JPH08279919A - Picture processor and its method - Google Patents

Abstract

PURPOSE: To apply proper gradation correction to a color picture by using the read values of a color chart and a prescribed pattern. CONSTITUTION: In the case of executing automatic gradation correction, a CPU 313 allows a reader part 301 to read out a color chart and a test pattern and finds out a correction value to be set up in a printer gradation correcting circuit 316 by operation based upon the read results. In the case of correcting a C color component e.g. input masking processing is turned off, R, G and B values obtained by reading out the C color part of the color chart are respectively set up as Rco, Gco, Bco and R, G and B values obtained by reading out the C color part with density Di of the test pattern are set up as Rci, Gci, Bci. Density is measured based upon an R signal, and when a C color component signal with density Dci is inputted, the contents of a table in the circuit 316 are changed so that the C color component signal with a prescribed value is outputted to correct the gradation of a printer part.

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 and a method thereof, for example, an image processing apparatus and a method thereof for correcting the gradation of a color image.

[0002]

2. Description of the Related Art A digital color copying machine incorporates a mechanism for correcting the influence of environmental changes and aging changes in a printer unit. One of them is automatic gradation using an image scanner unit as a measuring device. There is a correction function. This automatic gradation correction is carried out in the following procedure.

(1) The printer unit prints out a test pattern of a predetermined value in each color of CMYK (2) The image scanner unit reads the test pattern (3) The reading result of the test pattern indicates the floor of the printer unit Obtain the tonal characteristics and find the coefficient or table to correct it. (4) Set the obtained coefficient or table in the printer tone correction circuit. Is being stabilized.

[0004]

However, the above-mentioned technique has the following problems. In other words, when performing automatic gradation correction, when reading the CMYK test pattern, CC
There is a problem that an error occurs due to the dispersion of the D color filter. Hereinafter, this problem will be described in detail.

FIG. 2A is a diagram showing spectral sensitivity characteristics of RGB channels of a so-called three-line sensor. When trying to obtain an image with good color reproducibility by faithfully reading a color image, in order to prevent undetectable wavelength range,
As shown in the figure, there is a portion where the spectral sensitivity characteristics of the RGB channels overlap. Therefore, it is necessary to perform signal processing on the assumption that the spectral sensitivity characteristics of the RGB channels overlap to some extent.

FIG. 2B shows the spectral sensitivity characteristics of the B channel and the Y
In the figure showing the spectral reflection characteristics of the test pattern, the Y test pattern shows a high reflectance in the wavelength range of the R channel and the G channel, so the density of the Y test pattern is detected using the R channel or the G channel. I can't
Therefore, the B channel is used to detect the concentration.
However, when the spectral sensitivity characteristic of the B channel, that is, the spectral transmission characteristic of the B color filter varies, as indicated by the broken line in the figure, this effect reduces the density detection accuracy of the Y test pattern, and as a result, the It becomes impossible to perform gradation correction.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide an image processing apparatus and method capable of appropriately performing gradation correction on a color image.

[0008]

[Means for Solving the Problems] and

The present invention has the following structure as one means for achieving the above object.

The image processing apparatus according to the present invention has a holding means for holding a value obtained by reading a color chart whose value is known, and a value obtained by reading a pattern of a predetermined value composed of a plurality of color components forming a color image. , And a correction unit that corrects the gradations of the plurality of color components based on the values held by the holding unit.

Further, reading means capable of reading a color image, output means for outputting a pattern of a predetermined value composed of a plurality of color components forming a color image, and a color chart whose value is known by the reading means. Based on the reading means that holds the read value, the reading value of the pattern output from the output means by the reading means, and the value held by the holding means. And a correction unit that corrects.

Further, the image processing method according to the present invention comprises a first reading step of reading a color chart of which density is known and holding the value in a holding means, and a plurality of color components forming a color image. A second reading step of reading a pattern having a predetermined value, a value held by the holding means, and a value read in the second reading step, the gradations of the plurality of color components are corrected. And a calculation step for calculating the correction information.

Further, a reading step of reading a pattern of a predetermined value composed of a plurality of color components forming a color image by adding an optical filter means having a predetermined transmission characteristic, and the step of reading in the reading step. And a calculation step of calculating correction information for correcting the gradations of the plurality of color components based on the value of the pattern.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image processing apparatus according to an embodiment of the present invention will be described in detail below with reference to the drawings. In the following,
An example in which the present invention is applied to an image processing apparatus such as a digital color copying machine will be described. However, the present invention is not limited to this, and when outputting a read color image to an output means such as a display or a printer. Any image processing apparatus that corrects the gradation of a color image can be applied.

[0014]

[First Embodiment] FIG. 1 is a schematic view showing a configuration example of a digital color copying machine according to one embodiment of the present invention.

In FIG. 1, reference numeral 201 denotes an image scanner unit which reads a document image and performs digital signal processing. Reference numeral 200 denotes a printer unit, which is a unit that prints an image corresponding to the image of the original read by the image scanner unit 201 on a recording sheet in full color.

In the image scanner unit 201, the original 204 placed between the original pressure plate 202 and the original platen glass 203 is
The light from the halogen lamp 205 is irradiated, and the reflected light is guided to mirrors 206 and 207, and an image is formed on a three-line sensor 210 composed of a CCD by a lens 208. The lens 208
Is provided with an infrared cut filter 231 that removes infrared light.

The three-line sensor 210 color-separates the reflected light from the original 204 and sends an RGB signal of full-color information to the signal processor 209. The sensor line for reading each color component of the three-line sensor 210 is composed of 5,000 pixels each, so that the A3 size original 204 placed on the original platen glass 203 can read 297 mm in the lateral direction at a resolution of 400 dpi. You can
R (red), G (green), and B (blue) filters are formed on each line sensor. In addition, the halogen lamp 205 and the mirror 206 are at the speed v, and the mirror 2
At a speed v / 2, 07 mechanically moves in a vertical (sub-scanning) direction with respect to the electrical scanning (main scanning) direction of the three-line sensor 210 to scan the entire surface of the original 204.

Reference numeral 211 denotes a standard white plate for generating data for correcting the RGB data read by the three-line sensor 210, and showing a substantially uniform reflection characteristic with visible light.

The signal processing unit 209 includes a CPU for controlling the image reading operation, processes the input analog RGB signal,
The color components of MCYK are separated and sent to the printer unit 200. However, the signal processing unit 209 outputs one color component of MCYK to the printer unit 200 in response to one document scan of the image scanner unit 201.
Since it is sent to, a single printout is completed by scanning the document four times in total.

The image signal output from the signal processing unit 209 is input to the laser driver 212. Laser driver 2
12 is a semiconductor laser element according to the input image signal.
213 is modulated and driven. The laser light output from the semiconductor laser device 213 scans the photosensitive drum 217 via the polygon mirror 214, the f-θ lens 215 and the mirror 216, and forms an electrostatic latent image on the photosensitive drum 217. Magenta developer 21
9, the cyan developing device 220, the yellow developing device 221, and the black developing device 222 alternately contact the photosensitive drum 217,
The latent image formed above is developed with toner. The developed toner image is transferred from the recording paper cassette 224 or 225 to the recording paper wound around the transfer drum 223.

In this way, the recording paper on which the toner images of MCYK four colors are sequentially transferred is discharged to the outside of the apparatus after the toner images are fixed by the fixing unit 226.

FIG. 3 is a block diagram showing a configuration example of an image processing unit of an image processing apparatus according to an embodiment of the present invention. An RGB image signal output from a CCD is supplied to, for example, a laser driver of a printer unit. It is converted into a signal.

In the figure, reference numeral 313 denotes a CPU, which is constituted by, for example, a one-chip microcomputer, and which is built-in RO.
The entire embodiment is controlled according to a program stored in M or the like in advance.

Reference numeral 301 denotes a color CCD linear image sensor (hereinafter referred to as "CCD"), which is composed of an RGB 3-line CCD sensor, reads a document image, and outputs an RGB image signal. 302 is
The A / D converter converts the analog image signal output from the CCD 301 into a digital image signal. Reference numeral 303 denotes a shading correction circuit, which uses the shading correction coefficient stored in the correction memory 311 to detect unevenness in the amount of light generated in the reading optical system included in the image signal output from the A / D converter 302.
Correct sensitivity unevenness of CCD301. A pixel shift correction circuit 304 corrects a shift in the reading position included in the image signal output from the shading correction circuit 303. The deviation of the reading position is caused by the arrangement of the RGB lines of the CCD 301 in the sub-scanning direction. An input masking circuit 305 corrects the tint of each RGB signal by performing a matrix operation on the image signal output from the pixel shift correction circuit 304. 312 is a memory, and an input masking circuit 305
Is to be monitored by the CPU 313.

A LOG conversion circuit 306 converts the RGB image signal of the luminance information output from the input masking circuit 305 into a CMY image signal of the density information by, for example, table conversion. A black extraction circuit 307 extracts a black component from the CMY image signal output from the LOG conversion circuit 306, for example, by calculating the minimum value of CMY. An output masking circuit 308 performs a matrix operation on the CMYK image signal output from the black extraction circuit 307 to correct the tint of each CMYK signal. 30
9 is a selector, which is output from the output masking circuit 308.
By selecting any one of the CMYK image signals in accordance with the formation order of the color component images of the printer unit, the color component image signals are output in a frame sequential manner.

Reference numeral 310 denotes an f-value correction circuit, which converts the color component image signal selected by the selector 309, for example, by table conversion.
Correction is made based on the density reproduction characteristics of the printer section. 314
Is a selector that inputs the image signal from the f-value correction circuit 310 and the image signal from the test pattern generation circuit 315,
One of them is selected and output according to the instruction of 313. A printer gradation correction circuit 316 corrects the image signal output from the selector 314 based on the gradation characteristics of the printer unit by, for example, table conversion.

An operation / display unit 317 is provided with a display unit such as an LCD and an input unit composed of a keyboard and a touch panel. An operator inputs operation instructions and operating conditions of the apparatus, and a CPU 313 displays operation states of the apparatus. Display operating conditions. A backup memory 318 is composed of, for example, battery-backed DRAM or SRAM, and stores the set operating conditions of the apparatus, image processing parameters, and the like.

FIG. 4 is an example of a CMYK standard color chart.
In the present embodiment, when performing the automatic gradation correction of the printer unit, based on the value of this color chart read by the reader unit,
The reading accuracy of the reader unit is corrected. The color chart shown in the drawing is one in which the density value of each color component is measured in advance or is prepared so as to have a predetermined density. Here, the density of each color component is set to Dco, Dmo, Dyo, Dko.
And Since these values are input by the operator from the operation / display unit 317 or stored in the backup memory 318 in advance, the CPU 313 can know the density value of each color component of the color chart.

FIG. 5 is a diagram showing an example of a test pattern for printer gradation correction. It shows a plurality of density values for each CMYK color component.
The color pattern has (D1 to Dn) and is generated by the test pattern generation circuit 315.

When performing the automatic gradation correction in this embodiment, the CPU 313 causes the reader unit to read the color chart and the test pattern shown in FIGS. 4 and 5, and the printer gradation correction is performed by calculation from the result. The correction value to be set in the circuit 316 is calculated. The correction of the C color component will be described below as an example.

With the input masking processing turned off (through), the C color portion (density Dco) of the color chart shown in FIG.
Rco, Gco, and Bco are read RGB values, and RGB values obtained by reading the C color portion (density Dci) of the density Di of the test pattern shown in FIG. 5 are Rci, Gci, and Bci, respectively. When correcting the C color component, the density is measured by the R signal, so when the C color component signal of the density Dci is input,
The gradation of the printer unit is corrected by changing the contents of, for example, the table of the printer gradation correction circuit 316 so that the C color component signal having the value shown in Expression (1) is output. Dci * = Dco × log (Rci / Rco)… (1)

Since it is unrealistic to perform the calculation of equation (1) for all the densities (for example, 255 gradations),
It is realistic to set some representative density values Dci, find a corrected density value Dci * for the density values Dci, and find a corrected density value by interpolation between the representative density values.

FIG. 6 is a flowchart showing an example of the procedure of tone correction processing, which is executed by the CPU 303.

In step S1, the standard color chart shown in FIG. 4 is read by the reader unit, and each data is read according to the following correspondence.
It is stored in the work RAM or the like in the CPU 303. Dco ← → Rco Dmo ← → Gmo Dyo ← → Byo Dko ← → Gko

Next, in step S2, the printer section shown in FIG.
The test pattern shown in is output, the test pattern is read by the reader unit in step S3, and the next data is stored. Part C: Rci (i = 0 to n) Part M: Gmi (i = 0 to n) Part Y: Byi (i = 0 to n) Part K: Gki (i = 0 to n)

Next, in step S4, the density correction value is calculated by the following equation. Dci * = Dco × log (Rci / Rco) Dmi * = Dmo × log (Gmi / Gmo)… (2) Dyi * = Dyo × log (Byi / Byo) Dki * = Dko × log (Gki / Gko)

Next, in step S5, the obtained density correction values are set in the gradation correction table, and the density correction values other than the representative density values are obtained by interpolation and set, and then the process is terminated.

The order of "reading the standard color chart", "outputting the test pattern" and "reading the test pattern" shown in FIG. 6 is not limited to this, and "outputting the test pattern""reading the test pattern" It goes without saying that the order may be “reading of standard color chart”, or “output of test pattern”, “reading of standard color chart”, and “reading of test pattern”.

As described above, according to this embodiment,
In the process of correcting the gradation of the printer section, the deterioration of the test pattern reading accuracy due to the dispersion of the spectral sensitivity characteristics of each CCD RGB channel, that is, the spectral characteristics of the color filter, is corrected by comparison with the standard color chart. Therefore, the gradation correction of the printer unit can be properly performed.

In the above description, the density value of the standard color chart is input from the operation / display unit 317 or stored in the backup memory 318 in advance.
The density value of each color component or information corresponding to the density can be recorded on the chart by a bar code or the like as shown in FIG. By doing this, since the density value of each color component can be obtained from this barcode when reading the standard color chart, the work of setting the density value of the standard color chart can be omitted, and at the time of setting. It also has the effect of preventing mistakes. Further, not only the barcode but also the numbers on the chart may be recognized by the character recognition processing.

[0041]

Second Embodiment An image processing apparatus according to the second embodiment of the present invention will be described below. It should be noted that in the second embodiment, substantially the same configurations as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 8 is a diagram showing an example of a test pattern reading filter 801 used at the time of gradation correction of the printer unit.
Is a C pattern reading filter, 803 is an M pattern reading filter, 804 is a Y pattern reading filter, and 805 is a transparent portion without a filter. 9A to 9C are diagrams showing the spectral transmission characteristics of these filters.The spectral transmission characteristics of each filter are the portions where the spectral sensitivity characteristics of each RGB channel of the CCD overlap, that is, the wavelength at which the transmission characteristics of the RGB color filter overlap. Combined to eliminate the area.

When the tone correction test pattern 901 is read, the test pattern reading filter 801 is inserted into the optical path by moving means (not shown), as shown in FIG. By narrowing the wavelength range in which each RGB channel of the CCD 210 has sensitivity, it is possible to reduce the reading error caused by the dispersion of the spectral sensitivity characteristics. However, as shown in FIGS. 9A to 9C, the wavelength range transmitted by the test pattern reading filter 801 is a wavelength range in which the spectral reflectance of the corresponding color component is low, and the transmitted wavelength range is narrowed. The amount of light input to is reduced. In order to compensate for this decrease in light intensity, increase in irradiation light intensity or CCD210
The amplification factor of the signal output from is increased as compared with the normal processing mode.

Further, when the test pattern is read, the test pattern reading filter 801 may be placed on the original platen glass 203 and the test pattern 901 may be placed thereon to obtain the same effect.

As described above, according to this embodiment,
In the process of correcting the gradation of the printer section, the deterioration of the test pattern reading accuracy due to the variation of the spectral sensitivity characteristics of each RGB channel of the CCD, that is, the spectral transmission characteristics of the color filter, can be reduced to the CCD in the optical path of the reader section. This can be reduced by inserting a filter for correcting the spectral sensitivity characteristic only during the correction processing, and the gradation correction of the printer unit can be appropriately performed.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of a single device.

Needless to say, the present invention can also be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0048]

As described above, according to the present invention,
It is possible to provide an image processing apparatus and a method for appropriately performing gradation correction on a color image.

[Brief description of drawings]

FIG. 1 is a schematic view showing a configuration example of a digital color copying machine according to an embodiment of the present invention,

FIG. 2A is a diagram showing spectral sensitivity characteristics of RGB channels of a three-line sensor,

FIG. 2B is a diagram showing spectral sensitivity characteristics of B channel and spectral reflection characteristics of Y test pattern;

FIG. 3 is a block diagram showing a configuration example of an image processing unit of an image processing apparatus according to an embodiment of the present invention,

FIG. 4 is a diagram showing an example of a CMYK standard color chart,

FIG. 5 is a diagram showing an example of a test pattern for printer gradation correction;

FIG. 6 is a flowchart showing an example of the procedure of gradation correction processing;

FIG. 7 is a diagram showing another example of a CMYK standard color chart,

FIG. 8 is a diagram showing an example of a test pattern reading filter used when correcting a printer gradation according to a second embodiment of the present invention;

9A is a diagram showing spectral transmission characteristics of the filter shown in FIG.

9B is a diagram showing spectral transmission characteristics of the filter shown in FIG.

9C is a diagram showing the spectral transmission characteristics of the filter shown in FIG.

FIG. 10 is a diagram showing an example of a state in which a test pattern reading filter is inserted in the optical path when reading a tone correction test pattern.

[Explanation of symbols]

 301 Color CCD linear image sensor (CCD) 302 A / D converter 303 Shading correction circuit 304 Pixel shift correction circuit 305 Input masking circuit 306 LOG conversion circuit 307 Black extraction circuit 308 Output masking circuit 309 Selector 310 f value correction circuit 313 CPU 314 Selector 315 Test pattern generation circuit 316 Printer gradation correction circuit 317 Operation / display section 318 Backup memory

Claims (12)

[Claims] 1. A holding unit for holding a value obtained by reading a color chart whose value is known, a value obtained by reading a pattern of a predetermined value composed of a plurality of color components forming a color image, and the holding unit holding the value. And a correction unit that corrects the gradations of the plurality of color components based on the calculated values. 2. A reading unit capable of reading a color image, an output unit outputting a pattern of a predetermined value composed of a plurality of color components forming a color image, and a color chart whose value is known by the reading unit. A holding unit that holds the read value, a reading value of the pattern output from the output unit by the reading unit, and a gradation value of the plurality of color components based on the value held by the holding unit. An image processing apparatus comprising: a correction unit that corrects 3. The reading means includes a color filter
The image processing apparatus according to claim 2, further comprising a CCD sensor. 4. The image processing apparatus according to claim 2, wherein the output unit forms a color image with CMY or CMYK color components. 5. The gradation correction is performed based on a known value of the color chart, a value obtained by reading the color chart, and a value obtained by reading the pattern. The image processing apparatus according to claim 1 or claim 2. 6. The image processing apparatus according to claim 2, wherein the known value is displayed on the color chart, and the known value can be read by the reading unit. 7. An optical filter unit used when reading a pattern of a predetermined value composed of a plurality of color components forming a color image, and the optical filter unit based on the value of the pattern read by the filter unit. An image processing apparatus comprising: a correction unit that corrects gradations of a plurality of color components. 8. A reading unit capable of reading a color image, an output unit outputting a pattern of a predetermined value composed of a plurality of color components forming a color image, and the reading unit outputting from the output unit. An optical filter unit used when reading the pattern, and a correction unit that corrects the gradation of the plurality of color components based on the value of the pattern read by using the filter unit. Image processing device. 9. The reading means includes a color filter.
9. The image processing apparatus according to claim 8, further comprising a CCD sensor. 10. The image processing apparatus according to claim 9, wherein the filter unit removes a wavelength range in which the transmission characteristics of a plurality of color filters included in the reading unit are superimposed. 11. A first reading step of reading a color chart whose density is known and holding the value in a holding means, and a second reading of a pattern of a predetermined value composed of a plurality of color components forming a color image. Reading step, and a calculation step of calculating correction information for correcting the gradation of the plurality of color components based on the value held in the holding means and the value read in the second reading step. An image processing method comprising: 12. A reading step of reading a pattern of a predetermined value composed of a plurality of color components forming a color image by adding an optical filter means having a predetermined transmission characteristic, and the reading step read in the reading step. An image processing method for calculating correction information for correcting the gradations of the plurality of color components based on the value of the pattern.