JP4027098B2 - Image processing apparatus and image processing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing apparatus and an image processing method, and more specifically, a tone correction coefficient for converting image content of image information read by pre-scanning a scanner and image density characteristics at the time of main scanning from reading conditions. The present invention relates to an image processing apparatus and an image processing method.
[0002]
[Prior art]
In general, as a processing function of an image input device, parameters such as filter processing and gamma correction processing (histogram optimization) suitable for an image to be processed are determined based on input pre-scan image data, and the parameters are set. The image quality is improved by performing filter processing and gamma correction processing of the main scan image.
[0003]
Filter processing emphasizes or improves the local characteristics of the image to improve the image quality of the original image. An integral filter that reduces noise and a differential filter that enhances the edges in the image Etc.
[0004]
Another gamma correction process is a process for correcting gradation of image density. Examples of density gradation correction include processing for uniformly expanding or contracting the range of density values, nonlinear conversion for expanding or compressing a specific density region from other portions, and the like.
[0005]
Japanese Patent Laid-Open No. 2000-236452 discloses a method for performing a gamma correction process on an image to be processed using an appropriate tone curve. In this gamma correction method, the representative value indicating the distribution tendency is obtained from the histogram of the pre-scan (rough reading) input image, and the tone curve is corrected based on this representative value and applied to the gamma correction processing of the main scan image. is doing.
[0006]
[Problems to be solved by the invention]
However, in order for the gamma correction processing to the main scan image data by the conventional method described above to be performed satisfactorily, the histogram distribution in the pre-scan image data and the histogram distribution in the main scan image data need to be distributed at the same ratio. There is. However, in reality, the resolution of the pre-scan image is almost always lower than the resolution of the main scan image. In this case, the histogram distribution of the pre-scan image approaches the average value as the resolution decreases, so the main scan with higher resolution It is different from the histogram distribution of the image. Therefore, strictly speaking, the tone correction coefficient optimized from the histogram of the pre-scan image is not an optimum tone correction coefficient for the main scan image.
[0007]
The present invention has been made in view of such problems, and an object of the present invention is to provide a tone correction coefficient calculated from histogram distribution characteristics of the entire designated range on a pre-scan input document image. The Another object of the present invention is to provide an image processing apparatus or an image processing method that can determine an optimum tone correction coefficient for a main scan image and perform a gamma correction process.
[0008]
[Means for Solving the Problems]
In order to achieve such an object, the present invention includes a scanner unit for inputting image information on a document, and the scanner unit performs twice on the same document. In the image processing apparatus that executes image scanning and processes the image information input by the next main scan based on the image information input by the first pre-scan, the pre-scan obtained by pre-scanning the scanner is obtained. A density frequency distribution acquisition unit for obtaining data representing the density frequency distribution of an image in a predetermined range on the original image from the density level value of each pixel of the scanned image information, and the density frequency distribution acquired by the density frequency distribution acquisition unit Using the minimum density level value of the data representing the reference and the starting point of accumulation, the density value value is cumulatively calculated in the higher direction of the density level value, Cumulative frequency distribution acquisition means for obtaining a cumulative frequency distribution representing the relationship between the frequency level value and the cumulative calculation value; an approximate power function approximating the cumulative frequency distribution; and calculating the power of the pre-scan image from the power of the calculated function First γ value acquisition means for obtaining a first γ value representing a tone correction coefficient, and each of pre-scan and main scan resolution Γ value conversion means for converting the first γ value into a second γ value representing a tone correction coefficient at the time of the main scan, and executing the main scan for the scanner to obtain the main scan image information. An image tone that is inputted to obtain the density range, and performs conversion for tone correction processing on the inputted main scan image information based on the data representing the obtained density range and the second γ value And a correction means.
[0009]
The invention according to claim 2 is the image processing apparatus according to claim 1, wherein the first γ value and the density are set. frequency Based on the data from the distribution acquisition means, the image tone correction means for executing the tone correction processing of the pre-scan image information, the display means for receiving and displaying the output from the image tone correction means, and the display means A tone correction instruction input means for inputting a tone correction instruction input from an operator in response to the display of the pre-scanned image, and correcting the first γ value by the tone correction instruction from the tone correction instruction input means. Γ value correction means for generating a first corrected γ value, and the image tone correction means executes the image tone correction process when the first corrected γ value is input. It outputs to the said display means, It is characterized by the above-mentioned.
[0010]
The invention according to claim 3 is the image processing apparatus according to claim 2, wherein a main scan start instruction input from an operator in response to display of the pre-scan image on the display means is displayed. In response, the γ value converting means receives the first γ value or the first corrected γ value used by the image tone correcting means when creating the image output to the display device, and receives the second γ value. Tone correction factor during main scan The It is characterized by converting.
[0012]
Claims 4 The invention described in claim Any one of 1-3 The γ value converting means further includes a parameter indicating the type of the read original.
[0013]
Claims 5 The invention described in claim 1 4 The pre-scan that is executed to determine the tone correction coefficient at the time of the main scan of the processing target image is executed at a resolution different from that at the time of the main scan. It is what.
[0014]
Claims 6 The invention described in (1) has a scanner for inputting image information on a document, and the scanner performs two scans on the same document, and based on the image information input by the first pre-scan. In the image processing method for processing the image information input in the next main scan, a predetermined level on the document image is determined from the density level value of each pixel of the pre-scan image information obtained by pre-scanning the scanner. The density frequency distribution acquisition step for obtaining data representing the density frequency distribution of the image in the range, and the minimum density level value of the data representing the density frequency distribution acquired by the density frequency distribution acquisition step as a reference and accumulation start point Cumulative calculation of the concentration value numerical value in the direction of higher level value, and a cumulative frequency distribution representing the relationship between the concentration level value and the cumulative calculation value. A cumulative frequency distribution obtaining step, an approximate power function approximating the cumulative frequency distribution, and a first γ value representing a first γ value representing a tone correction coefficient of the pre-scan image from the calculated power number Value acquisition step and each of pre-scan and main scan resolution As a parameter, a γ value conversion step for converting the first γ value into a second γ value that represents a tone correction coefficient at the time of the main scan; An image tone that is inputted to obtain the density range, and performs conversion for tone correction processing on the inputted main scan image information based on the data representing the obtained density range and the second γ value And a correction step.
[0015]
Claims 7 The invention described in claim 6 An image tone correction step for performing tone correction of the pre-scan image information based on the first γ value and data from the density frequency distribution acquisition unit, and A display output step for receiving the output processed in the tone correction step and outputting the output to a display unit, and a tone correction for inputting a tone correction instruction input from an operator in response to the display of the pre-scan image by the display output step An instruction input step; and a γ value correction step of generating the first corrected γ value by correcting the first γ value according to the tone correction instruction received in the tone correction instruction input step, the image tone The correction step executes the image tone correction step and the display output step process when the first corrected γ value is input. It is characterized by that.
[0016]
Claims 8 The invention described in claim 7 The image processing method according to claim 1, further comprising a main scan start instruction input step that receives a main scan start instruction input from an operator in response to display of the pre-scan image by the display unit step, and the γ value conversion step includes: When receiving the main scan start instruction input in the main scan start instruction input step, the first γ value or the first correction used by the image tone correcting means when creating the image output to the display device. The tone correction coefficient at the time of the main scan is converted to the second γ value by inputting the finished γ value.
[0018]
Claims 9 The invention described in claim Any of 6-8 The parameter used in the conversion in the γ value conversion step further includes a parameter representing the type of the read document.
[0019]
Claims 10 The invention described in claim 6-9 4. The image processing method according to claim 1, wherein the pre-scan executed for determining the tone correction coefficient at the main scan of the processing target image is executed at a resolution different from that at the main scan. It is characterized by that.
[0020]
Claims 11 The invention described in (1) is a computer-readable storage medium storing a program, an image input step for pre-scanning a scanner to input image information, and pre-scan image information obtained in the image input step The density frequency distribution acquisition step for obtaining data representing the density frequency distribution of the image in a predetermined range on the original image from the density level value of each pixel, and the density frequency distribution acquired by the density frequency distribution acquisition step Using the minimum density level value of the data to be represented as a reference and starting point of accumulation, the density value is cumulatively calculated in the direction of higher density level value to obtain a cumulative frequency distribution representing the relationship between the density level value and the cumulative calculation value. A cumulative frequency distribution acquisition step, an approximate power function approximating the cumulative frequency distribution is calculated, and a pre-score is calculated from the calculated power number. A first γ value acquisition step for obtaining a first γ value representing a tone correction coefficient of a can image, and the first γ value as a parameter for tone correction at the time of the main scan, using the pre-scan and main scan conditions as parameters. Γ value conversion step for converting to a second γ value representing a coefficient, and data for representing the obtained density range by executing the main scan for the scanner and inputting the main scan image information to obtain the density range. And an image tone correction step of executing conversion for tone correction processing on the inputted main scan image information based on the second γ value.
[0021]
Claims 12 The invention described in claim 11 The floppy (registered trademark) disk, hard disk, magneto-optical disk, optical disk, CD-ROM, CD storing a program that can be read by the server computer and the client computer as the storage medium -R, magnetic tape, non-volatile memory card, ROM are used.
[0022]
Claims 13 The invention described in claim 11 or ~ 12 The storage medium according to any one of the above, wherein the storage medium is detachable from a server computer and a client computer.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
(First embodiment)
First, the outline of the operation of the image processing apparatus according to the first embodiment will be described according to a flowchart, and then the main tone correction coefficient (hereinafter referred to as γ coefficient) determination process, which is the main requirement of the present invention, will be described in detail.
[0025]
The image processing apparatus according to the present embodiment first calculates a preview γ coefficient that optimizes a preview image based on a preview image read at a low resolution during pre-scanning. Next, a preview conversion γ coefficient is converted with a previously prepared γ conversion table to create a density conversion table (hereinafter referred to as a γ table) that optimizes the density for the main scan image read during the main scan. Using the conversion table, the density of the main scan image read during the main scan is converted. Here, the γ conversion table is provided for each type of document, and is related to the resolution during pre-scanning and main scanning.
[0026]
FIG. 1 is a flowchart showing a schematic procedure of image reading and image processing of the image processing apparatus according to the first embodiment, and description will be made according to this.
[0027]
First, after the processing is started in step S100, the present image processing apparatus inputs the relatively low resolution preview image data read from the image reading apparatus in step S102, and at the same time, the book to be finally stored on the preview image. Get scan reading range information.
[0028]
Next, in step S104, a calculation for obtaining a preview γ coefficient based on a density distribution within a reading designated range on the preview image is performed by a preview γ coefficient calculation method described later.
[0029]
Next, in step S106, a γ table for density conversion is created from the γ coefficient calculated based on the density distribution of the preview image and information from the density distribution, and density conversion is performed on the preview image data input in step S102. Processing is performed to generate preview image data. The preview image data is sent to the display device, and the density conversion result is displayed to the operator. Thereafter, the process proceeds to step S110, and an operator response to the displayed image is input. When an operator response is received that the displayed density conversion result matches the operator's intention, the process proceeds to step S112, and the process proceeds to the main scan data processing.
[0030]
If the operator response is a γ fine adjustment instruction in step S110, a new γ coefficient is generated in accordance with the operator instruction, and the process returns to step S106. In this case, the loop from step S106 to S118 is a process for finely adjusting the γ table according to the operator response. The preview image is displayed again in step S108, and an operator instruction is waited in step S110.
[0031]
In step S112 and subsequent steps, processing that is the original purpose of the operator is executed. First, in step S112, the γ coefficient for main scan corresponding to the designated resolution at the time of the main scan intended by the operator is calculated using the γ coefficient value up to that point, and the γ table for density conversion is calculated. Create. Details of the calculation of the main scan γ coefficient will be described later.
[0032]
In step S114, the original is read at a resolution designated by the operator (main scan operation). In step S116, the minimum and maximum density values of the read image data are obtained, the density range of the input image data is detected, and the process proceeds to step S118. In step S118, the received original image (main scan image) data is converted using the γ table created based on the previously determined γ coefficient for main scan and the density range, that is, the density of the input image. By optimizing the distribution, image data in which optimum density gradation adjustment is performed according to the contents of the document image is created.
[0033]
In the above description, the density distribution of the main scan image using the γ table is optimized by the image processing apparatus. However, if the image reading apparatus has a function of accepting and processing the γ table from the outside, the process of step S114 is performed. Prior to the main scanning operation, a configuration is also possible in which the γ table is transferred from the image processing apparatus to the image reading apparatus, and the image reading apparatus optimizes the density distribution, that is, performs density conversion using the sent γ table.
[0034]
Next, the preview γ coefficient calculation procedure in this embodiment will be described in detail with reference to a flowchart and an example of a frequency distribution diagram.
[0035]
FIG. 2 is a flowchart for explaining the calculation of the preview γ coefficient according to the first embodiment, and shows details of step S104. FIG. 3 is a diagram showing a specific example of γ coefficient calculation, taking a document showing a certain density distribution as an example.
[0036]
In step S202 of FIG. 2, first, a density frequency distribution for each color is created, and the synthesized frequency distribution for all colors is calculated by adding and synthesizing the created density frequency distribution for each color. Here, it is assumed that the density value of each color is in color balance.
[0037]
In step S204, the minimum density value (hereinafter referred to as the shadow value) and the maximum value (hereinafter referred to as shadow values) and the actual density distribution from the density 0 (zero, ie, black) side from the combined density frequency distribution of each color. In step S206, the cumulative value of the frequency of each density is calculated in the direction from the minimum value to the maximum value using the density value as a variable. As a result, an accumulated value h (d) using the density value d as a variable is obtained.
[0038]
Next, in step S208, a curve h (d) represented by the cumulative value is compared with the following function values from the calculated cumulative values of the respective densities, and approximated using the least square method. The power number G of the power function is obtained.
g (d) = M (d-Shadow) ^ G
Here, the operator A ^ B is an operator representing A to the Bth power, and M is an arbitrary number used for approximation, and is a number for matching the maximum value. Here, in the case of 8-bit expression, the curve h (d) represented by the cumulative value that is actually compared with the above-described expression is h in which the range below the Shadow value is normalized to 0, and the Highlight value and the range beyond this are normalized to 255. '(D) is used.
[0039]
In the example shown in FIG. 3, the graph of γ = 1.99 obtained by the above-described method is superimposed on the accumulated value in the range of 31 to 255. Here, when superimposing, the curve represented by the power function is normalized so as to pass the point of the maximum accumulated value.
[0040]
As described above, a power function that uniformly converts the density distribution, that is, a γ coefficient is obtained. However, depending on the content of the type of the original image, the tone of the original image may be lost. Using a given parameter T
Preview screen γ coefficient = (G ^ T), 0 <T <1.0
The calculation is performed on the preview image. Here, T is a given parameter that controls the degree of further density correction with respect to the γ coefficient calculated based on the density distribution of the preview image. When this parameter T is 1.0, The correction amount corrected by T is zero, and the correction amount increases toward 0.0. When viewed from the overall correction amount, the correction amount is large when T = 1, and the density distribution of the original is corrected to be the most uniform. When 0.0, the correction amount is zero and the correction amount is input. Does not affect the concentration distribution. The initial value is T = 1. In this case, a gamma correction table using the calculated γ coefficient as it is is created and used.
[0041]
The conversion table based on the γ coefficient thus obtained is generally a γ table as shown in FIG. 4 or FIG. For example, when the density distribution is very biased to the black side, the gamma characteristic as shown in FIG. 4 (gamma≈0.24), and when the density distribution is slightly biased to the white side, the γ characteristic as shown in FIG. (Gamma≈1.6). 4 and 5 show cases where the minimum value of the density distribution is 0 in 8-bit representation (00h in hexadecimal notation) and the maximum value is 255 in 8-bit representation (FFh in hexadecimal notation). The axis is the input density level, and the vertical axis is the output density level.
[0042]
According to the algorithm for creating the density conversion table described above, it is possible to obtain a density conversion table that increases the contrast of the density region (range) in which the frequency distribution is concentrated. .
[0043]
Next, the actual scan γ coefficient calculation procedure according to the present embodiment will be described in detail with reference to an actual example of a γ coefficient reflection table corresponding to the main scan designated resolution and a density distribution diagram of image data at high resolution.
[0044]
FIG. 6 is a main scan γ coefficient reflection table according to the first embodiment. This figure shows a change in γ magnification depending on the resolution at the time of reading a photographic original determined experimentally. For example, the optimal γ value for a photographic document with a resolution of 600 dpi is 1 / 1.87 when the resolution is 1/8, in other words, the optimal γ value of an image read at 75 dpi is , When reading at 600 dpi, a γ value of 1.087 times is the optimum γ value.
[0045]
First, the pre-scan resolution and the main scan resolution specified by the operator are input to the conversion table shown in FIG. 6, and the γ coefficient magnification Kg at the main scan corresponding to the γ value at the pre-scan is obtained. . Then, from this γ coefficient magnification Kg and the γ coefficient G for preview obtained previously,
G ′ = Kg × G
The actual scan γ coefficient G ′ is calculated.
[0046]
For the input image data of the main scan, a γ table is created using the main scan γ coefficient G ′ as in the case of creating the preview γ table, and the image read in the main scan is created using the created γ table. By executing the density conversion, it is possible to perform density gradation conversion optimum for the reading resolution.
[0047]
FIG. 7 shows a density distribution of image data obtained by reading a document similar to that shown in FIG. 3 at a resolution of 400 dpi higher than that shown in FIG. The γ value in this figure is 2.13, which is distributed in the range of density levels 11 to 255. In FIG. 3, they are 1.99 and 31-255, respectively. The density distribution in the preview image of FIG. 3 having a relatively low reading resolution approaches the average value with the neighboring pixel data, so that the histogram shape is smoother than the density distribution of the main scan image as shown in FIG. Also changes slightly. As a result, it is understood that the optimum density conversion table varies depending on the resolution even when the photographic originals are the same. That is, a change occurs in the concentration range, and the frequency distribution also changes. As can be understood from FIGS. 3 and 7, the total number of pixels in the pre-scan shown in FIG. 3 is about 540,000 from the maximum cumulative value, and the total number of pixels in the main scan shown in FIG. The maximum value is about 15.8 million. Therefore, it is understood that the data amount at the time of pre-scan is reduced to about 1/29 at the time of the main scan in order to shorten the processing time.
[0048]
As described above, according to the image processing apparatus of the present embodiment, the cumulative frequency distribution is obtained from the combined density frequency distribution in the specified range on the input document image, the power function approximated to the cumulative frequency distribution is calculated, Furthermore, by calculating the γ coefficient corresponding to the designated main scan resolution from the number of powers of the power function, it is possible to create a density conversion table optimal for the image and optimize the density gradation. .
[0049]
(Second Embodiment)
The image processing apparatus according to the second embodiment includes a γ coefficient reflection table for main scan corresponding to the document type, and is used for the main scan by using three parameters of the preview γ coefficient, the main scan designated resolution, and the document type. It has a function of calculating the γ coefficient and creating a γ table and optimizing the density of the main scan image. In the following, a photo manuscript and an illustration manuscript will be described as examples.
[0050]
FIG. 8 is a diagram illustrating a γ coefficient reflection table for main scanning of the image processing apparatus according to the second embodiment. Here, the tables for the photographic original and the illustration original indicate the γ magnification shift according to the resolution at the time of reading the original determined experimentally. In general, illustration manuscripts occupy a larger area than a photographic manuscript because the area occupied by uniform colors is small.
[0051]
According to the second embodiment, it is possible to change a density gradation suitable for a scan of a main scan image even for a document having different characteristics.
[0052]
FIG. 9 is a block diagram for easily explaining the present invention for each of the above-described embodiments. FIG. 9 will be briefly described. In FIG. 9, image data from the scanner 900 is temporarily stored in a storage unit 901 configured from a large-capacity storage medium such as a hard disk. The stored data is input to the density conversion unit 921 or a block denoted by reference numeral 910 for tone correction coefficient calculation for density conversion executed by the density conversion unit 921. The output of the density conversion unit 921 is sent to a display device, stored in a storage device, or sent to an output device such as a printing device.
[0053]
Reference numerals 910 to 913 are blocks that process a pre-scan image obtained by pre-scan to obtain a tone correction coefficient suitable for the pre-scan image, and correspond to step 104 in FIG. Here, the number of powers of the approximate power function is finally obtained as a γ value that means a tone correction coefficient.
[0054]
Reference numeral 910 calculates a density frequency distribution while inputting a pre-scan image and obtaining a minimum value and a maximum value of each pixel data. The minimum value and the maximum value of the density values obtained here are sent to a correction table creation unit denoted by reference numeral 920. In addition, the density frequency distribution data is generated by a block denoted by reference numeral 911. Further, the minimum value and the maximum value of the cumulative frequency distribution are individual values specific to the document image and pre-scan conditions. Therefore, the normalized cumulative frequency distribution is obtained by setting a predetermined range, for example, the minimum value to 0 and the maximum value to 255. The normalized cumulative frequency distribution data is input to an approximate level confirmation block denoted by reference numeral 913. This block 913 receives the data from the block 911, controls the approximate power function calculation block 912 that approximates this data, and finally uses the least square method to calculate the power of the approximate power function. Ask.
[0055]
The number of powers from block 912 is sent to block 914 as a tone correction factor, i.e., a gamma factor. This block is a block for correcting the γ coefficient obtained from the pre-scan image, and is finely adjusted according to an instruction from the operator as described above. However, immediately after the pre-scan, the input γ coefficient value is sent to the block 920 as it is, and based on the input data including the minimum value and the maximum value of the density value from the block 910, a correction table, in this case, Then, a correction table for the pre-scan image is created. The created correction table is sent to the block 921, where the density conversion of the pre-scan image is performed. If the data after density conversion is a pre-scan image, it is sent to the display device and presented to the operator. The operator observes the presented image and, if necessary, operates block 914 to fine tune the γ coefficient value.
[0056]
In the processing described above, blocks 920 and 921 are processing pre-scan images. Next, when a main scan instruction is received from the operator as a result of the above operation or processing, the blocks 910, 920, and 921 execute processing on the main scan image. First, when an actual scan instruction is received from the operator, the γ coefficient for the pre-scan image stored in the block 914 at that time is confirmed or fine-tuned by the operator on the pre-scan image on the display device. The tone correction coefficient finally set to ok. The tone correction coefficient (γ coefficient) is input to a main scan γ coefficient conversion block 930 in which pre-scan resolution, main scan resolution, and document type information are input, and the γ for main scan is input. Converted to a coefficient. The block 920 inputs the γ coefficient from the block 930 during the main scan.
[0057]
At the same time, the scanner 900 scans the original image under the conditions of the main scan, and stores the main scan image in the storage unit 901. Thereafter, the block 910 reads the data from the storage unit, acquires the minimum value and the maximum value of the density level, and sends them to the block 920 as in the pre-scan.
[0058]
Obtaining the minimum / maximum value from block 910 and the gamma value for main scan from block 930, block 920 Luminance Create a density correction table for conversion. The created density correction table is used for density conversion of the main scan image in block 921, and the converted main scan image is output to, for example, a printing device, a storage device, or the like.
[0059]
Here, in block 920, the correction table is created as follows. For example, only the γ coefficient from the block 914 or the block 930 can obtain only the conversion characteristics as shown in FIGS. In this conversion characteristic, for example, as shown in FIG. 3, when the density level is 31 to 255 (in the case of 8 bits), the converted density value is in the range of about 110 to 255 in the case of the conversion characteristic shown in FIG. Moreover, in the case of the conversion characteristic shown in FIG. 5, it will be converted into the range of about 9-255. Instead of such a conversion, the block 920 inputs the minimum / maximum value so that a curve as shown in FIG. 4 or FIG. 5 is applied to the input density level range. For example, as shown in the curve of γ = 1.99 shown in FIG. 3, the input density level 0 to 30 is set to 0 as the output value, and the input density value in the range of the input density level 31 to 255 is shown in FIG. A curve of γ = 1.99 as shown in FIG. 5 is converted into a form compressed in the horizontal direction to (256-31) /256=0.879, and a combined conversion characteristic is obtained.
[0060]
When the conversion table is created as described above, the minimum density level, for example, level 31 can be converted to zero as the output density level. That is, when converted in this way, the density range becomes larger than when not converted. It is also possible to convert the converted minimum density value so as to be equal to the minimum density value before conversion.
[0061]
In the image processing apparatus and the image processing means described in the first and second embodiments, processing is performed on the assumption that the designated range is the same image type. However, prior to performing the determination according to the present invention, it is simple. It is within the scope of the present invention to perform the determination according to the present invention for each part after the image is divided into similar parts by an evaluation function or determination function.
[0062]
The procedure for dividing the image features into similar parts by the simple evaluation function or judgment function mentioned above is a technique conventionally known as image area separation processing, and details thereof will not be described here. .
[0063]
In the present invention, a storage medium storing software program codes for realizing the functions of the above-described embodiments is supplied to a system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores the storage medium. Needless to say, this can also be achieved by reading and executing the program code stored in the.
[0064]
In this case, the program code itself read from the storage medium realizes the novel function of the present invention, and the storage medium storing the program code constitutes the present invention.
[0065]
As a storage medium for supplying the program code, for example, floppy (registered trademark) disk, hard disk, magneto-optical disk, optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM Etc. can be used.
[0066]
In addition to executing the program code read by the computer, the functions of the above-described embodiments are realized, and an OS operating on the computer is actually processed based on an instruction of the program code. The functions of the above-described embodiment can also be realized by performing part or all of the above and processing thereof.
[0067]
Furthermore, after the program code read from the storage medium is written to the memory provided in the function expansion board inserted into the computer or the function expansion unit connected to the computer, the program code is read based on the instruction of the program code. A function expansion board or a CPU provided in the function expansion unit performs part or all of the actual processing, and the functions of the above-described embodiments can also be realized by the processing.
[0068]
The present invention can also be applied to the case where the program is distributed from the storage medium storing the program code of the software realizing the functions of the above-described embodiment to the requester via a communication line such as personal computer communication. Needless to say.
[0069]
【The invention's effect】
According to the present invention, a γ coefficient value that gives an optimum density conversion for a pre-scan image calculated from density frequency distribution data of a predetermined area of a pre-scan input original image is obtained, and from this coefficient value Since the γ coefficient for performing tone correction processing on the main scan image data is obtained by a predetermined table, the image data obtained by the main scan is converted to the optimum density gradation for the main scan image data. It becomes possible to convert.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a schematic processing procedure of an image processing apparatus according to a first embodiment of the present invention.
FIG. 2 is a flowchart showing a preview γ coefficient calculation procedure of the image processing apparatus according to the first embodiment of the present invention;
FIG. 3 is a diagram showing an outline of calculation for calculating a preview γ coefficient according to the first embodiment of the present invention;
FIG. 4 is a diagram showing an example of a γ table suitable for a photographic document obtained by an embodiment of the present invention.
FIG. 5 is a diagram showing another example of a γ table suitable for a photographic document obtained by an embodiment of the present invention.
FIG. 6 is a diagram illustrating a main scan γ coefficient reflection table according to the first embodiment of the present invention;
FIG. 7 is a diagram showing a density frequency distribution and a cumulative frequency distribution of main scan input image data according to the first embodiment of the present invention.
FIG. 8 is a main scan γ coefficient reflection table according to the second embodiment of the present invention;
FIG. 9 is a block diagram illustrating the present invention.
[Explanation of symbols]
900 scanner
901 Storage unit
910 Density minimum / maximum value, density frequency distribution processing section
911 Cumulative frequency distribution, normalization processing unit
912 Approximate power function calculator
913 Approximation level confirmation part
914 γ coefficient fine adjustment part
920 correction table creation unit
921 Density converter
930 Gamma coefficient conversion for main scan

Claims (13)

Scanner means for inputting image information on a document, the scanner means performs two scans on the same document, and the next book based on the image information input by the first pre-scan. In an image processing apparatus that processes image information input by scanning,
A density frequency distribution obtaining unit for obtaining data representing a density frequency distribution of an image in a predetermined range on a document image from density level values of individual pixels of pre-scan image information obtained by pre-scanning the scanner; ,
Using the minimum density level value of the data representing the density frequency distribution acquired by the density frequency distribution acquisition means as a reference and the starting point of accumulation, the density level value is cumulatively calculated in the higher density level value direction, and the density level value is calculated. A cumulative frequency distribution obtaining means for obtaining a cumulative frequency distribution representing a relationship between the cumulative calculation value and the cumulative calculation value;
A first γ value acquisition unit that calculates an approximate power function that approximates the cumulative frequency distribution, and obtains a first γ value that represents a tone correction coefficient of the pre-scan image from the power number of the calculated function;
Γ value conversion means for converting the first γ value into a second γ value representing a tone correction coefficient at the time of the main scan, using the respective resolutions of the pre-scan and the main scan as parameters;
The main scan is performed on the scanner and main scan image information is input to determine the density range. Based on the data representing the determined density range and the second γ value, the input main scan image is input. An image processing apparatus comprising: an image tone correction unit that executes conversion for tone correction processing on information. Image tone correction means for performing tone correction processing of the pre-scan image information based on the first γ value and the data from the density frequency distribution acquisition means;
Display means for receiving and displaying the output from the image tone correction means;
A tone correction instruction input means for inputting a tone correction instruction input from an operator in response to the display of the pre-scan image on the display means;
Γ value correcting means for correcting the first γ value by a tone correction instruction from the tone correction instruction input means to generate a first corrected γ value;
The image processing apparatus according to claim 1, wherein the image tone correction unit executes the image tone correction process and outputs the image tone correction process to the display unit when the first corrected γ value is input. . In response to a main scan start instruction input from an operator in response to the display of the pre-scan image on the display means, the γ value conversion means generates the image output to the display device when the image is output. 3. The tone correction coefficient at the time of a main scan is converted into a second γ value by inputting the first γ value or the first corrected γ value used by the tone correction means. Image processing apparatus. The image processing apparatus according to claim 1, wherein the γ value conversion unit further includes a parameter representing a type of the read document.   5. The pre-scan executed for determining a tone correction coefficient at the time of a main scan of an image to be processed is executed at a resolution different from that at the time of the main scan. The image processing apparatus according to 1. A scanner for inputting image information on an original; the scanner performs two scans on the same original; and based on the image information input by the first pre-scan, In an image processing method for processing input image information,
A density frequency distribution obtaining step for obtaining data representing a density frequency distribution of an image in a predetermined range on a document image from density level values of individual pixels of pre-scan image information obtained by pre-scanning the scanner; ,
Using the minimum density level value of the data representing the density frequency distribution acquired in the density frequency distribution acquisition step as a reference and starting point of accumulation, the density level value is cumulatively calculated in the higher direction of the density level value, and the density level value is calculated. And a cumulative frequency distribution obtaining step for obtaining a cumulative frequency distribution representing a relationship between the cumulative calculation value and
A first γ value acquisition step of calculating an approximate power function that approximates the cumulative frequency distribution, and obtaining a first γ value that represents a tone correction coefficient of the pre-scan image from the power number of the calculated function;
A γ value conversion step for converting the first γ value into a second γ value representing a tone correction coefficient at the time of the main scan, using the resolutions of the pre-scan and the main scan as parameters,
The main scan is performed on the scanner and main scan image information is input to determine the density range. Based on the data representing the determined density range and the second γ value, the input main scan image is input. An image processing method comprising: an image tone correction step for performing conversion for tone correction processing on information. An image tone correction step for performing tone correction of the pre-scan image information based on the first γ value and the data from the density frequency distribution acquisition unit;
A display output step of receiving the output processed in the image tone correction step and outputting the output to a display unit;
A tone correction instruction input step for inputting a tone correction instruction input from an operator in response to the display of the pre-scan image by the display output step;
A γ value correcting step of generating the first corrected γ value by correcting the first γ value according to the tone correction instruction received in the tone correction instruction input step;
The image processing method according to claim 6 , wherein the image tone correction step executes the image tone correction step and the display output step process when the first corrected γ value is input. A main scan start instruction input step for receiving a main scan start instruction input from an operator in response to the display of the pre-scan image by the display unit step, wherein the γ value conversion step includes the main scan start instruction input; When receiving the main scan start instruction input in step, the first γ value or the first corrected γ value used by the image tone correcting means when creating the image output to the display device is input. The image processing method according to claim 7 , further comprising: converting a tone correction coefficient during the main scan into a second γ value. The image processing method according to claim 6 , wherein the parameter used in the conversion in the γ value conversion step further includes a parameter representing a type of the read document. Pre-scan is performed to determine the tone correction factor during the main scanning of the processed image, any one of the claims 6-9, characterized in that it is performed at a resolution different from the time of main scanning An image processing method described in 1. An image input step for pre-scanning the scanner and inputting image information;
A density frequency distribution acquisition step of inputting pre-scan image information obtained in the image input step and obtaining data representing a density frequency distribution of an image in a predetermined range on the document image from the density level value of each pixel;
Using the minimum density level value of the data representing the density frequency distribution acquired in the density frequency distribution acquisition step as a reference and starting point of accumulation, the density level value is cumulatively calculated in the higher direction of the density level value, and the density level value is calculated. And a cumulative frequency distribution obtaining step for obtaining a cumulative frequency distribution representing a relationship between the cumulative calculation value and
A first γ value acquisition step of calculating an approximate power function that approximates the cumulative frequency distribution, and obtaining a first γ value that represents a tone correction coefficient of the pre-scan image from the power number of the calculated function;
A γ value conversion step for converting the first γ value into a second γ value representing a tone correction coefficient at the time of the main scan, using the resolutions of the pre-scan and the main scan as parameters,
The main scan is performed on the scanner and main scan image information is input to determine the density range. Based on the data representing the determined density range and the second γ value, the input main scan image is input. A computer-readable storage medium storing a program for executing an image tone correction step for performing conversion for tone correction processing on information. The storage medium according to claim 11 ,
As the storage medium, a floppy (registered trademark) disk, a hard disk, a magneto-optical disk, an optical disk, a CD-ROM, a CD-R, a magnetic tape, and a non-volatile storage storing a program that can be read by a server computer and a client computer A storage medium characterized by using a memory card and a ROM. The storage medium according to any one of claims 11 to 12 ,
The storage medium is detachable from a server computer and a client computer.

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