JPH11177825A - Image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform flexible gradation correction corresponding to the kind of an original and the characteristics of an output equipment without increasing a data amount and without causing gradation degradation. SOLUTION: In a gradation correction means 202, the inputted RGB signals of 12 bit/pixel are converted from a reflectivity measure into a density measure by a linear LUT, gradation correction is executed and they are turned to the image signals of 8 bit/pixel and outputted. Then, in an image processing part 102, the respective kinds of processings are executed so as to freely perform the correction corresponding to a mode and the characteristics of the original. The processings executed in the respective parts are controlled by signals outputted by a control means 213.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for performing gradation correction according to the characteristics of an image.

[0002]

2. Description of the Related Art In recent years, digital image input devices such as a flatbed scanner, a film scanner, a sheet feed scanner, and a digital camera have become widespread, and accordingly, a wide variety of correction processes are performed on an input image. Proposed. The correction processing performed on the input image includes, for example, correction for removing color turbidity and correction for removing moiré. One of the correction processing is processing for correcting the gradation of the image. Here, a conventional gradation correction processing technique will be described using a digital color copying machine as an example. FIG.
1 is a block diagram showing a configuration of a conventional digital color copying machine. The illustrated digital color copying machine includes an image input unit 101, an image processing unit 102, and an image output unit 103. The image processing unit 102 includes a gradation correction unit 1301, a color correction unit 1302, a black plate generation / under color removal unit 1303, a scaling unit 1304, a definition correction unit 1305, a gradation correction unit 1306, and a halftone generation unit. 1
307, detection means 1308, and control means 1309. Before color copying is performed, first, prescanning is performed. In the pre-scanning, the image input unit 101 outputs R of 8 bits / Pixel (bits per pixel).
When the (red), G (green), and B (blue) color signals are output to the image processing unit 102, the detection unit 1308
A series of detection processes are performed such as the size and position of the document, whether the document is a color document or a black and white document, detection of the density distribution of the document, and identification and separation of the picture area and the character area in the document. Then, information on various copying conditions is detected by the detecting unit 13.
08 to the control means 1309. Subsequent to the pre-scanning, scanning of the actual copying operation (main scanning) is performed.
After being supplied to 301 and subjected to gradation correction processing, it is supplied to color correction means 1302 to be converted into a Y (yellow) M (magenta) C (cyan) signal. The YMC signal is converted into an 8-bit / Pixel frame-sequential signal of one component of YMCK (black) by the black plate generation / under color removal unit 1303, and then processed by each unit and output to the image output unit 103. . In the case of four-color full-color copying, the main scan is performed four times, and YMC
Printing of four colors of K is performed.

[0003]

The tone correcting means 1301 of such a digital color copying machine performs the following tone correcting process. 1) Since the input RGB signal is a signal of a reflectance scale, the signal of the reflectance scale is converted into a signal of a density scale. 2) Generally, the RG input to the gradation correction unit 1301
Since the gray balance of the B signal is lost, the gray balance is corrected so that the output value of R = G = B when gray is input. Further, depending on the original to be copied, such as "character mode" or "photograph mode", the image quality is adjusted such that the gradation characteristic is set to a high contrast or to a gradual gradation characteristic. 3) Further, when copying an original having turbidity such as newspaper, tone correction is performed to remove fog in a low density region so as to eliminate the turbidity.

[0004] These tone correction processes are performed by the tone correction means 1.
In 301, a one-dimensional LUT (Look Up Table) is provided for each color of an input digital image signal.
Seen at the same time. However, in the above-described correction processing, the image signal is output with the same number of gradations as the input image signal. There is a problem that the number of gradations of the signal is reduced. For example, the number of output gradations when the gradation correction processing is performed in a form including the conversion from the reflectance scale to the density scale is lost by about 20% as compared with the number of input gradations. More specifically, each color is 8 bits / Pixel
8 bits / Pixel
Is output, the number of input gradations is 256.
The number of output gradations is generally 170 to 1
It is reduced to about 90 gradations. This gradation deterioration becomes large in a gradation range where the correction amount is large, and eventually leads to image quality deterioration such as generation of a pseudo contour and deterioration of graininess in a reproduced image.

In order to solve such a problem, a method of increasing the number of gradations of the image signal input to the gradation correction means 1301 with respect to the image signal to be output can be considered.
However, such a method has a problem that the capacity of the LUT becomes large. And, as mentioned above,
In order to switch the gradation characteristics in accordance with various copy modes, it is necessary to have gradation correction means for the required number of characteristics, so that the data capacity for correction further increases. Further, in order to realize a process of changing the correction condition according to the density distribution of the document, an LUT corresponding to the density information of the target document extracted by the detection unit 1308 is calculated and set in the gradation correction unit 1301. However, when the number of input gradations increases, the amount of calculation also increases, and as a result, the time from the end of pre-scanning to the start of main scanning becomes longer. there were. That is, in the conventional method of performing tone correction according to density information and a processing mode while converting a reflectance scale to a density scale with one tone correction unit, tone degradation occurs or tone correction is performed. However, there is a problem that the data for the communication increases.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and performs various tone correction processes according to image characteristics by increasing data for tone deterioration and tone correction. It is an object of the present invention to provide an image processing apparatus which can be realized without any problem.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention performs gradation correction of density scale image data with a gradation correction characteristic corresponding to a control signal and has a first gradation number. First tone correction means for outputting tone correction data,
Image data having a second gradation number higher than the first gradation number expressed on a reflectance scale is input, and the input image data has the first gradation number expressed on a density scale. Second tone correction means for converting the density scale image data and outputting the same, and control means for outputting the control signal to control the tone correction characteristics according to the characteristics or type of an image corresponding to the image data And characterized in that:

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1-1. Configuration of First Embodiment 1-1-1. 1 and 2 are diagrams showing an outline of a digital color copying machine to which the present invention is applied. FIG. 1 is a block diagram showing a schematic configuration of the first embodiment. As shown, the digital color copying machine of the present embodiment includes an image input unit 10.
1, an image processing unit 102 and an image output unit 103.

An image input unit 101 reads a color original and outputs a digital image signal indicating each of RGB primary color components to an image processing unit 102. For example, a CCD (C
Using a charge coupled device (charge coupled device) line sensor, 8 bits / Pixel for each color and a resolution of 400 dp in both the main scanning direction and the sub-scanning direction.
An RGB image signal Sn1 of i (dot per inch: number of dots per inch) is output.

The image processing unit 102 performs various processes on the RGB image signal Sn1 input from the image input unit 101, generates a YMCK image signal Symck, and outputs the YMCK image signal Symck to the image output unit 103. 1 bit / P
1600 dpi in the main scanning direction, 40 in the sub-scanning direction
The image signal Symck of 0 dpi is output.

The image output unit 103 outputs a color image to a medium such as paper based on the image signal Symck output from the image processing unit 102. For example, an image processing apparatus of an electrophotographic system corresponds thereto, an exposure unit such as a laser beam scan for scanning a photosensitive member, a developing unit for developing a latent image formed by the exposure unit with four primary colors, and a developing unit formed on the photosensitive member. The image forming apparatus includes a transfer unit that transfers an image onto a sheet, a fixing unit that combines the sheet and a color material that is transferred onto the sheet, a sheet conveying unit, and the like.

1-1-2. Next, the configuration of the image processing apparatus shown in FIG. 1 will be described in more detail. FIG. 2 is a diagram illustrating details of each unit of the first embodiment.

(1) Configuration of Image Input Unit 101 In the image input unit 101, the image signal Sh input by the image input unit 201 is supplied to the gradation correction unit 202, and the gradation is corrected by the gradation correction unit 202. Image signal Sn
1 is supplied to the detection unit 203 and the image processing unit 102.

The image input means 201 is 12 bit / Pi
xel RGB image signal Sh, a document mounting table on which a document to be read is mounted, a CCD line sensor for reading by separating color into three primary colors of light, RGB, and scanning in a direction perpendicular to the line sensor. Document scanning means,
It comprises an A / D (analog / digital) converter for converting the output value of the line sensor into a multi-valued digital image signal.

The gradation correction means 202 is 12 bit / Pi
The xel RGB image signal Sh is subjected to gradation correction, and the image signal Sh expressed on a reflectance scale is converted into an 8-bit / Pixel RGB image signal Sn1 expressed on a density scale.

The detecting means 203 detects information required at the time of copying from the RGB image signal Sn1 and outputs a control signal S1 to the control means 213.
Required information includes, for example, the size and position of the original,
There is a density level for automatically adjusting the density, for example, for a monochrome original and a color original. Automatic density adjustment means that when low-density pixels are detected from the background of the paper itself, such as newsprint, for example, the detected density distribution information is used to prevent the gradation corresponding to the background from being printed. Means to determine the number of gradations that will be the base reference point from.

(2) Configuration of Image Processing Unit 102 The image processing unit 102 converts the RGB image signal Sn1
The gradation correction means 204 performs gradation correction processing to generate an RGB image signal Sn1, and the color correction means 205 corrects the color characteristics of the RGB image signal Sn1 to correct the YMC image signal Sy.
mc is generated, and the YMC image signal Symc is supplied to the picture / character identification unit 206 and the black plate generation / under color removal unit 208. Then, the control signal S2 is supplied from the picture / character identification means 206 to the control signal generation means 207, and the control signal S3 is supplied from the control signal generation means 207.
To the black plate generation / under color removal unit 208, the control signal S4 to the definition correction unit 210, and the control signal S5 to the gradation correction unit 2.
11 and the control signal S6 are supplied to the halftone generation means 212.

The YMCK image signal Symck generated by the black plate generation / under color removal unit 208 from the YMC image signal Symc is converted into a scaling unit 209, a definition correction unit 210, a gradation correction unit 211, and a halftone generation unit. The processing is sequentially performed at 212 and output to the image output unit 103. The control signal generated by the control unit 213 based on the control signal supplied from the detection unit 203 is transmitted to the gradation correction unit 204, the color correction unit 205, the picture / character identification unit 206, and the control signal generation unit 207. Each is configured to be supplied.

As described above, in the present embodiment, the gradation correction which has been performed simultaneously in the image processing unit 102 can be corrected separately according to the appropriateness of the image input unit 101 and the image processing unit 102. It is composed. That is, by converting the reflectance scale to the density scale in the image input unit 101, the image data amount is reduced without deteriorating the gradation, and the image processing unit 102 can freely perform the gradation correction according to the processing mode or the like. It is configured as follows. The gradation correction means 204 corresponds to a first gradation correction means described in the claims, and the gradation correction means 202 corresponds to a second gradation correction means described in the claims.

1-2. Operation of First Embodiment Next, a detailed operation of the embodiment having the above configuration will be described. 1-2-1. Operation of Image Input Unit 101 First, the operation of the image input unit 101 will be described. The image input unit 201 reads a document placed on a document placing table, thereby obtaining RGB 12-bit / Pixel for each color.
1 digital signal Sh is generated. Here, CCD
Since the analog value read by the sensor is digitized, the signal output from the image input unit 201 is a reflectance scale. 12bit / Pixel RGB
The image signal Sh is subjected to gradation correction by a one-dimensional LUT in the gradation correction means 202, and is converted from a reflectance scale to a density scale and output as an 8-bit / Pixel image signal Sn1. As described above, the problem of the prior art that the number of gradations is reduced by using the LUT for converting the reflectance scale to the density scale and performing various gradation corrections is that the number of input gradations is reduced to the output gradation. The problem is solved by setting it higher than the number. By increasing the number of input gradations, high-precision correction can be performed, and by decreasing the number of output gradations, it is possible to prevent an increase in the amount of image data that imposes a burden on processing.

The detecting means 203 detects information necessary for the subsequent processing from the RGB image signal Sn1, and outputs the information to the control means 213 as a control signal S1.
A series of processing up to this point is performed as prescanning prior to the original copying operation.

When the information for correction is supplied to the image processing unit 102 as a control signal S1, a main scan is performed next.
In the main scanning, image signals scanned and input by the image input unit 101 are sequentially supplied to the image processing unit 102, and the image processing operation is performed in synchronization with the input operation.

1-2-2. Operation of Image Processing Unit 102 Next, the operation of the image processing unit 102 will be described. In the image processing unit 102, the RGB image signal Sn1 input in the main scan is sequentially processed in each unit illustrated in the drawing, and
The image is output to the image output unit 103 as a YMCK image signal Symck. The processing performed in each unit includes a control signal S1 indicating document information supplied by pre-scanning, and a control signal S1 output by the control unit 213 based on a mode specified via a user interface (not shown).
7 to 10. Documents include text, graphics printing, photographs, a mixture of characters and photographs, and printing in full color or black and white. Then, the user can select a desired mode from a plurality of modes so that the apparatus performs optimal printing according to the type of the document, for example, a full-color photograph mode.

Each section performs a process on the input image signal by using a predetermined coefficient, and outputs the calculation result as an image signal. A plurality of the predetermined coefficients are stored in accordance with the respective modes, and are appropriately selected and used in the calculation in each unit. Note that these coefficients are stored in a ROM (not shown), and when used in each processing unit, the values of R are determined based on a control signal from the control unit 213.
It is read from a predetermined address of the OM.

(1) Tone correction means 204 and color correction means 205 (from RGB image signal Sn1 to YMC image signal S
First, the RGB image signal Sn1 is subjected to gradation correction processing by the gradation correction means 204 according to the control signal S7, and is converted into the YMC image signal Symc by the color correction means 205. Here, FIG. 3 shows coefficient processing of the gradation correction unit 204 and the color correction unit 205. The table shown in the figure is
For the processing performed by the gradation correction means 204 and the color correction means 205, the relation between the designated mode and the coefficient is shown.

FIG. 3A is a diagram for explaining coefficients applied to the processing by the gradation correction means 204. Coefficient 1
Is a processing coefficient for correcting the gradation of a character or graphics document, and is a processing coefficient for enhancing the contrast of the document. The coefficient 2 is a processing coefficient for correcting the gradation of an original including a photograph, and is a processing coefficient for preserving the brightness and color density of the original and faithfully reproducing the copy as it is. I have. As described above, the automatic adjustment means that the automatic adjustment is performed so as to remove the fog of the background of the original such as newspaper. That is, in the case of the text, graphics printing, and text / photo modes, a process of automatically adjusting the background based on the density distribution information detected by the detection unit 203 is performed.

FIG. 4 is a diagram for explaining automatic adjustment of the background. The density adjustment LUT shown in FIG. 4 is created by calculation based on the background reference point detected by the detection unit 203. The gradation correction LUT shown in FIG.
This is coefficient 1 or coefficient 2 in (a). The synthetic LUT is
Using the coefficient 1 or coefficient 2 read from the ROM and the base reference point information supplied from the control unit 213,
This is synthesized and developed in the RAM table of the gradation correction means 204. Using this composite LUT, the input RGB image signal Sn1 is corrected, and the RGB image signal Sn2 is output.

As described above, the gradation correction means 204
By combining the type of coefficient and the automatic adjustment according to the eight types of modes that can be specified, free correction according to the mode can be realized with a small amount of correction data. Conventionally, tone correction for the input image and conversion from the reflectance scale to the density scale are simultaneously performed. In the present embodiment, however, the tone correction unit 202 has already converted the reflectance scale to the density scale. , The tone correction means 204 can perform tone correction using only the density scale, and the number of tones does not unnecessarily decrease.

Next, the processing in the color correction means 205 will be described. In the color correction means 205, the RGB image signal Sn
2, the YMC signal Symc based on the control signal S8.
Is generated. Here, FIG. 3B shows the color correction unit 20.
FIG. 9 is a diagram for explaining coefficients applied to the processing in FIG. In the table, coefficient 1 is a processing coefficient when a character is included,
This is a processing coefficient for reproducing characters clearly without color mixing. The coefficient 2 is a processing coefficient that emphasizes graphics and photographic elements, and is a processing coefficient that faithfully reproduces a subtle hue such as a photograph or a map. The coefficient 3 is a processing coefficient used in the monochrome mode, and is a processing coefficient for extracting only the brightness of the document. In this way, after the YMC image signal Symc is generated by switching the processing coefficient according to the characteristics of the original, the YMC image signal Symc is supplied to the picture / character identification unit 206 and the black plate generation / under color removal unit 207. Is done.

(2) Automatic Identification In the picture / character identification means 206, the YMC image signal S
For each pixel in the document, whether it is a picture portion or a character portion is identified based on ymc. Here, each pixel is classified into one of a "picture", a "black character", and a "color character". Note that picture / character identification is performed only when a control signal designating a document in which characters and photographs are mixed is input. In addition, the control signal generation unit 207 uses the control signal S2 indicating the picture / character identification result and the control signal S10 indicating the mode set by the user from the black plate generation / under color removal unit 207, the definition correction unit 210, Tone correction means 211,
And control signals S3 to S3
6 is generated.

(3) Black plate generation / under color removal means 207 (Y
From the MC image signal Symc to the YMCK image signal Symck
In addition, the black plate generation / under color removal unit 207 generates a K signal based on the YMC image signal Symc, and generates a YMCK image signal Symck according to the generated K amount. FIG. 5A is a diagram illustrating black plate generation / under color removal coefficients for generating the YMCK image signal Symck. For example,
In the case of the full-color photograph mode, the coefficient 1 is selected, and in the case of the full-color character mode, the coefficient 2 is selected. However, in the case of the black-and-white mode, it indicates that no processing is performed irrespective of characters and photographs.

(4) The halftone generation means 212 from the scaling means 209 (after the YMCK image signal Symck is generated) The YMCK image signal Symck output from the plate generation / under color removal means 207 is The enlargement or reduction processing in the main scanning direction is performed. The enlargement / reduction of the image is realized by combining the scaling processing in the main scanning direction and the enlargement / reduction processing in the sub-scanning direction by changing the document scanning speed in the image input unit 101.
The YMCK image signal Symck that has been subjected to the enlargement / reduction processing by the scaling unit 209 is supplied to the definition correction unit 210, and the processing for correcting the spatial characteristics for correcting blur and sharpening edges is performed. Will be applied. Here, 5 ×
This is realized by a well-known spatial filtering process using a convolution operation of five pixels (sub-scanning direction × main scanning direction). FIG. 5 (b)
FIG. 9 is a diagram illustrating a definition correction coefficient of definition correction. For example, in the case of the full-color character mode, the coefficient 1 is selected, and in the case of the full-color photograph mode, the coefficient 4 is selected. In the case of the black and white character mode, the coefficient 2 is selected, and in the case of the black and white photo mode, the coefficient 4 is selected.

In the gradation correcting means 211, the YMCK image signal Symc supplied from the definition correcting means 210
For k, the gradation characteristic is corrected in accordance with the halftone generation processing performed in the next step. FIG. 5C shows the gradation correction coefficient. For example, in the case of the full-color character mode, the coefficient 1 is selected, and in the case of the full-color photograph mode, the coefficient 3 is selected. In the case of the black and white character mode, the coefficient 4 is selected, and in the case of the black and white photo mode, the coefficient 6 is selected.

The multi-valued YMCK image signal Symck supplied from the gradation correcting means 211 is subjected to halftoning processing for generating a binary image in the halftone generating means 212. That is, multi-valued image data input at 400 dpi × 400 dpi (main scanning × sub-scanning direction) at 8 bit / Pixel is 400 dpi × 1600 dpi (main scanning × sub-scanning direction) at 1 bit / Pixel.
Of binary image data. FIG. 5D shows the halftone generation coefficient. For example, in the case of the full-color character mode, the coefficient 1 is selected, and in the case of the full-color photograph mode, the coefficient 3 is selected. In the case of the black-and-white character mode, the coefficient 1 is selected, and in the case of the black-and-white photo mode, the coefficient 1 is selected.

As described above, in the present embodiment, an input digital image signal is converted into a signal of a density scale that can be processed by the image processing unit 102 while preventing gradation deterioration in the image input unit 101, At 102, various processes are performed in accordance with the output of the image output unit 103, and finally output from the image output unit 103. Therefore, the type and characteristics of the document can be increased without increasing the data required for the process. Can be realized without causing the gradation degradation such as the pseudo contour and the graininess degradation.

2. Second Embodiment Next, a second embodiment will be described. In the second embodiment, unlike the first embodiment in which the processing coefficient is switched for each mode, a case will be described in which the processing coefficient is set according to each mode based on the reference LUT.

2-1. Configuration of Second Embodiment The configuration shown in FIG. 1 is the same as that of the first embodiment, but the configuration of the image processing unit 102 is different. FIG. 6 is a block diagram illustrating the configuration of the second embodiment. 2 illustrates the gradation processing of the present invention as in FIG. 2, but only a part of the image input unit 101 and the image processing unit 102 is illustrated for convenience. 6 are the same as those in the first embodiment, and those denoted by the same reference numerals as those in the first embodiment are also the same as those in the first embodiment, and therefore description thereof is omitted. .

The first storage means 604 stores the gradation correction means 2
02, the processing coefficient (reference LU)
T), and the second storage means 605
Are processing coefficients (reference LUT, processing coefficient 1, processing coefficient 2,...) Used in the gradation correction performed by the gradation correcting unit 204.
Processing coefficient n. Each processing coefficient is a coefficient equivalent to the processing coefficient shown in FIG. ) Are stored, each of which is composed of a RAM, a ROM, and the like. Note that the first storage unit 604 and the second storage unit 605 are one RAM
Alternatively, it may be configured by a ROM or a ROM and the stored data may be shared.

The calculating means 606 reads a predetermined processing coefficient from the second storage means 605, performs a predetermined calculation, and then supplies the calculation result to the gradation correcting means 204 as a processing coefficient. It is.

2-2. Operation of the Second Embodiment The operation of the second embodiment is performed when the copy mode is the full-color character mode with respect to the setting of the processing coefficients used in the correction processing by the gradation correction unit 202 and the gradation correction unit 204. Will be described as an example. First, in the tone correction unit 202, conversion from the reflectance scale to the density scale is performed with reference to the reference LUT stored in the first storage unit 604. A processing coefficient of a standard mode such as “text / photo mode” is suitable for the reference LUT. In this embodiment, the coefficient 2 described in the first embodiment (FIG. 3A) is used. I do.

Next, an LUT to be referred to when performing gradation correction by the gradation correction means 204 is set by calculation. The calculation means 606 selects a processing coefficient corresponding to the mode designated by the user from the processing coefficients 1 to n stored in the second storage means 605. In the present embodiment, since it is a full-color character mode, it has been described in the first embodiment (FIG. 3).
(A)) It corresponds to the coefficient 1. Then, a difference between the coefficient 1 selected according to the mode and the coefficient 2 equivalent to the reference LUT is calculated and set as a processing coefficient to be applied by the gradation correction unit 204. Here, FIG. 7 is a graph showing the correspondence between the input value and the output value for each LUT in order to explain the content of the calculation by the calculation means 606. The calculation means 606 stores the reference LUT from the second storage means 605.
= Processing coefficient 2 (FIG. 7A) and processing coefficient 1 (FIG. 7B) selected according to the mode are read, and a difference LUT (FIG. 7C) is obtained by calculation. This is supplied to the tone correction means 204.

FIG. 8 shows processing coefficients for gradation correction performed by the gradation correction means 204. In the copy mode in which the LUT corresponding to the coefficient 1 is used in the first embodiment, the calculating unit 606 is used instead of the LUT corresponding to the coefficient 1.
Is set. In the copy mode using the LUT corresponding to the coefficient 2, the coefficient 2
Is set in place of the LUT corresponding to, and a difference LUT through which the RGB image signal Sn1 obtained by the calculating means 606 passes. The pass-through is performed when the difference LUT obtained by the calculation means 606 is hardly different from the reference LUT. In this embodiment, since the LUT corresponding to the processing coefficient of the standard character / photo mode is used as the reference LUT, the difference correction amount between the LUT corresponding to the processing coefficient selected according to the mode and the reference LUT is This produces a very delicate image quality reproduction effect, and is very close to a plain image, so that there is no concern about gradation degradation.

As described above, there is provided a means for storing the reference LUT and the processing coefficient.
The correction is performed by the UT, and the gradation correction unit 204 performs the gradation correction that is the difference between the reference LUT and the LUT corresponding to the processing coefficient according to the mode. With the above configuration, it is possible to perform the correction with higher accuracy according to the mode.

3. Third Embodiment Next, a third embodiment will be described. When a scanner is used for inputting an image and a printer is used for image processing and output, the processing speed may be different, and the configuration cannot be the same as that of the first or second embodiment. In the third embodiment, a case where image data is stored using a page memory will be described.

3-1. Configuration of Third Embodiment FIG. 9 is a block diagram illustrating a schematic configuration of the third embodiment. As shown, the image input unit 101, the image processing unit 1
02, the image output unit 103, and the page memory 904,
And a memory interface 905. In the figure, components denoted by the same reference numerals as those in the first embodiment are the same as those in the first embodiment, and thus description thereof will be omitted. Page memory 9
Reference numeral 04 denotes an image storage unit that can store the RGB image signal Sn1 for one page for each color. Further, the memory interface 905 is connected to the page memory 9.
It controls reading / writing from / to the server 04.

As described above, by providing the image storage means between the image input unit 101 and the image processing unit 102, the input image data can be used to determine the size and density distribution of the original and whether or not it is a color original. After various settings are automatically performed by detecting the judgment and the copy magnification setting, various processing can be performed on the stored image data and output.
The pre-scan as in the first and second embodiments is not required, and only one scan is required for scanning, and processing can be performed even if the input speed and the processing speed are different.

FIG. 10 is a block diagram showing the details of each unit shown in FIG. As shown, the image input unit 101
The components constituting the image processing unit 102 are the same as those in the first embodiment (FIG. 2), and the memory interface 905 intervenes between the image input unit 101 and the image processing unit 102, so that the page memory 904 On the other hand, image data can be read and written. Further, the scaling unit 209 in the present embodiment performs two-dimensional scaling in the main scanning direction and the sub-scanning direction. The other configuration is the same as that of the first embodiment, and the description is omitted.

3-2. Operation of Third Embodiment Next, an operation of the third embodiment having the above configuration will be described. Similarly to the first embodiment, a 12-bit / Pixel reflectance scale RGB image signal Sh input by the image input unit 201 is subjected to gradation correction by the gradation correction unit 202 and an 8-bit / Pixel density scale. Is converted to an RGB signal. Then, the converted RGB image signal Sn1 is stored in the page memory 904 via the memory interface 905. Further, the RGB image signal Sn1 is supplied to the detecting means 203, and various kinds of information are detected as in the first embodiment. Next, the image processing unit 10
2 is supplied with image data stored in the page memory 904 via the memory interface 905.

As described above, even when a memory is interposed between the image input unit 101 and the image processing unit 102, a large amount of added value is provided because the gradation correction is performed in advance by the image input unit 101. The capacity of the page memory can be reduced, and the same effect as in the first embodiment can be obtained even when the processing speeds of the image input unit 101 and the image processing unit 102 are different.

4. Fourth Embodiment Next, a fourth embodiment will be described. In this embodiment,
The image read from the image input unit 101 is stored in the page memory 9.
The present invention is applied to an image processing device that stores the image data in an image display device 04 and displays the image data on a plurality of image display devices. When one original is read and output to a plurality of image display devices having different output conditions, such as a CRT display and a liquid crystal display, the tone characteristics differ depending on the output destination.
The gradation correction unit 202 performs correction common to the gradation characteristics of a plurality of output destinations.

4-1. Configuration of Fourth Embodiment FIG. 11 is a block diagram illustrating a configuration of the fourth embodiment. In the fourth embodiment, after the RGB image signal Sh input by the image input unit 201 is converted from the reflectance scale to the density scale by the gradation correction unit 202 and output as the RGB image signal Sn1, the memory interface 905 The image data stored in the page memory 904 is read out via the
5, a gradation correction process is performed, and image display means A1
It is configured to be output and displayed at 107. Also,
Similarly, the tone correction unit B1106 performs a tone correction process, and the image is displayed on the image display unit B1108. Further, the control signal S output from the arithmetic means 1110 accessible to the storage means 1109
According to 1, a and b, the gradation correcting means 202, the gradation correcting means A1105, and the gradation correcting means B1106
The configuration is such that appropriate gradation correction processing can be performed on the B image signal Sn1.

The tone correcting means A1105 and the tone correcting means B1106 sequentially read out the image data stored in the page memory 904 so that the image is displayed well on each of the image displaying means A1107 and the image displaying means B1108. Thus, tone correction is performed by a one-dimensional LUT. The image display unit A1107 and the image display unit B1108 convert the RGB primary colors into 8 bits / Pi.
This is a display means for displaying a color or multi-tone black and white image such as a CRT display or a liquid crystal display capable of displaying about 16.77 million colors in xel.

The storage means 1109 is a means for storing processing coefficients for correcting gradation characteristics, and is a calculating means 1110.
Is based on the processing coefficient stored in the storage unit 1109,
An LUT to be set in the gradation correction means 202, the gradation correction means A1105, and the gradation correction means B1106 is obtained by calculation, and data is written in the RAM table of each correction means. The processing coefficients stored in the storage unit 1109 include the image display unit A1107 and the image display unit B1.
108 are set according to the characteristics. In the present embodiment, in order to reduce the data capacity, multiplication and addition coefficients obtained by approximating the correction curve with a quintic function are stored, but other functions or one-dimensional LUT data itself may be used. The same components as those shown in the first to third embodiments are denoted by the same reference numerals, the description of the configurations is omitted, and the operation of the fourth embodiment having the above configuration will be described. .

4-2. Operation of Fourth Embodiment RGB of one page input from image input means 201
The RGB image signal Sh of 12 bits / Pixel for each color is
The gradation correction unit 202 performs gradation correction, converts the reflectance scale into a density scale, and outputs the RGB image signal Sn1 of 8 bits / Pixel for each color of RGB. The image signal Sn1 whose data volume has been reduced by this processing is accumulated in the page memory 904 via the memory interface 905. Then, the image signal Sn1 stored in the page memory 904 is supplied to the gradation correction unit A1105 and the gradation correction unit B1106 via the memory interface 905. In the tone correcting means A1105 and the tone correcting means B1106, processing is performed based on the processing coefficient set by the calculating means 1110, and the image signal Sna and the image signal Snb after the tone correction are output to the image displaying means A1107 and the image displaying means A1107. It is supplied to each of the display means B1108 and displayed on each image display means.

Tone correction means 202, tone correction means A11
05. The gradation correction performed by the gradation correction unit B1106 is based on the processing coefficient set by the calculation unit 1110. Here, FIG. 12 is a diagram illustrating the generation processing of the LUT corresponding to the processing coefficient in the calculating unit 1110. (A) is an LUT corresponding to a processing coefficient for correcting the display characteristics of the image display unit A1107, and (b) is an LUT corresponding to a processing coefficient for correcting the display characteristics of the image display unit B1108. The storage unit 1109 stores multiplication and addition coefficients obtained by approximating each processing coefficient by a quintic function.

In order to maintain the best display quality of the image, the gradation correction means A 1105 and the gradation correction means B 1106 output the image data input at 12 bits / Pixel at 8 bits / Pixel, respectively, and perform the gradation correction. Is desirably performed, but then the size of the LUT and the size of the page memory 904 increase. Therefore, the calculating means 1110 obtains a reference LUT representative of the characteristics of LUTA and B, and sets it in the RAM table of the gradation correcting means 202. This reference LUT is shown in FIG.
It is shown in (c). Then, a difference between the correction amount based on the reference LUT and the above-mentioned LUTA and LUTB is calculated, and the LUT is set in the gradation correction means A1105 and the gradation correction means B1106, respectively. The difference LU is shown in FIG.
TA ′, and the difference LUTB ′ are shown in FIG. In this way, before storing in the page memory 904, 1
Since the process of converting from 2 bits / Pixel to 8 bits / Pixel is performed, and then the gradation correction corresponding to the characteristics of each image display unit is performed, the capacity of the LUT and the page memory can be reduced without deteriorating the image display quality. be able to.

As one method of generating the LUT, there are one image display means A1107 and one image display means B11.
A method of selecting an LUT corresponding to a processing coefficient for correcting one of the characteristics 08 is considered. For example,
If one of the two UTLs is a standard one, the standard LUT may be used as a reference LUT. That is, when the image display unit A1107 is more frequently used than the image display unit B1108, the LUTA ((a) in the figure) is used as a reference LUT, and the LUTB ((b) in the figure) is used. May be set in the gradation correction means B1106.

On the other hand, from the viewpoint of gradation and image quality, the gradation correction means 202 uses 8 bits / pixel.
There is a method of using an LUT with as little gradation degradation as possible at the stage when it becomes 1. For example, when the LUT is generated at 12 bits / Pixel, the number of actual steps is counted, and the number of steps is larger, or the interval (range) between the rise from the output value of the LUT and the maximum output value saturation point is larger. In addition, a reference LUT in which there is less change in output value for one input step and less gradation omission after correction may be adopted.

Another example is that a reference LU is obtained from a multiplication / addition coefficient for generating an LUT for two screen display means.
There is a method of generating T. For example, LUTA and LU
Generate an average LUT of the two LUTs of the TB and use that as the reference LUT. Alternatively, a straight line connecting the smallest point (reference point) in the rise from the LUT output value 0 and the largest point (reference point) of the maximum output value saturation point is set as the reference LUT. Also, of the two LUTs,
An LUT having less gradation omission after correction due to a change in output value with respect to one input step is selected, and the selected LUT and the above-mentioned reference LUT are combined so that the rising and saturation points become the above-mentioned reference points. May be generated.

As described above, the first gradation correction is performed by obtaining a reference gradation correction condition for a plurality of different image processing conditions and image output conditions corresponding to the display characteristics of each display means. The difference from the reference correction condition is found and the second
Is performed, a display characteristic of each display means can be absorbed, and a digital image without gradation deterioration can be generated.

[0062] 5. Modifications The present invention is not limited to the above-described embodiments, and various modifications as described below are possible.

The numerical values used in the above embodiment are merely examples, and are not limited to the above numerical values as long as the present invention is applied. For example, in the first gradation conversion, the input is 12 bit / P
The output is set to 8 bits / Pixcel for the pixel, but is not limited to this as long as the number of input gradations is higher than the number of output gradations.
bit / Pixcel may be used. These may be set according to the characteristics of the LUT when converting from the reflectance scale to the density scale. Also, not limited to reflectance and density scale,
For example, it may be a lightness scale. Further, various modes and processing coefficients in the embodiment are also examples, and are not limited to the embodiment.

In the first to third embodiments, digital color copying has been described as an example. However, the present invention is not limited to this. For example, a scanner may be used for the image input unit 101, a computer may be used for the image processing unit 102, and a printer may be used for the image output unit 103. May be used.

Furthermore, in the fourth embodiment, the number of image output destinations is two. However, the present invention is not limited to this, and three or more output destinations may be provided. Further, a CRT display or the like is used as an output destination, but an output by a color printer or a multi-tone black and white printer may be used.

[0066]

As described above, according to the present invention,
Without increasing the amount of image data, it is possible to realize flexible gradation correction according to the type of the document and the characteristics of the output device without causing gradation deterioration.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment.

FIG. 2 is a diagram showing details of each unit of the first embodiment.

FIG. 3 is a diagram illustrating coefficient processing of a gradation correction unit and a color correction unit.

FIG. 4 is a diagram illustrating automatic adjustment of a base.

FIG. 5 is a diagram showing processing coefficients of each unit.

FIG. 6 is a block diagram illustrating a configuration of a second embodiment.

FIG. 7 is a diagram for explaining the contents of calculation by the calculation means.

FIG. 8 is a diagram illustrating processing coefficients of correction performed by a gradation correction unit.

FIG. 9 is a block diagram illustrating a schematic configuration of a third embodiment.

FIG. 10 is a block diagram showing details of each unit of the third embodiment.

FIG. 11 is a block diagram illustrating a configuration of a fourth embodiment.

FIG. 12 is a diagram illustrating a process of generating an LUT in a calculation unit.

FIG. 13 is a block diagram showing a configuration of a conventional digital color copying machine.

[Explanation of symbols]

 101 image input unit, 102 image processing unit, 103 image output unit, 201 image input unit, 202 gradation correction unit (second gradation correction unit), 203 detection unit, 204 gradation correction means (first gradation correction means), 205 color correction means, 206 picture / character identification means, 207 control signal generation means, 208 black ink generation, under color removal Means 209 scaling means 210 definition correction means 211 tone correction means 212 halftone generation means 213 control means (control means) 604 first storage Means, 605 second storage means, 904 page memory, 905 memory interface, 1105 gradation correction means A, 1106 gradation correction means B, 1107 image display means A, 1108 ..Image table Means B, 1109 · · storage means A, 1110 · · calculation means B

Claims (5)

[Claims] A first gradation correction unit for performing gradation correction of the density scale image data with a gradation correction characteristic corresponding to a control signal and outputting gradation correction data having a first gradation number; Image data having a second gradation number higher than the first gradation number expressed on a scale is input, and the density having the first gradation number expressed on the density scale is based on the input image data. Second tone correction means for converting and outputting the scale image data, control means for outputting the control signal to control the tone correction characteristics according to the characteristics or type of an image corresponding to the image data, An image processing apparatus comprising: 2. The image processing apparatus according to claim 1, wherein the control unit outputs the control signal based on a density distribution state of the density scale image data. 3. The image processing apparatus according to claim 1, further comprising a storage unit configured to store the density scale image data, wherein the second gradation correction unit is input via the storage unit. Performing gradation correction of the density scale image data. 4. A setting means for setting a representative gradation correction characteristic and a plurality of difference gradation correction characteristics, which are characteristic differences between the representative gradation correction characteristic and the plurality of gradation correction characteristics, respectively; A plurality of first tone correction means for performing tone correction of the density scale image data with characteristics; input of image data having a second tone number higher than the first tone number expressed by a reflectance scale; And a second tone correction means for converting the image data into density scale image data having the first number of tones expressed on a density scale based on the representative tone correction characteristic and outputting the same. An image processing apparatus characterized by the above-mentioned. 5. The image processing apparatus according to claim 4, wherein the setting unit sets any one of a plurality of preset gradation correction characteristics different from each other in the representative gradation correction characteristic. An image processing apparatus characterized by setting as characteristics.