JP4559128B2 - Image processing method, image processing apparatus, and computer program - Google Patents

Description

  The present invention relates to an image processing method, an image processing apparatus, and a computer program for realizing the image processing apparatus for reducing the density of a background included in an image obtained by optically reading a document.

  Conventionally, when a document image is read by an image reading device such as a scanner device, and print output is performed by the image forming device based on the read image data, if the read image data is output as it is by the image forming device, Phenomenon such as show-through may occur. For this reason, it is common to detect background fog or show-through in the read image data before output by the image forming apparatus, and perform density adjustment based on the detection result to remove the background. (For example, refer to Patent Documents 1 and 2).

  FIG. 10 is a flowchart showing a conventional background correction procedure. First, an original is scanned in the image reading device (step S21), and input image data from the image reading device is converted to be linear with respect to the density (step S22). Then, the background is detected from the converted image data (step S23). For example, in the method described in Patent Document 1, when the difference between the maximum value and the minimum value of RGB data is smaller than a predetermined threshold value, the minimum value of RGB data is extracted as a background candidate, and one of these is extracted. The smallest value is detected as the background density.

Next, it is determined whether or not a background is detected (step S24). If a background is detected (S24: YES), a background removal table is selected according to the detected background level (background density) (step S25). When the background is not detected (S24: NO), a table without background removal is selected (step S26). Then, density conversion is performed on the converted image data using the selected table (step S27), and the background is removed.
JP-A-11-27550 JP 2003-51946 A

In the above-described flowchart, the process of converting the RGB data with linear reflectance into the data with linear density is performed in the previous stage (step S22) in which the background is detected. In this process, the reflectance is R and the density is converted. If is D, it can be realized by performing the gamma correction according to the gamma curve represented by D = -log ₁₀ R. This gamma correction is generally a correction suitable for image reproduction, and tends to have poor gradation in the highlight area (low density area). However, since the highlight area information is important for the detection of the background area, if the background is detected using an image in which the gradation of the highlight area has been degraded by gamma correction, the background is detected well. There is a problem that it may not be possible.

  The present invention has been made in view of such circumstances, and performs a gamma correction using a first gamma value on an input image signal to generate a first correction signal, and based on the generated first correction signal. A background area is detected, gamma correction using a second gamma value different from the first gamma value is performed on the input image signal to generate a second correction signal, and the background area is generated with respect to the generated second correction signal. By performing a density conversion process according to the detection result, image processing can be performed to adjust the density of the background after successfully detecting the background area included in the input image It is an object to provide a method, an image processing apparatus, and a computer program for realizing the image processing apparatus.

An image processing method according to the present invention is an image processing method for detecting a ground region included in an image constituted by an input image signal based on the input image signal and performing image processing according to the detection result. A first table defining a correspondence relationship between a density value of the input image signal and a density value of the first correction signal to be generated to perform gamma correction using the value, and a first table different from the first gamma value. A second table that prescribes the correspondence between the density value of the input image signal and the density value of the second correction signal to be generated to perform gamma correction using a gamma value of 2. for the second table, Yes previously stored, generating a first table by adding the difference data indicating the difference between the first and second tables, using the first table has been made live Before Generating a first correction signal from the input image signal, and detecting a background area of the image based on the generated first correction signal, the input image using a second table which is stored in advance The method includes a step of generating a second correction signal from the signal, and a step of performing density conversion processing on the generated second correction signal in accordance with the detection result of the background region.

  In the present invention, the gamma correction performed in the previous stage for detecting the background area and the gamma correction performed in the previous stage for performing the density conversion process according to the detection result of the background area are executed using different gamma values. Therefore, it is possible to set a gamma value suitable for detecting the background area and a gamma value suitable for generating an output image, respectively, so that the background area can be accurately detected and the background density is set appropriately. An output image adjusted to be obtained.

An image processing apparatus according to the present invention detects a background area included in an image formed by an input image signal based on the input image signal, and performs image processing according to the detection result. First correction means for performing gamma correction using the value on the input image signal, second correction means for performing gamma correction using a second gamma value different from the gamma value on the input image signal, and the input image Means for storing a second table for defining a correspondence relationship between the density value of the signal and the density value of the second correction signal to be generated; and the second table and the input image signal are stored in advance. means for generating a first table by adding the difference data indicating the difference between the first table defining the correspondence between the density value of the first correction signal to be generated and the concentration value in the second table with Wherein the first and second correction means, Yes as performs gamma correction using the first and second table respectively, the first correction signal obtained by correcting the first correction means Detection means for detecting a background area of the image based on the image data; and means for performing density conversion processing on the second correction signal obtained by correction by the second correction means according to the detection result of the detection means; It is characterized by having.

  In the present invention, the first correction means for performing gamma correction using the first gamma value in the previous stage of detecting the background area, and the second stage in the previous stage of performing the density conversion processing according to the detection result of the background area. Since a second correction unit that performs gamma correction using a gamma value is provided, it is possible to set a gamma value suitable for detecting a background area and a gamma value suitable for generating an output image. Thus, the background area is detected with high accuracy, and an output image in which the density of the background is appropriately adjusted is obtained.

  In the image processing apparatus according to the present invention, the first gray level of the image based on the first correction signal in the area corresponding to the background area is larger than the gray level of the image based on the second correction signal. And a second gamma value is defined.

  In the present invention, the gamma value of the gamma correction executed by the first correction unit is determined so that the number of gradations in the region corresponding to the background region increases, so that the image corrected by the first correction unit is The number of gradations in the low density area (highlight area) corresponding to the background area can be increased, and the background area can be detected with high accuracy by the detection means at the subsequent stage.

  In the present invention, one of the table used for gamma correction by the first correction unit or the table used for gamma correction by the second correction unit is stored, and the other is generated from the stored table. Therefore, it is not necessary to store two types of tables such as a lookup table, and one of them only needs to be stored as difference data, so that an increase in the amount of data can be suppressed.

  In the present invention, one of the function used for gamma correction by the first correction unit or the function used for gamma correction by the second correction unit is stored, and the other is generated from the stored function. Therefore, it is necessary to store two types of functions, and an increase in data amount can be suppressed.

  The image processing apparatus according to the present invention includes means for outputting an image obtained by performing the density conversion process on the second correction signal.

  Since the present invention includes means for outputting an image obtained by performing density conversion processing, it can be applied to a printer device and a digital multifunction peripheral.

  The image processing apparatus according to the present invention further includes means for reading an image of a document, and generates an image to be output based on the image read by the means.

  In the present invention, since an image of a document is read and an image to be output is generated based on the read image, it can be applied to a scanner device and a digital multi-function peripheral.

A computer program according to the present invention includes a step of causing a computer to detect a ground region included in an image formed by the input image signal based on the input image signal, and a step of causing the computer to perform image processing according to the detection result. In the computer program having the above, the computer defines a correspondence relationship between the density value of the input image signal and the density value of the first correction signal to be generated in order to perform gamma correction using the first gamma value. The correspondence relationship between the density value of the input image signal and the density value of the second correction signal to be generated to perform gamma correction using the table 1 and the second gamma value different from the first gamma value. among the second table defining, for the second table stored in advance, Yes prestored, the difference between the first and second tables A step of generating a first table by adding to the difference data, to the computer, the step of generating a first correction signal from the input image signal using the first table generated and the computer, the step of the step of detecting a background area of the image based on the first correction signal is generated, the computer is from the input image signal using a second table which is stored in advance produce a second correction signal And a step of causing the computer to perform a density conversion process according to the detection result of the background area on the generated second correction signal.

  In the present invention, the gamma correction performed in the previous stage for detecting the background area and the gamma correction performed in the previous stage for performing the density conversion process according to the detection result of the background area are executed using different gamma values. Therefore, it is possible to set a gamma value suitable for detecting the background area and a gamma value suitable for generating an output image, respectively, so that the background area can be accurately detected and the background density is set appropriately. An output image adjusted to be obtained.

  According to the present invention, the gamma correction performed in the previous stage for detecting the background area and the gamma correction performed in the previous stage for performing the density conversion process according to the detection result of the background area are executed using different gamma values. . Therefore, it is possible to set a gamma value suitable for detection of a background area and a gamma value suitable for generation of an image for output, respectively, so that the background area can be detected with high accuracy and the density of the background can be set. Appropriately adjusted output images can be acquired.

  According to the present invention, the first correction means for performing gamma correction using the first gamma value in the previous stage for detecting the background area, and the second gamma in the previous stage for performing the density conversion processing according to the detection result of the background area. Second correction means for performing gamma correction using the value. Therefore, it is possible to set a gamma value suitable for detection of a background area and a gamma value suitable for generation of an image for output, respectively, so that the background area can be detected with high accuracy and the density of the background can be set. Appropriately adjusted output images can be acquired.

  In the case of the present invention, the gamma value of the gamma correction executed by the first correction unit is determined so that the number of gradations in the area corresponding to the background area increases. Therefore, the image corrected by the first correction unit can increase the number of gradations in the low density region (highlight region) corresponding to the background region, and the detection unit in the subsequent stage can accurately detect the background region. be able to.

In the case of the present invention, one of the table used for gamma correction by the first correction unit or the table used for gamma correction by the second correction unit is stored, and the other is generated from the stored table. ing. Thus, 2 even when subjected types of gamma correction, it is no need to store the two types of tables such as lookup tables, it is possible to suppress an increase in the data amount reduced.

  In the case of the present invention, one of the function used in the gamma correction in the first correction unit or the function used in the gamma correction in the second correction unit is stored, and the other is generated from the stored function. ing. Accordingly, even when two types of gamma correction are performed, it is not necessary to store two types of functions, and an increase in data amount can be suppressed to a low level.

  In the case of the present invention, since it is provided with means for outputting an image obtained by performing density conversion processing, it can be applied to a printer device and a digital multifunction peripheral.

  According to the present invention, since an image of a document is read and an image to be output is generated based on the read image, it can be applied to a scanner device and a digital multifunction peripheral.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
In the present embodiment, an embodiment in which the image processing apparatus according to the present invention is applied to a scanner apparatus will be described. FIG. 1 is a block diagram showing a schematic configuration of an image processing apparatus according to the present embodiment. The image processing apparatus according to the present embodiment is generally configured by a control unit 1, a storage unit 2, an operation unit 3, an image reading unit 4, an image processing unit 5, and an image output unit 6. The control unit 1 includes a CPU. The CPU reads and executes a control program stored in the storage unit 2 in advance, and controls each of the above-described hardware units, so that the image processing apparatus of the present invention as a whole. Make it work. The operation unit 3 includes an operation button for accepting a user operation such as an original reading density and an instruction to start reading, a liquid crystal display for displaying an operation guide, and the like.

  The image reading unit 4 includes a light source that irradiates light to a reading document, an image sensor such as a CCD (Charge Coupled Device), and the like, and receives a reflected light image from the document set at a predetermined reading position. An image is formed on the image sensor to generate RGB (R: Red, G: Green, B: Blue) analog electrical signals. The generated analog electrical signal is output to the image processing unit 5.

  The image processing unit 5 converts the analog electrical signal output from the image reading unit 4 into a digital signal, then converts RGB reflectance signals into density signals, and various density adjustment processes according to the read image Execute. Image data obtained by performing these density adjustment processes is output to the image output unit 6.

  The image output unit 6 includes a communication interface such as a USB interface or a SCSI interface in order to transmit image data output from the image processing unit 5 to an information processing apparatus such as a personal computer, and is connected to the communication interface. The image data is transmitted to the information processing apparatus according to a predetermined protocol.

  FIG. 2 is a block diagram illustrating details of the image processing unit 5. The image processing unit 5 includes an AD conversion unit 51, a shading correction unit 52, an input tone correction unit 53, a region separation processing unit 54, a color correction unit 55, a black generation and under color removal unit 56, a spatial filter processing unit 57, an output floor. A tone correction unit 58 and a gradation reproduction processing unit 59 are provided.

  The AD conversion unit 51 converts RGB analog signals input through the image reading unit 4 into digital signals. The shading correction unit 52 performs processing for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image reading unit 4 on the digital RGB signal output from the AD conversion unit 51.

  The input tone correction unit 53 converts RGB reflectance signals into density signals (gamma conversion) and performs background detection processing. Then, image quality adjustment processing such as background density correction and contrast is executed based on the background detection result. The input tone correction unit 53 may perform processing for adjusting color balance in addition to the processing described above. The present invention particularly relates to the input tone correction unit 53, and details thereof will be described later.

  The region separation processing unit 54 separates each pixel in the input image into one of a character region, a halftone dot region, and a photograph (other) region based on the RGB signal. Based on the separation result, the region separation processing unit 54 displays a region identification signal indicating which region the pixel belongs to as a color correction unit 55, a black generation and under color removal unit 56, a spatial filter processing unit 57, and an output tone correction unit. 58 and the gradation reproduction processing unit 59, and the RGB signal output from the input gradation correction unit 53 is output to the subsequent color correction unit 55 as it is.

  The color correction unit 55 performs processing for removing color turbidity based on spectral characteristics of CMY (C: cyan, M: magenta, Y: yellow) color materials including unnecessary absorption components in order to realize color reproduction faithfully. It is.

  The black generation and under color removal unit 56 generates black (K) signals from the CMY three-color signals after color correction, and subtracts the K signals obtained by black generation from the original CMY signals to generate new CMY signals. The generation processing is performed, and the CMY three-color signal is converted into a CMYK four-color signal. As an example of black generation processing, a method of generating black using skeleton black is known. In this method, the input characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, and the undercolor removal rate is If α (0 <α <1), the black generation and under color removal processing can be expressed by the following equation.

  The spatial filter processing unit 57 performs spatial filter processing using a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 56, based on the region identification signal, and outputs by correcting the spatial frequency characteristics. Processing is performed to prevent image blurring and graininess deterioration. For example, a region separated as a character by the region separation processing unit 54 is subjected to sharp enhancement processing to enhance the reproducibility of black characters or color characters, and emphasizes high frequency components. For the region separated as a halftone dot region by the region separation processing unit 54, low-pass filter processing for removing the input halftone dot component is performed.

  The output tone correction unit 58 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio corresponding to the characteristics of the output destination.

  The gradation reproduction processing unit 59 performs gradation reproduction processing that finally separates an image into pixels and performs processing so that each gradation can be reproduced. For example, for a region separated into a photograph by the region separation processing unit 54, binarization or multi-value processing is performed on the screen with an emphasis on gradation reproducibility, and the region separation processing unit 54 separates it into characters. The binarization or multi-value processing is performed on a high-resolution screen suitable for high-frequency reproducibility.

  The image data processed by each processing unit in this manner is temporarily stored in an image memory (not shown), read at a predetermined timing, and transmitted to the outside through the image output unit 6.

  Hereinafter, the gamma conversion processing, background detection processing, and background correction processing executed by the input tone correction unit 53 will be described. FIG. 3 is a block diagram showing the internal configuration of the input tone correction unit 53. The input tone correction unit 53 includes a first gamma conversion unit 531 that functions as a first correction unit of the present invention, a second gamma conversion unit 532 that functions as a second correction unit, a background detection unit 533 that functions as a detection unit, and A background correction unit 534 functioning as means for performing density conversion processing is provided. The image data converted by the first gamma conversion unit 531 is output to the background detection unit 533, and the background detection unit 533 detects the background. The image data converted by the second gamma conversion unit 532 is output to the background correction unit 534, and background density correction is performed based on the detection result of the background.

  The first gamma conversion unit 531 performs gamma conversion (gamma correction) so that the gradation of the highlight region can be obtained, and the second gamma conversion unit 532 converts the reflectance linear image data into density linear data. Gamma conversion (gamma correction) is performed. Therefore, the first gamma conversion unit 531 and the second gamma conversion unit 532 are configured to perform gamma correction according to the gamma curves that define the respective conversion characteristics. FIG. 4 is a graph showing conversion characteristics of the first gamma conversion unit 531 and the second gamma conversion unit 532. FIG. 4A shows a first gamma curve showing the conversion characteristics of the first gamma conversion unit 531, and FIG. 4B shows a second gamma curve showing the conversion characteristics of the second gamma conversion unit 532.

  In the graph shown in FIG. 4A, the horizontal axis indicates the density value (RGB value) for the input image data, and the vertical axis indicates the density value (RGB value) of the output image data obtained by gamma conversion. Yes. The correspondence between the density value of each pixel of the input image data and the density value of the corresponding pixel in the output image data is defined by the first gamma curve shown in FIG. FIG. 4A shows two types of gamma curves represented by the symbol “◯” and gamma curves represented by the symbol “●”, both of which are used as the first gamma curve in the first gamma conversion unit 531. Can be used. According to such a first gamma curve, the number of gradations is increased in the highlight region (for example, the density range of [640, 1024]) corresponding to the background region, that is, the gradation property is improved. Density conversion is performed. Therefore, it is not necessary to reduce the amount of information in the highlight area at the time of gamma conversion, and the background detection unit 533 described later can detect the background in detail.

  Such gamma conversion can be realized, for example, using a lookup table in which input density values and output density values are uniquely associated, and output density values defined by the input density values and the first gamma curve. Is stored in the first gamma conversion unit 531, and when the image data is input to the first conversion unit 531, the corresponding output density value is obtained from the lookup table. Perform gamma conversion.

  Note that the gamma curve used in the first gamma conversion unit 531 is not limited to that shown in FIG.

  Similarly, in the graph shown in FIG. 4B, the horizontal axis indicates the density value (RGB value) for the input image data, and the vertical axis indicates the density value (RGB value) of the output image data obtained by gamma conversion. Is shown. The correspondence between the density value of each pixel of the input image data and the density value of the corresponding pixel in the output image data is defined by the second gamma curve shown in FIG. The second gamma curve is performed to convert reflectance linear image data into density linear data.

  Such gamma conversion can be realized using a look-up table in which input density values and output density values are uniquely associated as described above. That is, a lookup table representing the correspondence between the input density value and the output density value defined by the second gamma curve is held in the second gamma conversion unit 532, and image data is input to the second gamma conversion unit 532. Then, gamma conversion is performed by obtaining the corresponding output density value from the lookup table.

  Note that the gamma curve that can be used in the second gamma conversion unit 532 is not limited to that shown in FIG.

  In the example shown in FIG. 4, when gamma conversion is performed, 10-bit input image data is converted to 8-bit output image data. However, 10-bit image data is output. Of course, the input image data need not be limited to 10 bits.

  In the present embodiment, the first gamma conversion unit 531 and the second gamma conversion unit 532 are configured to have lookup tables corresponding to the first gamma curve and the second gamma curve, respectively. Only the corresponding data may be stored, and the first gamma curve may be obtained by storing difference data and adding to the second gamma curve data at the time of conversion. That is, the first gamma conversion unit 531 and the second gamma conversion unit 532 function as means for storing one table (lookup table) and means for generating the other table in the present invention.

  Alternatively, the first gamma curve and the second gamma curve may be held as functions, and an output density value that is gamma corrected by an arithmetic process may be acquired. That is, the first gamma conversion unit 531 and the second gamma conversion unit 532 function as means for storing one function and means for generating the other function in the present invention.

  The background detection unit 533 detects the background based on the RGB signal converted by the first gamma conversion unit 531 so that the gradation of the highlight area can be obtained. As a technique for detecting the background, a known technique can be employed. For example, the background is detected using the technique described in Japanese Patent Application Laid-Open No. 2003-51946. In the technique described in the above publication, first, a background is determined by creating a histogram using input image data and comparing the frequency of this histogram with a plurality of predetermined thresholds. In this background determination process, the background is determined by the following three steps. That is, the histogram is searched in a predetermined direction, the frequency of the density classification is compared with the first threshold value, and the first process for determining whether or not to perform the subsequent process and the determination to perform the subsequent process. A second step of determining whether or not there is a background candidate by comparing the frequency of the density category with a second threshold, and when it is determined that there is a background candidate, the frequency is the second A third step of determining the presence or absence of a background by adding the frequency of the density category that is equal to or greater than the threshold and the frequency of the density category that is adjacent to the density category and exists in the search direction, and comparing with the third threshold value; The background correction processing is performed based on the above.

  The background correction unit 534 performs background correction according to the detection result of the background detection unit 533 on the image data converted into the linear density by the second gamma conversion unit 532. FIG. 5 is a graph showing the characteristics of density conversion executed during the background correction. The horizontal axis represents the input density value, and the vertical axis represents the output density value. Although five types of conversion curves are depicted in FIG. 5, one conversion curve is selected according to the detection result of the background detection unit 533, and density conversion processing is performed according to the selected conversion curve. For example, when no background is detected by the background detection unit 533, density conversion is performed using a conversion curve represented by a symbol □. In this case, since the output density value is equal to the input density value, the density conversion is not substantially performed. When the background detection unit 533 detects a background in a relatively high density area, a conversion curve represented by a symbol x is selected, and density conversion is performed so that the detected background can be removed satisfactorily. Similarly, as the detected background density decreases, the conversion curve represented by the symbol ◯, the conversion curve represented by the symbol ●, and the conversion curve represented by the symbol △ are selected in this order to remove the background. Density conversion processing is performed.

  Such density conversion processing can be realized using a lookup table in which input density values and output density values are uniquely associated. That is, when the background correction unit 534 holds a look-up table representing the correspondence between the input density value and the output density value defined by each of the conversion curves described above, when image data is input to the background correction unit 534. The density conversion process is performed by obtaining the corresponding output density value from the lookup table.

  FIG. 6 is a flowchart for explaining the background correction procedure by the input tone correction unit 53. When the input tone correction unit 53 acquires the input image data (RGB signal) (step S11), the first gamma conversion unit 531 converts the input image data so that the low density tone is good ( Step S12). The converted image data is set as first image data, and the first image data is output to the background detection unit 533.

  Next, the background detection unit 533 detects the background based on the first image data output from the first gamma conversion unit 531 (step S13). The background detection result is output to the background correction unit 534. The background correction unit 534 determines whether a background is detected based on the background detection result output from the background detection unit 533 (step S14). If it is determined that a background has been detected (S14: YES), a background removal table is selected according to the detected background level (step S15). That is, the lookup table stored in the background correction unit 534 is selected according to the density area where the background is detected. If it is determined that the background is not detected (S14: NO), a table without background removal is selected (step S16). That is, a lookup table corresponding to the conversion curve represented by □ is selected from the conversion curves shown in FIG.

  Next, the second gamma conversion unit 532 converts the input image data so as to be linear with respect to the density (step S17). The converted image data is set as second image data, and the second image data is output to the background correction unit 534. Then, the density conversion of the second image data is performed using the table selected in step S15 or step S16 (step S18).

  In this embodiment, after the table is selected in step S15 or step S16, the conversion process by the second gamma conversion unit 532 is performed. However, the conversion process by the first gamma conversion unit 531 and the second gamma conversion process are performed. Of course, the conversion processing by the conversion unit 532 may be executed in parallel.

Embodiment 2. FIG.
In the first embodiment, the gamma conversion by the first gamma conversion unit 531 and the gamma conversion by the second gamma conversion unit 532 are processed in parallel. However, these processes may be executed sequentially. Of course. In the present embodiment, a mode in which two gamma conversions are sequentially executed will be described. Note that the overall configuration of the image processing apparatus and the internal configuration of the image processing unit 5 are the same as those in the first embodiment, and thus description thereof will be omitted.

  FIG. 7 is a block diagram showing an internal configuration of the input tone correction unit 53 'according to the present embodiment. As in the first embodiment, the input tone correction unit 53 ′ includes a first gamma conversion unit 531 ′, a second gamma conversion unit 532 ′, a background detection unit 533 ′, and a background correction unit 534 ′. I have. A background detection unit 533 ′ is connected to the subsequent stage of the first gamma conversion unit 531 ′, a second gamma conversion unit 532 ′ is connected to the subsequent stage, and a background correction unit 534 ′ is connected to the subsequent stage.

  The first gamma conversion unit 531 ′ and the background detection unit 533 ′ perform the same processing as that described in the first embodiment. That is, the first gamma conversion unit 531 ′ performs gamma correction according to the first gamma curve shown in FIG. 4A, and the background detection unit 533 ′ converts the image subjected to gamma correction by the first gamma conversion unit 531 ′. Based on this, the background is detected. The image data used for detecting the background is output to the second gamma conversion unit 531 '.

  The second gamma conversion unit 532 'performs a correction having a characteristic inverse to that of the first gamma curve and a gamma correction according to the second gamma curve shown in FIG. The image data subjected to gamma correction by the second gamma conversion unit 532 'is output to the background correction unit 534', and the background correction based on the detection result by the background detection unit 533 'is performed in the background correction unit 534'.

Embodiment 3 FIG.
In the first embodiment, the image processing apparatus according to the present invention is applied to the scanner apparatus, and the image output unit 6 transmits image data to an external information processing apparatus. A configuration in which the present invention is applied to a copying machine or a digital multifunction machine having a function of forming a read image on a recording sheet may be employed. That is, in the present embodiment, the image output unit 6 functions as a means for forming an image on a recording sheet. Note that the overall configuration of the image processing apparatus and the internal configuration of the image processing unit 5 are the same as those in the first embodiment, and thus description thereof will be omitted.

  FIG. 8 is a schematic configuration diagram illustrating details of the image output unit 6. The image output unit 6 in the present embodiment includes image forming stations 600a, 600b, 600c, and 600d corresponding to the respective colors of black (K), cyan (C), magenta (M), and yellow (Y). , Black (K), cyan (C), magenta (M), and yellow (Y) in this order are superimposed and transferred onto a recording sheet to form a multicolor image.

  Hereinafter, the configuration of the image forming station 600a corresponding to black (K) will be described as an example. The image forming station 600a includes a photosensitive drum 601a disposed in contact with the upper surface of the paper conveying belt 610. Around the photosensitive drum 601a, a charger 602a, a writing optical system 603a, a developing device 604a, and a cleaning unit 605a. Is arranged. Further, a transfer roller 606a is provided on the lower surface side of the sheet conveying belt 610 so as to face the photosensitive drum 601a.

  The charger 602a employs a non-contact charger type charger in addition to a roller-type or brush-type charger that comes into contact with the photosensitive drum 601a, and uniformly distributes the surface of the photosensitive drum 601a to a predetermined potential. Charge. The writing optical system 603a is a laser scanning unit including a writing head or a laser irradiation unit in which issuing elements such as EL (Electro Luminescence) and LED (Light Emitting Diode) are arranged in an array, a reflection mirror, and the like. By exposing according to the image data output by the unit 5, an electrostatic latent image corresponding to the image data is formed on the photosensitive drum 601a. The developing device 604a supplies black toner to the electrostatic latent image formed on the photosensitive drum 601a to make a visible image. The transfer roller 606a transfers the toner image on the photosensitive drum 601a generated by the visualization to the recording paper conveyed by the paper conveyance belt 610. The cleaning unit 605a removes and collects toner on the photosensitive drum 601a remaining after the transfer of the toner image.

  With such a configuration, the image forming station 600a performs image formation by transferring a black toner image onto a recording sheet. The configurations of the other color image forming stations 600b to 600d are basically the same as those of the black (K) image forming station 600a. The image forming stations 600b to 600d are photosensitive drums 601b to 601d and chargers 602b to 602d. Writing optical systems 603b to 603d, developing devices 604b to 604d, cleaning units 605b to 605d, and transfer rollers 606b to 606d. Note that the symbols b, c, and d attached to the respective symbols correspond to cyan (C), magenta (M), and yellow (Y) colors, respectively.

  In the image output unit 6 having the configuration shown in FIG. 8, the image forming operation is performed as follows. The recording paper on which an image is formed is conveyed from the paper supply unit 620 by the conveyance roller 621 and is sent onto the paper conveyance belt 610. The paper transport belt 610 is rotationally driven by a driving roller 611 and a driven roller 612, and the recording paper carried by the paper transport belt 610 is transported in the direction of the white arrow in the figure. At this time, each of the image forming stations 600a to 600d sequentially superimposes and transfers the toner images of the respective colors at a predetermined timing, thereby forming a multicolor image on the recording paper. The recording paper on which the multicolor image is formed is conveyed to the fixing unit 630, and the multicolor toner image is fixed on the recording paper by thermocompression bonding. Then, the recording paper is discharged through a paper discharge unit (not shown).

  In this embodiment, the image forming stations 600a to 600d are arranged in the order of black (B), cyan (C), magenta (M), and yellow (Y) from the upstream side to the downstream side in the sheet conveyance direction. However, it is not limited to this order, and the color order is arbitrarily set.

Embodiment 4 FIG.
In the present invention, the image processing method may be recorded on a computer-readable recording medium in which a computer program to be executed by a computer is recorded. As a result, it is possible to provide a portable recording medium on which a computer program for performing the image processing is recorded.

  FIG. 9 is a schematic diagram showing a configuration of an image processing system constructed by installing a computer program according to the present invention. In the figure, reference numeral 100 denotes an information processing apparatus such as a personal computer or a workstation. The information processing apparatus 100 includes an image input device 110 such as a flat head scanner, a film scanner, and a digital camera, a sheet such as paper and an OHP film. Peripheral devices such as an image forming apparatus 120 such as an ink jet printer or a laser printer provided with an image forming means, and an image display apparatus such as a CRT display or a liquid crystal display are connected. In addition, the information processing apparatus 100 includes a reading device such as an FD drive or a CD-ROM drive for reading the computer program from a recording medium 101 such as an FD or CD-ROM that records the computer program according to the present invention. Yes. The computer program read by the reading device is stored in a predetermined storage area in the information processing device 100. A CPU (not shown) of the information processing apparatus 100 implements the image processing method as described above by loading and executing the computer program of the present invention from the storage area. That is, a configuration in which the information processing apparatus 100 performs background detection and background correction on the image input through the image input apparatus 110 using the technique of the present invention, and the image forming apparatus 120 forms an image with the background correction on the recording paper. It becomes.

  With this configuration, the image processing method can be used according to the user's preference. For example, when the present image processing method is executed by this image processing system, it becomes easy to arbitrarily change the parameter settings of each unit, and it is used again according to the result displayed on the image display device. Processing according to the user's preference. In order to change a parameter, it is set by directly inputting a numerical value using a keyboard or a mouse or dragging a symbol representing a parameter.

  As the recording medium 101 for recording the computer program according to the present invention, in addition to the FD and CD-ROM described above, optical recording media such as MO, MD, and DVD, magnetic recording media such as hard disks, IC cards, and memory cards Further, it is also possible to use a semiconductor memory such as a card-type recording medium such as an optical card, a mask ROM, an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), a flash ROM, or the like.

  When the information processing apparatus 100 includes a modem or the like as a communication means for connecting to a server apparatus or the like via a communication network, the server apparatus stores the computer program of the present invention in advance, and the server The computer program may be downloaded from an apparatus and installed in the information processing apparatus 100.

It is a block diagram which shows schematic structure of the image processing apparatus which concerns on this Embodiment. It is a block diagram explaining the detail of an image process part. It is a block diagram which shows the internal structure of an input gradation correction | amendment part. It is a graph which shows the conversion characteristic of a 1st gamma conversion part and a 2nd gamma conversion part. It is a graph which shows the characteristic of density conversion performed in the case of background correction. It is a flowchart explaining the procedure of the background correction | amendment by an input gradation correction | amendment part. It is a block diagram which shows the internal structure of the input gradation correction | amendment part which concerns on this Embodiment. It is a typical block diagram explaining the detail of an image output part. It is a schematic diagram showing a configuration of an image processing system constructed by installing a computer program according to the present invention. It is a flowchart which shows the procedure of the conventional background correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control part 2 Memory | storage part 3 Operation part 4 Image reading part 5 Image processing part 6 Image output part 53 Input tone correction part 531 1st gamma conversion part 532 2nd gamma conversion part 533 Background detection part 534 Background correction part

Claims (6)

In an image processing method for detecting a ground region included in an image formed by an input image signal based on the input image signal and performing image processing according to the detection result,
A first table defining a correspondence relationship between a density value of the input image signal and a density value of the first correction signal to be generated to perform gamma correction using the first gamma value; and the first gamma Of the second table that prescribes the correspondence between the density value of the input image signal and the density value of the second correction signal to be generated in order to perform gamma correction using a second gamma value different from the value, for the second table stored, Yes previously stored, generating a first table by adding the difference data indicating the difference between the first and second tables, the first has been made live generating a first correction signal from the input image signal by using a table, and detecting a background area of the image based on the generated first correction signal, a second table which is stored in advance It was used An image processing method comprising: generating a second correction signal from the input image signal; and performing density conversion processing on the generated second correction signal in accordance with a detection result of a background area. . In an image processing apparatus that detects a background region included in an image that is constituted by an input image signal based on the input image signal and performs image processing according to the detection result.
First correction means for performing gamma correction on the input image signal using a first gamma value; and second correction means for performing gamma correction on the input image signal using a second gamma value different from the gamma value; Means for storing a second table for defining a correspondence relationship between the density value of the input image signal and the density value of the second correction signal to be generated; first table by adding the difference data indicating the difference between the first table defining the correspondence between the density value of the first correction signal to be generated and the concentration value input image signal has the second table And means for generating
The first and second correction means perform gamma correction using the first and second tables, respectively .
Detection means for detecting a ground area of the image based on a first correction signal obtained by correction by the first correction means, and a second correction signal obtained by correction by the second correction means An image processing apparatus comprising: a means for performing density conversion processing according to a detection result of the detection means.   The first and second gamma values are determined so that the number of gradations of the image by the first correction signal in the region corresponding to the background region is larger than the number of gradations of the image by the second correction signal. The image processing apparatus according to claim 2, wherein the image processing apparatus is provided. The image processing apparatus according to claim 2 or claim 3, characterized in that it comprises means for outputting an image obtained by applying the density conversion process on the second correction signal. 5. The image processing apparatus according to claim 4 , further comprising means for reading an image of a document, and generating an image to be output based on the image read by the means. In a computer program comprising the steps of causing a computer to detect a background area included in an image constituted by the input image signal based on the input image signal, and causing the computer to perform image processing according to the detection result.
A first table defining a correspondence relationship between a density value of the input image signal and a density value of the first correction signal to be generated to perform gamma correction using a first gamma value on the computer; A second table defining the correspondence between the density value of the input image signal and the density value of the second correction signal to be generated to perform gamma correction using a second gamma value different from the gamma value of 1. among them, with respect to the second table stored in advance, Yes previously stored, comprising the steps of generating a first table by adding the difference data indicating the difference between the first and second tables, the computer, test and step of generating a first correction signal from the input image signal using the first table generated and the computer, the background area of the image based on the first correction signal is generated A step of, in the computer, the step of from the input image signal using a second table which is stored in advance produce a second correction signal, to the computer, the second correction signal is generated, the base And a step of performing density conversion processing according to the detection result of the area.

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