JP3521472B2 - Image data converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
Images used in image forming devices such as printers and digital copiers.
An image data conversion apparatus, particularly an image forming apparatus
A predetermined image using the image data conversion information
Convert the data to the desired tone reproduction curve (Tone
Image data conversion to obtain an action curve (TRC)
It concerns the device. [0002] 2. Description of the Related Art Conventionally, laser beam printers, etc.
As an image forming apparatus, for example, a semiconductor laser is used.
Laser beam on the photosensitive drum according to the input image data.
Scans the camera and exposes it on the photosensitive drum according to the image data.
A latent electrostatic image is formed, and this electrostatic latent image is
Develop to form black and white or color images
Some are configured as follows. By the way, such a laser beam printer
And the like, the charging characteristics of the photosensitive drum, the light source
Output intensity of conductor laser, charging characteristics of developer in developing unit
Changes with environmental changes such as temperature and humidity, and with time.
When these characteristics change, the image quality, especially halftone
The image quality fluctuates significantly. Therefore, especially for color images
Especially for laser beam printers, etc.
Fluctuation in color tone due to density change of each color for halftone images
Is a big problem, but adjusting color tone is very complicated.
There is a need for automation. [0004] Therefore, due to these environmental changes and changes over time,
In order to suppress fluctuations in color reproducibility,
Develop on the photosensitive drum and detect the density of this developed image
The detection signal is fed back, and various image forming parameters
Control one or more of the meters to reproduce the specified gradation
A method of obtaining characteristics has been considered. [0005] Among the feedback methods, the look
The input image data is stored using an up table (LUT).
Converts the image data into constant image data.
The technique of controlling gender is a relatively new technique.
In this technique, several types of reference gradation patterns are sensed.
They are formed on the optical drum at a predetermined timing, and these
By measuring the density of the quasi-tone pattern, the current
Detect the tone reproduction curve (TRC) characteristic and store it in advance
Difference from the set target tone reproduction curve (TRC) data
Lookup table (LUT) to compensate for minute
Calculate the data. Basically, the tone reproduction curve (TR
C) When the value of the look-up table (LUT) is
The tone reproduction curve (TRC)
To lower the look-up table (LUT) data
Control. Further, the lookup table (LU)
Control operation of gradation reproduction curve (TRC) data using T)
Will be described. The current tone reproduction song that has been detected
The line (TRC) is the target gradation reproduction as shown in FIG.
If it is higher overall than the curve (TRC), for example,
Input image data C₁Target tone reproduction curve
According to (TRC), the image density is D₁Should be
However, in the current tone reproduction curve (TRC), the image density is D
₁’. In this case, the current tone reproduction curve
Target tone reproduction curve (TRC) in (TRC)
Image density D equal to the image density of₁Input image data to obtain
Value C_TwoAsk for. That is, if the input image data is C₁of
Target image density D₁To get the current gradation
According to the reproduction curve (TRC), the input image data₁Or
La C_TwoIt can be seen that it is sufficient to convert to Therefore, the input screen
Image data C₁Look-up to convert
In the table (LUT), the input image data C₁To C_Two
Conversion data L_TwoIs rewritten as shown in FIG.
As shown, a new look-up table (LUT)
Calculate all values. The look-ahead obtained in this manner is
Lookup table (LUT) data
Input image data by writing to the RAM for
Data into the specified image data to obtain the desired tone reproduction curve
(TRC) is controlled to obtain the characteristic. Such technology
Is disclosed, for example, in JP-A-63-113568.
Have been. Here, the input image data is 8-bit data.
For a look-up table (LUT),
Usually, an input / output of 8 bits is used. like this
In an 8-bit look-up table (LUT),
To 255 only. I
Also, for example, if the input image data has the maximum density “255”
However, due to the trouble on the printer side,
Consider the case where the desired maximum density cannot be obtained. This
If you want to increase the current concentration to the desired maximum concentration
However, the input image in the look-up table (LUT)
Convert the value of data "255" to "260"
Even if you try (even a 9-bit lookup table
), The image data bus is 8 bits
Because it is, it is meaningless. Assuming that the image data "260"
Data on an 8-bit bus, this data
260-255 = 5, which is a completely different value.
In other words, all the values above "256"
Replace the data "255" with "255"
Will be used for bulls. As a result, for example, "260"
Data is discarded, but it is essentially
Lookup table (LUT) control for density higher than degree
You can't get it out with technology
No. [0009] SUMMARY OF THE INVENTION
The conventional technology has the following problems. You
That is, in the laser beam printer,
Charging characteristics of body drum, output of semiconductor laser as light source
The strength and the charging characteristics of the developer in the developing unit change with the environment and time.
When the tone reproduction curve (TRC) fluctuates
There is a case. Now, the gradation of the laser beam printer
As shown in FIG. 13, the current curve (TRC)
It has risen once, but after a while the original
Consider the case of returning to the state. Something like this
Turns on the device first in the morning with a normal printer
Prints immediately after printing.
This is a frequent occurrence in data centers. As the cause
Indicates that the density of the printer has actually increased or
For detecting the gradation characteristic by chance when measuring the curve (TRC)
Noise appeared on the sensor and the density seemed high
And so on. In any case, the tone reproduction curve (TRC)
Once measured as shown in FIG.
Control circuit of user beam printer lowers image density
To lower the look-up table (LUT) data
Control so that This lookup table (LU
The control for lowering the data of T) is, as described above,
Input image data C₁Target tone reproduction curve
According to (TRC), the image density is D₁Should be
However, in the current tone reproduction curve (TRC), the image density is D
₁’. In this case, the current tone reproduction curve
Target tone reproduction curve (TRC) in (TRC)
Image density D equal to the image density of₁Input image data to obtain
Value C_TwoAsk for. That is, if the input image data is C₁of
Target image density D₁To get the current gradation
According to the reproduction curve (TRC), the input image data₁Or
La C_TwoIt can be seen that it is sufficient to convert to Therefore, the input screen
Image data C₁Look-up to convert
In the table (LUT), the input image data C₁To C_Two
Conversion data L_TwoIs rewritten as shown in FIG.
As shown by a dashed line, a new look-up table (L
UT) is calculated. As a result, this lookup
New data of the cable (LUT) is as shown in FIG.
Has a target data curve of (C₁-C_Two) Only in the figure
Obtained by translating to the right. In addition, always
, New data is not always obtained by parallel movement. So
Therefore, the input image data corresponds to the maximum density “25”.
Even if the value is "5", the value corresponding to the maximum density after conversion
Is 255- (C₁-C_Two), Which is more than "255"
It becomes a small value. Then, this "255- (C₁−
C_Two) "Is a new look-up table
Is not written in the LUT (LUT).
Will be lost. Thus, apparently the image density of the printer
Goes down as shown in FIG. After a while, the printer
Or, when the sensor status returns to normal,
The line (TRC) also returns to its original state.
Cable (LUT) data has been changed lower
As shown in FIG.
The reproduced tone reproduction curve (TRC) is detected. Therefore, in the next control, as shown in FIG.
Up the look-up table (LUT) data
It is going to return to the original, but the previous control
Then B = 255- (C₁-C_Two) Is the maximum
Therefore, a lookup table larger than this maximum value B
Since the data of (LUT) does not exist in the table,
Table data for large input image data
And the current look-up table (LUT) data
It cannot be calculated by reference. That
Therefore, such a look-up table (LUT) is used.
14 shows the controlled tone reproduction curve (TRC) in FIG.
It becomes the shape of the head as shown. Note that the same
This means that even in the area corresponding to the lowest density,
It also happens when trying to increase the density again by decreasing the degree. As described above, the conventional image data conversion device
If so, look up table (LUT) as described above
When calculating the data of the
In the table (LUT), the input image data “0 to 25”
No meaning for data outside the range of "5"
Was ignored. If you only control once, then the problem is
It does not happen, but iterative lookup table (LU
When the control is performed by rewriting the data of T), as described above,
Was missing because it was meaningless
Therefore, look-up table (LUT) for the next time
Correct data is not available when calculating
There was a problem. In other words, look-up table
The maximum / minimum value of the LUT (LUT) is
It can be small, but not large
is there. Therefore, the above-mentioned conventional image data conversion device is used.
Laser beam printer, the maximum or minimum density
To get the maximum or minimum concentration
There was a problem that it became impossible. Accordingly, the present invention has been made to solve the above-mentioned problems of the prior art.
It was done to solve a point.
At this time, a desired tone reproduction curve (TRC) is obtained.
Image data using a look-up table (LUT)
Lookup table when converting to other data
Even if the maximum or minimum value of (LUT) is changed,
The maximum or maximum value for obtaining the desired tone reproduction curve (TRC)
Always keep the desired image data without losing small value data.
Data can be converted to the target gradation reproduction curve.
Image data conversion that can always reproduce (TRC)
It is to provide a device. [0015] SUMMARY OF THE INVENTION The present invention provides an input image
Look for converting data according to image data conversion information
Up table (LUT) and the target of the image forming apparatus
Storage means for storing a tone reproduction curve,
By the stored target tone reproduction curve and detection means
Compare the current tone reproduction curve of the detected image forming device
Input image data so that both tone reproduction curves match.
Look-up based on the current tone reproduction curve data
Change image data conversion information in the drop table (LUT)
An image data conversion apparatus comprising
Image data used in lookup table (LUT)
Over the range larger than the number of bits
A second storage means for storing a value obtained by extrapolating the data.
Of the tone reproduction curve stored in the second storage means
Lookup table by using as needed
(LUT) to change the image data conversion information.
Has been established. Here, if necessary,
Missing in the image data conversion information of the table (LUT)
When looking up, for example, look-up table
Image data conversion information on the high density side of the
Control on the side and look-up table (LU
The image data conversion information on the low density side of T) is further added to the low density side.
This becomes necessary when control is performed. [0016] In the image data conversion device according to the present invention, the
Image data used in the backup table (LUT)
Data of the tone reproduction curve over a range larger than
And a second storage means for storing a value obtained by extrapolating
Needs data of gradation reproduction curve stored in storage means
The lookup table (LU)
T) is configured to change the image data conversion information.
The image forming apparatus detected by the detecting means
Matches current tone reproduction curve with target tone reproduction curve
In order to make the look-up table
(LUT) when changing the image data conversion information
Image data of lookup table (LUT)
Suppose that control was performed to decrease the maximum value of the conversion information.
However, the data for obtaining the maximum value of the tone reproduction curve
2 is stored in the second storage means.
Lookup using the tone reproduction curve data stored in the column
Change the image data conversion information of the backup table (LUT)
To obtain a desired tone reproduction curve (TRC)
The maximum or minimum data for
Can always be converted to the desired image data
The tone reproduction curve (TRC) can be always reproduced
It works. [0017] BRIEF DESCRIPTION OF THE DRAWINGS FIG.
I will tell. FIG. 2 shows an image data conversion apparatus according to the present invention.
Shows one embodiment of a laser beam printer to which
It is. In FIG. 2, reference numeral 21 denotes a feeling as an image carrier.
This shows an optical drum, and the photosensitive drum 21
Is predetermined along the direction of the arrow by the driving means (not shown).
It is designed to be rotationally driven at a rotational speed of. Above feeling
The surface of the photosensitive drum 21 is provided around the optical drum 21.
A scorotron charger 22 for uniformly charging the surface;
Optical system 23 and yellow, magenta, and shea, respectively.
Four color cartridges containing developer of each color
Imager 24a, 24b, 24c, 24d and transfer charger 2
5 and the color of each color sequentially formed on the photosensitive drum 21.
Intermediate transfer belt for transferring and holding toner images in a superimposed state
26 are sequentially arranged along the rotation direction of the photosensitive drum 21.
Is placed. Further, around the intermediate transfer belt 26
Is overlapped on the intermediate transfer belt 26.
Intermediate rotation of the toner image of the specified number of colors
Transfer paper 2 conveyed to a position facing photoreceptor belt 26
Transfer roll 2 for batch transfer onto 0
7 and a recording medium on which the toner image of the predetermined number of colors has been transferred.
Transported recording paper 20 to fixing unit 29 described below
Transport belt 28 and the transport belt 28
Fixing device 2 for fixing a toner image on fed recording paper 20
9 are arranged. The surface of the photosensitive drum 21 is made uniform.
As the scorotron charger 22 for charging the second color
Stable and uniform charging is possible during subsequent image formation
And a scorotron charger using two or more discharge wires
It is desirable to use. The color developing units 24a, 24b,
Each of 24c and 24d has a known configuration, for example.
Although a two-component developing device can be used, particularly,
The tip of the ear of the two-component developer consisting of a carrier is exposed
Surface of body drum 21 and photosensitive drums 21 for the second and subsequent colors
Make sure that the developing roller is not in contact with the toner image formed on it.
Of the two-component developer carried on the
The photoconductor drum 21 is disposed so as to face the surface of the photoconductor drum 21.
Is used. Further, each of the color developing units 24a,
4b, 24c, 24d
Does not disturb the toner image formed on the photosensitive drum 21.
AC voltage to obtain the desired high image quality
To apply DC voltage (DC + AC voltage)
To adjust the AC component of the developing bias, for example.
It has become. FIG. 3 shows the laser beam printer of FIG.
FIG. 2 is a schematic configuration diagram showing a laser optical system used. The laser optical system 23 has a laser
Laser 31 driven by a laser drive circuit
, A collimator lens 32, a polygon mirror 33,
fθ lens 34. And the above half
The conductor laser 31 is output from a laser drive circuit described later.
ON / OFF modulated by the input image data 36
Laser modulated by the so-called pulse width modulation method
The beam 35 is emitted. From this semiconductor laser 31
The emitted laser beam 35 is transmitted to the collimator lens 3.
When the light is irradiated on the surface of the polygon mirror 33 through
In addition, the surface of the polygon mirror 33 rotating at high speed
Is reflected and deflected by the photoconductor drum via the fθ lens 34.
21 along the main scanning direction (the axial direction of the photosensitive drum 21).
Scanning exposure. The laser beam pump constructed as described above
In the linter, the surface of the photosensitive drum 21 is a scorotron band.
After being uniformly charged to a predetermined potential by the
A laser optical system 23 is provided on the surface of the photosensitive drum 21.
The image corresponding to the image information of the first color is scanned and exposed.
An electrostatic latent image is formed. Formed on this photosensitive drum 21
The developed first-color electrostatic latent image is the first-color developing device.
If the toner is developed by the yellow color developing device 24a,
-It becomes an image. This first color yellow toner image is
Due to the charging of the photo charger 25, the intermediate transfer member belt 26
Is electrostatically transferred to Then, the first color toner
The photosensitive drum 21 on which the image has been formed is transferred to a transfer process or a cleaning process.
The charging, exposure, and development steps are repeated
Similarly, the process is repeated for a predetermined number of colors, and the photosensitive drum 21
Yellow, magenta, cyan and bra sequentially formed on top
The four color toner images of the
The images are sequentially transferred onto the intermediate transfer belt 26. And this
Four-color toner images formed on the intermediate transfer belt 26
Is for recording on the intermediate transfer belt 26 at a predetermined timing.
By the transfer roll 27 contacting via the paper 20
Is transferred onto the recording paper 20 in a lump.
The paper 20 is transported to the fixing device 29 by the transport belt 28.
Sent. The fixing device 29 fuses the four color toner images.
The recording paper 20 is fixed on the recording paper 20 in a melt-mixed state.
20 is discharged out of the machine, and the color image forming process is completed.
You. Further, the photosensitive drum after the above-mentioned transfer step is completed.
The surface of the drum 21 is exposed to residual toner
Cleaning device having a blade,
After the residual toner is removed by the
Therefore, the residual charge is further erased, and the next color image forming process is performed.
Be prepared for it. In this embodiment, the laser beam
Using the intermediate transfer belt 26 as a linter,
Although an apparatus for forming an original image has been described, it is not limited to this.
Is not specified.
Recording paper holding a color toner image on the intermediate transfer drum
Or intermediate transfer media to transfer
Equipped with an image forming device and multiple photoreceptor drums.
Each toner image formed on each photosensitive drum is
On the recording paper that is sequentially conveyed to the transfer position of the photosensitive drum
Where full-color images are formed by sequential transfer
A so-called tandem type color image forming apparatus may be used.
Of course. By the way, such a laser beam printer
In the above, a color image is recorded as described above.
However, the quality of the recorded color image depends on the photoconductor
Charging characteristics of the camera 21 and the output of the semiconductor laser 31 as a light source
Strength, color developing units 24a, 24b, 24c, 24d
The charging characteristics of the developer inside change the environment such as temperature and humidity.
And these characteristics change with the passage of time.
As a result, the image quality, particularly the halftone image quality, fluctuates significantly. That
For the above laser beam printers,
Large changes in color tone due to changes in the density of each color
I do. Therefore, the laser beam pump of the above color is used.
In the linter, as shown in FIG.
Multiple reference toner images of each color
It is formed over the gradations, and the reference
The density of the toner image is measured by a density sensor 10 as shown in FIG.
Of each color of these detected multiple gradations
Based on the reference toner image density, as shown in FIG.
It is configured to determine a sex reproduction curve (TRC).
Then, based on the obtained tone reproduction curve (TRC),
Input image data using an image data converter.
By changing the target tone reproduction curve (TR
C). FIG. 1 is applied to the above laser beam printer.
FIG. 2 is a block diagram showing a converted image data conversion device. In the drawing, reference numeral 1 denotes an image reading device (not shown)
Input through the I / F circuit from a PC or computer
The input image data 1 is a predetermined image
A conversion means for converting based on data conversion information
This is a lookup table (LUT).
Table (LUT) 2 is the gradation reproduction of the printer
Input image data such that the curve (TRC) has predetermined characteristics.
Is a device for converting data 1 into other image data 3.
You. The image in the lookup table (LUT) 2
The image data conversion information is rewritten by a CPU described later.
Output data 3 for input image data 1
By converting to an arbitrary value, the tone reproduction curve (TR
C) can be changed. That is, the input image data
Arbitrarily set the tone reproduction curve (TRC) for data 1
It can be. 4 is a look-up table (LUT) 2
Therefore, it has a pulse width corresponding to the converted image data 3.
Analog screen generator that outputs a pulse width modulated signal
Neerator (ASG), 5 is analog screen generator
Based on the pulse width modulation signal 6 output from the
This is a laser drive circuit that drives the conductor laser 31. 7 is a program stored in the ROM 8 in advance.
Of the look-up table (LUT) 2 based on the
CPU for performing control for changing the conversion data, 9 is an input image
Tone reproduction curve (TRC) in the optimum condition for data 1
As storage means to hold the conversion data for obtaining
The RAM 9 is provided by the CPU 7.
Is controlled. 10 is a look-up table (LUT) 2
Over a range larger than the bit number of the image data used in
The value obtained by extrapolating the data of the tone reproduction curve
RAM as a storage means for
RAM 9 is controlled by the CPU 7. FIG. 6 shows the analog screen generator.
FIG. 4 is a block diagram showing a data (ASG) 4. In FIG. 6, reference numeral 40 denotes an image reading device or a computer.
Computer, etc., via an I / F circuit (not shown).
The input image data 41 represents the input image data 40
Bit-quantized analog signal (256 gradations)
D / A converter with the function of
First triangular wave generation for generating a triangular wave based on the block 43
, A divider 44 for dividing the image clock 43 into １ ／
The frequency divider, 45, is frequency-divided to 1/2 by this 1/2 frequency divider
First triangular wave generator based on the image clock 43
Generation of a second triangular wave for generating a half-period triangular wave of 42
, 46 and 47 are output from the D / A converter 41.
8-bit quantized data 48 and first and second triangles
Triangular wave signals 49, 5 output from the wave generators 42, 45
The comparator 51 compares the comparators 46 and 4 with each other.
Select any pulse width modulation signal output from 7
Selected based on the trigger signal 52 and output to the laser drive circuit
Selector. Then, the analog screen generator
The data 4 includes an image reading device and a host computer (not shown).
Input image having gradation information for each pixel to be printed
Image data 40 is input via an I / F circuit (not shown).
Then, the input image data 40 has an 8-bit amount.
Image conversion by the D / A converter 41 having
D / A conversion is performed based on the lock 43, and this analog signal
Are converted into comparators 46 and 47
Sent to Also, the triangular wave generators 42 and 45
Triangular wave of the same cycle and 1/2 cycle synchronized with lock 43
And the triangular wave signals 49 and 50 are also
It is sent to 46 and 47. These comparators 46, 47
Triangle wave signals 49 and 50 and input converted to analog signal
The image data 48 is compared with the gradation of the input image data 48.
Outputs a pulse with a length proportional to the information, and this output
Pulsed by the laser drive circuit
Sent as a width modulated signal. The analog screen generator described above
(ASG) has a triangular wave generator and two comparators
However, these triangular wave generators and comparators are only one
Of course, it may be configured to be provided. In the above configuration, the image according to the above embodiment is
With a laser beam printer using an image data converter
Is to obtain a predetermined gradation reproduction characteristic as follows.
The image data is converted. That is, the above laser beam
Image quality of color images recorded by
2, as shown in FIG.
The output intensity of a certain semiconductor laser, the color developing device 24a,
The charging characteristics and the like of the developer in 24b, 24c and 24d
Easy conversion due to environmental changes such as temperature and humidity and changes over time
When these characteristics change, the image quality, especially the halftone image quality,
Fluctuates significantly. Therefore, the laser beam pump of the above color is used.
In the linter, at a predetermined timing, as shown in FIG.
Um, yellow, magenta, and shea on the photosensitive drum 21
The reference toner image of the four colors of black and
And the density of the reference toner image of each of these multiple tones.
The density is detected by a density sensor 10 as shown in FIG.
Output, each color of these detected multiple gradations
Based on the reference toner image density, as shown in FIG.
A tonality reproduction curve (TRC) is obtained. This
Here, the predetermined timing is, for example, a laser bead.
When the power of the beam printer is turned on or when the laser beam
When a certain period of time has passed after turning on the printer,
After several prints, after a certain number of days have passed. Now, the gradation of the above laser beam printer
The sex reproduction curve (TRC) as shown in FIG.
For the target tone reproduction curve (TRC)
Once dropped, but after a while it returned to its original state
Think about it. In FIG. 7, a tone reproduction curve (TRC) is shown.
Is measured once, the CPU 7 determines the image density
Lookup Table (LUT) 2
Calculate in the direction to lower the image conversion data. That is, an example
For example, if the input image data is C₁In the case of the target floor
If the tone reproduction curve (TRC), the density is D₁Becomes
Of the current tone reproduction curve (TRC)
If the concentration is D₁’And the target density (D
₁-D₁’). Therefore, the CPU
In the gradation reproduction curve (TRC) of₁Becomes
Input image data C_TwoAsk for. As a result, the CPU 7
If the tone reproduction curve (TRC) is equal to the target curve
As shown in FIG.₁In the case of
Force image data 1 is C_TwoLookup table to be
(LUT) to L_TwoRewrite to As described above, the CPU 7 performs the gradation reproduction.
So that the curve (TRC) is equal to the target curve
Requires all values in lookup table (LUT) 2
Rewrite accordingly. Lookup table at this point
The maximum value of (LUT) 2 is the current tone reproduction curve (TR
C) is smaller than “255” due to the lowering of C). Soshi
Thus, look-up table (LUT) 2 is
By changing, the tone reproduction reproduction of the printer
The line (TRC) goes down as shown. Here, the difference from the conventional method is shown in FIG.
Extrapolate the target tone reproduction curve (TRC)
When the force image data 1 has a gradation property corresponding to a range of 256 or more,
The current curve (TRC) is also calculated and stored in the RAM 10
It's just around the corner. The target tone reproduction curve (TR
There are various methods for extrapolating C).
Slide the current gradation reproduction curve (TRC) in parallel
Extrapolation is performed. Also, the target gradation
The sexual reproduction curve (TRC) is calculated using a cubic curve,
A method of extrapolating by approximation with a line is used. Next, the state of the printer or sensor is
As shown in FIG. 8, the gradation reproduction curve (T
Assume that RC) has returned. Then, as described above, the gradation
Because the sex reproduction curve (TRC) is set low,
The tone reproduction curve (TRC) detected at this time is shown in FIG.
As shown in the figure, the gradation is lower than the target
It is detected as a sex reproduction curve (TRC). This time CPU
In the lookup table (LUT) 2 calculation by
Extrapolated current tone reproduction curve (TRC) and previous control
Lookup of the input range of 256 or more saved at the time of
The data of the top table (LUT) 2 is used. Then
Lookup table (LUT) 2 is the same as the original target
The shape of the reproduced tone reproduction curve (TRC) is restored. I
Therefore, it is recorded by the laser beam printer
The tone reproduction curve (TRC) is also as shown in FIG.
Then, it will be restored. As described above, in the above embodiment, the look-up
Of image data used in the lock table (LUT) 2
Of the tone reproduction curve (TRC) over a range larger than
As a second storage means for storing a value obtained by extrapolating data
A RAM 10 is provided, and the gray scale stored in the RAM 10 is reproduced.
Use the current curve (TRC) data as needed
Image data of the lookup table (LUT) 2
Is configured to change the conversion information.
Laser printer detected by sensor 10
Reproduction that targets the current gradation reproduction curve (TRC)
Lookup by CPU 7 to match the curve
The image data conversion information of the table (LUT) 2
When the last operation, look-up table (LUT)
2 to reduce the maximum value of the image data conversion information.
The maximum value of the tone reproduction curve (TRC)
The data for obtaining is stored in the RAM 10
The tone reproduction curve (TR) stored in the RAM 10
Lookup table (LUT) using data of C)
3 by changing the image data conversion information.
Value or minimum value for obtaining the tone reproduction curve (TRC)
The desired image data is always saved without losing the value data.
Can be converted to a target tone reproduction curve (T
RC) can always be reproduced. Embodiment 2 FIGS. 9 and 10 show a second embodiment of the present invention.
This shows an embodiment, and the same parts as those in the above embodiment are the same.
Explaining with the reference numerals, in this embodiment,
Example 1 is the end point on the higher density side of the tone reproduction curve (TRC)
, But the density of the tone reproduction curve (TRC)
This shows the case when applied to the lower end point.
The operation is the same as in the above embodiment. But different
Of the tone reproduction curve (TRC)
Density "falls down" and later "rises" back
The present invention is equally applicable in situations. Other configurations and operations are the same as those of the above embodiment.
Therefore, the description is omitted. [0048] The present invention has the above-described structure and operation.
The purpose is to reproduce the desired gradation.
Lookup image data to obtain a curve (TRC)
Converting to other data using a map table (LUT)
The maximum value of the lookup table (LUT) or
Even if the minimum value is changed, the desired tone reproduction curve (TR
C) the maximum or minimum data to obtain is lost
And can always be converted to the desired image data.
Always reproduce the target tone reproduction curve (TRC)
Can provide image data conversion device that can
You.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing one embodiment of a control unit of a laser beam printer to which an image data conversion device according to the present invention is applied. FIG. 2 is a configuration diagram showing a laser beam printer. FIG. 3 is a configuration diagram showing a laser optical system. FIG. 4 is a schematic diagram showing a reference image pattern. FIG. 5 is a graph showing a relationship between input image data and density and conversion data. FIG. 6 is a block diagram showing an analog screen generator. FIGS. 7A and 7B are graphs respectively showing a relationship between input image data and density and conversion data. FIGS. 8A and 8B are graphs respectively showing the relationship between input image data and density and conversion data. FIGS. 9A and 9B are graphs respectively showing a relationship between input image data and density and conversion data according to the second embodiment of the present invention. FIGS. 10A and 10B show a second embodiment of the present invention.
7 is a graph showing a relationship between input image data and density and conversion data according to the first embodiment. FIG. 11 is a graph showing a relationship between input image data and density and conversion data in a conventional example. FIG. 12 is a graph showing a relationship between input image data and density and conversion data in a conventional example. FIGS. 13A and 13B are graphs respectively showing a relationship between input image data and density and conversion data in a conventional example. FIGS. 14A and 14B are graphs respectively showing the relationship between input image data and density and conversion data in a conventional example. [Description of Signs] 1 Input image data, 2 Look-up table (LU
T), 3 other image data, 4 analog screen generator, 7 CPU, 9 RAM, 10 RAM (second storage means).

Claims (1)

(57) [Claim 1] Look-up table (LUT) for converting input image data according to image data conversion information
Storage means for storing a target gradation reproduction curve of the image forming apparatus; and a target gradation reproduction curve stored in the storage means and the image detected by the detection means provided in the image forming apparatus. Image data conversion information of a look-up table (LUT) based on the data of the current tone reproduction curve with respect to the input image data so that the tone reproduction curves of the forming apparatus are compared with the current tone reproduction curve. An image data conversion device comprising an arithmetic means for changing the tone reproduction curve data over a range larger than the number of bits of image data used in the look-up table (LUT). And a tone reproduction curve data stored in the second storage means is used as needed to generate a look-up table (LUT) image. An image data conversion device for changing image data conversion information.