and outputs a background candidate value 313. The evaluation result 305, the determination result 310, and the determination result 312 are input to the background determination circuit 314. Based on these, the background determination circuit 314 determines whether the above-described pixel block is the background portion. That is, when the image portion is not a flat, bright and pale image portion, it is determined to be a background portion, and a determination result 315 is output.
The background density storage circuit 316 is a circuit that stores the above-described detected background density 311, and receives the above-described background candidate value 313 and the determination result 315, and stores the background density 311 stored according to the determination result 315. Rewrite the background candidate value 313. That is, if the background is determined, the background value is updated to the background candidate value 313, and the background density 311 that cannot be determined as the background is maintained. The background density stored in the background density storage circuit 316 is initialized at the beginning in the main scanning direction, and is maintained until the next determination is performed.
[0029]
On the other hand, the delay circuit 304 delays the input image signal by the size of the above-described pixel block, and outputs the delayed image signal to the background removal circuit 318.
The background density 311 is also input to the background removal circuit 318, and the background removal circuit 3186 corrects and outputs an image signal according to the background density 311. In this correction, for example, as shown in FIG. 4, the gradient of the conversion characteristic is controlled so that the image signal value equal to the detected background density is constant, and the correction based on the conversion characteristic is performed.
[0030]
【The invention's effect】
According to the first and second aspects of the present invention, it is possible to follow a two-dimensional variation without requiring a pre-scan, and to perform background removal without recognizing a continuous tone highlight area as background.
[Brief description of the drawings]
FIG. 1 is a view schematically showing a mechanism of a type of copying machine embodying the present invention.
FIG. 2 is a diagram schematically showing an electrical unit of the copying machine shown in FIG.
FIG. 3 is a diagram illustrating details of a background removal circuit.
FIG. 4 is a diagram illustrating a relationship between a detected background density and a change characteristic.
[Explanation of symbols]
101 Scanner unit
102 Printer unit
103 manuscript
104 Platen
105-1 Halogen lamp
105-2 Halogen lamp
106 First mirror
107 Second mirror
108 Third mirror
109 lens
110 CCD
111 Image processing unit
112 polygon mirror
113 fθ lens
114 4th mirror
115 Photoconductor drum
116 Polygon motor
117 Charger
118 Developing unit
119 Transfer belt
120-1 Paper cassette
120-2 paper cassette
121-1 Recording paper
121-2 Recording paper
122-1 Paper feed roller
123-1 Registration Roller
123-2 Registration Roller
124 Transfer Charger
125-1 Thermal fixing unit
125-2 Thermal fixing unit
126 cleaning unit
127 cleaning unit
201 Operation display unit
202 Copier
203 System control unit
204 LAN (Local Area Network) Connection Device
205 LAN
206 Workstation
207 Personal computer
208 A / D conversion circuit
209 Scanner control circuit
210 Carriage drive motor
211 Original size sensor
212 γ conversion circuit
213 Image area separation circuit
214 area control circuit
215 Filter circuit
216 color correction circuit
217 Magnification circuit
218 gradation processing circuit
219 Image processing control circuit
220 LD control circuit
221 LD
222 Printer control circuit
223 motor
224 motor
225 High voltage power supply
226 Paper size sensor
227 TPD (Touch Panel Display)
228 keyboard
229 Operation display control circuit
301 image signal
302 Evaluation circuit
303 Extraction circuit
304 delay circuit
305 Evaluation result
306 Extraction result
307 first comparison circuit
308 Second comparison circuit
309 Candidate value calculation circuit
310 Judgment result
311 Background density
312 Judgment result
313 Background value
314 Background judgment circuit
315 Judgment result
316 background density memory circuit
318 Background Removal Circuit
319 Background detection circuit

Claims (2)

Background density detection means for detecting the background density of an image based on color image data composed of a plurality of color components;
A background density correction unit that corrects the color image data based on the background density detected by the background density detection unit;
The background density detection means,
Storage means for storing background density;
Evaluation means for evaluating the flatness of image data in each area for each color component when the main scanning direction is divided into a plurality of areas,
Extracting means for extracting a representative value of image data in an area for which flatness has been evaluated by the evaluating means;
Comparison means for comparing a difference between the background density stored in the storage means and the representative value extracted by the extraction means with a predetermined threshold,
Prediction means for predicting the background density based on the background density stored in the storage means and the representative value extracted by the extraction means,
The storage unit stores the background density predicted by the prediction unit according to the evaluation result by the evaluation unit and the comparison result by the comparison unit,
The image processing apparatus according to claim 1, wherein the background density correction unit corrects the color image data based on the background density predicted by the prediction unit stored in the storage unit. 2. The image processing apparatus according to claim 1, wherein the comparison by the comparing unit is performed for each color component extracted by the extracting unit.

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