JPH1075366A - Recorder and gradation control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To warrant desired gradation reproduction performance at all times even when different paper is used and a line number output is changed by recording a reference output image in the reference image generating process prior to actual recording. SOLUTION: A mode changeover section 2 switches the mode between the input image recording mode and the reference image mode. Selectable line kind number of reference image data are provided. Then a control circuit section 10 outputs the reference image data in response to the selected line number from a reference image data storage section 11 depending on the selection of the line number by the user through a user interface section 9. A gradation correction data generating section 20 generates intensity modulation data for each input dot coverage as to each of image data from the reference output image so that the gradation reproduction characteristic is equal to an ideal gradation reproduction curve in the reference image mode and the generated intensity modulation data are written in a direct lookup table(DLUT) 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording apparatus for recording image information on a recording and display medium, such as a color hard copy apparatus and a digital color printer, and a gradation control method therefor.

[0002]

2. Description of the Related Art Generally, input image data of a recording apparatus as described above is signal data having a linear value with respect to density gradation. On the other hand, input data versus output density characteristics of a recording display medium, for example, paper, are generally not linear.

For example, in the case of a copying machine, when halftone data is used for tone reproduction, the tone reproduction curve under certain conditions is not a straight line 31 as shown in FIG. 32, 33 or 34.

In the conventional tone correction method, in order to inversely convert the chromaticity to obtain a desired tone reproduction, for example, FIG.
In the case of a printing apparatus showing a tone reproduction curve as shown by a curve 32 of FIG. 5, in order to inversely convert a desired tone reproduction, for example, a linear tone reproduction, into a chromaticity that can be obtained, FIG. Thus, the input dot coverage (dot area ratio) Cin
(%) Conversion.

However, in the case of curve 32, FIG.
As shown in FIG. 7, since the gradation of the low density portion cannot be finely assigned, it is not possible to obtain the optimum gradation reproduction. Similarly, in the case of the curve 33, the gradation of the high-density part cannot be finely assigned in both the high-density part and the low-density part. No reproduction can be obtained.

Therefore, conventionally, gradation density correction has been performed. For example, "Image forming apparatus" described in JP-A-3-159758 and JP-A-3-149249
In the "laser scanning type image forming apparatus" described in Japanese Patent Application Publication No. 672 or the "recording apparatus" described in Japanese Patent Application Laid-Open No. 54-86353, a recording system is assumed assuming the standard paper / standard line number of the apparatus. Are set so as to secure desired desirable gradation reproducibility.

Japanese Patent Application Laid-Open No. 3-159758 discloses an "image forming apparatus" which generates density gradation data in accordance with input multi-valued pixel data and writes an electrostatic latent image on a photosensitive member based on the data. By appropriately controlling the irradiation time of the light beam and the light emission intensity, good tone reproduction can be achieved even in a low-density region and a high-density region.

A "laser scanning type image forming apparatus" described in Japanese Patent Application Laid-Open No. Hei 3-249672 scans and exposes a laser beam whose emission pulse width and emission intensity are modulated on the basis of image data, and scans the laser beam. By controlling both or at the time of rising and falling, and shaping the dot shape into a circle or a semicircle, improved graininess and smooth gradation reproduction meaning that adjacent gradation steps are small Is to achieve.

Further, in a "recording apparatus" described in Japanese Patent Application Laid-Open No. Sho 54-86353, the toner density on the photosensitive drum is detected and compared with the signal light of the original document. Is scanned, and the original signal light and the toner density on the photosensitive drum are linearly corrected to obtain good tone reproduction.

[0010]

By the way, in a recording system such as a silver halide photographic recording system and a sublimation type thermal transfer recording system in which a recording display medium on which an image is formed is made of a special paper, the customer can use glossy paper / matte paper / Since paper such as coated paper / plain paper cannot be selected, as described above, the tone reproduction characteristic can be adjusted in advance according to the paper to be used.

On the other hand, a recording and display medium on which an image is formed is not a specific sheet, such as an electrophotographic recording system, an ink jet recording system, and a thermal transfer recording system as disclosed in the above-mentioned prior art publications. According to the recording method, customers can use glossy paper / matte paper / coated paper /
Paper such as plain paper can be freely selected.

However, if the paper actually used by the customer is not the standard paper, the difference in the thickness and basis weight of the paper,
The mechanical dot gain changes due to a difference in physical characteristics between the paper surface and the inside of the paper. The optical dot gain also changes due to the presence or absence of a paper surface coat layer, differences in whiteness of the paper, differences in optical physical quantities such as the average free optical path length, and the like.

Therefore, even if the design parameters of the recording system are set on the assumption that the standard paper is used as in the prior art described above, and the desired preferable gradation reproducibility is ensured, the paper actually used is the standard paper. If not, as described above,
Since the mechanical and optical dot gains change, good tone reproduction cannot always be obtained. Even if the whiteness of the paper and the solid colorimetric value (so-called solid colorimetric value) of the color material on the paper are matched, the halftone reproducibility ultimately changes greatly depending on the paper.

Further, when the same recording apparatus can use different line number outputs properly, a desired preferable gradation reproducibility is as follows.
Since the standard number of lines is ensured, if the number of lines is simply changed, even when the same paper is used, the halftone reproduction characteristic greatly changes depending on the number of lines.

An "image forming apparatus" described in JP-A-3-159758 or JP-A-3-24949
In the "laser scanning image forming apparatus" described in Japanese Patent No. 672 or the "recording apparatus" described in Japanese Patent Application Laid-Open No. 54-86353, it is unnecessary to secure a desired preferable gradation reproducibility. Since the gradation steps are thinned out, the number of usable quantization steps is reduced, and the image reproducibility of the device is suppressed, so that an optimum image quality cannot be provided.

In the case of printing, a skilled operator operates a printing machine, finely adjusts the desired granularity / sharpness / color reproduction / gradation reproduction, and outputs while confirming. It is possible to select the optimum setting for the paper from the viewpoint of image quality. However, this method requires the presence of a skilled operator to guarantee the image quality, and requires a long time for adjustment and is not responsive, so low-cost printers and copiers and printers that require on-demand output are required. This is an inappropriate method.

The present invention has been made in view of the above problems, and has been made in consideration of the following circumstances, regardless of the type of paper used by a skilled operator.
It is an object of the present invention to provide a gradation control method for a recording apparatus that can always guarantee a desired gradation reproducibility even when the number of lines changes, and a recording apparatus to which the method is applied.

[0018]

In order to solve the above-mentioned problems, the present invention relates to adjusting the density of each gradation on a recording display medium for each gradation image pattern corresponding to the value of input image data. A gradation control method for a recording apparatus, comprising: a gradation density adjustment control unit capable of changing control data; and outputting an output image corresponding to the input image data to the recording display medium, wherein By changing the control data in a plurality of ways and changing the density for each tone in a plurality of ways for each of the plurality of tone image patterns, a plurality of tone patches are obtained for each of the tone image patterns. A reference image generating step of outputting a reference output image formed on the recording and display medium; a reference image reading step of reading a reference output image generated by the reference image generating step; For each of the plurality of tone image patterns of the reference output image read in the image reading step, a tone patch suitable for a target tone characteristic is extracted from among the plurality of tone patches. A density adjustment data storing step of storing the control data used to form the extracted tone patch as control data for density adjustment of a corresponding tone image pattern; and obtaining an output image of the input image data. And a recording step of recording a gradation image pattern corresponding to the value of the input image data by density adjustment based on the density adjustment control data stored in the density adjustment data storage step. Is provided.

[0019]

In the present invention having the above-described structure, the reference output image is recorded in the reference image generation step prior to the actual recording of the input image data on the paper used for recording.

That is, as an example, when a plurality of gradation image patterns within the gradation reproduction range are recorded by converting image data into data of the input halftone coverage Cin, 0%, 12. 5%, 25%, 37.5%, ...,
As 100%, as the input halftone coverage Cin,
Prepare reference image data of several values.

Then, the reference output image is formed by recording the images of the plurality of input halftone coverage values Cin on the paper to be used. In this case, the input halftone coverage Cin of each input halftone coverage Cin is formed. When recording each value image, the tone density control data of the tone density adjustment control unit is changed in a plurality of ways to form a plurality of tone patches as an image of each input halftone coverage Cin ( FIG. 4 described later
reference).

After the recording of the reference output image on the paper used in the reference image generation step is completed, the reference output image is read in the reference image reading step.

Then, in the next density adjustment data storing step, the image of the input halftone coverage Cin value of the read reference output image is selected from a plurality of tone patches, and A tone patch conforming to the characteristic is extracted, and the value of the density adjustment control data used to form the extracted tone patch is determined by the corresponding tone image pattern, that is, each input halftone coverage Cin. Is stored as control data for density adjustment at the time of recording the value of.

Thus, the preparation prior to the actual recording is completed. In the recording step of recording the input image data using the sheet, the density for each input halftone coverage Cin is adjusted based on the density adjustment control data stored in the density adjustment data storage step. Recorded. Accordingly, an output image of the input image data can be obtained without changing the halftone coverage pattern of the input image data and in a state where the desired tone reproduction characteristics are always obtained.

As described above, the control data for density adjustment is held according to the paper using the reference image, and the actual recording is performed using the control data for density adjustment, whereby the paper is changed. However, an output image can always be recorded in a state of desired gradation reproduction characteristics.

A plurality of reference images are prepared in accordance with the number of lines that can be output, and a plurality of control data for density adjustment at the time of output of each number of lines are stored in advance in accordance with the paper, and output by the user. When the number of lines is selected, the recording process is performed using the control data for density adjustment according to the number of lines, so that even when the number of lines changes, the desired tone reproduction characteristic is always maintained. Output images can be recorded.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a gradation control method according to the present invention and a recording apparatus to which the method is applied will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a configuration example of a recording apparatus according to this embodiment. The recording device according to this embodiment includes:
In the example of a color copier, the input image reading unit 1
A mode switching unit 2, a halftone data forming unit 3, an image pattern generating unit 4, an image writing unit 5, an intensity modulation circuit unit 6 for writing intensity, a DLUT (direct lookup table) 7, and a recording unit. The apparatus includes a device unit 8, a user interface unit 9, a control circuit unit 10, a reference image data storage unit 11, and a gradation correction data generation unit 20.

The input image reading section 1 reads a document image to be copied and recorded, obtains, for example, red (R), green (G), and blue (B) color image data. ^The image data is converted into image data L ^* a ^* b ^* expressed in the ^* a ^* b ^* space and output.

The mode switching unit 2 includes an input image recording mode for outputting a copy image of the image read by the input image reading unit 1 and a reference for generating a reference image and generating and holding gradation correction data based on the reference image. The mode is switched with the image mode. That is, in the recording apparatus of this embodiment, the mode can be switched between the input image recording mode, which is the normal mode, and the reference image mode by the mode switching key provided on the user interface unit 9. In the input image recording mode, the mode switching unit 2 selects the image data from the input image reading unit 1 and outputs the selected image data to the halftone dot data forming unit 3 by the switching control by the control circuit unit 10. In the case of, the image data of the reference image from the reference image data storage unit 11 is selected and output to the halftone dot data forming unit 3.

The reference image data storage unit 11 receives the reading control from the control circuit unit 10, and in the reference image mode, the toner colors yellow (Y), magenta (M), cyan (C), and black. Reference image data is output for each of (K). The reference image data of each toner color has a plurality of values of the input halftone coverage Cin as a plurality of gradation image patterns within the gradation reproduction range, as shown in FIG. , 25%, 37.5%, 50%,
It consists of 9 types: 67.5%, 75%, 87.5%, and 100%. Note that this reference image data is also CIEL
^It consists of image data L ^* a ^* b ^* expressed in ^* a ^* b ^* space.

In the case of this example, since the recording apparatus can select and change the number of screen lines, the reference image data corresponding to each line number is different from the reference image number. It is stored in the data storage unit 11. In other words, the reference image data is provided for the number of selectable lines. Then, in response to the user's selection of the number of lines through the user interface unit 9, the control circuit unit 10 controls the reading so that the reference image data corresponding to the selected number of lines is output from the reference image data storage unit 11. .

The halftone data forming section 3 converts the image data L ^* a ^* b ^* from the mode switching section 2 into yellow, magenta,
Cyan and black toner color image data Y, M,
C, K, and the image data Y, M, C,
Each of K forms halftone data Y%, M%, C%, and K% of the input halftone coverage Cin corresponding to the gradation image data, and outputs it to the image pattern generation unit 4. At this time,
The value of each input halftone coverage Cin is also notified to the control circuit unit 10 and used for controlling the modulation of the writing intensity in the input image recording mode described later.

The image pattern generating section 4 generates drawing data of an image pattern corresponding to the value of each input halftone coverage Cin, and outputs the drawing data to the image writing section 5.

The image writing unit 5 constitutes a scanning exposure unit, scans the photosensitive drum with laser light in accordance with the drawing data from the image pattern generating unit 4, and forms an electrostatic image corresponding to the drawing data. The latent images are sequentially formed on the photosensitive drum. At this time, the intensity of the laser beam can be changed and controlled by the intensity modulation circuit section 6, and fine adjustment of the gradation density is possible.

In the reference image mode, the intensity modulation circuit section 6 controls the intensity level (exposure intensity) of the laser beam in the image writing section 5 for the image data of one input halftone dot coverage value under the control of the control circuit section 10. level)
Is changed to -3 to 7 in 11 steps in one level step as shown in FIG. Note that the input dot coverage Ci
When n is 0% and when it is 100%, the intensity level is not changed and is fixed at the intensity level 0.

In the input image recording mode,
The intensity changing circuit section 6 controls the D
Each of the image data Y, M, C, and K in the image writing unit 5 based on the intensity modulation data corresponding to the input halftone coverage value of each of the image data Y, M, C, and K set in the LUT 7 The intensity level of the laser beam is modulated.

That is, in the input image recording mode, the control circuit unit 10 refers to the DLUT 7 using the value of the input halftone coverage Cin of the image data Y, M, C, K from the halftone data forming unit 3 as reference data. Then, the corresponding intensity modulation data is read out from the DLUT 7, and the intensity modulation circuit 6
Performs intensity modulation of laser light based on the read intensity modulation data.

Each image data Y, M, C, K of the DLUT 7
The intensity modulation data for each input halftone coverage Cin with respect to
The data is generated and written by the gradation correction data generating unit 20.

The recording unit 8 converts the electrostatic latent image written on the photosensitive drum with the image data Y, M, C, and K by the image writing unit 5 using yellow, magenta, cyan, and black toners. Develop and transfer to paper to obtain output image OT. In the reference image mode, a reference output image REF is obtained as the output image OT.

In the reference image mode, the gradation correction data generator 20 converts each of the image data Y, M, C, and C from the reference output image REF so that the gradation reproduction characteristics become equal to the ideal gradation reproduction curve. It generates intensity modulation data for each input halftone coverage Cin for K, and writes the generated intensity modulation data to the DLUT 7.

The gradation correction data generation unit 20 includes an image reading unit 21 for reading the reference output image REF, a reading calibrator 22, a gradation reproduction curve detection unit 23, an ideal gradation reproduction curve storage unit 24, And an optimum gradation step extracting unit 25.

In this embodiment, as the ideal tone reproduction curve, it is assumed that the relationship between the input halftone coverage Cin and the chromaticity data L ^* , a ^* , b ^* or C ^* is linear. Ideal tone reproduction curve storage unit 24 for each toner color
Is stored in

In this case, for example, the document "Color R"
search and Application V
ol. 18, Number 1, pp. 41-46,
Feb. 1993, "Optimal Dens
ity-Divisionfor Color-Ima
ging Systems ”,
For magenta, cyan, and black, the relationship between the input halftone coverage Cin (%) and the chromaticity data L ^* is linearly assigned. For yellow, the input halftone coverage Cin (%) and the chromaticity data b ^* or C ^* are assigned. The linearly allocated values are used as ideal tone reproduction curves.

The image reading section 21 has a plurality of color filters having different passing wavelength characteristics, and as described above, for each of the yellow, magenta, cyan, and black toner colors formed on the paper to be used. And outputs the image data L ^* , a ^* , and b ^* for each toner color of the read result to the tone reproduction curve detection unit 23. This image reading unit 2
1 can be shared by the input image reading unit 1.

The reading and calibrating unit 22 is for calibrating the image data L ^* , a ^* , and b ^* of the reading result based on the ground color of the paper. This is because the data of the ideal tone reproduction curve is recorded in the storage unit 24 assuming a predetermined standard sheet, so that even if the assumed ideal tone reproduction curve is linear, the level shift is performed depending on the paper. This is to correct such a situation. That is, the read calibration unit 22 uses the portion where the input halftone coverage Cin is 0% and the portion where the input halftone coverage Cin is 100% to obtain the standard, that is, the ideal tone reproduction stored in the ideal tone reproduction curve storage unit 24. The deviation from the curve (distance of inclination or translation) is found, and the image data L ^* , a ^* , and b ^* of the read result are calibrated accordingly. The calibrated image data L ^* , a ^* , and b ^* are supplied to the tone reproduction curve detection unit 23.

The tone reproduction curve detecting section 23 reads the chromaticity data obtained by reading the reference output image REF by the image reading section 21 and the input coverage Cin () stored in the ideal tone reproduction curve storage section 24. %) And the ideal tone reproduction curve data in which the chromaticity corresponding to (%) is linearly distributed, and the tone reproduction curve of the reference output image REF is changed to any one of the curves 32, 33, and 34 shown in FIG. Is detected. Then, the detection data is sent to the optimum gradation step extraction unit 25.

The optimum gradation step extracting section 25 stores the type of the gradation reproduction curve of the reference output image 7 detected by the gradation reproduction curve detecting device 23 and the ideal gradation stored in the ideal gradation reproduction curve storage section 24. By comparing with the tone reproduction curve data, the set value of the intensity modulation data of the image writing unit 5 necessary for obtaining ideal tone reproduction is extracted for each toner color.

The optimum gradation step extracting section 25 writes the set values of the intensity modulation data necessary for obtaining the ideal gradation reproduction for each of the extracted toner colors in the corresponding areas of the DLUT 7.

[Reference Image Mode] In the recording apparatus configured as described above, in the reference image mode, a reference output image is generated, and the operation of generating and storing laser intensity modulation data for gradation correction is described below. Will be described.
First, generation of a reference image will be described.

FIG. 3 is a flowchart of a procedure for generating a reference image. When the user specifies the reference image mode through the user interface unit 9 and instructs to generate a reference image, the routine of the flowchart in FIG. 3 is started. At this time, the number of output lines is also specified, and a reference output image at the number of lines is generated.

First, in step 101, the data (0%) of the first input halftone coverage Cin of the reference image data for the first toner color, for example, yellow, is read. The read data of the input halftone coverage Cin is converted into halftone data in step 102,
In step 103, the data is converted into data of the halftone image pattern.

In the next step 104, it is determined whether or not the data is the first or last data of a plurality of input halftone coverages Cin prepared as reference image data for the color. First (0%) or last (1
If the data is determined to be (00%) data, the process proceeds to step 105, where the writing intensity level (laser light intensity) in the image writing unit 5 is set to level 0, and an image is written on the photosensitive drum.

On the other hand, if it is not the first or last data, the process proceeds to step 106, where the write intensity level is changed from level-3 to level 7 as shown in FIG.
The image is written to the photosensitive drum in steps of level 1 and sequentially changed to 11 steps.

After step 105 or 106, the process proceeds to step 107, where it is determined whether there is next reference image data for the toner color or whether there is reference image data for another toner color. When it is determined that there is reference image data, the process proceeds to step 108, where the next reference image data (data of the next input halftone coverage) is read. And step 1
02, and repeats the above-described processing of step 102 and subsequent steps.

If it is determined in step 107 that the writing of all the reference image data has been completed, the process proceeds to step 109, where the reference image is recorded on the paper to be used and output as the reference output image REF. This ends the routine.

As described above, for each of the toner colors of yellow, magenta, cyan, and black, the image writing intensity level for each of the data of the input halftone coverage in increments of 12.5% as shown in FIG. To -3 to 7,
The reference image changed in 11 stages is recorded on, for example, one sheet. The output may be performed on a plurality of sheets for each toner color.

FIG. 4 shows the pattern of the reference output image on the paper for each color. As shown in FIG. 4, the reference output image for each color has an input halftone coverage Cin of 0.
In the case of% and 100%, there is one gradation patch, but in the case of 12.5% to 87.5%, 11 gradation patches Pt are obtained according to 11 levels of intensity levels. .

Using the reference output image generated as described above, in the input image recording mode, the write intensity of the image writing section 5 is changed via the intensity modulation circuit section 6 so that the tone reproduction characteristic becomes an ideal tone reproduction curve. An intensity modulation level to be controlled is generated so as to be equal, and is written and held in the DLUT 7.

FIG. 5 is a flowchart showing an example of a processing routine for generating and holding the intensity modulation level. In the reference image mode, the processing routine shown in FIG.
It is set to 1 and is started when the user inputs a reading start instruction through the user interface unit 9.

When this processing routine is started, in step 201, a reference output image is read. The image reading unit 21 has a color filter as described above, and reads, for each color, the above-described reference image of each of the yellow, magenta, cyan, and black toner colors.

Next, the process proceeds to step 202, where read data for one color is extracted. Then, in the next step 203, using the read data with the input halftone coverage Cin of 0% and 100% for the color, the input halftone coverage Cin of the ideal tone reproduction curve is 0% and 10%.
Calibrate each read data to match the 0% point.

For example, when the processing target is magenta, cyan, or black and the input halftone coverage C
Consider a case where the relationship between in (%) and the chromaticity data L ^* has a linear characteristic such as an ideal tone reproduction curve 40 shown in FIG. The ideal tone reproduction curve 40 is set, for example, on standard paper, and the level of white or solid changes depending on the paper. Therefore, the 0% point of the input dot coverage Cin of the read data and 10%
The value of the 0% point is defined as the point of 0% of the input halftone coverage Cin in the ideal tone reproduction curve 40 and 10%.
Calibrate each read data to match the value of the 0% point. This makes it possible to obtain read data that matches the ideal tone reproduction curve 40.

As shown in FIG. 6, the read data values of the intensity levels of the 11 stages with respect to the values of the input halftone coverage Cin thus calibrated are represented by symbols as shown in FIG. Of each input dot coverage Cin (%) and chromaticity data L ^{* of} each intensity level
Is plotted as shown in FIG. 7 and FIG.

In step 204, a tone reproduction curve for the toner color is obtained using the read data. This is represented by a line connecting the values of the input halftone coverages whose intensity level is 0, as shown by the dotted lines in FIGS. 7 and 10. In this case, it is not necessary to know the tone reproduction curve exactly, and the ideal tone reproduction curve 40
It suffices to know which of the curves 32, 33 and 34 shown in FIG.

After step 204, step 205
And from among the plot data corresponding to the eleven tone patches in each of the input halftone coverages Cin for the toner color, the plot of the tone patch on the ideal tone reproduction curve 40 or the closest Search plot data. Then, the intensity level of the found gradation patch is determined as a corrected intensity level for each input halftone coverage Cin.

Then, in the next step 206, the correction intensity level for each input halftone coverage Cin for the toner color is stored in the DLUT 7.

For example, when the gradation reproduction curve for a certain toner color is as shown by the dotted line in FIG. 7, the search is performed in the direction of the intensity level higher than the intensity level 0 in each input halftone coverage Cin. Then, there is gradation patch data that matches or is close to the ideal gradation reproduction curve 40. Therefore, in step 205, the data of the gradation patch is found as shown in FIG. Then, in step 206, the found intensity level is set as a set intensity level (correction intensity level) of each input halftone coverage of the toner color, as shown in FIG.
This is stored in the LUT 7.

When the gradation reproduction curve for a certain toner color is as shown by the dotted line in FIG. 10, the gradation reproduction curve is calculated at a predetermined value of the input halftone coverage Cin. Crosses the tone reproduction curve 40. Therefore, when the input halftone coverage smaller than the intersection is searched in the direction of the intensity level higher than the intensity level 0,
When there is gradation patch data that matches or is close to the ideal gradation reproduction curve 40, and when the input halftone coverage larger than the intersection is searched in the direction of the intensity level lower than the intensity level 0, the ideal level There is gradation patch data that matches or is close to the tone reproduction curve 40.

Therefore, in step 205, FIG.
As shown in (5), data of a tone patch that matches or is close to the ideal tone reproduction curve 40 is found. Then, in step 206, as shown in FIG. 12, the DLU is used as the set intensity level (correction intensity level) of the input halftone coverage of the toner color, as shown in FIG.
This is stored in T7.

As described above, for each toner color,
Each input halftone coverage Ci as shown in FIGS. 9 and 12
The set intensity level for each n is stored in the DLUT 7.
When the number of lines can be selected in a plurality of ways, a reference output image is generated for each of the lines in exactly the same manner as described above, and the set intensity level (correction intensity) for each toner color at each number of lines is obtained. Level) and generate DLU
It is stored in T7. Thus, the reference image mode ends.

[Input Image Recording Mode] In the input image recording mode, the tone reproduction curve always approximates the ideal tone reproduction curve 40 based on the set intensity level stored in the DLUT 7 as described above. So that
Recording of the input image data is executed.

FIG. 13 is a flowchart of a processing routine in the input image recording mode. When the normal mode is selected by the user interface unit 9, the document is set on the image reading unit 1, and the start button is pressed, the processing routine of FIG. 13 is executed.

First, in step 301, the setting is made so as to use the data of the DLUT 7 for the selected number of lines. Then, in the next step 302, the input image is read, and the image data is sent to the dot data forming unit 3 as shown in FIG. And step 3
In step 03, input dot coverage data for each toner color is formed for each pixel. Next, step 30
Then, the process proceeds to step S4, where the image pattern generator 4 generates an image pattern based on the halftone data.

Then, in step 305, step 30
Reference is made to the set intensity level for the set number of lines of the DLUT 7 according to the value of the input halftone coverage Cin for each toner color recognized in step 3. Then, a set intensity level corresponding to the value of the input halftone dot coverage Cin is read out, the laser light is intensity-modulated based on the set intensity level, and an exposure image for each toner color is written on the photosensitive drum.

In this case, when there is no value directly corresponding to the input halftone coverage Cin, the coverage Cin
The set intensity levels corresponding to the input halftone coverage are calculated by linear interpolation using both the set intensity levels, and the set intensity levels corresponding to the input halftone coverage are read out. FIG. 14 shows an example of intensity modulation of the laser beam at this time. FIG.
In the example of No. 4, the intensity level is modulated as 0, 0, 1, 7, -3, -1.

When writing of the exposure image is completed as described above, in step 306, development using toner of each color is performed, and recording is performed on paper. Then, in step 307,
Discharge the paper on which the image is recorded.

As described above, when the input image is recorded by modulating the image writing intensity, as can be seen from FIGS. 9 and 12 described above, the tone reproduction curve of the output image is the ideal reproduction curve. The tone reproduction curve 40 is equal to or approximate to the tone reproduction curve 40, and a desired tone reproduction can be obtained. In this case, a desired tone reproduction can be obtained without any change in the halftone dot pattern in the input halftone coverage Cin (%), that is, without impairing the graininess. In this example, since the ideal tone reproduction curve is a straight line,
For example, when trying to obtain gradation reproduction of 8 bits = 256 steps, there is no need to reduce the number of gradation quantization at all.

When the user selects the number of lines,
Data of a set intensity level corresponding to the selected number of lines is read out from the DLUT 7 and write intensity modulation is performed in the image writing unit 5, so that even if the number of output lines changes, desired gradation reproduction is always performed. It is obtained.

As described above, according to the present invention, it is not necessary to change the halftone dot pattern in each input halftone coverage Cin (%) at all.
Any halftone pattern such as a halftone screen, an FM screen, and an error diffusion screen can be used.

Further, in order to change the set intensity level to correspond to the ideal gradation reproduction curve, if the intensity level range set in the reference image data is made large, the optical dot gain and mechanical dot gain will Even with such a distorted tone reproduction curve, it is possible to find a set intensity level that always intersects the ideal tone reproduction curve, that is, obtains the same reproduction as the ideal tone reproduction curve.

In the case of a recording apparatus in which the type of paper can be changed and selected in a plurality of ways, the above-mentioned reference output image is generated in advance for all the papers to be used, and the set intensity level corresponding to the reference output image is set to DLUT7. In the input image recording mode, depending on the paper selection,
By reading the corresponding paper setting intensity level from the UT 7, the same operation and effect as described above can be obtained.

In the above embodiment, the case where the ideal tone reproduction curve is a straight line has been described. However, the ideal tone reproduction curve does not need to be a straight line, but is a predetermined curve. Of course it is good.

Although the above-described embodiment relates to a copy machine, the present invention can be applied to a color printer and other recording devices. Further, the recording and display medium is not limited to paper, but may be, for example, a board.

[0085]

As described above, according to the present invention, desired gradation reproducibility can always be guaranteed even if the recording / display medium, for example, the paper is changed, or the line frequency output is changed.

Further, since the gradation image pattern shape is not changed and the gradation density is finely adjusted to correspond to the ideal gradation reproduction curve, any halftone dot pattern and any kind of paper can be handled. Further, desired gradation reproduction can be obtained without deteriorating the graininess and without reducing the number of gradation quantization.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of a recording apparatus according to the present invention.

FIG. 2 is a diagram for explaining an example of reference image data used in the method of the present invention.

FIG. 3 is a diagram showing a flowchart of generation of a reference output image in one embodiment of the method of the present invention.

FIG. 4 is a diagram for explaining generation of a reference output image in one embodiment of the method of the present invention.

FIG. 5 is a flowchart showing an example of a procedure for generating and holding a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 6 is a diagram used to represent a tone reproduction characteristic of a reference output image.

FIG. 7 is a diagram for explaining generation of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 8 is a diagram for explaining generation of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 9 is a diagram showing an example of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 10 is a diagram for explaining generation of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 11 is a diagram for explaining generation of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 12 is a diagram showing an example of a set intensity level for gradation correction in one embodiment of the method of the present invention.

FIG. 13 is a flowchart illustrating an image recording procedure according to an embodiment of the recording apparatus according to the present invention.

FIG. 14 is a diagram provided for describing an example of gradation density adjustment according to an embodiment of the recording apparatus according to the present invention.

FIG. 15 is a diagram illustrating an example of a tone reproduction characteristic of the printing apparatus.

FIG. 16 is a diagram for explaining a conventional gradation correction method.

FIG. 17 is a diagram for explaining a conventional gradation correction method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Input image reading part 2 Mode switching part 3 Halftone data forming part 4 Image pattern generating part 5 Image writing part 6 Intensity modulation circuit part 7 DLUT 8 Recording device part 9 User interface part 10 Control circuit part 11 Reference image data storage part 20 Tone correction data generation part 21 Image reading part 22 Reading calibrator 23 Tone reproduction curve detection part 24 Ideal gradation reproduction curve storage part 25 Optimum gradation step extraction part 40 Ideal gradation reproduction curve

Claims (3)

[Claims] A tone density adjustment control unit capable of changing control data relating to density adjustment for each tone on a recording display medium for each tone image pattern corresponding to a value of input image data; A gradation control method for a recording apparatus that outputs an output image according to input image data to the recording display medium, wherein a plurality of the control data are provided for each of the plurality of gradation image patterns within a gradation reproduction range. Reference image generation that outputs a reference output image in which a plurality of gradation patches are formed on the recording display medium for each of the gradation image patterns by changing the density for each gradation in a plurality of ways. A reference image reading step of reading a reference output image generated by the reference image generating step; and the plurality of reference output images read by the reference image reading step. For each of the tone image patterns, a tone patch suitable for a target tone characteristic is extracted from the plurality of tone patches, and the control data used to form the extracted tone patch. To
A density adjustment data storage step of storing as control data for density adjustment of the corresponding tone image pattern, and when obtaining an output image of the input image data, a tone image pattern corresponding to the value of the input image data, A recording step of performing density adjustment based on the density adjustment control data stored in the density adjustment data storage step, and recording. 2. A means for generating reference image data corresponding to a plurality of gradation image patterns among gradations that can be taken by input image data, and a gradation corresponding to a value of the reference image data in a reference image mode. Image pattern generating means for generating an image pattern and generating a gradation image pattern according to the value of the input image data when in the input image recording mode; and recording the gradation image pattern from the image pattern generation unit for each of the gradation image patterns. An image generating unit for generating an output image on a recording display medium, the image generating unit including a gradation density adjustment control unit capable of changing control data relating to density adjustment for each gradation on a display medium; Density adjustment data holding means for holding density-adjustment control data for each gradation, and a gradation image pattern corresponding to a value of the input image data when in the input image recording mode. Control is performed based on the control data of the density adjustment data holding means, so that the density adjustment at the time of image generation is performed, and in the reference image mode, each of the gradation image patterns corresponding to the value of the reference image data is controlled. The tone density adjustment control unit is controlled so that the control data is changed in a plurality of ways and the density for each tone is changed in a plurality of ways, so that a plurality of levels are provided for each of the tone image patterns. Control means for outputting a reference output image in which a patch is formed on the recording and display medium; reading the reference output image, and for each of the plurality of gradation image patterns of the read reference output image, Of the plurality of gradation patches, a gradation patch suitable for the target gradation characteristic was extracted and used to form the extracted gradation patch. The control data,
And a tone correction data generating means for storing in the density adjustment data holding means as control data for density adjustment of a corresponding tone image pattern. 3. The density adjustment control data is stored in the density adjustment data storage means for each number of lines that can be selected and changed by a user. In the image recording mode, control data for density adjustment at the selected number of lines is read from the density adjustment data holding means in response to a user's selection change of the number of lines, and the density is read. 3. The recording apparatus according to claim 2, wherein the density adjustment at the time of generating the input image is performed based on control data for adjustment.