How To Define The Correct Ash Balance in The Special Closure Skin Care Gift Box Printing Process?

How to define the correct ash balance in the Special Closure Skin Care Gift Box printing process?

Gray balance refers to yellow, magenta and green three color plates according to different dot area ratio ratio to generate neutral gray on the printed matter. The accuracy of gray balance directly affects the tone level and color reproduction in the printing and reproduction. Therefore, the correct gray balance control is very important in the whole printing process, which is the guarantee of qualified printing quality.

In the process of standardization, data-oriented and standardized printing production, the quality control of printing link is usually monitored by specially designed measurement and control strips. Besides CMYKRGB color scale, gray balance color scale (such as C50M40Y40, etc.) is essential on the measurement and control strips. In the process of use, the measurement and control strip first ensures that the field density or chroma of CMYK reaches the standard range, and then further fine-adjusts each ink color of CMYK through the reproduction of gray balance color scale, so that the gray balance color scale can achieve accurate neutral gray.

However, in the printing production, we often meet that the field density or chroma of CMYK is already within the standard range, but the visual color bias phenomenon still exists in the neutral gray label. Although sometimes the neutral gray label is forcibly adjusted to gray phase by changing the depth of CMYK ink, the field density or chroma of CMYK has already deviated greatly from the standard tolerance. Some hues also occur larger anomalies, it can be said that one loses the other. What's more, even if you change the CMYK ink shade, you still can't get accurate reproduction of neutral gray!

What causes it? The conclusion is that the CMY combination value of the gray balance color label on the control strip is not suitable for the printing conditions at this time, in other words, the unreasonable configuration of gray balance dot value leads to the difficulty of neutral gray balance, or the correct control is not carried out according to the corresponding process requirements of the gray balance standard! If the grey balance dot value configuration is not reasonable, how to set the correct grey balance CMY combination value so as to make printing control more accurate? The answer is to conduct standardized management of plate making printing, and determine the accurate grey balance according to the corresponding process of different standards.

First, the definition of gray balance based on traditional printing standards

Traditional printing standards have no restrictions on printing materials and are applicable to all kinds of printing conditions. Under different printing conditions, the grey balance is in a dynamic state, that is, the grey balance combination value changes with the printing conditions, but no matter how it changes, as long as the CMY combination value meets the neutral grey requirements, it can be defined as the final grey balance value under the printing conditions, such as: C50M39Y39, C50M40Y40, C50M41Y41 and so on are all possible. Once the grey balance combination value is determined, in the later printing production, the CMY value of the neutral grey label on the control strip is set as this value for grey balance printing control, so as to achieve good results.

Appendix: The main parameters of process control under traditional printing standards are as follows:

(1) Field density (△SID: ±0.05)

(2) Network expansion (△Dotgain: ±3%)

(3) Relative contrast (△K: ±10%)

(4) Overprint rate (△T: ±10%)

1. Density method defines gray balance

The printing process is controlled according to the traditional printing standard process parameters, and the CMY separation density of different color blocks is measured by spectrophotometer (such as X-Rite518/528, etc.) according to the printed gray balance guide table. The CMY combination value corresponding to the color block with the most equal CMY separation density is the gray balance value.

2, color method to define gray balance

According to the traditional printing standard process parameters to control the printing process, according to the printed gray balance guide table, using a spectrophotometer (such as: X-Rite528, etc.) to measure the different color blocks of L*a*b* chroma value, a*, b* chroma value and calculated according to the paper compared, its tolerance is △a* : ±1, △b* : The CMY combination value corresponding to the color block within the range of ±2 is the gray balance value. Or you can use Eyeone to measure the P2P meter and automatically calculate the grey balance with the relevant professional computing tools.

Note: gray balance chroma formula (calculate standard value according to paper a*, b* value)

Wanted a*= a*_paper * (100-C%)/ 100;

Wanted b* = b*_paper *(100-C%) / 100;

Ii. Definition of grey balance based on ISO12647-2 printing standard

ISO12647-2 is currently the international standard for offset printing, its full name is "printing technology - screen color separation, proof and printing process control (offset)", it is completed by ISO/TC130 printing technical committee drafting and revision. Because the standard for printing materials (paper and ink) appearance of color regulation, but also to control the tone of the dot expansion standard and tolerance for definition, so ISO12647-2 standard based on these premises recommended gray balance value, the value is a fixed CMY combination. In addition, ISO TS10128 recommends three control methods that meet the ISO12647-2 standard. That is, the dot expansion curve (TVI curve) fitting technology recommended by European Fogra/Ugra PSO, the neutral gray density curve (NPDC curve) fitting technology recommended by American IEDAliance/GRACol G7 and the CMYK-CMYK gambit conversion technology based on DeviceLink ICC. Therefore, the grey balance defined by TVI and NPDC control mode is mainly explained below.

1. PSO-TVI control mode defines grey balance

The gray balance value defined by ISO12647 (PSO-TVI) standard is: C25M19Y19, C50M40Y40, C75M64Y64, that is, as long as the process is controlled according to ISO12647 (PSO-TVI) standard, the reproduction of neutral gray is guaranteed. However, because dot expansion value is relative value, and there is a certain tolerance range, so ISO12647 (PSO-TVI) standard can not specify the corresponding neutral gray density value (ND value), so even if the paper and ink chroma and dot expansion value in the standard range, gray balance in visual consistency may still be different.

Attachment: The main parameters of process control under ISO12647 (PSO-TVI) printing standard are as follows:

(1) paper color in line with ISO12647-2 standards (△L: ±3, △a: ±2, △b: ±2)

(2) ink chroma in line with ISO2846-1 standard (CMYK △E≤5, RGB △E≤6)

(3) Network expansion (△Dotgain: ±3~4%)

(4) Grey balance (C25M19Y19, C50M40Y40, C75M64Y64)

2. Grey balance is defined by G7-NPDC control mode

In order to make up for the deficiency of PSO-TVI control mode in the definition of gray balance, the G7-NPDC control mode based on ISO12647-2 standard comes into being. The standards of printing materials (paper and ink) are similar, and the control level is no longer the dot expansion value, but the neutral gray density value (ND value) with a clear definition. Therefore, ISO12647 (G7-NPDC) standard not only stipulates the fixed gray balance value, but also stipulates the visual density of gray balance. Therefore, as long as the process is controlled according to ISO12647 (G7-NPDC) standard and meets the requirements of NPDC standard curve, grey balance is relatively the best in terms of visual consistency.

Appendix: The main parameters of process control under ISO12647 (G7-NPDC) printing standard are as follows:

(1) paper color in line with ISO12647-2 standards (△L: ±3, △a: ±2, △b: ±2)

(2) ink chroma in line with ISO2846-1 standard (CMYK △E≤5, RGB △E≤6)

Note: Paper △E≤3, CMYK△H≤2.5 are also required to comply with G7 ColorSpace requirements

(3) gray balance

C2M1Y1, C4M3Y3, C6M4Y4, C8M5Y5, C10M7Y7, C15M11Y11, C20M15Y15, C25M19Y19, C30M23Y23, C35M27Y27, C40M31Y31, C45M36Y36, C50M40Y40, C55M 45Y45, C60M50Y50, C65M55Y55, C70M60Y60, C75M66Y66, C80M72Y72, C85M78Y78, C90M84Y84, C95M92Y92, C100M100Y100

■ Neutral grey density control point HighlightRange (HR)

HR_cmy=ND(50c, 40m, 40y) -ND (paper) = 0.54; Absolute HC_cmy= L*57.5

Highlight Contrast (HC)

HC_cmy=ND(25c, 19m, 19y) -ND (paper) = 0.25; Absolute HC_cmy=L*75.7

■ ShadowContrast (SC)

SC_cmy=ND(75c, 66m, 66y) -ND (paper) = 0.90; Absolute SC_cmy=L* 39.5

Note: The ND value is measured under the condition of unpolarized light lens, reduced white paper and dry condition.

(4) Network expansion (△Dotgain: ±3~4%)