The type and control of outlet expansion

Signal bar: Mainly used for human visual evaluation prints, with relatively simple functions and direct expression of the appearance quality information of prints. Such as the United States Printing Foundation invented GATF star, GATF digital signal, color signal and so on.

Test strip: A multi-function marker element based on densitometer detection and evaluation, usually based on a combination of visual identification and densitometer testing, and a wax-assisted chart and curve for numerical calculations. Such as Bruner test strip.

· Control bar: It is a multifunctional control tool that combines visual evaluation and test evaluation of signal strips and test strips. Such as: Bruner third generation test strip.
First, the formation of outlet expansion

Classified by outlets

1, linear expansion: refers to the printing network of the edge of a direction to expand, originally printed dot is a square, prismatic, circular, chain-shaped, linear expansion is that the network point in a direction of linear expansion.

2, the expansion of the area:

The printed dots expand around, and the dot area enlarges, which is generally proportional to the length of the edge of the dot. In other words, the dot area is large, and the length of the edge of the dot also increases at this time.

3, increase the density:

The increase in density is proportional to the area of ​​the printing dot, the density increases, the ink is large, the ink is large, and the dot area is large.

According to the printing outlets change classification

1, normal expansion. This kind of printing dot enlargement is allowed, that is to say, the dots expand normally, the density of the center position is high, and the density of edge positions is low.

2, ghosting outlets. This kind of printing dot enlargement is not allowed, and dot ghosting occurs during printing, which seriously affects the color effect of dots.

3, there is no regular network expansion. When there are no regular dot gains, there is no rule in the printed dots. The dots will be expanded around. This will easily result in stencils and dirty prints, which will affect the quality of the printed products. This ruleless dot gain is not allowed. . The network expansion scope does not exceed 15%, 12%, and 10%.
Second, the relationship between the number of lines and the length of the edge

Since the dot change occurs in the surrounding area of ​​the printing dot, the more dots per unit area, the more the surrounding dots of the dot, and the greater the amount of change in the dot, which shows that the dots of the thin cable are enlarged. Larger, and the corresponding coarse network cable network expansion is smaller.

Printed outlets may be divided into coarse or fine outlets depending on their use. Fine print products for close-range viewing must use fine outlets such as periodicals, graphic magazines, and trademarks. The printing products that are seen from afar are all made with coarse dots, such as large-scale advertisement stickers and posters. The dots are in inches. That is, within a one-inch area, the common cable has 60 lines/inch, 90 lines/inch, 133 lines/inch, 150 lines/inch, and 175 lines/inch.

For example, the dot area is also 60%, the blank area is 40%, one is 60 lines/inch, one is 175 lines/inch, and the 175 line/inch dot expansion will be much larger than 60 lines/inch. This shows that the 175 lines/inch fine line has a long edge length, so the dot enlargement is larger. The length of the 60-line/inch coarse cable edge is short, so the dot expansion is smaller.
Third, signal bar control network expansion

GATF digital signal strip

The GATF digital information strip is a 27-line/cm coarse dot substrate with 80-line/cm-flattened 0-9 numbers in the middle. The density of the digital 2 in the signal strip is the same as the background density. .

Specific use is as follows:

1. The GATF digital signal bar assumes that the coarse net does not change and the dot does not expand. Observe the difference in density between the digits and the ground color with the naked eye.

2. In the original version, the area of ​​1-7 digital dots was successively reduced by 3%-5%, and 7-9 was decremented by more than 5%. The area of ​​No. 0 dot was the largest, and that of No. 9 dot was the smallest.

3. Since it is assumed that the coarse wire does not expand at all, the dot gain is determined based on the same digital and background density.

Example 1: Digital 5 has the same background density. At this time, from the beginning of data 2, the digital transfer has three levels of printing dots (a reference with 2 as the fixed dot does not expand, and the transfer is reduced by 3%-5% for 3 levels). Digital 5 has expanded its network by 9%-15%.

Example 2: The number of GATF signal bars is 1, which is the same as the background color density. Digital 2 is used as a reference and the transfer is made in one stage. The dot size is reduced by 3%-5%.

Using data 2 as a reference, 2 used to be a narrowing of outlets, followed by an expansion of outlets.

Star site control

Thirty-six black and white wedge lines of equal width are emitted from the center of the circle, with a small degree of whiteness at the center of the circle.

Stars are based on the size of the central white point to determine the size of the dot expansion.

The central white spot is large, indicating that the dot expansion is small.

The large white center point indicates that the outlets have been enlarged.

As a testing tool for testing dot gains, the role of the star is to be able to identify the type of dot gain.

1. The white spot in the center of the star sign is oval, indicating that the outlets have directional expansion. When the center white dot of the star sign shows "→0 ←", this type of ellipse indicates that the net point is expanded to the left and right, which is called horizontal expansion; the dot network shows that the "O" is called an up and down expansion network. Or called vertical expansion.

2. If there is ghosting at the center of the star, the small white point in the middle will not only become smaller, but also appear as an "8" or "∞" shape, which indicates that the dot ghosts and ghosts will appear.

In summary, the feature of the GATF data signal strip is that it can provide a data. Dot gains give a quantitative amount, and stars can identify the types of dot gains. Both have their own uses and benefits, and they can be used to complement each other.
Fourth, the test strip control network expansion

During the printing and printing process, when the test strips control the expansion of the printing dots, the Bruner test strip is correspondingly the most widely used.

The composition of the Bruner test strip:

50% 50% 75% 75% Field

Thin and thick

Fine: Indicates fine dot: Indicates coarse dot

Bruner test strips remain unchanged and do not expand as a reference.

The calculation of outlet expansion

1. With reference to the coarse network cable as a reference comparison section, the Bruner test strip's coarse and fine meshes are 30 lines/inch and 150 lines/inch, respectively. Therefore, the 30-line/inch coarse network segment is ignored and the 30-line/inch coarse network is not expanded.

2, using the density and dot area of ​​the characteristic curve

According to DR=tg1/1-a

a=1-10 -DR

The density value is equal to the area difference.

When testing with the Bruner test strip, use a density meter to measure the coarse mesh first, then measure the fine mesh, and then use the fine mesh-rough mesh = dot gain value.

Brunner's calculation of network expansion

1, select 50% of the test points

Dot enlargement = (fine net density - coarse net density) × 100% = D fine - D thick (where: D represents density)

2. Select 75% of test strips

Dot Expand = (Fine Density - Coarse Density)/2 x 100%

The Bruner method calculates the advantages of dot gain

1. The Bruner test strip is easy to calculate.

2, can eliminate the test error. If there is an absolute density error during the test. There are absolute errors in testing fine and coarse dots.

Dot enlargement = (D fine-D thick) × 100%

3. Since the coarse and fine nets are measured at the same place and at the same time, the drying conditions of the inks are the same and the inks are less affected by the printing inks, and thus have nothing to do with the wet and dry ink.

Calculate the disadvantages of dot gain using the Bruner test strip method

1, there is an absolute error. It uses a=1-10-DR

This formula assumes that the ink is completely absorbed on the paper, and the paper is totally reflected. However, in the actual printing process, it is absolutely impossible for 100% of the ink to be fully absorbed. The whiteness of the paper is different, and 100% of total reflection is impossible.

When the dot gain (50%) = (fine net - coarse net)/Dr × 100%, the Bruner test strip cannot be tested at this time.

2, there are some limitations.

50% (0.3-0.5) is beyond this range.

75%, (0.6-0.8) outlets expanded by more than 15% will not be calculated.

Selection of test points

1. As far as possible, the test points should be arranged at the largest point of the network expansion (50% outlets).

2, try not to choose the test point in the outlets and outlets at the corner. Because the corner is unstable. Corners at outlets will change.

Test point selection principle

1, the middle tone: If the character's skin color and facial parts, richer in detail, the quality requirements of the higher manuscript, you can use 40% and 50% of the test points.

3, for the average general product, you can use 75% of the test points.

Test point error

1, currently used are generally copied Bruner test strip, there is a copy error.

2, the test strip is generally used in a single color, so there is a color overlay error.

In addition, the first generation, second generation, and third generation Bruner test strips are widely used by various printing manufacturers. The third generation Bruner printed test control strip, which was developed in 1984 and is divided into 7 sections, can be used for years according to the required size. The contents of the control strip test include: color standard; 25%-75% segment; Bruner's three segment field, 50%, special micrometric segment; neutral ash reduction segment; print edition reduction segment; printing plate resolution segment; Four-color three-section test section.

It has the following test functions: measuring ink layer density; monitoring the expansion of network points; checking the distortion and ghosting of dots at the time of printing; judging the resolution of the printing plate and the accuracy of exposure; controlling the specific changes in printing depth, proofing, or depth of printing when printing, checking The area of ​​the network is evenly connected to the area of ​​different areas; the control of printing fine dots; gray balance detection; detection of overprint percentage; detection of three-color Y, M, C reduction of black density and hue; detection of monochrome ink printing density.

In actual production, the test strips are widely used in the printing, proofing, printing, and mechanical debugging of the plate making.
V. Bruner Test Control Strip Inspection Project

1. The sharpness of the image; 2. Whether the printing overlay is accurate; 3. The control of print contrast; 4. Reproduction of printed tone; 5, printing ink color reproduction; 6, detection of mechanical failures; 7, detection and evaluation of ghosting; 8, the expansion of network types and types.

Reprinted from: CPC Chinese Print Community