CN101819378B - Method for testing screen line number and screen angle for printed matter - Google Patents

Abstract

The invention discloses a method for testing screen line number and screen angle for a printed matter, which comprises the following steps of: designing a print screen ruler, wherein the print screen ruler is semicircular, the horizontal scale is the screen line number, and the circumferential scale is the screen angle; segmenting the screen line number in a certain range, selecting the line width matched with a laser typesetter, storing and calculating the data, and outputting the print screen ruler through the laser typesetter; and placing the obtained print screen ruler on a printed image to be tested, moving the print screen ruler until clear moire fringe appears on the print screen ruler, and obtaining the screen line number and screen angle of the image to be tested, namely the screen line number and screen angle corresponding to the circular arc passing through the centre of a circle of the moire fringe. The method for testing the screen line number and screen angle for the printed matter has the advantages of high degree of automation, convenient use, and quantized reflection of the screen line number and screen angle for the printed matter.

Description

The method of a kind of testing of printed product screen frequency and screen angle

Technical field

The invention belongs to technical field of packaging and printing, relate to a kind of method of testing of printing parameter, be specifically related to the method for a kind of testing of printed product screen frequency and screen angle.

Background technology

At present, printing industry also relies on experience for the identification of printed matter screen frequency and screen angle, and the recognition methods of adopting is to rely on veteran master worker to make line number and angle usually, removes net then in scanning.Its precision is low, and automaticity is not high.The method of utilizing Moire fringe to produce the method identification screen frequency of principle and screen angle yet there are no and relates to, so utilize the netting twine chi that the printed matter of screening is tested screen frequency and angle, has good application prospects.

Summary of the invention

The method that the purpose of this invention is to provide a kind of testing of printed product screen frequency and screen angle has solved existing dependence experience and has determined screen frequency and screen angle, the problem that precision is low and automaticity is not high.

The technical solution adopted in the present invention is, the method for a kind of testing of printed product screen frequency and screen angle is specifically implemented according to following steps:

Step 1: design and printing reticulate pattern chi, printing reticulate pattern chi is semicircle, horizontal scale is a screen frequency, the circumference scale is a screen angle, screen frequency in the certain limit is cut apart, choose the live width that matches with laser photocomposing machine, data-storing is calculated, by laser photocomposing machine output printing reticulate pattern chi;

Step 2: the printing reticulate pattern chi that step 1 is obtained is placed on the printed images to be measured, mobile printing reticulate pattern chi is until see Moire fringe clearly on printing reticulate pattern chi, the screen frequency and the screen angle of the circular arc correspondence by the Moire fringe center of circle are the screen frequency and the screen angle of testing image.

Characteristics of the present invention also are,

Design and printing reticulate pattern chi in the step 1 wherein, specifically implement according to following steps:

1) screen frequency is cut apart according to being spaced apart 0.5-2Lpi;

2) calculate netting twine chi live width and netting twine chi radius;

3) setting output counts;

4) count according to the netting twine chi live width, netting twine chi radius and the output that obtain, with laser photocomposing machine output printing netting twine chi.

Calculating netting twine chi live width wherein and netting twine chi radius, specifically implement according to following steps:

1) calculate the critical conditions that Moire fringe forms according to following formula:

$e=-\frac{P_1{P}_2}{\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000078329800011.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}^2+{P_2}^2-2P_1{P}_2\cos \mathrm{\&alpha;}}}$

Wherein e is the moire cycle, P ₁, P ₂The distance that is respectively adjacent two look versions between two neighbour nodes on the screening direction separately, α is two differential seat angles between the double exposure netting twine;

2) with the suitable netting twine chi live width of computer Simulation calculation, make netting twine chi live width should satisfy the critical condition that moire produces, specifically implement: import a line width values according to following steps, calculate live width/2 values, live width/3 values, the moire cycle of the critical conditions that the Moire fringe that live width/2 values, live width/3 values and last step are obtained forms makes comparisons, line width values until input forms Moire fringe, and this live width is netting twine chi live width;

3) calculate netting twine chi radius according to following formula:

R＝H ₃+C ₃+(C ₄/2)-(C ₃/2)

Wherein R is a netting twine chi radius; H ₃It is a last concentric circles radius; C ₃It is the live width of a last screen density correspondence; C ₄It is the live width of present screen frequency correspondence.

Wherein setting output is counted, and setting every live width is 10 laser spots, and output is counted and become 10 times of relations with the site live width.

The beneficial effect of the method for testing of printed product screen frequency of the present invention and screen angle is, the automaticity height is easy to use, quantization means printed matter screen angle and screen frequency.

Description of drawings

Fig. 1 is the outside drawing of the printing netting twine chi of the inventive method embodiment employing;

Fig. 2 is that the inventive method embodiment judges printed matter screen angle and screen frequency figure.

Among the figure, 1. print the netting twine chi.

Embodiment

The present invention is described in detail below in conjunction with the drawings and specific embodiments.

The method of testing of printed product screen frequency of the present invention and screen angle, corresponding identifying object are the chromatograp that Y, M, C, K four looks add reticulated printing.With screen frequency and screen angle is research object, at present in the printing screen frequency commonly used be 80Lpi to 200Lpi, wherein 175Lpi is the most commonly used; Hectographic printing screen angle commonly used is 15 °, 30 °, 75 °, 90 °, and the site differential seat angle is set to 30 ° or 30 ° of multiples; So the present invention is in algorithm for design, the range of application of related netting twine chi is present print field screen frequency and a screen angle commonly used.In colored printing chromatography process, if screen angle is improper, be easy to generate the moire phenomenon, this is a kind of fault that will be avoided in the printing.The critical conditions that this method utilizes Moire fringe to form, in conjunction with the practical application parameter of printed matter, designing can testing of printed product screen frequency and the method for screen angle.

The method of testing of printed product screen frequency of the present invention and screen angle, specifically implement according to following steps:

Step 1: design and printing reticulate pattern chi, printing reticulate pattern chi is semicircle, horizontal scale is a screen frequency, the circumference scale is a screen angle, screen frequency in the certain limit is cut apart, choose the live width that matches with laser photocomposing machine, data-storing is calculated, by laser photocomposing machine output printing reticulate pattern chi.Specifically implement according to following steps:

(1) screen frequency is cut apart according to being spaced apart 0.5-2Lpi;

(2) calculate netting twine chi live width and netting twine chi radius

The critical conditions that Moire fringe forms is: the cycle of moire can calculate according to following formula Tollennar in theory:

$e=\frac{P_1{P}_2}{\sqrt{{{\mathrm{<figure-callout\; id="1"\; label="P"\; filenames="HSA00000078329800011.png"\; state="\{\{state\}\}">P</figure-callout>}}_1}^2+{P_2}^2-2P_1{P}_2\cos \mathrm{\&alpha;}}}$

Wherein e is the moire cycle, is two bee-lines between the moire; P ₁, P ₂Be respectively the shortest distance between adjacent two lines on the both direction, the distance of two promptly adjacent look versions between two neighbour nodes on the screening direction separately; α is two differential seat angles between the double exposure netting twine.When angle α be provided with improper, general angle more hour, the spacing of the Moire fringe of formation increases, this moment is big during to the minor increment that can differentiate above human eye, human eye just can be found moire.So the live width that calculates is greater than the resolution 0.006mm of human eye.

With the suitable netting twine chi live width of computer Simulation calculation, suitable netting twine chi live width should satisfy the critical condition that moire produces, specifically implement: import a line width values according to following steps, calculate live width/2 values, live width/3 values, the moire cycle of the critical conditions that live width/2 values, live width/3 values and Moire fringe are formed makes comparisons, purpose is to form Moire fringe, if live width/2 value, critical value that live width/3 values form greater than Moire fringe, then Ci Shi line is counted segmentation precision and should be improved.In the netting twine chi candlestick chart is arranged, it is the live width of the screen frequency that will survey that the negative and positive live width is added up.According to the mechanism formula that Moire fringe forms, land and negative line live width ratio are 1: 2 when screening; So if land is too wide, too severe for the absorption of light, the effect that makes the diffraction decorative pattern form is bad, influences the result of use of netting twine chi.If live width is the same in measurement group, the moire that produces like that is square, rather than concentric circles, so live width makes the live width of the screen density of variation, do circular, so always have an angle can with the most tangible moire of screening formation of printed matter.

Netting twine chi radius R is calculated by following formula:

R＝H ₃+C ₃+(C ₄/2)-(C ₃/2) (2)

Wherein R represents netting twine chi radius; H ₃It is a last concentric circles radius; C ₃It is the live width of a last screen density correspondence; C ₄It is the live width of present screen frequency correspondence.Use for convenient printing, the initial concentric circles radius that is provided with among the present invention is 5.

(3) setting output counts

The output of the setting laser film setter proportionate relationship with screen frequency of counting.The principle that the output of film setter is counted is set: film setter output generally be that every live width is 10 laser spots, and this output is counted and will be become the integral multiple relation with the site live width.What take among the present invention is 10 times of relations.

(4) mark netting twine chi

Count according to the netting twine chi live width, netting twine chi radius and the output that obtain, with laser photocomposing machine output netting twine chi.The diameter of semicircle is a screen frequency, and unit is line/inch; The circumferential of semicircle is screen angle.

Step 2: the printing reticulate pattern chi that step 1 is obtained is placed on the printed images to be determined, mobile printing reticulate pattern chi is until see Moire fringe clearly on printing reticulate pattern chi, the screen frequency and the screen angle value of the circular arc correspondence by the Moire fringe center of circle are the screen frequency and the screen angle of image to be determined.

Embodiment

Step 1: choosing screen frequency is 175 line/inches, cuts apart according to being spaced apart 1dpi, is divided into the 165-185 half-tone gradation.Calculate live width/2=0.0726mm of 175/dpi; Live width/3=0.0484mm, as shown in table 1.Be provided with laser photocomposing machine output and count=live width that 4/dpi matches; As shown in table 1, be example, then R=H with 175 lines ₃+ C ₃+ (C ₄/ 2)-(C ₃/ 2) (R=22.0940mm wherein; H3=21.9480mm; C3=0.1460mm; C4=0.145mml calculates data-storing, this circle that draws, according to the method, the concentric circles of the 165-185 line/inch that in like manner draws.Utilize Moire fringe principle formula, screen frequency is consistent in same set of forme, so formula can be converted into

When angle more hour, be bordering on 0 ° for this netting twine chi algorithm mitre joint, this moment, the moire spacing was big more, had surpassed the resolution of human eye, this moment, human eye can be seen Moire fringe.Export printing reticulate pattern chi by laser photocomposing machine.And printing netting twine chi marked.As shown in Figure 1, the 300,200,150,120,85,55,65,100,133,175, the 250th of the DDI of the semicircle of printing netting twine chi 1, the reading of screen frequency, unit are line/inches; Semicircle circumferentially go up mark according to counterclockwise 15 °, 45 °, 60 °, 75 °, 90 °, 105 °, 120 °, 135 °, 150 °, 165 ° be the number of degrees of screening.

The live width of table 1 175/dpi

Step 2: given printed images is judged, obtained printed matter screen frequency and screen angle.As shown in Figure 2, in the testing of printed product magenta color screening parameter is set.According to the design concept of netting twine chi, the screening live width that is provided with on live width and the printed matter of netting twine chi has formed Moire fringe, has formed the tangible circular decorative pattern of rule this moment, and the screen frequency of center of circle correspondence is 133 line/inches; Screen angle is 15 °.

Screen frequency and screen angle for netting twine chi testing of printed product is described theoretically:

1, the principle of the formation of Moire fringe illustrates netting twine chi test screen frequency correctness.Because the netting twine chi is the transmission product, so be transmission for light, so rule is the cosine grating, transmitance is:

$T_1\left(x\right)=\frac{1}{2}[1+\cos (2\mathrm{\&pi;}\frac{1}{d_1}x];---\left(3\right)$

$T_2\left(x\right)=\frac{1}{2}[1+\cos (2\mathrm{\&pi;}\frac{1}{d_2}x];---\left(4\right)$

(d wherein ₁, d ₂Be the space periodic of grating x direction, promptly be equivalent to screen frequency in the printing) if shine with the unit strength plane light wave, its penetrating light intensity is:

$\begin{array}{cc}T& \left(x\right)=\begin{array}{cccc}{T}_1& \left(x\right)& \&CenterDot;T_2& \left(x\right)\end{array}\end{array}$

$=\frac{1}{4}\{1+\cos \left(2\mathrm{\&pi;}\frac{1}{d_1}x\right)+\cos \left(2\mathrm{\&pi;}\frac{1}{d_2}x\right)+\frac{1}{2}\cos [2\mathrm{\&pi;}(\frac{1}{{\mathrm{<figure-callout\; id="1"\; label="d"\; filenames="HSA00000078329800011.png"\; state="\{\{state\}\}">d</figure-callout>}}_1}+\frac{1}{d_2}x)]+\frac{1}{2}\cos [2\mathrm{\&pi;}(\frac{1}{d_1}-\frac{1}{d_2})x\left]\right\}---\left(5\right)$

The 5th in this calculating formula is the difference item, is the item that produces Moire fringe.Have only and work as

The time can form Moire fringe.This seasonal q=d ₁-d ₂Ordinal number equation for the equal difference striped.The line number that is equivalent to netting twine chi and printed matter this moment just coincide, so can use the screen frequency of netting twine chi testing of printed product.

2, utilize the correctness of optical principle explanation netting twine chi test screen angle of the transmitance of site.

(1) light intensity distributions of site

At first the site is reduced to the direct light grid of oblique placement, the screen angle of netting twine is α, and screen frequency is d ₁, its transmissivity is:

$T_1(x,y)=\frac{1}{2}[1+\cos 2\mathrm{\&pi;}\frac{x\cos \mathrm{\&alpha;}+y\sin \mathrm{\&alpha;}}{d_1}]---\left(6\right)$

(2) transmitance of netting twine chi and optical principle

$T_2(x,y)=\frac{1}{2}[1+\cos 2\mathrm{\&pi;}\frac{\sqrt{x^2+y^2}}{d2}]---\left(7\right)$

When line number that uses netting twine chi testing of printed product and angle, the transmitance of the two stack has formed Moire fringe, and (6) (7) formula is brought in the ordinal number equation to be had:

$\frac{x\cos \mathrm{\&alpha;}+y\sin \mathrm{\&alpha;}}{d_1}-\frac{\sqrt{x^2+y^2}}{d_2}=q---\left(8\right)$

Has only the d of working as ₁=d ₂Can produce tangible Moire fringe during=d, then have

$x\cos \mathrm{\&alpha;}+y\sin \mathrm{\&alpha;}-\sqrt{x^2+y^2}=\mathrm{qd}---\left(9\right)$

Following formula is expanded into:

x ²sin ²α+y ²cos ²α-2xycosαsinα+2q·d·xcosα+2q·d·ysinα-q ²d＝0 (10)

Because (10) criteria of right and wrong equation is supposed true origin O is turned over the θ angle, is had by the rotation of coordinate formula

$\mathrm{tg}2\mathrm{\&theta;}=\frac{-(2\cos \mathrm{\&alpha;}\&CenterDot;\sin \mathrm{\&alpha;})}{{\sin }^2\mathrm{\&alpha;}-{\cos }^2\mathrm{\&alpha;}}=\frac{-\sin 2\mathrm{\&alpha;}}{-\cos 2\mathrm{\&alpha;}}=\mathrm{tg}2\mathrm{\&alpha;}---\left(11\right)$

As seen can cancellation xy item with rotation of coordinate α angle (being screen angle), just rotation netting twine chi when using the netting twine chi has formed Moire fringe when angle just equals screen angle, screen angle that therefore can the testing of printed product.

Claims (4)

1. the method for testing of printed product screen frequency and screen angle is characterized in that, specifically implements according to following steps:

Step 1: design and printing reticulate pattern chi, printing reticulate pattern chi is semicircle, horizontal scale is a screen frequency, the circumference scale is a screen angle, screen frequency in the certain limit is cut apart, choose the live width that matches with laser photocomposing machine, data-storing is calculated, by laser photocomposing machine output printing reticulate pattern chi;

Step 2: the printing reticulate pattern chi that step 1 is obtained is placed on the printed images to be measured, mobile printing reticulate pattern chi is until see Moire fringe clearly on printing reticulate pattern chi, the screen frequency and the screen angle of the circular arc correspondence by the Moire fringe center of circle are the screen frequency and the screen angle of testing image.

2. the method for testing of printed product screen frequency according to claim 1 and screen angle is characterized in that, the design and printing reticulate pattern chi in the described step 1 is specifically implemented according to following steps:

1) screen frequency is cut apart according to being spaced apart 0.5-2Lpi;

2) calculate reticulate pattern chi live width and reticulate pattern chi radius;

3) setting output counts;

4) count according to the reticulate pattern chi live width, reticulate pattern chi radius and the output that obtain, with laser photocomposing machine output printing reticulate pattern chi.

3. the method for testing of printed product screen frequency according to claim 2 and screen angle is characterized in that, described calculating reticulate pattern chi live width and reticulate pattern chi radius are specifically implemented according to following steps:

1) calculate the critical conditions that Moire fringe forms according to following formula:

$e=\frac{P_1{P}_2}{\sqrt{{P_1}^2+{P_2}^2-2P_1{P}_2\cos \mathrm{\&alpha;}}}$

Wherein e is the moire cycle, P ₁, P ₂The distance that is respectively adjacent two look versions between two neighbour nodes on the screening direction separately, α is two differential seat angles between the double exposure netting twine;

2) with the suitable reticulate pattern chi live width of computer Simulation calculation, make reticulate pattern chi live width should satisfy the critical condition that moire produces, specifically implement: import a line width values according to following steps, calculate live width/2 values, live width/3 values, the moire cycle of the critical conditions that the Moire fringe that live width/2 values, live width/3 values and last step are obtained forms makes comparisons, line width values until input forms Moire fringe, and this live width is reticulate pattern chi live width;

3) calculate reticulate pattern chi radius according to following formula:

R＝H ₃+C ₃+(C ₄/2)-(C ₃/2)

Wherein R is a reticulate pattern chi radius; H ₃It is a last concentric circles radius; C ₃It is the live width of a last screen density correspondence; C ₄It is the live width of present screen frequency correspondence.

4. the method for testing of printed product screen frequency according to claim 2 and screen angle is characterized in that, described setting output is counted, and setting every live width is 10 laser spots, and output is counted and become 10 times of relations with the site live width.

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