A method of flexographic dot generation

Abstract

A kind of flexographic dot generation method, for converting multi-value digital image into binary image with dot, the present application provides a kind of flexographic dot generation method, comprising the following steps: step S1, read the digital image pixel gray value needing flexographic printing;Step S2, set the minimum length-width limit value and the minimum screening line limit value of linear dot;Step S3, set the parameter needing screening, and according to the pixel gray value read in step S1 and the minimum length-width limit value and the minimum screening line limit value of linear dot set in step S2, the width of corresponding dot and the length of dot are calculated.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of printing technology, and particularly relates to a flexographic printing dot generation method. BACKGROUND

[0002] Flexographic printing technology needs to convert a multi-value digital image into a binary image with dots to be printed by a flexographic printing device. Generally, amplitude modulation or frequency modulation screening is used to generate dots, and currently, amplitude modulation technology is mainly used. When flexographic printing uses amplitude modulation technology to generate dots, the dot shape commonly used is a circle.

[0003] Compared with other commonly used printing technologies, flexographic printing is more prone to dot loss in high light areas, and the dot becomes solid too early due to tone jump in dark tones. Therefore, many scholars and experts have conducted related research to control the dot problem, and some have improved from the perspective of hardware and consumables such as printing plates, ink viscosity, and anilox rollers, and some have optimized from the process perspective of plate making, printing pressure, and dot generation method. At present, there are some research results on the dot generation method of flexographic printing technology, but they have not been widely applied. In China, the amplitude modulation technology with circular dots still occupies the mainstream of the market. The main reason is that the new dot generation method is relatively complex and has high use cost. Therefore, compared with other printing technologies, the flexographic printing product still generally has the problems of high light dot loss and dark tone dot becoming solid too early. SUMMARY

[0004] The present application is to solve the above problems, and aims to provide a flexographic printing dot generation method. To this end, the present application provides the following technical solutions:

[0005] The present application provides a flexographic printing dot generation method, which has the following characteristics: reading the pixel gray value of a digital image to be flexographically printed; setting the minimum length-width limit value and the minimum screening line number limit value of a linear dot; setting the required screening parameters, and calculating the corresponding dot width and dot length according to the pixel gray value read in step S1 and the minimum length-width limit value and the minimum screening line number limit value of the linear dot set in step S2.

[0006] In the flexographic printing dot generation method provided by the present application, the pixel gray value of one pixel can be read in step S1.

[0007] In the flexographic printing dot generation method provided by the present application, the pixel gray values of multiple pixels can be read in step S1 to generate dots in parallel.

[0008] In the flexographic printing dot generating method, the minimum length-width limit of the linear dot can be not less than 30 microns.

[0009] In the flexographic printing dot generating method, the screening parameters can include a screening line number and a screening angle.

[0010] In the flexographic printing dot generating method, the step S3 can include the following sub-steps: step S3-1, setting the width of the dot to be equal to the minimum length-width limit and calculating the length of the dot according to the screening line number set in the screening parameters; step S3-2, judging whether the length of the dot is greater than the minimum length-width limit, and if the result is no, entering step S3-3, and if the result is yes, entering step S3-4; step S3-3, taking the length of the dot calculated according to the screening line number equal to the minimum screening line limit as the length of the dot; step S3-4, judging whether the length of the dot is greater than the dot pitch, and if the result is no, entering step S3-5, and if the result is yes, entering step S3-6; step S3-5, taking the length of the dot calculated according to the screening line number set in the screening parameters as the length of the dot; and step S3-6, taking the length of the dot equal to the dot pitch calculated according to the screening line number set in the screening parameters, and recalculating the width of the dot at this time.

[0011] In the flexographic printing dot generating method, the dot pitch can be equal to the reciprocal of the screening line number set in the screening parameters.

[0012] In the flexographic printing dot generating method, the calculation formula 1 of step S3-1 can be as follows:

[0013] (e=a,

[0014] )

[0015] In step S3-3, the length of the dot is recalculated by formula 2, and the calculation formula of formula 2 is as follows:

[0016] (e=a,

[0017] )

[0018] In step S3-5, if the length of the corresponding dot calculated by formula 1 is greater than the minimum length-width limit and less than the dot pitch, the result calculated by formula 1 meets the requirements and does not need to be recalculated.

[0019] In step S3-6, the length of the corresponding screen dot obtained by the calculation of formula 1 is greater than the minimum length-width limit value, and is greater than the screen dot pitch, then the length and width of the screen dot are recalculated by formula 3, formula 3 is:

[0020]

[0021]

[0022] In the formula, a represents the minimum length-width limit value, b represents the minimum screen ruling limit value, c represents the screen ruling in the screen parameter, e represents the calculated width of the corresponding linear screen dot, f represents the calculated length of the corresponding linear screen dot, g represents the screen dot pitch, and k represents the gray value.

[0023] Effects of the application

[0024] The application provides a new soft printing screen dot generation method, which adopts linear screen dot matching variable screen ruling amplitude modulation technology, so that the problems of easy loss of highlight screen dot and early change of dark tone screen dot into solid area of existing soft printing products are improved, the linear screen dot length value is changed, so that the problems are effectively reduced, meanwhile, the linear screen dot is small in scale in one direction (such as the width direction), and looks more fine than a circular dot with the same area, the gap size between circular screen dots is very small, and it is difficult to remove the material to generate sufficient gaps during plate making, the gap between linear screen dots is large, and it is relatively easy to remove the material to generate sufficient gaps during plate making, so that the tone jump problem is improved.

[0025] Therefore, the application has low technical difficulty, simple screen dot production method, and low use cost, compared with the soft printing technology adopting circular screen dots, the problems of easy loss of highlight screen dot and early change of dark tone screen dot into solid area are solved, and the difficulty and production cost of soft printing are reduced. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a flow chart of soft printing screen dot generation in the embodiment of the application;

[0027] Figure 2 is a flow chart of calculating linear screen dot size in the embodiment of the application;

[0028] Figure 3 is a linear screen dot effect diagram in a uniform color block with a gray value of 2% in the embodiment of the application.

[0029] Figure 4 is a linear screen dot effect diagram in a uniform color block with a gray value of 10% in the embodiment of the application.

[0030] Figure 5 is a linear dot effect diagram in a uniform color block with a gray value of 20% in an embodiment of the present application. DETAILED DESCRIPTION

[0031] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the following embodiments are combined with the drawings to specifically describe the flexographic dot generation method of the present application.

[0032] <EMBODIMENT>

[0033] Figure 1 is a flowchart of flexographic dot generation in an embodiment of the present application.

[0034] Step S1, reading the pixel gray value of the digital image of flexographic printing. Only one pixel value is read, or multiple values are read to realize parallel dot generation. For example, a pixel gray value of 10% K is read, that is, the gray value of 10% is black (black ink is represented by K).

[0035] Step S2, setting the minimum length-width limit value and the minimum screening line number limit value of the linear dot. The minimum length-width limit value of the dot is adjusted according to the device performance of the output printing plate. A smaller minimum length-width limit value is set on the premise of ensuring that the dot at the highlight of the printing plate is not lost, and the minimum length-width limit value of the dot can be set to 30 microns. The minimum screening line number limit value is for the dot at the highlight. By reducing the screening line number (which should be smaller than the screening line number set in the screening parameter), the length value of the linear dot is increased, so that the dot will not be lost in the plate making process because it is too small. The minimum screening line number limit value is set on the premise of avoiding too small dots at the highlight.

[0036] Step S3, setting the screening parameter. According to the multiple value digital image gray value read in step S1 and the minimum length-width limit value and the minimum screening line number limit value of the linear dot set in step S2, the width and length of the corresponding linear dot are calculated.

[0037] Figure 2 is a flowchart of calculating the size of the linear dot in an embodiment of the present application.

[0038] As Figure 2As shown, step S3 has the following sub-steps: step S3-1, setting the width of the screen dot equal to the minimum length-width limit value, and calculating the length of the screen dot according to the screening line number set in the screening parameter; step S3-2, judging whether the length of the screen dot is greater than the minimum length-width limit value, the judging result is no, then entering step S3-3, the judging result is yes, then entering step S3-4; step S3-3, the length of the screen dot is taken as the screen dot length value calculated when the screening line number is equal to the minimum screening line number limit value; step S3-4, judging whether the length of the screen dot is greater than the screen dot pitch, the judging result is no, then entering step S3-5, the judging result is yes, then entering step S3-6; step S3-5, the length of the screen dot is taken as the screen dot length calculated when the screening line number is set according to the screening parameter; step S3-6, the length of the screen dot is equal to the screen dot pitch calculated according to the screening line number set in the screening parameter, and the width of the screen dot at this time is recalculated according to the length of the screen dot.

[0039] Figure 3 is a line screen dot effect diagram in a uniform color block with a gray value of 2% in an embodiment of the present application.

[0040] Setting the screening line number as 150lpi and the screening angle as 37.5°, the pixel gray value read in the first step is 2%K, the minimum length-width limit value is set as 30 microns, and the minimum screening line number limit value is set as 75lpi; then first setting the width of the line screen dot equal to the minimum length-width limit value, and calculating by formula 1:

[0041] (e=a,

[0042] )

[0043] (wherein, a represents the minimum length-width limit value, c represents the screening line number in the screening parameter, e represents the width of the corresponding line screen dot calculated, f represents the length of the corresponding line screen dot calculated, and k represents the gray value.) The length of the 2%K screen dot under the screening line number of 150lpi is calculated as 19.1 microns, which is less than the minimum length-width limit value; therefore, the minimum screening line number limit value is used for screening, and the length of the screen dot is calculated by formula 2:

[0044] (e=a,

[0045] )

[0046] (wherein, b represents the minimum screening line number limit value.) The length of the line screen dot is calculated as 75.5 microns, which is greater than the limit value of 30 microns, so the length of the screen dot is set as 76.5 microns, and the screen dot effect diagram obtained is as shown in Figure 3 .

[0047] Figure 4 is a line screen dot effect diagram in a uniform color block with a gray value of 10% in an embodiment of the present application.

[0048] In the same case, if the read pixel value is 10% K, the dot length calculated by formula 1 is 95.6 microns, which is greater than the minimum length-width limit and less than the dot pitch, meeting the requirements in the embodiment, so the dot length is directly assigned as 95.6 microns, and the obtained dot effect diagram is as shown in Figure 4 .

[0049] Figure 5 is a linear dot effect diagram in a uniform color block with a gray value of 20% in the embodiment of the application.

[0050] In the same case, if the read pixel value is 20% K, the dot length calculated by formula 1 is 191.1 microns, which is greater than the minimum length-width limit and the dot pitch, so the dot length is set equal to the dot pitch calculated according to the screening line number set according to the screening parameters, and the dot width is recalculated according to formula 3:

[0051]

[0052] (wherein g represents the dot pitch.) The dot width at this time is calculated as 33.9 microns, and the obtained dot effect diagram is as shown in Figure 5 .

[0053] Effects of the embodiment

[0054] The application adopts the variable-amplitude technology of linear dot matching variable screening line number. In the embodiment, the length, width and dot pitch of the linear dot are calculated through step S3 and its sub-steps, so that the soft printing effect is better. In the highlight, the application increases the linear dot length value by reducing the screening line number, so that the dot will not be lost in the plate making process because it is too small, and the phenomenon of absolute dot in the highlight is improved. At the same time, the soft printing technology using circular dots will make the dot gap size very small at the dark tone, and it is relatively difficult to remove this part of material to produce enough gap during plate making. The linear dot is relatively small in one direction (such as the width direction), so that the gap between the linear dots is relatively large, and it is relatively easy to remove this part to produce enough gap during plate making, so that the step jump problem is improved.

[0055] Therefore, the soft printing dot generation method of the application not only has a simple method of generating dots and low production cost, but also improves the problems of easy loss of highlight dot, premature change of dark tone dot to solid, and step jump in the prior art.

[0056] The above embodiments are preferred cases of the application and do not limit the protection scope of the application.

Claims

1. A method for generating flexographic halftone dots, characterized in that, Includes the following steps: Step S1: Read the pixel grayscale values ​​of the digital image to be flexographically printed; Step S2: Set the minimum length and width limits and the minimum number of screen lines for linear dots; Step S3: Set the halftone parameters, and calculate the width and length of the corresponding halftone dots based on the pixel grayscale values ​​read in step S1 and the minimum width and length limits and minimum halftone line count limits set in step S2. The screen parameters include the number of screen lines and the screen angle. Step S3 has the following sub-steps: Step S3-1: Set the width of the halftone dot to be equal to the minimum length and width limit, and calculate the length of the halftone dot according to the number of halftone lines set in the halftone parameters; Step S3-2: Determine whether the length of the dot is greater than the minimum length and width limit. If the determination result is no, proceed to step S3-3; if the determination result is yes, proceed to step S3-4. In step S3-3, the length of the halftone dot is taken as the halftone dot length value obtained when the number of halftone lines is equal to the minimum number of halftone lines limit; In step S3-4, it is determined whether the length of the dot is greater than the dot spacing. If the result is no, proceed to step S3-5; if the result is yes, proceed to step S3-6. In step S3-5, the length of the dot is taken as the length of the dot obtained when calculating the number of screen lines according to the screen addition parameters; In steps S3-6, the length of the halftone dot is equal to the halftone dot spacing calculated according to the number of halftone lines set by the halftone parameters, and the width of the halftone dot at this time is recalculated accordingly.

2. The flexographic halftone dot generation method according to claim 1, characterized in that: in, In step S1, the grayscale value of a pixel is read.

3. The flexographic halftone dot generation method according to claim 1, characterized in that: in, In step S1, the pixel grayscale values ​​of multiple pixels are read to achieve parallel generation of halftone dots.

4. The flexographic halftone dot generation method according to claim 3, characterized in that: in, The minimum length and width limit of the linear dots is not less than 30 micrometers.

5. The flexographic halftone dot generation method according to claim 1, characterized in that: in, The spacing between the dots is equal to the reciprocal of the number of screen lines set in the screen parameters.

6. The flexographic halftone dot generation method according to claim 1, characterized in that: in, The calculation formula 1 for step S3-1 is: e = a, In step S3-3, the grid length is recalculated using formula 2. The formula for formula 2 is as follows: e = a, In step S3-5, if the length of the corresponding dot calculated by formula 1 is greater than the minimum length and width limit and less than the dot spacing, then the result calculated by formula 1 meets the requirements and does not need to be calculated again. In steps S3-6, if the length of the corresponding dot calculated using Formula 1 is greater than the minimum length and width limit and also greater than the dot spacing, then the dot length and width are recalculated using Formula 3, which is: In the formula, a represents the minimum length and width limit, b represents the minimum screen ruling limit, c represents the screen ruling in the screen ruling parameters, e represents the width of the corresponding linear halftone dot, f represents the length of the corresponding linear halftone dot, g represents the halftone dot spacing, and k represents the grayscale value.

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