Analysis of Color Mark and Its Influencing Factors in Printing Process (II)

Color element

　　 Color-coded elements are divided into objective color-coded elements (measured by densitometers or other devices) and subjective color-coded elements (estimated by the human eye), but not all color codes contain all of these elements. The general color scale contains the following contents.

(I) Objective elements

10% Hue/Highlight

High light refers to halftone dots whose dots are between 1% and 20%. They are patches of uniform density. They are printed with cyan, magenta, yellow, and black inks. These values ​​are for visual purposes. The evaluation of the platemaking process is useful because oversensitizing the positive plates can “shrink” or discard these small dots. These blocks can also be used to measure the value of highlight dots when the machine is in operation. Some color standards even contain 3% to 5%. Outlets.

25% tone/quarter tone

These uniform color patches contain a dot value of 25%, and a more accurate quarter-tone range of 20% to 40%. They are commonly printed on cyan, magenta, yellow, and black, sometimes with red, green, and blue. Overprinted and printed, and sometimes printed with three- and four-colour balance elements.

50% color/midtone

These uniform patches contain a dot value of 50% and a more accurate halftone range of 40% to 60%. They are commonly printed on cyan, magenta, yellow, and black, and are sometimes printed with red, green, and blue overprints. There are also three- and four-color gray balance elements available for printing. Midtones are very important for people to evaluate the quality of images.

75% color/three-quarter color

Three-quarters of the tone value is important to ensure that the color is clear and distinct during a particular printing process. For example, printing with 85% chromaticity in newspaper printing does not produce a print contrast because the chromaticity value is usually printed in the field, so a chromaticity value of 65% or 70% is sufficient when printing newspapers. When selecting the colorimetric value for printing the contrast, a critical three-quarter chromaticity value is to be determined which maintains vivid color under good printing conditions and fullness under bad printing conditions.

Shadow

The tone contains a halftone dot with a color value of about 85% or up to 95% and 98% of uniform color patches. This colorimetric value provides a basis for the visual inspection of the platemaking process because overexposed plates fill or block empty areas. These objects can be used to measure in-memory dot duplication in dark areas of the image.

Some color mark manufacturers have piled up highlights and dark spots on a color scale to facilitate rapid detection of extreme halftone dot copying.

Monochrome field

Solid color patches for each printing primaries can be used to measure solid ink density and calculate dot gain and print contrast. Measurements of these color patches can also be used to estimate chromaticity errors and gray balance of the primary colors, which is helpful in determining the characteristics of the printing process.

Bicolor overprint

The two-color overprinting field can be used to measure the accuracy and gray balance of the color shades of the green, red, and blue overprints for trap printing.

Three-color overprint

Three-color overprinting is composed of equal parts of yellow, blue and green dots. It is often used to detect color balance, and it can be printed in a brownish color compared to gray balance color blocks.

Tri-color overlay printing can be used to objectively measure the type of field density printed on the press by three-color printing. The on-site overprinting object also allows for the subjective and objective measurement of the accuracy of the third color overprint on the basis of the previous two colors that have been overprinted.

Four-color black block

The total dot area coverage refers to the total area coverage (TAC). These values ​​are used to evaluate the total density after overprinting. SWOP stipulates that the total value of the half tone of the dark part in the color separation process cannot exceed 300% (Remember: 400% of the field part in all four-color printing is the maximum value); the color standard required in the publishing field It often includes color blocks with a total area of ​​300%. In general, the combination of tones of this object requires about 79% of cyan, 68% of the product, 68% of yellow, and 85% of black. In contrast, the standard SNAP for Non-Heat Mode, AARP, and SPP, specifies that the total dot area should not exceed 260%. In the shaded area of ​​SNAP, the color separation values ​​of color separation generally range from 70% to 80% of cyan, 70% to 80% of product, 70% to 80% of yellow, and 20% to 50% of black.

The four-color black block can be used to measure the above total dot area. At the same time, it also takes into account the factors that register shifting at this point on the tone curve.

Sometimes, in the specification that the actual image portion also uses the total halftone area, these color patches are also used as the under color removal. In order to obtain this maximum value, the color separation operator often uses a color separation method to reduce the halftone dot value and remove the color halftone dot value from the dark tone printing area without affecting the visual effect of the shadowed region of the image. .

Color balanced hexagon

The color balance hexagon developed by Brunner Systems is an element used to describe the color balance conversion. The hexagon contains gray balance color patches superimposed with 50% cyan, 41% product, and 41% yellow halftone to indicate the smaller dot gain (including unevenness) of the three printing primaries during color conversion. The effect of the expansion of outlets). The hexagonal shape is measured with a density meter, and after special software processing, the dot enlargement values ​​of the three printing primaries can be displayed separately.

(b) subjective elements

　　 Gray balance

The gray balance element refers to a neutral gray colored patch produced by the overprinting of the cyanine half-tone tonality. The color blocks are used to print black with the same chromaticity value, and the degree of change of the gray balance can be visually estimated quickly. Since dot enlargement, double-shadow, reprint, or overprint will cause the change of three kinds of printing chromatic colors, this change can be expressed by the conversion between neutral gray and reddish, bluish, yellowish gray or color.

The gray balance color patches contained in the color scale include various portions of the tone reproduction curve, having a quarter tone, a mid tone, and a three quarter tone.

Visual assessment of network expansion, blur, and ghosting

According to the GATF's network expansion ladder, the 200 lines per inch of the screen's background color are divided into ten levels with halftone dot values. These levels of screen background use a uniform 65 lines per inch, with the numbers from 0 to 9 representing the ten levels.

In the printing process, some figures are deeper than the background, and some are lighter than the background. Because the density difference is small, the corresponding density value of one of the numbers will be the same as the background, and the human eye will not be able to detect it. This value shows the relative size of dot gain or dot loss. Higher values ​​indicate higher dot gain, while lower values ​​indicate dot loss.

According to the Rochte te r In s titu te of Technology (Rochester Institute of Technology) literature, RIT Bull's Eye Target is designed to examine dot area changes, double shadows, and blurs. This color code is printed in only one color. The color blocks form a concentric ring shape. The outer ring is the thinnest and deepens inwards. The thickness of the outermost layer is related to the screen line of 200 lines per inch. The thickness of the inner layer is related to the screen line of 65 lines per inch.

Dot enlargement and dot loss are shown by the apparent weight change of the printed color patches. Dot enlargement will make the outer portion of the color block darker than the center portion; the extreme dot expansion will cause the outer ring to melt. Loss of dots will make the outer part of the color block thinner and will disappear when it is extreme.

B u ll's E ye shows the dot enlargement in the same direction for two relative darknesses, ie ghosting. The degree of blackening indicates the degree of ghosting. However, the generation of the black horizontal stripes of the Bull's Eye color patches indicates that blurring has occurred.

The GATF data points out that the measurement scale of the blurring phenomenon consists of a thin line screen with horizontal lines, including a SLUR word. The background is the same thin line screen, but the lines are vertical. Because the vertical and horizontal lines have the same number of lines, the word SLUR cannot be seen with the eyes. Ghosting is directional, or it can increase the background density, lighten the word SLUR, or it can make the SLUR word density increase, which makes the background lighter. In any case, words will appear.

S ta r Ta rge ts (Star Patches) allow operators to distinguish dot gains, ghosts, and blurs. S ta r Ta rgets consists of thick lines that emanate from a transparent circle. Of these lines, the innermost point is related to 200 lines per inch of screen, and the outermost point is related to 65 lines per inch of screen. The other screen lines between lines 65 and 200 per inch are represented by these thick lines.

When the network expansion occurs, the middle point becomes large and round, and the larger the increase in the size of the middle circle, the more serious the network expansion. When the number 8 on the color standard block appears, the reprint failure occurs; when the elongated elliptical type is formed on the color standard block, ghosting occurs, and the elongated direction and the direction of the ghost image have a certain amount of clipping. angle.

FOGRA E lem en t D and G re tag C ircu lar e E le m ents are also other types of ghosting color patches of the same principle, but adopt the opposite design.

Mechanical network expansion

GATF has developed a mechanical dot enlargement scale II color patch that can be used to visually detect mechanical half-tone dot size changes. According to reports, the color block shows seven situations in which the actual dot size increases: 2%, 5%, 8%, 11%, 4%, 17%, and 20%. This color patch can be used to visually estimate the expansion of mechanical dots: a dot with a known radius is placed on the film.

And close to a specific line. When a dot touches a particular line after contact, platemaking, or printing, the inspector knows that the dot has actually been scaled by the scale shown (for example, if 11% of the color blocks touch the line, then a 40 % of outlets have increased to 51% of outlets). Although not very accurate, such elements can provide a basis for making or printing problems, and can be estimated with a small magnifying glass.

Continuity tone ruler

Some color scales include a continuous tone scale for estimating the exposure and development of the plate. Gretag produced a color scale consisting of a ruler consisting of vertical continuous cyan, magenta, yellow, and black tapes with density values ​​of 1.5, 1.2, 0.9, and 0.6. The operator can observe which density value disappears and which density value exists to determine and control the exposure of the plate.

GCA/GATF P roo f C om pa ra to r (Proof Comparator)

Contains other graphic elements consisting of a variety of hard-to-replicate colors, such as flesh tones, a series of sensitive chalks, and neutral grays, as well as a series of highlights, midtones, and shadow tones. In this way, subtle changes in color can be easily detected without special training and special equipment.