The process of copying printed matter is to convert the continuously-adjusted manuscript into a half-tone halftone color separation plate, and then transfer it to the substrate through the ink, thereby copying and expressing the original manuscript. Therefore, in the whole process, the transmission of dots and the transfer of ink are one of the key factors in the replication results. The main content involved in monitoring them is the main job of print quality management. The standardization and dataization of quality management is a method generally recognized and adopted by all countries in the world. Measurement and control strips and measuring instruments are necessary tools and conditions for realizing and implementing standardization and dataization. Measurement and control strips and measuring instruments make the quality management have a scientific basis, make the quality control of each process have rules, rules and rules, and gradually replace the qualitative work method based on experience, while reducing In order to avoid the phenomenon of mutual peeling between the upper and lower processes, it ensures high-quality and efficient production.
At present, there are not many companies that use measurement and control strips and measuring instruments for quality management in China's printing companies to achieve international standards, or that they can use them proficiently. Some companies are already using measurement and control strips and measuring instruments, but the measurement and control strips themselves are not standard (made after repeated copying many times) or the measurement instruments have not been calibrated as necessary; some companies have measurement and control strips but they will not use them and do not understand The various functions and functions of measurement and control strips; some have purchased the measuring instruments and used them as decoration, and still acted on experience; some companies have not applied the measurement and control strips and measuring instruments to all products, nor the whole process of production. Use; There are many companies that do not need measurement control strips and measuring instruments at all, relying on some of the teacher's experience to monitor the quality, etc., resulting in unstable printing quality.
This article gives some explanations and discussions about the measurement and control strips, and hopes to bring you some practical information to promote the implementation of printing quality management and achieve the effect of throwing bricks and introducing jade.
The concept of measurement and control strip
Control Strip (Control Strip) is an important medium for the implementation of digital printing quality control. It is a test tool obtained by using sophisticated technology to make geometric shapes such as dots, lines and solid areas on film or software (electronic documents). It is composed of many test areas, sections and blocks with different functions, which are used to judge and control the quality of graphics and text information units during film production, publishing, proofing and printing.
Classification of measurement and control strips
1. According to the appearance of the control strip
Traditional film-type measurement and control strips: Such film-type measurement and control strips are based on film as a carrier and exist in physical form. All need to go to a special production and production agency to buy. Called the original. It is generally not possible to copy, because the accuracy and tone level of the copy after copying do not meet the requirements. The measurement and control strips appearing in this form are generally used for printing, but some are also used for printing control. The requirements for the storage environment are relatively high, and friction and scratching should be avoided.
Digital measurement and control strip: appears in the form of electronic files. It is mostly based on PS language, so it is sometimes called PS measurement and control strip. Common formats are PS, EPS and PDF. Copying and copying is possible, but format conversion is not recommended. Commonly used with CTP system and digital printing system.
2. According to the process link used in the measurement and control strip
Exposure control strip: The actual use is mainly to control the exposure process. Therefore, it is called the printing test strip. Generally exist in the form of film as the carrier.
CTP digital measurement and control strip: The actual use is mainly the CTP publishing process. Therefore, it is called CTP digital measurement and control strip. Generally exist in the form of documents.
Printing measurement and control strip: The actual use is mainly to control the printing process. Depending on the front-end prepress system, it can be in the form of film or digital.
In fact, from the perspective of the entire printing process, if it is divided according to the process link used by the measurement and control strip, more categories can be divided. For example, the files used in the process of scanning and color management characterization also belong to the measurement and control strip. But under normal circumstances, our most common is the measurement and control strips used in the two process links of publishing and printing, so only these two types are divided here. In addition, many measurement and control strips actually do not clearly distinguish between the publishing and printing links, that is to say, the common measurement and control strips can be used in the publishing and printing links in many cases, that is, the measurement and control strip contains the control module for publishing. The control module of the printing process. The reason for this division depends on the main information provided by the specific measurement and control strip.
3. The grade of quality information provided by the measurement and control strip
Signal bar: It is composed of several signal blocks, which can timely reflect the expansion or contraction of dots during printing, axial ghosting or circumferential ghosting, underexposure or overexposure during printing, and resolution of the printing plate. Its characteristics are: only ordinary magnifying glass or human eyes can detect quality problems, no expensive special equipment is required; easy to use, easy to master; simple structure, low cost; can only provide qualitative quality information, can not provide accurate The quality index data is called the signal bar.
Test strip: It consists of several zones, segment test units (blocks) and a small number of signal blocks. It not only has the function of certain signal strips, but also passes special instruments (color reflection densitometer with polarizing device and scaled High magnification magnifying glass) Measure on the specified test unit, and then calculate some index values ​​of printing quality by special formulas for evaluation, adjustment and storage. It is suitable for the control, measurement and evaluation of the printing quality of high-end products.
Introduction of commonly used measurement and control strips
Introduce several commonly used measurement and control strips
1. Fuji Step Guide P copy control strip (with photo 1)
The Fuji SteP Guide P of Japanese FUJI printing and controlling strip has 15 steps, the density interval of each step is 0.15, and the density range reaches 2.15. Through this control bar, you can detect the printing time and developer concentration. Appropriate exposure conditions can be obtained by adjusting the exposure time. From the exposure test, it can be seen that 1.4 times the time will affect the change of one tone, and 2 times the time will change the two tone. According to the standard that the blank part is not inked, it is recommended that the printing plate will be whitened in 3 stages; after the PS plate is printed, the graphics and text should maintain a certain print resistance, which is reflected on the test strip as 5 to 6 stages of poor development, which is the development The liquid concentration is an appropriate concentration. For example, the numbers 4 ---- 8, 4 ----- 9, etc. can be seen.
2. Ugra Plate Control Wedge (PCW) 1982 Exposure Control Strip (Picture 2)
Swiss Ugra plate printing control strip, Ugra plate control wedge (PCW) 1982 plate printing control strip function is divided into five functional sections, each with its own different functions.
The first paragraph: used to control the development of the printing plate, you can also check the exposure of the printing plate, quantitative adjustment to control the exposure. (Figure 3)
Method for quantitative adjustment of exposure:
Increase and decrease series
Exposure multiple
Reduce Level 2
0.50
Reduce one level
0.70
Reduce by half
0.84
standard value
1.00
Increase by half
1.20
Add one level
1.40
Add two levels
2.00
The second stage: the micron coil is used to control the exposure time. (Figure 4)
It consists of a pair of Yin-Yang microcoil pairs with a certain width, a total of 12 groups, and the line width is 4 ~ 70 microns. When the Yin / Yang lines restored on the printing plate are symmetrical, it indicates that the exposure and development are optimal. It is used to test the resolution of plate materials and help to determine the exposure.
The third segment: the network segment, divided into 10 blocks from 10% network points to 100% field. Used to check the exposure and development, check the quality of the dots and the degree of reduction when printing. It is also used as a benchmark for printing characteristic curve measurement. (Figure 5)
Section 4: Fine screen lines along different angles allow the printer to visually inspect the printing machine for dot deformation and ghosting. Normally, the line width is the same in all directions. When the line width is different, it indicates that ghosting and distortion have occurred. (Figure 6)
Fifth paragraph: Fine dots are divided into positive images 0.5% to 5% and negative images 95% to 99.5%. It is used to check the reproducibility of two-pole dots. The difference between the minimum and maximum dots of the two-pole dots is the reproduction range of dots. (Figure 7)
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3. Fogra Print Control Strip DKL printing measurement and control strip (Figure 8)
Also called "German Fogra PMS measurement and control strip", FOGRA PMS color control strip is designed by German Printing and Reproduction Technology Association. It consists of a solid field, a dot block, an overprint block, and a microwire block for controlling the exposure of printing plates and films. The size of the control bar is 8mm × 530mm, and various elements are arranged irregularly and repeatedly in the length direction. The elements included include solid, solid superimposed blocks, and dot blocks for controlling dots (the dot percentage is 2%) , 3%, 4%, 5%, 40% and 80%), dot deformation block, gray balance block and microwire block (6μm ～ 30μm) for controlling the exposure of the printing plate. It is generally supplied in rolls of 2m to 5m in length, and customers can cut them according to their needs.
(1) Solid area: Detect the solid density of printing and control the amount of ink.
(2) Overprint area: when detecting multi-color overprinting, the printing ink is accepted first and then the ink is printed.
(3) Plate exposure control area: detect the close contact between the film and the plate to determine the exposure of the plate. Proofing guarantee
2% reproduction; the printing plate guarantees 3% reproduction; the exposure control is 3-4 levels higher than the corresponding exposure of the plate resolution.
(4) Ghosting and deformation: it is composed of vertical lines, horizontal lines and 45 ° diagonal lines between them, used to check whether axial ghosting and circumferential ghosting are in and to what extent. It can also indirectly detect whether the pressure and blanket are slack, whether the amount of ink and water is too large.
(5) Mesh adjustment area: detect the increase of intermediate adjustment dots. It can also be used in conjunction with the measurement of solid color patches to obtain printing contrast through the calculation formula. Among them, the color patch with 40% dot coverage can detect mid-tone dot expansion; the color patch with 80% dot coverage can detect dark tone area dot expansion, and at the same time, it can detect printing contrast with the solid color patch.
(6) Gray balance area: The color balance block printed by 3 colors is close to neutral gray. Can detect the gray balance of printing.
4. Brunner (Brunner) printed measurement and control strip (Figure 9)
The first generation Brunel measurement and control strip in 1968, mainly in three sections, consisting of a solid section, a 50% coarse dot section, a 50% fine dot section, and a 75%, 50% three-segment section consisting of mesh adjustment dots , 25% three-color neutral gray balance section is composed of six sections, which are arranged in a cycle according to the four colors.
In 1973, the second-generation Brunel measurement and control strip added a micro-testing standard and increased 75% of the coarse and fine mesh segments to form a five-segment form. It was combined with the printing fine mesh control segment, neutral gray segment, and overprinting segment. combination.
In 1981, the third generation of standard Brunel measurement and control strips consisted of color mark room, multi-color overprinting section, 25% to 75% dot section, Brunal three-segment field, 50% ultra-micrometer section, neutral It consists of gray balance section, 0.5% ～ 5% printing detection section, printing plate resolution section, four-color three-section type.
Brunel control strip is a quality inspection tool recommended by China's printing standards. It is used for the measurement and calculation of spot density, dot gain, dot distortion and printing contrast (K value) of proofing and printing. It can also be used for visual inspection. At present, most of the latest control strips with 7 control sections are used, but in actual The most commonly used in printing is Brunal's three-stage test strip. The following highlights its role and use. (Figure 10)
Figure-Brunel's three-stage test strip
The role of a solid patch
(1) Measure the proof, the solid density of printing and the degree of ink inking.
(2) Measure and calculate the three major characteristics of the three primary color inks, namely color shift, gray scale and efficiency.
Controlling the optimal solid density value of the four-color ink is not only the core of digital color management for proofing and printing, but also the core of digital color management for the entire copy process. The solid density (the thickness of the ink layer) has a great influence on the quality of the proofs and prints. If the density of the field is too large, the dots will increase more, the printed product is rough, and the density of the field is too small, then the color saturation will be insufficient. Therefore, the best point on the field must be reached. Specifically, the best field density is between 75% and 80%. The minimum increase of the network dots or the maximum solid density value within the premise of a reasonable increase. That is, the solid density when the K value is the largest is the best solid density, because the thickness of the ink layer is closely related to the density measured by a reflection densitometer. The absorption characteristics of the ink layer depend on the ink hue, ink layer thickness and ink Color properties and density.
A representative proof, the solid density range of the printed wet ink layer is shown in the table. In the actual proofing and printing process, not only all technical measures must be taken to achieve the best solid density value, but also the consistency of solid density. To achieve the same density of left, center and right, the error is ± 0.05D. In printing, a product and a printed part must be obtained, and the ink color from the start-up printing to the halfway to the final printing is consistent, which needs to be obtained by measuring the control conditions and density meter.
C
M
Y
K
Coated paper
1.6
1.45
1.35
1.90
Matte paper
1.6
1.45
1.35
1.90
Writing paper
1.35
1.25
1.10
1.45
Newsprint
1.00
0.95
0.75
1.10
Two 50% coarse segments
The 50% thick mesh segment is composed of 10 lines / cm mesh dots with 50% mesh area. Its main functions are:
(1) Visually observe the change of dot increase and decrease directly.
(2) Calculate the increase of 50% of the outlets.
In actual production, the operator often observes the change of 50% coarse mesh segment and uses it to determine the change of the dot. Generally, the dot increases, and the square points of the 50% coarse mesh segment will inevitably take a serious angle. If it is larger, the dots decrease.
The formula for increasing value of dots mentioned above is of general significance, and the calculation of the increase value of 50% dot area is based on the principle of the comparison of coarse and fine dots, based on the equal total area of ​​coarse and fine dots. The line number ratio is 1: 6, that is, the circumference of a 50% thin dot is 1/6 of the thick dot. The sum of the perimeters of a row of six fine dots is equal to the circumferential length of a thick dot. The sum of 6 rows of fine dots is 6 times that of coarse dots. Therefore, under the same conditions, the increase of fine dots is much, so based on the 50% coarse screen segment, taking the difference between the density of thick and thin, you can find the increase value of proofing and printing 50% dot area .
50% increase in dot area = (fine network segment density-coarse network segment density) × 100%
If the measured density of 50% coarse network is 0.30 and the density of 50% fine network is 0.45, substitute it into the formula
50% increase in dot area = (0.45-0.30) × 100 = 15%
This method is simple and accurate, and is suitable for on-site management.
Three fine dots micro-measurement section
The fine-mesh micro-measurement section, also called ultra-micro measurement element, is the core part of Brunel system. The fine mesh segment is composed of equal width lines of 60 lines / cm, and its total dot area is 50%. The fine mesh segment divides the fine mesh area into four with equal width large crosshairs. The formation of dots per 1/4 area is exactly the same. But the directions are different, and its main functions are as follows: (Figure 11)
Figure --- An enlarged view of the 50% fine mesh micro-measurement section
(1) The outer corner of each 1/4 grid is composed of 6 lines / mm of equal width fold line, which is used to check whether there is sliding deformation and ghosting of the dots during printing. If the four corner lines of the proof are deformed, it means that the printed dots have slipped. Slide horizontally, the vertical line becomes thicker, slide vertically, and thicker horizontally.
(2) There are 13 dots in the first row near the crosshairs. The row of dots inside is small black dots from large to small, and the side is corresponding to 12 small black dots from large to small. Correspondingly, there are 12 hollow white dots from large to small, which are 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 8%, 10%, 12%, 15 %, 20% of the positive points and negative points are arranged correspondingly.
Judging the changes of dots in printing, proofing and printing, it can be observed with a magnifying glass of 25 times. If the PS plate is used for printing, 10 small black spots can be printed out, then 2% of the small dots are complete. The standard exposure and development of the printing plate should reach the yin and yang points corresponding to the alignment. During proofing and printing, in the absence of a density meter, the dots can be used to visually increase the data (as shown in the figure). Observe that there are several translucent small holes, indicating how much the dots have increased. If there are a few translucent in the 12 small white holes, it shows how much the dots increase. If the 12 small white holes are completely dead, it means that the dots increase by 20%. If 10 small white holes are dead, there are 2 small white holes, which means that the dots increase by 15%; if there are 4 small white holes, it means that the dots increase by 10%. The general proofing specifications should retain 4 small white holes.
(3) There are four 50% standard square dots in every 1/4 block, which are used to control the depth change of the printing plate during proofing, proofing and printing. If 50% of the standard square dots have a large angle, the dots will increase, otherwise, if the four corners are off, the dots will shrink. (Figure 12)
Figure --- Visual inspection of dots increase or decrease [next]
5. American GATF star visual signal bar
(1) GATF star structure: 36 black wedge lines and 36 white wedge lines are placed in a 10mm circle. A small white dot with a center diameter of 1mm.
(2) GATF star principle: the magnifying effect of the star is determined by the specially designed geometry. When the dots increase and ghosting occurs during the printing process, the wedge-shaped lines will have an equal amount of expansion in each direction or an equal amount of orientation.
(3) GATF star application: started to be used in conjunction with various signal bars in 1961 to check dot gain, ghosting, deformation, and determine the resolution of the printing plate.
There are two types of stars, Yin and Yang. If the edge of the paper is small, the diameter of the star can be reduced to 1/4 inch, the tip of the wedge is very sensitive to reflect, and the ink consumption can be controlled by visual inspection: when the ink volume is moderate and the dots are not deformed, the center of the star is white; When the amount of ink is too large, a large black circle appears in the middle of the star; when the amount of ink is insufficient, the blank circle in the middle of the star expands and the dots shrink; when the dots are deformed laterally, the black circles expand longitudinally into an ellipse; when the dots deform longitudinally, black The circle expands laterally into an ellipse; the ghost appears on the dots, then the center circle disappears, and an "8" shape outline appears; the "8" shape expands laterally, and the ghost image is generated vertically; the "8" shape expands vertically, and the ghost image is generated horizontally ; Black dots appear in the center circle, the amount of ink is too large. (Figure 13)
6. Ugra / Fogra Digital Print Control Strip
Digital prepress technology usually uses laser recording equipment to output a full-page layout of color separation film. After the direct plate-making technology is put into practical application, the step of using the film as the data recording medium is no longer necessary, but the result of the digital prepress operation is directly recorded on the printing plate. In addition, small batch printing can also use digital printing machines to record digital prepress job results, digital proofing is similar to this.
Due to the operational characteristics of digital printing, the measurement and control strips used for analog printing cannot be output to film or printing plates and then printed on paper as a means of plate making, printing quality inspection and control. Any industrial production needs to be carried out in accordance with the prescribed quality standards. The quality standards for digital printed products can be implemented with reference to the standards established by traditional printing processes. But digital printing only has product quality inspection standards, and it also needs specific means to achieve product quality inspection and control. To this end, the Swiss Printing Research Promotion Association UGRA and the German Printing Research Association FOGRA launched a collaboration to develop laser imaging digital printing measurement and control strips, named UGRA / FOGRA Digital Control Strip, hereinafter referred to as digital printing measurement and control strips or simply measurement and control strips. UGRA / FOGRA digital printing measurement and control strips are defined in PostScript language and adopt a modular structure, so they have great flexibility.
The digital printing measurement and control strip consists of three modules, of which module 1 and module 2 are used to monitor the printing and copying process, and module 3 is used to monitor the exposure adjustment. The size of each measurement control color patch is about 6 mm × 6 mm (sometimes may be Or greater than this value). Since the control block included in the module 3 is mainly used to monitor the exposure recording process of digital printing, it is designed to correspond to the PostScript measurement and control strip used by UGRA / FOGRA to check and control the output of the film. (Figure 14)
Module 2
(Figure 15)
Module 1
The advantage of using a modular structure is that users can freely choose any module in typesetting software or page formatting software, and can arrange the control color blocks in a row or column along the printing direction to form the required measurement and control strip. In addition to the measurement control block, the text in the measurement and control bar also contains details related to the exposure resolution in DPI. These texts can be used to measure the fineness of digital printing equipment screening and text scanning conversion. The main content of the text is the user name and the license number of the digital printing and control strip. The user name must be specified at the time of order, usually the company name.
Module 1
Contains the following 8 solid color patches: 1 for cyan, magenta, yellow and black solid patches, 3 for "cyan + magenta", "cyan + yellow", "magenta + yellow", "cyan One "+ magenta + yellow" solid color patch. These control patches are used to control the acceptable performance of digital printing inks and the superimposed printing effect of the three subtractive primary colors.
Module 2
(1) Color balance control color block: The color block is a specified gray tone value and is related to the output of the film. It actually contains two color blocks, of which the right color block is 80% black, used to control the mesh tone screening effect; the left color block is composed of 75% cyan, 62% magenta, and 60% yellow, the purpose is to 80% black color block comparison. If the gray balance is not well controlled during printing, the color block will exhibit color components.
(2) Solid area: The solid area contains 4 solid color blocks, arranged in the order of black, cyan, magenta, and yellow, and a color block is placed every 4.8 mm. The first solid color block (black block) is next to the color balance control color block. It is stamped with yellow on its four corners to check the printing color sequence, that is, yellow is printed before black or black is printed before yellow.
(3) D control block: D is Direction, so D control refers to the direction control, that is, the sensitivity of screening by using a specific copy technology, copy equipment and printing material combination in different directions.
The D control blocks are divided into four groups, one for each of cyan, magenta, yellow and black. Each group contains 3 color blocks with a total size of 6 mm × 4 mm. When composing digital printing measurement and control strips, they are usually arranged in the order of black, cyan, magenta, and yellow, and the position is behind the solid color block. The three color blocks are screened with linear dots, and the screen angles are 0, 45 and 90 from left to right. The number of screen lines used for each color block is 48 lines per cm, and the tone value is 60% (60 %black). The main reason why the 60% tone value is used instead of the intermediate tone value (50%) is that the color patch after output is slightly darker than the intermediate tone, which can more clearly identify the direction sensitivity of the screening process.
Theoretically, when the same number of screen lines and dot shapes are used, the three color patches should have the same density value. If the actual measured three density values ​​are significantly different, it indicates that the copy technology, copy equipment and printing material combination used by the user is too sensitive in a certain screen direction.
(4) Mesh control block 40% and 80%: the control block also has 4 groups of cyan, magenta, yellow and black, each group of control blocks is composed of 40% and 80% two color blocks, using 150 LPI Screening. This number is consistent with the recording accuracy used in most commercial prints. The two mesh tone control color patches are asymmetrically distributed with the midtone dot percentage, which represents a percentage of dots that are slightly lighter (closer to midtone) and closer to the ground than the midtone. Different digital printing processes adopt different screen copying technologies, and different output effects will be obtained. Therefore, these two control blocks can be used to evaluate the performance and behavior characteristics of specific digital printing screening technology, and to measure whether the screening technology can obtain the required recording effect. When forming the measurement and control strip combination, they are arranged in the order of black, cyan, magenta and yellow, and the position is behind the D control block.
Module 3
The module includes 15 gray blocks of different degrees, each color block has the same size (6 mm × 10 mm), and is printed with black ink. 15 color blocks make up 5 columns, each column contains 3 color blocks, but different dot structure is adopted. The ink coverage of the color blocks is 25%, 50%, and 75%, respectively, where the leftmost column is 25%, the second, third, and fourth columns are 50%, and the fifth column is 75%.
The reason for printing these color blocks with black ink is very simple, that is to save the space occupied by the measurement and control strip. The first line of the control block is always copied with the highest recording resolution achievable by the output device, the second line of color block recording resolution is one-half of the first line, and the third line is one-third of the first line One. Thus, the large dot structure can be seen from the second and third row of color patches. The second, third, and fourth columns of the control block are all 50% black. The second column is named 50cb (Checker Board), and they are all lattice-like patterns; the third column contains horizontal lines; the fourth column contains vertical lines.
In theory, after module 3 is printed, the tone value of each column of color patches should be the same, the only difference is the recording resolution; in the row direction, the 3 color patches in the middle of each row should be copied to the paper. The same tone value. Therefore, if there is a difference in the tone of the three color blocks in each row, this difference must be related to the copy method. The cause of the difference can be found from the angle of the network line. When outputting, the recording equipment should be adjusted to minimize the difference in tone in the line direction. When the tone values ​​of the color blocks in the column direction are different, it reflects the influence of the number of screen lines on the replication effect.
Module connection
The module 3 of the digital printing and control strip is used alone, and the assembly of module 1 and module 2 is in principle free, but in order to arrange more regularly, the following order can be adopted: first arrange the balance control block; then black, green, Magenta and yellow solid blocks, plus black D control blocks and black mesh tone screening control blocks; followed by black, cyan, magenta, and yellow solid block, plus cyan D control blocks and cyan mesh tone adjustments Net control block; followed by black, cyan, magenta and yellow solid blocks, followed by magenta D control block and magenta mesh tone screening control block; finally black, cyan, magenta and yellow solid blocks , And then add the yellow D control block and the mesh tone control block.
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