*by Ron Ellis *

Being able to maintain a press calibration is as important as the initial calibration procedure itself. G7 has been a great tool for US printers because in addition to providing a calibration method it provides a target and set of aims for all the devices in the plant. Prior to G7 most US printers used the press as the target. This approach was problematic because the press is normally the least stable device in the print workflow due to mechanical variation. Also multiple presses seldom print the same unless they are identical types and are well maintained. The aims provided by G7 are based on color, and can be used on any cmyk print devices in the workflow. This concept of a reference print condition is very important because without a target you cannot control your process. You have to have something to reference and compare against. The G7 calibration is a procedure used to align the printing machine to these G7 aims. This calibration is not a one-time procedure, as press conditions are constantly changing, and presses will drift away from the G7 print condition over time.
能够维持印刷机校准与初始校准程序本身一样重要。 G7 对于美国打印机来说是一个很好的工具,因为除了提供校准方法之外,它还为工厂中的所有设备提供了一个目标和一组目标。在 G7 之前,大多数美国印刷商都使用印刷机作为目标。这种方法存在问题,因为由于机械变化,印刷机通常是印刷工作流程中最不稳定的设备。此外,多台印刷机很少打印相同的内容,除非它们是相同的类型并且维护良好。 G7 提供的目标是基于颜色的,可以在工作流程中的任何 cmyk 打印设备上使用。参考打印条件的概念非常重要,因为没有目标,您就无法控制流程。你必须有一些东西可以参考和比较。 G7 校准是用于将印刷机与这些 G7 目标对齐的程序。此校准不是一次性过程,因为印刷机条件不断变化,并且随着时间的推移,印刷机将偏离 G7 印刷条件。

The Importance of Efficiency and Manufacturing
The recent recession has made the US printers who survived much more lean and efficient. It is clear that print margins are not increasing and the biggest gains are to be made by improving the process through automation and efficiency. In printing workflows this means reducing make-ready and quickly getting up to color so that you are printing sellable sheets. Once we know the target print condition, we can then tell when we are and are not achieving it. This allows us to know when the press is deviating, and to know when we need to correct it. In the past many printers would periodically fingerprint their press and then run with that calibration until the press drifted to the point where they could no longer match proofs – or even worse, until they would lose a customer over the poor print quality. In the hyper-efficient world of contemporary printing this will no longer be sufficient. Printers need to control their process – or risk going out of business.
最近的经济衰退使幸存下来的美国印刷商变得更加精简和高效。很明显,印刷利润并没有增加,最大的收益是通过自动化和效率改进流程来实现。在印刷工作流程中,这意味着减少印刷准备工作并快速上色,以便您印刷可销售的纸张。一旦我们知道了目标打印条件,我们就可以判断何时达到或未达到目标。这使我们能够知道新闻何时出现偏差,并知道何时需要纠正。过去,许多印刷商会定期对印刷机进行指纹识别,然后以该校准运行,直到印刷机漂移到无法再匹配校样的程度 – 或者更糟,直到他们因印刷质量差而失去客户。在当代印刷的超高效世界中,这将不再足够。印刷商需要控制他们的流程——否则就有倒闭的风险。

The Importance of Measurement
To control your process you need to measure constantly, and compare against your reference print condition. As Peter Drucker said, “What gets measured gets managed.” If you are not measuring, then you have no idea how you are printing. Not measuring means you are running blind – it means you don’t fully know what you are doing in the pressroom. Fortunately there are devices and software that allow you to measure and track every sheet pulled from the press. For example with a Techkon SpectroJet or SpectroDrive, every sheet scanned can go into a database for immediate viewing, as well as trending and export to a number of external apps as well. The cost of these devices is lower than they ever have historically been –automated press sheet measurement can now be done for 30% of the cost of a comparable system a few years ago. Measurement is important. It is how we see when a press is drifting and the way we can predict if you will be able to get a proof to press match. With that in mind remember G7 is a temporary print condition based on the mechanical conditions at the time of calibration – the press conditions will change.
为了控制您的流程,您需要不断测量,并与参考打印条件进行比较。正如彼得·德鲁克(Peter Drucker)所说:“能衡量的东西就能得到管理。”如果您不进行测量,那么您就不知道如何打印。不衡量意味着你是盲目的——这意味着你不完全知道自己在新闻发布室里做了什么。幸运的是,有一些设备和软件可以让您测量和跟踪从印刷机上拉出的每张纸。例如,使用 Techkon SpectroJet 或 SpectroDrive,扫描的每张纸都可以进入数据库以供立即查看、趋势分析并导出到多个外部应用程序。这些设备的成本比以往任何时候都低——现在完成自动印张测量的成本仅为几年前同类系统的 30%。测量很重要。这是我们如何看待媒体漂移的方式,也是我们预测您是否能够获得媒体匹配证据的方式。考虑到这一点,请记住 G7 是基于校准时的机械条件的临时印刷条件 – 印刷条件将会改变。

Comparing to the G7 Reference Print Condition
与 G7 参考打印条件比较
Once the calibration is achieved we can use G7 metrics as well as the recorded mechanical print attributes to monitor the print condition. G7 provides us with different metrics than previous methods. The key difference is that with G7 we are measuring color and not mechanical print attributes such as density and dot gain. Mechanical print attributes vary across different printing machines based on substrate, mechanical conditions, ink and other variables. While mechanical print attributes are valuable for telling us if anything has changed on that specific press, they are not useful for telling us if we have achieved a color match. To assess conformance we will compare these new G7 metrics against the G7 reference print condition. The reference print condition we will be comparing to (such as GRACoL or SWOP) is a description of color. Basic G7 aims that describe the color and weight of the gray balance which are also contained in the reference print condition.
完成校准后,我们可以使用 G7 指标以及记录的机械打印属性来监控打印条件。 G7 为我们提供了与以前的方法不同的指标。主要区别在于,对于 G7,我们测量的是颜色,而不是密度和网点增大等机械印刷属性。根据基材、机械条件、油墨和其他变量,不同印刷机的机械印刷属性有所不同。虽然机械印刷属性对于告诉我们该特定印刷机是否发生任何变化很有价值,但它们对于告诉我们是否已实现颜色匹配没有用处。为了评估一致性,我们将这些新的 G7 指标与 G7 参考打印条件进行比较。我们将要比较的参考打印条件(例如 GRACoL 或 SWOP)是对颜色的描述。基本G7的目的是描述灰平衡的颜色和权重,这些也包含在参考打印条件中。

What Do We Measure for G7
我们为 G7 衡量什么
For G7 we measure different attributes than many press and production staff are used to. It is important to understand LAB and how to measure LAB as many of the key G7 metrics are based on LAB measurements. The basic G7 metrics are based on a gray measurement and refer to a print condition called G7 Gray, which is only concerned with the gray color and weight. G7 Targeted is another G7 print condition, which has additional metrics, related to the complete colorspace. For example GRACoL and SWOP are G7 colorspaces, which have paper, solids and overprints, specified in addition to the gray aims. These additional metrics make it easier to match the complete colorspace in addition to matching the gray.
对于 G7,我们测量的属性与许多媒体和制作人员习惯的不同。了解 LAB 以及如何测量 LAB 非常重要,因为许多关键的 G7 指标都基于 LAB 测量。基本的 G7 指标基于灰度测量,并指称为 G7 灰度的打印条件,它仅与灰度颜色和重量有关。 G7 Targeted 是另一个 G7 打印条件,它具有与完整色彩空间相关的附加指标。例如,GRACoL 和 SWOP 是 G7 色彩空间,除了灰色目标之外还指定了纸张、实心和叠印。除了匹配灰色之外,这些附加指标还可以更轻松地匹配完整的色彩空间。

G7 Gray Metrics G7 灰度指标
Here is a summary of what we measure to assess the basic G7 gray print condition:
以下是我们评估基本 G7 灰色打印条件的测量结果的总结:

  • NPDC Curve: The Neutral Print Density Curve specifies the weight of the G7 curve. Patches such as the HC (Highlight Range, 25. 19, 19), HR (50, 40, 40) , and SC (75, 66, 66) can be measured to assure that the NPDC for both the CMY and K channels is correct.
    NPDC 曲线:中性打印密度曲线指定 G7 曲线的权重。可以测量 HC(高光范围、25、19、19)、HR(50、40、40)和 SC(75、66、66)等色块,以确保 CMY 和 K 通道的 NPDC 均满足正确的。
  • Gray Balance: The gray balance metric specifies the color of the gray across the G7 curve. Patches such as the HC (Highlight Range, 25. 19, 19), HR (50, 40, 40) , and SC (75, 66, 66) can be measured to assure that the NPDC for both the CMY and K channels is correct
    灰平衡:灰平衡度量指定 G7 曲线上的灰色颜色。可以测量 HC(高光范围、25、19、19)、HR(50、40、40)和 SC(75、66、66)等色块,以确保 CMY 和 K 通道的 NPDC 均满足正确的
  • The values for both of the above are calculated based on the substrate and the maximum neutral density on that print combination. This means these G7 metrics change based on the paper. The Techkon SpectroDens is one device that automatically calculates the new aim based on the combination of the paper and substrate.
    上述两个值都是根据基材和该印刷组合的最大中性密度计算的。这意味着这些 G7 指标会根据该论文而发生变化。 Techkon SpectroDens 是一种根据纸张和基材的组合自动计算新目标的设备。

When reading these patches it is fairly obvious if the weight and gray balance are off. An example would be a GRACoL proof, of which the HR value should always be L57, A 0 B* -1. The tolerance to set for each varies depending on the print process. Proofs are very repeatable, while offset, flexo and other print processes all have varying degrees of variation across the print run.
当阅读这些色块时,重量和灰平衡是否关闭是相当明显的。一个例子是 GRACoL 证明,其 HR 值应始终为 L57、A 0 B* -1。每个设置的容差因打印过程而异。打样的可重复性很高,而胶印、柔印和其他印刷工艺在整个印刷过程中都有不同程度的变化。

G7 Targeted Metrics G7 目标指标
For G7 Targeted we have additional metrics that are of value. These are as follows:
对于 G7 Targeted,我们还有其他有价值的指标。具体如下:

  • ISO Solid Ink Values: ISO solid ink values are specified in LAB. Matching the ISO or other G7 target solid ink value assures that the ink is the correct color. The tolerance for the solid ink value is 5 deltaE. A device such as the Techkon SpectroDens has a mode that will tell you the deltaE as well as possible ink moves to correct the solid ink value.
    ISO 固体墨水值:ISO 固体墨水值在 LAB 中指定。匹配 ISO 或其他 G7 目标固体墨水值可确保墨水颜色正确。固体墨水值的公差为 5 deltaE。 Techkon SpectroDens 等设备有一种模式,可以告诉您 deltaE 以及可能的墨水移动,以校正固体墨水值。
  • ISO Overprint Ink Values: ISO overprint ink values are specified in LAB. Matching the ISO of other G7 target solid ink value assures that the overprints are the correct color. While ISO does not require that the overprint values are met, G7 Targeted does make this a requirement. The overprint is actually more important than the solids because this indicates the color achieved when ink is printed with another ink. The tolerance for the overprint is 5 deltaE. Devices such as the Techkon SpectroDens have a mode that will tell you the overprint as well as the LAB value, which you can use to correct the overprint.
    ISO 套印油墨值:ISO 套印油墨值在 LAB 中指定。匹配其他 G7 目标固体墨水值的 ISO 可确保套印颜色正确。虽然 ISO 不要求满足叠印值,但 G7 Targeted 确实提出了这一要求。套印实际上比实心更重要,因为它表示用另一种油墨印刷时所达到的颜色。叠印容差为 5 deltaE。 Techkon SpectroDens 等设备有一种模式可以告诉您叠印以及 LAB 值,您可以用它来纠正叠印。

Mechanical Print Attributes
We also want to measure the following mechanical print attributes:

  • Density: Density will assure us that the sheet is in the proper condition as compared to our benchmark. If we are not at the density achieved during our calibration (with slight variation allowed for paper color changes) then the LAB values referred to above will not be valid.
    密度:密度将确保我们的板材与我们的基准相比处于正确的状态。如果我们未达到校准期间达到的密度(纸张颜色变化允许轻微变化),则上述 LAB 值将无效。
  • Dot Gain: Dot gain, when compared to the benchmark calibration dot gain will show us if a specific unit is printing different our out of spec. Typically this is at least the 50% tint, and often the 25% and 75% tints as well. This information can be used for guidance by a press operator to correct a press issue.
    网点增大:与基准校准网点增大相比,网点增大将向我们显示特定单位的打印是否与我们的规格不同。通常,这至少是 50% 的色调,通常也是 25% 和 75% 的色调。该信息可用于指导印刷机操作员纠正印刷机问题。

Using the Measurements to Maintain G7 Print Conditions
使用测量值维持 G7 打印条件

A colorbar with the above elements is essential. Using the above we can measure and monitor all of the key metrics necessary to assess G7 compliance as well as machine consistency.
具有上述元素的颜色条是必不可少的。使用上述内容,我们可以测量和监控评估 G7 合规性以及机器一致性所需的所有关键指标。

For example, XYZ customer based in XXX, has a Techkon SpectroDrive. When they pull a sheet they lay it on the console and scan the sheet. In 8 seconds they have all the information about that sheet and if it matches the G7 aim. The data is live and is used by the pressman for process control, and also can be used offline for trending purposes. (Additional software can automatically create new press curves if needed.) Here is a typical production scenario.
例如,位于 XXX 的 XYZ 客户拥有 Techkon SpectroDrive。当他们拉出一张纸时,他们将其放在控制台上并扫描该纸。 8 秒内,他们就获得了有关该表格的所有信息以及它是否符合 G7 的目标。这些数据是实时的,可供印刷人员用于过程控制,也可以离线使用以用于趋势分析。 (如果需要,附加软件可以自动创建新的压力曲线。)这是一个典型的生产场景。

  • The pressman loads plates and begins running up to color.
  • Even though he is at the right density he notices that the Y solid is failing with a deltaE of 8, as well as the YC overprint, with a deltaE of 9.
    尽管他的密度正确,但他注意到 Y 固体的 deltaE 为 8,以及 YC 叠印的 deltaE 为 9,都失败了。
  • Gray balance as measured on the HR patch is also off, showing the sheet as being slightly too Blue.
    HR 色块上测量的灰平衡也出现偏差,显示纸张稍微偏蓝。
  • All of the above measurements can be seen on his Techkon Expresso console with a few clicks on the touchscreen.
    只需在触摸屏上点击几下,即可在他的 Techkon Expresso 控制台上看到上述所有测量结果。
  • Looking at the Y ink value he notices it shows the Y as being too blue.
    查看 Y 墨水值时,他注意到 Y 的颜色太蓝。
  • The press operator goes to the fountain, noticing the Y ink is contaminated.
    印刷机操作员走到墨斗处,发现 Y 墨水已被污染。
  • After scooping out the ink and replacing it he begins to run again.
  • This time his Y solid comes in correct, and his CY overprint is also passing.
    这次他的 Y 实体正确,他的 CY 套印也通过了。

His gray is still slightly off based on paper color. He moves the ink density slightly to correct for paper color, and then begins running in production mode.

Take Control of Your Print
Other typical scenarios involve detecting problems with a specific unit requiring adjustments to blankets, rollers. In some cases mechanical or environmental conditions have changed to the point where ink will need to be re-targeted or plate curves adjusted. These same live measurements can be used with a variety of software to perform these adjustments automatically.

The important message is to measure – all the time. Once measuring against a G7 reference print condition you will know when you are moving away from the ability to have quick make-readies and efficient production. The first step to taking control of your print is to know how you are printing. Without it you are just printing to chaos.
重要的信息是始终进行衡量。一旦根据 G7 参考印刷条件进行测量,您就会知道何时会失去快速准备和高效生产的能力。控制打印的第一步是了解打印方式。没有它,你的打印只会一片混乱。