JP2000083171A - Image processing unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow an image processing unit to flexibly cope with a change in a gamma curve through formulation of the gamma curve by processing data with a data processing means that processes the data in parallel. SOLUTION: In the image processing unit, which is provided with an ALU 405 that uses parameters different in the unit of each pixel to execute parallel processing, an external data RAM 401 that stores in advance the parameters, and a G411a register that loads required data from the external data RAM 401 and whose contents are referenced by the ALU 405 in the case of conducting an arithmetic operation, and which applies parallel gamma conversion to an input density based on the parameters loaded to the G register 411a to decide an output density, pluralities of conversion equations corresponding to each density level are stored in the external data RAM 401, the ALU 405 selects a converstion equation in response to a density level set by a density setting section that is provided separately and decides the output density based on the selected conversion equation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a so-called image processing apparatus for processing an image signal, such as a copying machine, a facsimile, a printer, and the like, and more particularly, to an image processing apparatus characterized by density (gradation) correction.

[0002]

2. Description of the Related Art For example, in a digital copying machine,
The original placed on the contact glass is scanned, photoelectrically converted line by line, and the obtained image signal is converted into digital data, and then subjected to predetermined image processing to generate a recording signal. The laser element is optically modulated according to the signal to form a latent image corresponding to the original image on the photoconductor. In the image processing, various processes such as color correction, γ correction, shading correction, MTF correction, gradation conversion, and scaling are performed.

[0003]

In the conventional gamma correction, the output density corresponding to the input density is stored in an external memory for the entire density range, and the density data corresponding to the input density address is read out. Concentration. for that reason,
Naturally, the amount of memory data has increased, and the flexibility in changing the γ curve has been lacking. Further, similar density conversion may be performed based on the expression of Yule-Nelsen, or may be performed based on the quantization characteristics of gradation quantization. The density conversion based on these is also performed by a density correction curve (density correction curve). Had the same problem from using the characteristic).

Accordingly, a first object of the present invention is to provide an image processing apparatus in which the density correction characteristics can be easily changed and the density correction data amount can be reduced.

Therefore, a second object of the present invention is to provide an image processing apparatus capable of flexibly coping with a change in the density correction curve by formulating the density correction curve by processing the data by means of data processing means capable of parallel processing. Is to provide.

A third object is to divide the density range,
It is an object of the present invention to provide an image processing apparatus capable of reducing a data amount by having a parameter for each section.

[0007]

According to a first aspect of the present invention, there is provided an image processing apparatus comprising: an input unit for inputting an image signal of one raster; and an image of one raster input by the input unit. Density correction calculating means for determining the output density by performing density conversion on the input density in parallel by a calculator provided with signals in parallel, and output means for serially outputting the output density obtained by the calculating means And external data storage means for rewritably storing parameters required for the density conversion.

[0008] The second means is the first means, further comprising a program unit for controlling an arithmetic expression and input / output of the arithmetic means, wherein the arithmetic means converts the density of the input image signal into the output density. A conversion formula described in a program of the program unit is used.

A third means is the second means, wherein the entire range of the input density is divided into a plurality of ranges, and the divided coordinates used for conversion in each section and the coefficients of the conversion formula in each range are represented by the following values. It is stored in the rewritable external data storage means.

[0010] A fourth means is the third means, wherein the arithmetic expression used in the arithmetic means is a coefficient unique to each input density range, and can be operated in parallel by the same program. I do.

[0011] An image processing apparatus according to a fifth means is provided.
An arithmetic unit for executing parallel processing using different parameters for each pixel unit, an external data storage unit for storing the necessary parameters in advance, and loading necessary data from the external data storage unit, A register which can be referred to by the calculating means; density determining means for performing output density conversion by performing density conversion on input density in parallel based on parameters loaded into the register; density level for setting density level Setting means, wherein a plurality of conversion formulas corresponding to density levels are stored in the external data storage means, and the calculating means selects the conversion formula from the density levels set by the density level setting means, The density determining means determines the density based on the obtained conversion formula.

The sixth means is an input means for inputting an image signal of one raster, and a processing unit provided in parallel with the image signal of one raster inputted by the input means, in parallel with the input density. Density correction calculating means for performing conversion to determine output density, output means for serially outputting the output density obtained by this calculating means, and external data storage for rewritably storing parameters required for the density conversion Means for loading necessary data from the external data storage means, and a register which can be commonly referred to by the arithmetic unit at the time of calculation, and density level setting means for setting a density level. Is divided into a plurality of ranges, a division coordinate used for conversion in each of the divided sections, a coefficient of a conversion formula in each range, and a plurality of density conversion levels. A conversion formula corresponding to the density level set by the density level setting means is selected from the external data storage means in which a corresponding conversion formula is stored in advance, and the calculator and the register file of each of the calculators are stored by the calculator. , The operations are performed in parallel by the same program based on the selected conversion formula.

A seventh means is the sixth means, wherein the number of density range divisions corresponding to a plurality of density levels is stored in advance in the external data storage means, and the arithmetic means is set by the density level setting means. The number of density range divisions is selected according to the determined density level.

The eighth means is the sixth means, wherein the external data storage means is connected to an external CPU via a bus, and stores one number of density range divisions and one conversion formula for each section. Further comprising a selector for switching the connection between the external data storage means and the data processing means having the register and the external data storage means, wherein the external CPU responds to a setting from the concentration level setting section. It is characterized in that the number of density range divisions stored in the external data storage means and the conversion formula for each section are rewritten to change the content of the density conversion setting.

Ninth means according to the sixth means, further comprising an operation unit connected to the external CPU and the bus via the selector, wherein the content of the density conversion setting is input by an operation input from the operation unit. It is characterized by changing.

According to a tenth aspect, in the sixth aspect, the operation section reads out the content of the external data storage section which is currently set, and displays the content on the operation section.

The eleventh means is the first, fifth and sixth means, wherein the density conversion is a density conversion based on gamma conversion, a density conversion based on Nielsen's equation, and a density conversion based on gradation quantization. Characterized by being performed by any of

[0018]

Embodiments of the present invention will be described below with reference to the drawings.

1. Overall System Configuration FIG. 17 shows the overall system configuration of the embodiment of the present invention, and is a block diagram showing a schematic configuration of a digital copying machine to which the image processing apparatus according to the present invention is applied. The digital copying machine includes a reading unit (scanner) 10 and a control unit 2.
0 and an image forming unit (printer) 30.

As can be seen from the block diagram shown in detail in FIG. 18, the reading section 10 includes a document table 11, an exposure lamp 13 positioned below the document table 11, and illuminating a document 12 placed on the document table 11. Reflection mirror group 1 for guiding reflected light from a document exposed by exposure lamp 13 to CCD 14
5. an amplifier 16 that performs processing including A / D conversion and shading correction and amplifies the image signal from the CCD 14, the exposure lamp 13 and the reflection mirror group 15
And a scanner control unit 17 for controlling a scanner equipped with the scanner.

The control unit 20 includes an IPU (image processing unit-image processing unit) 21, a selector unit 22,
It comprises a storage unit 23, a system control unit 24, and an operation unit 25. The system control unit 24 can perform two-way communication with a personal computer 50 as a host computer, and can also function as an external output device (printer) of the personal computer 50. At this time, the image information can be taken from the storage medium 51. In addition, IPU
The image signal amplified from the amplifier 16 is input to the amplifier 21, and the image signal processed by the IPU 21 is processed by the image forming unit 3.
0 is output to the writing unit 31. The system control unit 24 is configured to be able to communicate bidirectionally with the scanner control unit 17 of the reading device 10 and the plotter control unit 32 of the image forming unit 30.

The image forming section 30 includes a writing section 31, a plotter control section 32, a photosensitive member 33, a charging charger 34, a developing device 35, a transfer charger 36, a separation charger 37,
A cleaning device 38, a static elimination charger 39, and a fixing device 40;
1, 42, 43, 44 and the paper supplied from any of these paper feed trays are supplied to the transfer charger 36 and the separation charger 37 via the registration roller 45, and the fixed transfer paper is discharged. A paper discharge tray 47 that discharges paper through the paper rollers 46 is provided.

The image forming process of the digital copying machine having the above components is as follows.

The original 12 placed on the original table 11 is scanned and exposed by an exposure lamp 12 movable along the original table 11. The reflected light of the scan-exposed document enters the CCD 14 via the mirror group 15 and is reflected by the CCD 14.
Is photoelectrically converted in accordance with the intensity of light, and is converted into an electric signal. The image signal read by the CCD 14 is amplified by the amplifier 16 to a predetermined voltage amplitude, and thereafter, the A / D conversion circuit performs 2 n-th gradation (25 in this embodiment) per pixel.
(6 gradations). Then, the shading correction circuit uses the illuminance unevenness of the light source and the CCD 14
The variation in sensitivity among the elements is corrected, and the image data is input to the IPU 21 together with the image synchronization signal. The scanner control unit 17 detects various sensors and controls a drive motor and the like to execute the above process, and sets various parameters in the shading processing unit and the IPU 21. The above process is the reading process.

Next, the IPU 21 increases the resolution of two-dimensional real-time scaling processing, characters, line images, etc.
TF correction processing, spatial filter processing that removes signal noise and performs smoothing processing to improve the reproducibility of photographs, etc., gamma correction processing according to the density setting function, and gradation processing that performs intermediate processing according to the image quality setting function Processing is performed.

The image forming unit 30 further sends the image data from the IPU 21 to the writing unit 31, and modulates the photoconductor 33, which is uniformly charged by the charging charger 34 and rotates at a constant speed, with the image data from the writing unit 31. Exposure is performed by using the laser light. An electrostatic latent image is formed on the surface of the photoconductor 33 by the laser beam, and the electrostatic latent image is developed with toner by the developing device 35 to form a visualized toner image on the surface of the photoconductor 33. Is done. Then, the paper feed trays 41 to
The transfer paper fed from any one of the transfer rollers 44 and waiting at the nip position of the registration roller 45 is conveyed at a timing synchronized with the rotation of the photoconductor 33, and the toner on the photoconductor is transferred to the transfer paper by the transfer charger 36. Electrotransfer is performed, and the transfer paper is separated from the surface of the photoconductor 33 by the separation charger 37.
The separated transfer paper is conveyed to a fixing device 40, where the image on the transfer paper is heated and pressed to fix the image on the transfer paper. The transfer sheet on which the fixing is completed is discharged onto a discharge tray 47 by a discharge roller 46.

On the other hand, the toner image wave remaining on the photoreceptor after the electrostatic transfer and the cleaning device 38 are pressed against the photoreceptor 33 to remove the same, and the photoreceptor 33 is discharged by the discharging charger 39. The plotter control unit 32 performs detection of various sensors and controls a drive motor and the like in order to execute the above process. Thus, the image forming process is performed.

FIG. 19 is a block diagram showing the internal configuration of IPU 21. The signal path of the copying operation will be described with reference to FIG. The image data input from the image reading unit 10 (scanner) includes a scanner image correction unit 21-1, a scaling unit 21-2, a filter unit 21-3, a scanner mask unit 21-4, a γ processing unit 21-5, and Image quality processing unit 21-6
After the predetermined processing is executed in the write output control unit 31
The write output control unit 31-1 sets a control signal to an output mode and outputs data to a write system. The scanner mask section 21-4 trims or masks data at a designated position on the document. The gamma processing section 21-5 performs density conversion, and the image quality processing section 21-6 performs error diffusion, dither processing, phase control, and the like. The γ processing unit 21-5
Can be replaced by a density correction processing unit based on Nielsen's equation or a density correction processing unit based on gradation quantization as described later.

2. DSP (Digital Signal Processor)
First, a DSP as a data processing means used in the present invention
Is shown in FIG. This figure is a diagram showing the operation of γ correction and the register configuration of the DSP. In FIG.
The SP includes a plurality of 8-bit registers 404-R0 to 404-RN connected via an external data RAM 401, an address bus 402 and data, and a CS bus 403;
A 16-bit ALU (Ar) that can be operated by loading data from each of the registers 404-R0 to RN and that can store the operation result in each of the 8-bit registers 404-R0 to RN.
ithmetic and Logic Unit) 405-1, 405-2,
, 405-3,... Connected to each of the ALUs 405, and controls the circuit connection in the loading and storing of the 8-bit register 404, and is used for data input / output. 1,409-
., A program RAM 410 storing a γ correction control program, and a global (G) register 411a connected to the multiplexer 409.
And a global processor unit 411 provided with Note that both the program RAM 410 and the global processor unit 411 are connected to the address bus 402, the data, and the CS bus 403, respectively.

The ALUs 405-1, 405-2, 40
.. Represent accumulator registers 406, respectively.
-1, 406-2, 406-32,... And temporary registers 407-1, 407-2, 407-3,. The operation is performed, and the operation result is stored in the accumulator. Also, each ALU 405 has T registers 408-1, 408
., 408-3... One bit is provided so that each ALU 405 can independently select whether or not to execute program processing according to the value.

The register 404-R0 is an input density register, 404-R1 is an x coordinate register of section coordinate values, 404-R2 is a y coordinate register of section coordinate values, 40
4-R3 is a coefficient register, 404-R4 is an output density register, and 404-RN is a section number register.

Such a configuration is called a PE (processing element), and a plurality of such PEs are arranged in parallel and operated in parallel according to a single program. In the present invention, the data of one pixel is 1A
If processing is performed by the LU, the configuration is such that one raster is arranged in parallel.

3. γ conversion equation In this embodiment, the conversion equation for realizing γ conversion is 1
The following equation was used. The gamma correction control program stored in the program RAM 410 includes a conversion formula given by a linear expression for input data, and calculates an output density for the input density by the following Bell calculation. Procedures are stored in advance. That is, in the present embodiment,
A linear linear equation is approximated for each section obtained by dividing a commonly used γ curve into n sections in the input density range. The correction curve approximated by the linear expression is conceptually shown in FIG.
Shown in In FIG. 2, and the section coordinate _{P n (x n, y n} ) and (1), an approximate straight line coefficients in the interval to a _n. However, the coefficient a _n is obtained by a _n = the coordinates of two points _{(y n + 1 -y n)} / (x n + 1 -x n) ··· (2). Accordingly, the output density is obtained by the output density = a _n (input density _{-x n) + y n ··· (} 3).

[0034] However, if you have to quantize the output density in 256 gradation is determined in the output density = int {a _n * (input density _{-x n) -y n} ··· (} 4), the input if during the concentration of the P ₄ and P _5, the input density coordinate data _{P 4 (x 4, y 4} ), from the coefficient data a _4,
The output density is, as shown in FIG. 3, output density = int {a ₄ * (input density−x ₄ ) −y ₄ } (5).

[0035] In order to perform γ conversion of 3.1 section determining the formula (3) or (4) the interval coordinate _{P n (x n, y n} ) for use in converting the input density determined and the coefficient a _n Must. The algorithm for determining the section coordinates and coefficients will be described with reference to the flowchart shown in FIG.

In this algorithm, first, step 1
01, one raster of the input density is stored in the input density register 404-
Stored in R0. Next, at step 102, the T register 408 is initialized and "1" is set. At the same time, the section number data N is fetched from the external data RAM 401 and loaded into the section number register 404-RN. The T
The register 408 has one bit for each ALU 405,
Only the ALU 405 in which the value of the T register 408 is “1” can execute the program.

When the processing in step 102 is completed, in step 103, 1 is subtracted from the value of the section number register 404-RN. That is, in the section number register 404-RN,
In step 102, the number n of sections obtained by dividing the input density range is loaded, and is decremented by one for each calculation of the input density section determination. Then, at step 104, each AL
U405 confirms the value of T register 408 and executes the processing of step 105 and thereafter only when it is "1". In step 105, coordinate data P _n−1 (x _n−1 , y _n−1 ) and coefficient data an ₋₁ corresponding to the number n of sections after subtracting ₁ are stored in the global processor unit 411 from the external data RAM 401.
The x coordinate register 404-R1 and the y coordinate register 404-R2 used by each ALU 405 via the register 411a.
And to the coefficient register 404-R3. The G register 411a can be commonly accessed by the previous ALU 405. When the transfer is completed in this way, in step 106, the ALU 405 sets the input density register 404-R
Subtract x _n-1 of the P _n-1 coordinate from the value of 0. Then, the coordinate data x _n-1 and y _{n-1 of} P _n-1 used in step 107
And the coefficient an _-1 again in the x, y coordinate registers 404-R1,
Write back to 404-R2 and coefficient register 404-R3. Thereafter, in step 108, the sign bit of the subtraction result is stored in the T register 408. This operation is repeated until n = 0 (step 109).

However, when the sign bit in step 108 is "0" from the result of the subtraction in step 106, in other words, the ALU 405 in which the section of the input density is confirmed.
Then, the subsequent processing of steps 105 to 108 is skipped, and all ALUs 405 in one raster can independently store necessary coordinate data and coefficient data in a register. In this way, the loop of steps 103 to 109 is repeated for the number of sections, and all A
After the section of the input density assigned to the LU 405 is determined, the output density is calculated by the above equation (4) in step 110, and the output density of one raster is output to the outside in step 111. However, the expression of R3 in step 110 of the flowchart is a value a _n of the coefficient register 404-R3, R1
Indicates the value _xn of the x coordinate register 404-R1, and R2 indicates the value of the y coordinate register 404-R2.

3.2 Specific Calculation Example The control after the density section of each input data of one raster is determined is as follows.

As shown in FIG. 5, the input density register 404
The input density data stored in -R0 is a = 2 in the figure.
Control for determining a section by the algorithm of FIG. 1 in each case of 40, b = 200, and c = 50 will be described.

The input density range is from 0 to 255, and a case where the range is equally divided into eight is considered. The number of intervals in this case, the section coordinate P _n, the coefficient a _n data external data RAM4
One example set to 01 is shown in FIGS. First, all ALUs 405 have their own input density registers 40
4-R0 and n = 7 in the external data RAM 401, x ₇ =
223, y ₇ = 220, a ₇ = 35/32 are stored in the G register 4
Load and subtract via 11a. In this case, since the subtraction result R0−x ₇ = 240−223> 0 in step 106 is positive, the T register 408− as shown in FIG.
"0" is set to 1 and the operation after n = 6 is not performed.

On the other hand, because the subtraction result R0-x ₇ = 200-223 <0 and the subtraction result R0-x ₇ = 50-223 <0 for c Lee is negative, the T register 408-2 "1" Is set, thereby performing processing for the next section of n = 6.
Here, n = 6, x ₆ =
191, y ₆ = 200, a ₆ = 20/32 are stored in the G register 4
Load and subtract via 11a.

[0043] Then, since the subtraction result R0-x ₆ = 200-191> 0 at ALU405 Lee is positive, T as shown in FIG register 408-
“0” is set to 2. On the other hand, since the subtraction result R0-x ₆ = 50-191 <0 for c negative, the T register 408-3 is set to "1". Therefore, the ALU 405 does not perform the processing after n = 5 because the T register 408-2 is "0". Therefore, each of the registers 404-R 1, R 2, R 3-
R1, 404-R2, 404-R3 are not rewritten,
Section coordinate data and coefficient data are held.

On the other hand, the ALU 405 continues to perform the subtraction processing until the cycle of n = 1, and as shown in FIG.
_{x 1, R2 = y 1,} R3 = a 1 is set. And
After repeating this cycle until n = 0, each ALU 40
5 simultaneously executes the operation of equation (4) in step 110,
The calculation result is stored in the output density register 404-R4.
In this manner, the section is determined based on the density of each ALU 405, and it becomes possible to perform calculations simultaneously with the same program using each parameter.

In this configuration, an 8-bit register 404, an ALU 405, and an external data RAM 40 for inputting input image data from the outside and further outputting data to the outside.
1. Program RAM 410, G register 411a, accumulator register 406, temporary register 40
7. Equipped with a T register 408, an external data RAM
Reference numeral 401 stores in advance each parameter when a processing operation is performed using a different parameter for each pixel. The register 404 is loaded from there according to conditions. Thus, when a digital signal processor (DSP) that performs parallel processing performs a processing operation using different parameters for each pixel, an external RAM 401 in which necessary parameters are stored in advance, and the external RAM 401 stores conditions necessary for each parameter. The loadable register 404 makes it possible to perform parallel processing using each parameter in the same program, thereby reducing the amount of programs, the amount of external memory, and increasing the processing speed. Setting of Density Level It is also possible to provide a density level setting unit for adjusting the density level of the output image and adjust the density level to a desired density level. Hereinafter, two cases will be described.

4.1 Density Level Setting (Part 1) In order to set a plurality of conversions for the input image density, a plurality of conversion equations corresponding to the set numbers, in other words, coordinate data and coefficient data are shown in FIG. Are stored in advance in the plurality of external data RAMs 1-n (401-1-n), and the selector 413 responds to the setting signal from the density level setting unit 412 by the selector 413.
n, the global processor unit 411
Can be connected to the address bus 404 and the data bus 403.

With this configuration, it is possible to perform output density conversion according to the characteristics of the input image and to adjust the density of the output density. For example, in order to improve the output reproducibility of an input image having a low contrast in a specific density range, the coefficient data (1
It is necessary to adjust the following equation (slope) to a small value. Also,
Adjustment of the coefficient data is also required to set the density of the output density.

Note that, in FIG. 9, all components not particularly described are configured in the same manner as in FIG.

4.2 Density Level Setting (No. 2) The example shown in FIG. 9 is characterized by having a plurality of conversion formulas corresponding to the setting of the density level. It may be configured to have a plurality of them in advance corresponding to the density level setting. This example is shown in FIG. With this configuration, it is possible to reduce the number of density range divisions for an image or the like having a small density gradation depending on the original. Decreasing the number n of density range divisions results in a reduction in the number of density conversion flow cycles and a reduction in the number of processing cycles.

FIG. 10 shows only the external data RAM 401 relating to the setting of the density level and the components related thereto, but the parts not particularly described are constituted in the same manner as the parts in FIGS. 4 and 9. I have.

[0051] 4.3 to external CPU and the external bus connection to the data RAM external data RAM401 coordinate data P _n of 1 types, the coefficient data a _n, capable of storing density range division number n regions. As shown in FIG. 11, the external CPU 414 can be connected to the external data RAM 401 through the selector 413.
It is possible to write in a predetermined area of the external data ram 401. The external CPU 414 is a global processor unit 411
Before the start of the density conversion main control flow, the selector 413 is switched to the external CPU 414 by the mode switching signal 416.
And switching the connection state of the external data RAM 401, the coordinate data P _n, coefficient data a _n and concentration range when the writing to the predetermined area is completed the division number n, the global processor unit 411 and the external data selector 413 again R
Switch to the connection state with AM401. by this,
The data written in the external data RAM 401 is loaded to the ALU 405 via the global processor 411. The external CPU 414 performs main control of the system including the image processing apparatus, and can start inputting an image after completion of writing to the external data RAM 401, and can control the timing of executing the density conversion processing.

FIG. 11 shows only the external CPU 414, the external data RAM 401 relating to the setting of the density level, and the components related thereto, but the parts which are not particularly described are the parts shown in FIGS. 4, 9 and 10. It is configured similarly to.

4.4 Connection between External CPU, External Data RAM, and Operation Unit (Part 1) In the example of FIG. 11, connection between external CPU 414 and external data RAM 401 and external data RAM 401 in response to an instruction from density setting unit 412 And the global processor unit 411
FIG. 12 shows an example in which the operation unit 415 can access the external data RAM 401. In this example, the external data RAM 401 stores one set of coordinate data P _n , coefficient data a _n , and density range division number n.
Is an area that can be stored. As shown in FIG.
PU 414 is connected to external data RAM through selector 413
The area can be connected to 401 and the area can be read / written.

In the operation unit 415, the external data RAM 40
Conversion equation to be set to 1 (coordinate data P _n and coefficient data a _n )
And the density range division number n can be set. Operation unit 415
Is composed of a liquid crystal display 415a and a touch panel 415b as shown in FIGS. 13 to 15, and can be displayed and input. In the initial state, the display of the copy operation unit 415 is as shown in FIG. Therefore, the “density conversion setting” 4 of the liquid crystal display 415 a
When the display of 15c is pressed, first, as shown in FIG.
The setting item of the density range division number n is displayed. Therefore, input a numerical value from 1 to n with the ten keys 415d,
By pressing the display of "setting OK" 415e, the input of the density range division number n is completed.

Subsequently, the screen is switched to the coordinate data and coefficient data input screen shown in FIG. 15, and set values are inputted from the ten keys 415d in the order of the divided sections 1 to n. When the input of all the sections is completed, the display of "setting end" 415f is pressed. At this point, the set value set on the setting screen from the operation unit 415 is transferred to the external CPU 414.

The external CPU 414 sets the selector 413 to the external CP by the mode switching signal 416 before the start of the density conversion main control flow of the global processor unit 411.
When the connection state between the U414 and the external data RAM 401 is switched, and the writing of the set coordinate data Pn, coefficient data an and density range division number n into a predetermined area is completed, the selector 413 is switched to the global processor unit 4 again.
11 is connected to the external data RAM 401. Thus, the data written in the external data RAM 401 is loaded to the ALU 405 via the global processor unit 411. External CPU 414
Performs the main control of the system including the image processing apparatus, and can start the input of an image after the writing to the external data RAM 401 and control the timing of executing the density conversion processing.

In FIG. 12, the external CPU 414, the operation unit 415, and the external data RA related to the density level setting are set.
Although only the M401 and its related components are shown, each part not specifically described is shown in FIG. 4, FIG. 9, FIG.
1 is configured in the same manner as each section.

4.5 Connection of External CPU, External Data RAM, and Operation Unit (Part 2) In this example, as in 3.4, the external data RAM 401 has one connection.
The coordinate data P _n , the coefficient data a _n , and the number n of density range divisions are assumed to be areas that can store therein. As shown in FIG. 11, the external CPU 414 sends the external data RA through the selector 413.
It can be connected to M401, and the area can be read / written. The operation unit 415 allows the user to confirm the conversion formula (coordinate data P _n and coefficient data a _n ) set in the external data RAM 401 and the setting of the density range division number n. This operation unit 4
One example of 15 will be described with reference to FIGS.

In the initial state, the display of the copy operation unit 415 is as shown in FIG. Therefore, pressing the display of "density conversion setting confirmation" 415g of the liquid crystal display 415a, the current density range dividing number n as shown in FIG. 16, the settings of the coordinate data P _n and the coefficient data a _n is displayed. The operation unit 415 displays “concentration conversion setting confirmation” 41
When the display of 5 g is selected, a write request to the external data RAM 401 is issued to the external CPU 414 and the external C
The PU 414 receives this, switches the selector 413 to the connection state between the external CPU 414 and the external data RAM 401 by the mode switching signal 416, and thereafter, from a predetermined area in the external data RAM 401, the density range division number n, coordinate data P _n and leading the coefficient data a _n is transferred to the operation unit 415. The operation unit 415 receives the transfer and displays it as a set value on the display panel 415a.

The other parts, which are not particularly described, have the same construction as the parts shown in FIGS. 4, 9, 10, 11 and 12.

5. Other Embodiments When reproducing a gradation image such as a photograph or a painting, a halftone method is used. The halftone method is a method in which a gradation image is classified into a group of minute elements, and the gradation of the gradation is represented by the magnitude of the area ratio of the minute elements. This means that in lithographic and relief printing, the thickness of the ink cannot be changed, and in any part of the image, the transfer of ink from the plate to a non-printed material, such as paper, that is, printing, is in principle constant at a constant thickness. Because it is done. When creating a copy of a document image given by printing, it is desired that the copied copy image faithfully reproduces the tone of the document image. However, in the halftone method, a non-linear characteristic is generally required in shading due to the property of a halftone image.

[0062] In the printed matter of half tone, indicating the halftone dot area ratio A, the concentration D, when the density of the solid printing portion and D _s, in FIG. 20 as an expression representing the relation between D and A in any location The Yule-Nelsen equation is known. This equation is an equation for obtaining a halftone dot area ratio corresponding to the screen ruling of a printing press particularly when realizing area gradation processing with halftone dots. In this equation, n is a parameter that changes depending on the type of paper to be printed, and n ≧ 1, but the value increases as the light diffusivity of the paper increases. FIG. 21 is a graph showing the relationship of the Yule-Nelsen equation for various values of n. Since the relationship between the halftone dot size and the print density fluctuates due to differences in image forming conditions, etc., in order to obtain a printed material that faithfully reproduces the tone of the original, a continuous tone image of the original in the shading process in image formation is required. Cannot be shown by a single characteristic curve as to what characteristics are ideally realized by shading.

Such a relationship is the same as in the case of the above-mentioned γ-conversion, and even in the case of performing the conversion based on the Yule-Nelsen equation, it is possible to perform processing in the same manner as in the above-described embodiment. . That is, if the γ conversion unit in FIG. 19 is configured to perform the density conversion by replacing the γ conversion unit with the Nielsen equation in FIG. 20, the same processing can be performed by the method described in the γ conversion.

Similarly, the present invention can be applied to quantization in gradation conversion as shown in FIG. That is, as can be seen from FIG. 22, there is a specific relationship between the input density and the output density, and the characteristics of this relationship are used, or this characteristic is converted into an equation, and the γ conversion is described as an example. If applied to the embodiment, processing can be performed in the same manner as in the above-described embodiment.

[0065]

As described above, according to the first aspect of the present invention, an input means for inputting an image signal of one raster and an arithmetic operation in which the image signal of one raster input by the input means are provided in parallel. Density correction calculating means for determining the output density by performing density conversion on the input density in parallel by a device,
Since output means for serially outputting the output density obtained by this calculating means and external data storage means for rewritably storing the parameters necessary for the density conversion are provided, the Flexibility can be increased.

According to the second aspect of the present invention, the image processing apparatus further includes a program section for controlling an arithmetic expression and input / output of the density correction operation means, and the conversion of the density of the input image signal into the output density by the operation means. Since the conversion formula described in the program of the program unit is used, the flexibility in changing the density conversion curve can be enhanced by formulating the density conversion curve.

According to the third aspect of the invention, the entire range of the input density is divided into n ranges, and the division coordinates used for conversion in each section and the coefficients of the conversion formula in each range are rewritten. Since the data is stored in a possible external data storage means, the data amount can be reduced.

According to the fourth aspect of the present invention, the arithmetic expression used by the density correction calculating means is a coefficient unique to each input density range, and can be calculated in parallel by the same program. The flexibility at the time of change can be increased, and the amount of data can be reduced.

According to the fifth aspect of the present invention, the arithmetic means for executing parallel processing using different parameters for each pixel, the external data storage means for storing the necessary parameters in advance, and the external data storage means The necessary data is loaded from the data storage means, and the output density is determined by performing density conversion in parallel with the input density based on the register which can be referred to by the arithmetic means at the time of calculation and the parameters loaded into the register. And a density level setting unit for setting a density level. The external data storage unit stores a plurality of conversion formulas corresponding to the density levels, and the arithmetic unit is set by the density level setting unit. The conversion formula is selected from the obtained density levels, and the density determination means determines the density based on the selected conversion formula. Density conversion corresponding to the level is possible.

According to the sixth aspect of the present invention, there is provided a density level setting means for setting a density level, wherein the calculating means divides the entire range of the input density into a plurality of ranges and stores the divided ranges in the external data storage means. The division coordinates used for the conversion in each of the divided sections, the coefficients of the conversion formula in each range, and the conversion formulas corresponding to a plurality of density conversion levels are converted in correspondence with the density level setting from the density level setting unit. Since a selection is made and calculations are performed in parallel by the same program based on the selected conversion formula, density conversion corresponding to the output density level becomes possible.

According to the seventh aspect of the present invention, since there are a plurality of conversion formulas corresponding to the density level and a plurality of density range division numbers, density conversion corresponding to the output density level can be performed and the processing cycle can be reduced. Reduction becomes possible.

According to the eighth aspect of the present invention, the external data storage means is connected to the external CPU via a bus so that the external CPU can access the external data storage means. In addition to performing the density conversion, the density conversion according to the characteristics of the input image can be performed, and the processing cycle can be reduced.

According to the ninth aspect of the present invention, the external CPU
And an operation unit connected to a bus via the selector, and the content of the density conversion setting is changed by the operation input from the operation unit, so that the output density can be freely adjusted according to the characteristics of the input image. Become.

According to the tenth aspect of the present invention, the operation section can read out and display the contents of the currently set external data storage means, so that the adjustment values can be easily confirmed.

According to the eleventh aspect of the present invention, the first aspect is provided.
The effects of the present invention can be obtained for any of density conversion based on gamma conversion, density conversion based on Nielsen's equation, and density conversion based on gradation quantization.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an algorithm of density conversion of an image processing apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between a γ correction curve approximated by a straight line, coordinate data, and coefficient data according to the embodiment;

FIG. 3 is a diagram showing an example of an arithmetic expression for gamma correction according to the embodiment.

FIG. 4 is a diagram illustrating a gamma correction operation and a register configuration according to the embodiment.

FIG. 5 is a step 103 in the flowchart of FIG. 1;
FIG. 7 is a diagram showing a specific example of the operation from step to step 109, showing an example of an initial state of a register.

FIG. 6 is a step 103 in the flowchart of FIG. 1;
FIG. 9 is a diagram showing a specific example of the operation from step to step 109, showing the state of the register when the number of divisions of the density range is n = 7.

FIG. 7 is a step 103 in the flowchart of FIG. 1;
FIG. 9 is a diagram showing a specific example of the operation from step to step 109, showing the state of the register when the density range division number n = 6.

FIG. 8 is a step 103 in the flowchart of FIG. 1;
FIG. 9 is a diagram showing a specific example of the operation from step to step 109, showing the state of the register when the number of density range divisions n = 1 to 0.

FIG. 9 is a diagram illustrating an example of a gamma correction operation and a register configuration showing an example having a plurality of conversion formulas corresponding to density levels and the number of density range divisions.

FIG. 10 is a diagram illustrating an operation of γ correction and a configuration of a register, showing an example in which a plurality of density range division numbers n are provided in advance corresponding to density level settings.

FIG. 11 is a diagram showing the operation of a gamma correction and the configuration of a register in which an external CPU can access an external data RAM to change a conversion formula corresponding to a density level and a density range division number.

FIG. 12 is a diagram illustrating an example in which an operation unit is further connected to the configuration of FIG. 11;

FIG. 13 is a diagram illustrating a display state of an operation unit.

FIG. 14 is a diagram illustrating a setting screen of a density range division number n of the operation unit.

FIG. 15 is a diagram showing a setting screen of coordinate data and coefficient data of an operation unit.

FIG. 16 is a diagram showing a setting confirmation screen of coordinate data and coefficient data set from the operation unit.

FIG. 17 is a block diagram schematically illustrating a system configuration of an image forming system to which the image processing apparatus according to the embodiment of the present invention is applied.

18 is a block diagram showing the system configuration of FIG. 17 in further detail.

FIG. 19 is a block diagram showing details of an IPU in FIG. 18;

FIG. 20 is another view illustrating another embodiment,
Here is the Yule-Nelsen equation.

FIG. 21 is a graph in which the relationship of the Yule-Nelsen equation for various values of the parameter n that changes depending on the type of paper is developed in a graph.

FIG. 22 is a diagram illustrating a relationship between an input density and an output density in gradation quantization.

[Explanation of symbols]

 401 External data RAM 404-R0 Input density register 404-R1 Coordinate register 404-R2 Coordinate register 404-R3 Coefficient register 404-R4 Output density register 404-RN Section number register 405 ALU 406 Accumulator register 407 Temporary register 408 T register 409 MUX 410 Program RAM 411 Global processor unit 411a Global register

Claims (11)

[Claims] An input means for inputting an image signal of one raster, and an input unit for inputting the image signal of one raster, performs density conversion in parallel with respect to the input density by an arithmetic unit provided in parallel. Density correction calculating means for determining the output density; output means for serially outputting the output density obtained by the calculating means; and external data storage means for rewritably storing parameters required for the density conversion. Image processing device provided. 2. The image processing apparatus according to claim 1, further comprising a program unit for controlling an arithmetic expression and input / output of the arithmetic unit, wherein the conversion of the density of the input image signal into the output density by the arithmetic unit is described in a program of the program unit. The image processing apparatus according to claim 1, wherein a conversion formula is used. 3. The entire range of input density is divided into a plurality of ranges, and divided coordinates used for conversion in each section and coefficients of a conversion formula in each range are stored in the external data storage means whose values can be rewritten. 3. The image processing apparatus according to claim 2, wherein the image is stored. 4. The image processing apparatus according to claim 3, wherein the arithmetic expression used in the arithmetic means is a coefficient unique to each input density range, and the arithmetic processing can be performed in parallel by the same program. 5. An arithmetic unit for executing parallel processing using different parameters for each pixel unit, an external data storage unit for storing the necessary parameters in advance, and storing necessary data from the external data storage unit. Load
A register which can be referred to by the calculating means at the time of calculation; density determining means for performing density conversion on the input density in parallel based on parameters loaded into the register to determine an output density; and setting a density level. Density level setting means, wherein a plurality of conversion formulas corresponding to the density levels are stored in the external data storage means, and the calculation means selects the conversion formula from the density levels set by the density level setting means. An image processing apparatus, wherein the density determining means determines a density based on the selected conversion formula. 6. An input means for inputting an image signal of one raster, and an arithmetic unit provided in parallel with the image signal of one raster input by the input means, performs density conversion on input density in parallel. Density correction calculating means for determining the output density; output means for serially outputting the output density obtained by the calculating means; external data storage means for rewritably storing parameters necessary for the density conversion; Load the required data from external data storage means,
A register that can be commonly referred to by the computing unit at the time of computation; andconcentration level setting means for setting a concentration level.The computing means divides the entire range of the input density into a plurality of ranges, and The divided coordinate used for conversion in each section, the coefficients of the conversion formula in each range, and the conversion formulas corresponding to the plurality of density conversion levels are set by the density level setting means from the external data storage means which is stored in advance. Selecting a conversion formula corresponding to the determined density level, and performing parallel calculations with the same program based on the selected conversion formula with reference to the register and the register file of each calculation unit by the calculation unit. An image processing apparatus characterized by the above-mentioned. 7. A density range division number corresponding to a plurality of density levels is stored in said external data storage means in advance, and said calculating means divides said density range according to the density level set by said density level setting means. The image processing apparatus according to claim 6, wherein the number is selected. 8. The external data storage means is connected to an external CPU via a bus, stores the number of density range divisions and a conversion formula for each section, and connects the external CPU to the external data storage means. And a selector for switching a connection between the data processing means having the register and the external data storage means, wherein the external CPU has a density range stored in the external data storage means according to the setting of the density level setting means. 7. The image processing apparatus according to claim 6, wherein the number of divisions and the conversion formula for each section are rewritten to change the content of the density conversion setting. 9. The image processing apparatus according to claim 8, further comprising an operation unit connected to the external CPU via a bus via the selector, wherein the content of the density conversion setting is changed by an operation input from the operation unit. The image processing apparatus according to any one of the preceding claims. 10. The image processing apparatus according to claim 9, wherein the operation unit reads out the content of the currently set external data storage unit and displays the content on the operation unit. 11. The density conversion according to claim 1, wherein the density conversion is performed by one of density conversion based on gamma conversion, density conversion based on Nielsen's equation, and density conversion based on gradation quantization. 7. The image processing device according to any one of claims 6 and 7.