JP3603907B2 - Image data processing method and apparatus - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an image data processing method and apparatus for converting multi-gradation image data, that is, multi-valued image data to binary image data by comparing it with threshold data, and more particularly to an output of a color scanner in the field of printing and plate making. The present invention relates to an image data processing method and an apparatus suitable for being applied to a halftone generating device such as a unit or an image setter and capable of preventing a gradation jump or a so-called tone jump.
[0002]
[Prior art]
In an image reading output device, for example, as a halftone dot generating device, after image information of a document is photoelectrically read to obtain multi-valued image data, the multi-valued image data is compared with threshold data to obtain binary image data. (Also referred to as halftone image data).
[0003]
Then, a laser beam which is turned on / off based on the binary image data is scanned and exposed on the film coated with the photosensitive material, thereby producing a film master on which a halftone image is formed.
[0004]
In this case, the halftone image formed on the film original is expressed by forming blackened pixels so that a halftone dot area ratio corresponding to the gray level of the multi-valued image data is obtained. .
[0005]
FIG. 5 shows a typical halftone image 1 having a halftone area ratio of 50%. As shown in FIG. 5, a halftone image 1 having a halftone area ratio of 50% is formed by blackening each pixel 3 in the regions 2a and 2b. Here, the blackened area 2a and the area 2b are in contact at point 4. Further, it is in contact with a blackened area of an adjacent halftone image (not shown) having a halftone area ratio of 50% at a point 4.
[0006]
However, when forming the halftone dot image 1, at the point 4 where such a blackened pixel 3 is in contact, a part of the laser beam or the like when forming each pixel 3 is superimposed, so that the point 4 spreads. An accurate halftone dot area ratio of 50% cannot be obtained, and tone distortion, that is, a so-called tone jump occurs at the time of reproducing gradation or the like.
[0007]
Then, the halftone image on the film original plate created in this way is used for the reverse process of inverting the negative film to the positive film, the plate making process of creating a plate from the positive film, and printing using the plate. It is formed on printed matter through the process.
[0008]
However, when an accurate halftone dot area ratio cannot be reproduced, that is, when a tone jump occurs, it occurs not only in the process of preparing a film original by the image reading and outputting apparatus but also in each of the above-described steps subsequent thereto. I know that.
[0009]
FIG. 6A shows the relationship between the multivalued image data and the dot area ratio in the step of creating the film original, and FIG. 6B shows the halftone dots on the film original in the step of reversing the negative film to the positive film (returning step). FIG. 6C shows the relationship between the area ratio and the halftone dot area ratio on the positive film, FIG. 6C shows the relationship between the halftone dot area ratio on the positive film and the halftone dot area ratio on the plate in the process of forming the plate, and FIG. 4 shows a relationship between a dot area ratio on a printing plate and a dot area ratio on a printed material in a printing process. FIG. 6E shows the relationship between the multivalued image data obtained by accumulating the relationships shown in FIGS. 6A to 6D and the dot area ratio on the printed matter.
[0010]
In this way, between the output halftone dot area ratio and the desired halftone dot area ratio in each step, whether to output on a film original as a recording medium using a laser beam, perform negative / positive inversion, , Printing with ink, and other output conditions such as how to set the screen ruling, the screen dot angle, and the screen shape. As shown in FIG. 6A to FIG. 6D, in each step, if there is a discontinuous portion with respect to the input, as shown in FIG. In this case, there is a problem that discontinuities in each process are accumulated and a tone jump caused by the discontinuity is remarkable.
[0011]
FIG. 7 shows a schematic configuration of the technique described in Japanese Patent Application No. 6-131959 and the drawings filed by the present applicant for solving the occurrence of such a tone jump.
[0012]
In FIG. 7, for example, 8-bit multi-valued image data S having a value of 0 to 255 is supplied to an output calibration table 12 via a terminal 11, and an output device (image output device) Is corrected and output as 10-bit calibration image data Sa. Here, the individual difference of the output machine means a variation of each output machine (manufacturing variation of a beam system or the like, change over time (liquid fatigue of an automatic developing machine, contamination of an optical system, etc.), etc.).
[0013]
The calibration image data Sa is supplied to the screen calibration table 13. In the screen calibration table 13, the output condition ｛the condition of the output machine and the recording medium (photosensitive material), ie, whether the output of the plate making film or the output of the printing plate, It also includes conditions such as color proof output. The correction is performed for each｝ and output as 12-bit calibration image data G. The calibration image data G created in this way is supplied to the comparison input terminal of the comparison unit 14.
[0014]
On the other hand, 10-bit threshold data Pa defined for each desired screen ruling, angle, and mesh shape is supplied to one input terminal of the synthesizing unit 16 via the terminal 15, and 2-bit random number data Ra is supplied to the terminal. It is supplied to the other input terminal through 17.
[0015]
The synthesizing unit 16 creates the 12-bit threshold data I by adding the 2-bit random number data Ra to the lower side of the LSB of the 10-bit threshold data Pa, and supplies it to the reference input terminal of the comparing unit 14. . The lower two bits including the LSB of the created 12-bit threshold data I are random number data Ra.
[0016]
The comparison unit 14 performs a comparison operation of G> I → 1 (on, blackening) and G ≦ I → 0 (off, non-blackening) with respect to the calibration image data G and the threshold data I. The binary image data Ha is supplied to a terminal 18. A halftone image is formed on a predetermined recording medium or the like in the output device based on the binary image data Ha.
[0017]
[Problems to be solved by the invention]
As described above, according to the technology described in Japanese Patent Application No. 6-131959 and the drawings of the present applicant, it is possible to output a halftone image having a tone characteristic without tone jump. It is excellent in that the effect is achieved.
[0018]
However, in this technique, hardware or software for generating random number data Ra is required, and since the comparison unit 14 compares 12-bit data, the line area for data transmission and the number of data lines are reduced. It is relatively large, and the hardware or software of the comparison unit 14 itself becomes relatively heavy.
[0019]
In practice, the above-mentioned technology can sufficiently function even when applied to a halftone image having a screen ruling of 300 lines or more, for example, a high ruling of about 500 lines. The performance and specifications are a little too high to be applied exclusively to halftone images with medium or small number of lines less than lines.
[0020]
The present invention has been made in view of such a problem, and an object of the present invention is to provide an image data processing method and apparatus capable of preventing occurrence of tone jump at low cost.
[0021]
It is another object of the present invention to provide an image data processing method and an image data processing method capable of relatively shortening the execution time when solving the problem of the conventional technique by software.
[0022]
[Means for Solving the Problems]
The method of the present invention, for example, as shown in FIGS.
An image data processing method for converting supplied m (m> 2) -bit multi-valued image data S into binary image data Ha for generating a halftone image,
｛M + n (n= 1A threshold data calibration process of calibrating the gradation of the threshold data P of 1 bit and converting the data into threshold data T of m bits;
A comparing step of comparing the supplied m-bit multi-valued image data S with m-bit threshold data T whose tone has been calibrated and converting it into binary image data Ha;
It is characterized by having.
[0023]
In addition, the device of the present invention
An image data processing apparatus for converting supplied m-valued (m> 2) -bit multi-valued image data S into binary image data Ha for generating a halftone image,
｛M + n (n= 1, 2,...)} Bits of threshold data P are arrangedNetPoint threshold matrix storage means 24,
The (m + n) -bit threshold data P read from the halftone dot threshold matrix storage means 24 is subjected to gradation calibration to m-bit threshold data T, and the m-bit threshold data T after gradation calibration is output. Threshold calibration table storage means 23,
M-bit threshold data after gradation calibrationMatrixM-bit threshold data for storingMatrixStorage means 22,
The supplied m-bit multi-valued image data S and m-bit threshold dataMatrixStorage means 22M-bit threshold data matrix stored inMeans for comparing with the m-bit threshold data T read out from the memory after the gradation correction and converting the same into binary image data Ha21When,
A halftone dot threshold matrix which is connected to the halftone dot threshold matrix storage means 24 and the threshold calibration table storage means 23 and corresponds to the halftone dot condition HC when the halftone image is generated from the halftone dot threshold matrix storage means 24 And dot selecting means for selecting the threshold calibration table 23 corresponding to the desired post-process after conversion from the threshold calibration table storage means 23 into the binary image data Ha.25And the following.
[0024]
Further, the device of the present invention
Threshold calibration table 23Comes outOutput calibration table 12 for compensating for individual differences, The output condition of the post-processing apparatus including the output device 32 is corrected.And a table 13.
In addition, the device of the present invention
The output condition of the post-processing device including the output device 32 is at least one condition among the type of recording medium (photosensitive material), exposure condition, printing condition, halftone dot shape, screen ruling, and halftone dot angle. Features.
[0025]
[Action]
According to the present invention, the supplied (m + n) -bit threshold data P is converted into the m-bit threshold data T whose gradation has been calibrated by the threshold calibration table storage means 23, and the supplied m-bit multi-value image is supplied. The data S is compared with m-bit threshold data T whose gradation has been calibrated and converted into binary image data Ha.
[0026]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0027]
FIG. 1 shows a configuration of this embodiment (an example of an image data processing apparatus to which an example of an image data processing method is applied). In FIG. 1, components corresponding to those shown in FIGS. 5 to 7 are denoted by the same reference numerals.
[0028]
In FIG. 1, for example, multi-valued image data S of 8 (m = 8) bits is supplied through a terminal 11 to a comparison input terminal of a comparison unit 21 such as an 8-bit comparator. The reference input terminal of the comparison unit 21 is supplied with 8-bit threshold data T in which the number of elements in the matrix is, for example, 0, 1,..., 255 from a 10-bit halftone threshold matrix 22. .
[0029]
A plurality of halftone threshold matrices 24 that can be selected by the halftone selector 25 are prepared in accordance with a condition HC that is a combination of a halftone shape, a screen ruling, and a halftone angle (called a halftone condition). This halftone dot threshold matrix 24 is for forming one or more halftone dots at a time, and here is for forming one halftone dot to avoid complexity. And It is assumed that the halftone dot threshold matrix 22 is also for forming one halftone dot.
[0030]
In the halftone dot threshold matrix 24, the number of elements of the matrix is, for example, 10 bits, and among these elements, 10 (m + n = 10; n = 2) takes a value of 0, 1,..., 1023. Bit threshold data P is stored in an appropriate array. In this sense, the halftone dot threshold matrix 24 is also referred to as a halftone dot 10-bit threshold matrix 24.
[0031]
In the above, the case where the number of elements of the halftone dot threshold matrix 24 is 10 bits has been described. Even when the number of elements is not 1024, the threshold value of any element number can be handled by normalizing by 1023. Can be done. That is, when the matrix elements are {0, 1,..., I,..., N}, they can be handled in the same way by setting {0,..., I / N × 1023,. In this case, the decimal point may be rounded off or truncated.
[0032]
The 10-bit threshold data P output from the halftone dot threshold matrix 24 is supplied to the threshold calibration table 23 (a plurality of which are also prepared), and the 8 (m = 8) -bit threshold corrected for gradation is provided. It is converted to data T. As will be described in detail later, the threshold value calibration table 23 includes output conditions related to the post-processing apparatus for processing the binary image data Ha 種類 type of recording medium (photosensitive material), exposure conditions, printing conditions, halftone dots, screen lines. 6 is a table for performing tone calibration based on at least one condition｝ PC among numbers and halftone dot angles.
[0033]
As described above, the 8-bit threshold data T whose gradation has been calibrated is stored in a matrix in which the number of elements of the matrix is, for example, appropriate for each element of the 10-bit halftone threshold matrix 22.
[0034]
In the comparing unit 21, for the 8-bit multi-valued image data S supplied to the comparison input terminal and the 8-bit threshold data T supplied to the reference input terminal from the halftone threshold matrix 22, S> T → 1 ( A magnitude comparison operation of ON, blackening) and S ≦ T → 0 (off, non-blackening) is performed, and binary image data (dot image data) Ha having a value of 1 or 0 of the comparison operation result is supplied to a terminal. 18.
[0035]
In practice, the halftone dot threshold matrix 24 and the threshold calibration table 23 in which 10-bit data is stored do not require much high speed at the time of writing and reading, so that relatively inexpensive hard disks, magneto-optical disks and the like are used. The halftone dot threshold matrix 22 that is stored in the large-capacity data recording means and stores the 8-bit threshold data T is read out at high speed by random access according to the address of the multi-valued image data S, and the multi-valued image Since it is necessary to supply the data S in synchronization with the data S, it is stored in an expensive but high-speed data storage means such as a semiconductor ROM and a RAM.
[0036]
The output condition PC and the halftone condition HC are actually input signals to the halftone selector 25, but here, in order to facilitate understanding, the input means ( (Keyboard, mouse, etc.), and is supplied to the threshold calibration table 23 and the halftone threshold matrix 24, and is also a selection signal for selecting the desired threshold calibration table 23 and the desired halftone threshold matrix 24. Shall be. The dot selector 25 can be easily configured using a personal computer or the like.
[0037]
FIG. 2 shows an example of a threshold value calibration table creating apparatus for creating the threshold value calibration table 23 in FIG. In FIG. 2, components corresponding to those shown in FIG. 1 are denoted by the same reference numerals or the same reference numerals with an A appended.
[0038]
The output conditions in this threshold value calibration table creation device are determined by the desired dot shape, screen ruling, dot angle, etc., that is, the dot threshold matrix 24 prepared for each dot condition HC, the laser scanning device and the automatic The output machine 32 including the developing machine, etc., the return device 33, the plate making device 34, the printing machine 35, the ink of the printing machine 35, and the recording paper 37 on which the halftone test image 36 is formed by the ink. I do. Here, it should be noted that the output device 32, the return device 33, the plate making device 34, and the printing device 35 are post-process devices when viewed from the data processing device of FIG. That is, the output terminal 18 of the data processing device of FIG. 1 is connected to the input side of the output device 32.
[0039]
The threshold value calibration table creation device of FIG. 2 includes a test pattern generation unit 31. The test pattern is preferably, for example, a test pattern in which the image signal level changes continuously or discretely at predetermined intervals over the entire optical density range. For example, as shown in FIG. 3, the test pattern 51 in which the value of the test data Q forming the test pattern increases by about 2% (Q = 0, 20, 40,..., 1000, 1020) is selected.
[0040]
Next, the 10-bit test data Q forming the test pattern 51 is sequentially compared with the 10-bit threshold data P forming the halftone threshold matrix 24 by the comparing unit 21A. The binary test data (dot test data) HT is created.
[0041]
That is, in the comparing unit 21A, for example, the dot pattern threshold matrix 24 is formed for each test data Q of 0, 20,..., 1020 forming the test pattern 51 by the density pattern method. .., 10-bit threshold data P having a value of 1023 is compared to generate binary dot binary test data HT for each test data Q.
[0042]
The output device 32 records a halftone dot test image as a latent image on a film original through a scanning optical system by a laser beam based on the created binary test data HT for halftone dots. The film original on which the halftone dot test image is recorded is developed and fixed by an automatic developing machine to produce a negative film original K1.
[0043]
The negative film original K1 is turned into a film original K2 as a positive film by a return device 33. Then, after a printing plate K3 is created by a plate making device 34, the printing plate 35 is put on a predetermined recording paper 37. Is printed with the predetermined ink to obtain a printed material K4 on which the final halftone dot test image 36 is formed.
[0044]
The dot test image 36 formed on the printed matter K4 is, for example, a dot test image corresponding to the test pattern 51 shown in FIG.
[0045]
Therefore, the dot area ratio for each test data Q of the dot test image 36 formed on the recording paper 37 is measured by a measuring device such as a densitometer or a dot area ratio meter (hereinafter, referred to as a dot area ratio meter). Measurement is performed at 38, and the measurement data is obtained. Based on the measurement data and the threshold data P from the halftone dot threshold matrix 24, the threshold calibration table creating unit 39 creates the threshold calibration table 23.
[0046]
Next, a process of creating the threshold calibration table 23 by the threshold calibration table creating unit 39 will be described.
[0047]
In FIG. 4, the curve indicated by the solid line indicates the halftone dot area measurement data 101 obtained in all the steps of the threshold value calibration table creating apparatus in the example of FIG. In FIG. 4, to facilitate understanding, the length of the horizontal axis from the origin to the maximum value 1023 of the threshold data P and the length of the vertical axis from the origin to the halftone dot area ratio of 100% are set to the same length. . In this case, when the threshold data P and the halftone dot area ratio are in a proportional relationship forming a bisector 102 (shown by a dashed line) of the axis angle XOY, it is optimal that a tone jump does not occur. Is the condition. Therefore, for example, it is desirable that the value of the threshold data P be a value 511 that is half of the value of the maximum value 1023, and the halftone dot area ratio be 50%.
[0048]
Here, in order to convert the 10-bit threshold data P into gradation-calibrated 8-bit threshold data T, first convert the 10-bit threshold data P into gradation-calibrated 10-bit threshold data P '. I do.
[0049]
In this case, as understood from FIG. 4, the value 511 of the threshold data P may be converted to a value 270 as the value of the threshold data P '. Similarly, for example, threshold data P = 690 may be converted into threshold data P '= 690, and threshold data P = 900 may be converted into threshold data P' = 960. In this manner, the 10-bit threshold data P can be converted to the 10-bit threshold data P 'whose gradation has been calibrated.
[0050]
Next, the gradation-calibrated 10-bit threshold data P 'is converted to gradation-calibrated 8-bit threshold data T.
[0051]
In this case, it is sufficient to simply convert the 10-bit value to the 8-bit value, so that the values 0 to 3 of the 10-bit threshold data P ′ are mechanically converted into the values of the 8-bit threshold data T in the same manner. , And the values 1020 to 1023 may be converted to the value 255.
[0052]
In this way, the threshold calibration table 23 for converting the 10-bit threshold data P into the 8-bit threshold data T whose gradation has been calibrated can be created.
[0053]
To explain the contents of the threshold calibration table 23 more specifically, in the example of FIG. 4, for example, the threshold data P = 511 is converted into the threshold data P ′ = 270, and the values 268 to 271 of the threshold data P ′ are converted into the threshold data T Is converted to a value 67 (268 ÷ 4) in the threshold calibration table 23, so that the threshold data P = 511 is converted to threshold data T = 67. Further, the threshold data P = 690 is converted into the threshold data P ′ = 690, and the values 688 to 691 of the threshold data P ′ are converted into the value 172 (688 ÷ 4) of the threshold data T. , Threshold data P = 690 is converted to threshold data T = 172. Further, the threshold data P = 900 is converted into the threshold data P ′ = 960, and the values 960 to 963 of the threshold data P ′ are converted into the value 240 (960 ÷ 4) of the threshold data T. , Threshold data P = 900 is converted to threshold data T = 240.
[0054]
Similarly, using the threshold value calibration table creating device of FIG. 2, the other halftone threshold matrixes 24 having different halftone shapes, screen rulings, halftone angles, etc., that is, different halftone conditions HC are used. A threshold calibration table 23 is created.
[0055]
The threshold calibration table 23 is preferably created in all processing steps (all processing steps) by the threshold calibration table creating apparatus shown in FIG. 2, but the negative film master K1 or the film master K2 in the middle of the processing steps is preferred. The upper halftone image may be measured by the halftone dot area meter 38 to create the threshold value calibration table 23. Also, without measuring the dot area ratio (usually referred to as dot%) in each step shown in the example of FIG. The variation of the area ratio may be obtained by a simulation method (calculation) to create the threshold value calibration table 23.
[0056]
Thus, by inputting a desired halftone condition (screen ruling, halftone angle, halftone shape, etc.) HC by the halftone selector 25, the halftone threshold matrix 24 corresponding to the desired halftone condition HC is input. Is selected and supplied to the threshold value calibration table 23.
[0057]
Further, by inputting a desired output condition PC, in other words, a post-process condition by the halftone dot selector 25, the threshold calibration table 23 corresponding to the output condition PC is selected. Then, the 10-bit threshold data P output from the selected halftone dot threshold matrix 24 is converted into 8-bit threshold data T whose gradation has been calibrated by the selected threshold calibration table 23. At this time, it should be noted that a plurality of threshold value calibration tables 23 for different processes correspond to one halftone threshold value matrix 24.
[0058]
The 8-bit threshold data T whose tone has been calibrated and output from the selected threshold calibration table 23 is stored in each element of the halftone threshold matrix 22 of 10 bits, for example, in which the number of elements of the matrix is 10 bits.
[0059]
The configuration of the halftone threshold matrix 22 is a matrix configuration in which 10-bit threshold data P in each element of the halftone threshold matrix 24 is replaced with 8-bit threshold data T whose tone is calibrated. Just think.
[0060]
In this way, the binary image data (halftone image data) Ha of the comparison operation result in the comparison section 21 in the example of FIG. 1 is supplied to the output device 32, and the output device 32, the return device 33, and the plate making device are provided. 34. Since the halftone image on the printed matter K4 created through the printing machine 35 uses the threshold data T whose gradation has been calibrated as the threshold data, no tone jump occurs.
[0061]
In addition, since the number of comparison bits of the comparison unit 21 is 8 bits, the configuration of the comparison unit 21 is simpler than the configuration of the comparison unit 14 in FIG. Is configured by hardware, the configuration of the image data processing apparatus of FIG. 1 including the wiring and the like can be simplified, and the cost can be reduced. In other words, the occurrence of tone jump can be prevented at low cost.
[0062]
When the comparison unit 21 is configured by software, it is sufficient to handle 8-bit data, so that the execution time of the software can be reduced as compared with the comparison unit 14 of FIG. 7 that handles 12-bit data. In other words, the execution time of software for preventing the occurrence of tone jump can be relatively shortened.
[0063]
Further, the number of elements of the matrix is 10 bits, and the threshold data to be stored is a halftone dot threshold as a threshold data storage device in which 8-bit threshold data T having values of 0, 1,... Since the matrix 22 stores 8-bit threshold data T whose tone has been calibrated, the matrix data is stored in, for example, a general commercially available basic 8-bit image output device (input image data is 8 bits, By incorporating the threshold data into an 8-bit image output device, it is possible to prevent the occurrence of tone jumps on the output image of the generally available 8-bit image output device. It becomes possible to incorporate a key correction method. The halftone dot threshold matrix 22 can be provided in the form of a suitable storage medium such as a magnetic disk such as a ROM, a RAM, a floppy disk or a hard disk, a magneto-optical disk, a magnetic card, or a magnetic tape.
[0064]
As described above, according to the above-described embodiment, the halftone selector 25 as the halftone selection means selects (corresponds to) the halftone conditions HC such as the desired screen ruling, halftone angle, halftone shape, and the like. In addition to selecting the point threshold matrix 24, the threshold calibration table 23 corresponding to the output condition PC in the desired post-process is selected. As described above, a plurality of threshold value calibration tables 23 can correspond to one halftone threshold value matrix 24.
[0065]
With respect to the 10-bit threshold data P from the selected halftone dot threshold matrix 24, 8-bit gradation data T-corrected by the selected threshold calibration table 23 is created. Creates a halftone dot threshold matrix 22 having 10 bits of elements.
[0066]
The 8-bit threshold data stored in the 10-bit element of the halftone threshold matrix 22 according to the address of the 8-bit multi-valued image data S supplied to the comparison unit 21 through the input terminal 11. T is read out and compared with the 8-bit multi-valued image data S by the comparing unit 21 to create binary image data Ha.
[0067]
Here, if the halftone threshold matrix 24 and the threshold calibration table 23 selected by the halftone selector 25 have already been selected once, they are stored in the halftone threshold matrix 22 without being read out again. What is necessary is just to read out the 8-bit threshold data T that has been subjected to the gradation correction conversion and supply it to the comparison unit 21.
[0068]
In the data processing apparatus of FIG. 1, a portion other than the comparison unit 21 is a general halftone generator, which can generate a binary image (halftone image) from 8-bit image data and an 8-bit threshold matrix. Equipment. ｝ Can be easily connected, and in such a connection, it is possible to prevent a tone jump from being generated on a halftone image output from the general halftone generator. To be precise, the halftone dot threshold matrix 22 without high-quality tone jump can be supplied to the outside.
[0069]
Further, the present invention is not limited to the above-described embodiment, and the threshold calibration table 23 may be divided into two such as the output calibration table 12 and the net calibration table 13 as shown in FIG. In this case, as described above, the output calibration table 12 is a table for calibrating an optical system unique to the output device 32 and a change with time of the processing liquid, and the mesh calibration table 13 measures, for example, the negative film original K1. 9 is a table for correcting characteristics of a recording medium (photosensitive material) and the like created from the result of the above. In the example of FIG. 7, the output calibration table 12 is configured to convert 8-bit data (multi-valued image data S) into 10-bit data (calibrated image data Sa). The network calibration table 13 may be configured to convert 10-bit data (calibration image data Sa) to 8-bit data (threshold data T: see FIG. 1). Of course, both tables 12 and 13 may be configured to convert 8-bit data into 8-bit data. Note that a desired output calibration table 12 and a desired halftone calibration table 13 can be selected according to the output condition PC selected by the dot selector 25.
[0070]
As described above, even when the threshold calibration table 23 is divided into the output calibration table 12 and the halftone calibration table 13, these are once selected and the halftone threshold matrix 22 is set, and the threshold calibration table 23 is set. When the halftone dot threshold matrix 22 is desired, it is needless to say that there is no need to newly create threshold data T for calibrating the halftone dot threshold matrix 22. That is, the threshold value data T stored in the halftone dot threshold value matrix 22 may be read out and compared with the multi-valued image data S by the comparing unit 21.
[0071]
【The invention's effect】
As described above, according to the present invention, the supplied (m + n) -bit threshold data is converted into gradation-corrected m-bit threshold data by the threshold calibration table, and the m-bit input multi-valued image data is converted. Is converted to binary image data by comparing with the m-bit threshold data that has been calibrated for gradation.
[0072]
In this case, the data to be compared is m-bit data. However, as the threshold data, (m + n) -bit data whose gradation is calibrated to m bits is used. The effect of preventing the occurrence of the distortion of the gradation on the image, that is, the so-called tone jump, is achieved.
[0073]
The present invention may be performed by either hardware or software. When the present invention is performed by hardware, the apparatus configuration is simplified and the cost can be reduced. The effect of shortening is achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention.
FIG. 2 is a block diagram showing a configuration of an example of an apparatus for creating a threshold calibration table in the example of FIG.
FIG. 3 is a diagram illustrating an example of a test pattern output from a test pattern generation unit in the example of FIG. 2;
FIG. 4 is a diagram showing an example of a characteristic measurement of a dot area ratio relating to a dot test image in the example of FIG. 2;
FIG. 5 is a diagram for explaining an example of a halftone image having a halftone dot area ratio of 50%;
FIGS. 6A to 6D are characteristic diagrams used to explain the relationship between input and output when calibration is not performed in each of a film original plate forming step, a returning step, a printing plate forming step, and a printing step. FIG. 6E is a diagram used to explain the relationship when the input / output characteristics shown in FIGS. 6A to 6D are accumulated.
FIG. 7 is a block diagram provided for explaining a conventional technique.
[Explanation of symbols]
21: comparison unit 22: halftone threshold matrix
23: threshold calibration table 24: halftone threshold matrix
S: 8-bit multi-valued image data
T: 8-bit threshold data calibrated for gradation
P: 10-bit threshold data

Claims (4)

An image data processing method for converting supplied m (m> 2) -bit multi-valued image data into binary image data for generating a halftone image,
A threshold data calibration process of calibrating {m + n (n = 1 , 2,...)} Bits of threshold data and converting it to m bits of threshold data;
A comparing step of comparing the supplied m-bit multi-valued image data with the tone-calibrated m-bit threshold data to convert the m-bit multi-valued image data into the binary image data;
An image data processing method comprising: An image data processing apparatus for converting supplied m (m> 2) bit multi-valued image data into binary image data for generating a halftone image,
{M + n (n = 1 , 2, ...)} and the threshold matrix storage means for halftone threshold data bits Ru arranged,
Threshold calibration table storage for calibrating the tone of the (m + n) -bit threshold data read from the halftone dot threshold matrix storage means to m-bit threshold data and outputting the m-bit threshold data after the tone calibration. Means,
And m-bit threshold data matrix storage means for storing threshold data matrix m bits after the gradation calibration,
The supplied m-bit multi-valued image data is compared with the m-bit threshold data after the tone calibration read from the m-bit threshold data matrix stored in the m-bit threshold data matrix storage means , Comparing means for converting to binary image data;
A halftone threshold matrix corresponding to halftone conditions when the halftone image is generated from the halftone threshold matrix storage unit, the halftone threshold matrix being connected to the halftone threshold matrix storage unit and the threshold calibration table storage unit. Selecting and selecting a threshold calibration table corresponding to a desired post-process after conversion into the binary image data from the threshold calibration table storage means,
An image data processing device comprising: An output calibration table for correcting the individual difference of the threshold calibration table output machine, according to claim 2, characterized in that is composed of a table for correcting the output conditions of the process equipment after including the output device Image data processing device. The output condition of the post-processing apparatus including the output device is at least one of a type of recording medium (photosensitive material), an exposure condition, a printing condition, a halftone dot shape, a screen ruling, and a halftone dot angle.
4. The image data processing apparatus according to claim 3, wherein:

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