Flexo adjustment in Illustrator: focus on specific object types

Gradients are very commonly used and it’s easy to control cut-off levels for flexo ink drop-off with a few simple considerations.

Continuing the mini-series targeting the issue of ink drop-off in flexo printing using Adobe Illustrator, this article concentrates on specific object types and situations to watch out for. Once again, the ability to simulate or compensate for drop-off levels is possible directly in Illustrator exclusively with the use of Phantasm CS Studio and Publisher. However, note that we will also be adjusting some objects types such as drop shadows using tools only available in Phantasm CS Publisher.

Why detail the handling of specific object types? Well, Illustrator is a much more complex animal than Photoshop in terms of the number of different objects that may be created or placed within a document. Many of these various object types have an array of possible applications and uses. The most common objects which require special consideration and attention are to be found in this article.

Important: before you continue reading, it’s essential that you have read the first article in this series: Handling flexo printing ink drop-off in artwork using Illustrator.

Process CMYK gradients

Gradients are very commonly used and it’s easy to control cut-off levels for flexo ink drop-off with a few simple considerations. Let’s commence by creating a gradient in a CMYK document that starts with CMYK white and ends with a red shade using each of the 4 process inks:

Keeping this gradient selected, open the Phantasm CS Curves Filter tool via Filter » Phantasm CS » Curves in Illustrator CS3 or below or Object » Filters » Phantasm CS » Curves in Illustrator CS4 or above. It is critical that, when applying a flexo cut-off curve to a gradient that the Accurate Gradient Adjustment option is ticked. To access this option, you need to view the advanced options via the Curve tool’s pull-down menu shown below:

At the bottom of the extended option area, the option presents itself with an associated slider control:

By ticking the option and increasing the Max Stops level to the upper limit value of 100, Phantasm CS will ensure that additional stops are intelligently added to the gradient to produce the desired result. Without these additional color stops in the gradient, the color cut-off levels described in the previous article would have no apparent affect. For more information on how this Phantasm CS option works, please refer to the user manual.

WIth a 10% cut-off applied the gradient is adjusted as shown below (original on top, adjusted beneath with automatically-updated color stops shown in the Gradient panel beneath):

It can be noticed that the cut-off transitions are slightly blurred. This is due to the minimum distance the gradient’s color stops can be placed next to each other. Even though the neighbouring color stops have stepped color changes, the gradient still blends between these which produces what appears to be a blurred boundary. In reality, these would not cause a problem with simulating flexo ink drop-off within Illustrator, and wouldn’t feature if the compensation approach is taken described in the previous article. However, it a more abrupt cut-off is essential in a gradient adjusted for flexo, then it’s possible to opt for the Auto Rasterize option found in Phantasm CS’ color tools. This overrides the Accurate Gradient Adjustment controls and first rasterizes the selected object(s) before committing a color adjustment. The rasterization is based on the settings defined in Effect » Document Raster Effects Settings…, so it’s important to ensure the correct resolution is first set along with other options present!

To demonstrate the difference between using the Accurate Gradient Adjustment option and Auto Rasterize, the two gradients adove were adjusted using the different options. The top gradient uses Accurate Gradient Adjustment whilst the lower uses Auto Rasterize.

For control of spot color gradients, please refer to the special Spot color article’s sub-section.

Linked artwork

Linked artwork, typically image files, can not be controlled by Phantasm CS. By their nature, linked external files are controlled outside the Illustrator document as they may be applied in other documents and any change made to them would affect all associated documents.

To simulate or compensate for flexo ink drop-off in Illustrator, first embed the linked files. Embedded images can always be extracted from the document using Phantasm CS Studio and Publisher Edit Image tool (discussed in this article), or Phantasm CS Publisher’s Link Images tool.

Transparencies

Transparencies of all types applied to an object, or an overlaid object, can upset any carefully-defined flexo cut-off Curve. Therefore its is usually essential to first flatten any transparency before cut-off curves are considered. This can be achieved using the Object » Flatten Transparency… tool.

Transparency types to be aware of:

• Native transparency modes typically applied via the Transparency panel
• Opacity Masks created using the Transparency panel
• Images with alpha channels
• Transparencies integral to certain live Effects including Gaussian Blur but excluding Drop Shadows and Glows which are dealt with separately in the following section
• Transparency levels within Gradients (Illustrator CS4 and above) and Gradient Meshes (Illustrator CS5)

Note that a vector clipping mask is not a transparency and doesn’t require expanding.

Drop Shadow and Glow live Effects (best practices)

Some of the most widely used live Effects include Drop Shadows and Inner/Outer Glows. It’s important to understand how these are constructed by Illustrator internally in order to understand best practices to adjust for ink drop-off.

Let’s take the example of applying a purple (100% Cyan + 100% Magenta) drop shadow to the letter “A”…

The process Illustrator takes is as follows:

1. The object onto which the shadow will be applied (1) is duplicated, the duplicate is then rasterized as a grayscale image, inverted in color and blurred (2)
2. A rectangle of solid color defined by the user in the Drop Shadow window (in this case purple) is drawn to match the size of the blurred duplicate (3)
3. The blurred duplicate and the solid color rectangle is combined as an Opacity Mask where the black area of the raster mask equates to 100% transparent areas
4. This opacity mask then has the optional transparency type and transparency level determined in the Drop Shadow window applied and placed beneath the original object (4) to complete the effect

It’s important to note that the shadow effect is not made of varying levels of color. The solid color rectangle combined with the opacity mask defines the fading levels of color for the shadow. This same principle also applies to Inner and Outer Glows – the only real differences being a lack of offset.

With this knowledge, it becomes logical to state that a color curve cut-off will not have the desired effect on a drop shadow or glow live Effect due to the transparency being the key factor. Of course, it’s possible to flatten the effect and transparency but this does negate any future changes. And as it’s such a common set of effects, there is a better way with Phantasm CS Publisher.

One of the tools introduced in the top-level of the Phantasm CS range was the ability for the live Effect variants of the Curves and Levels tools to control the bitmap alpha channel of any image – including those found in other underlying live Effects. Therefore, to apply a cut-off level to the previous drop shadow example, select the object with the drop shadow or glow and open Effect » Phantasm CS » Curves and select Bitmap Alpha from the Channel drop-down menu as shown below:

Note: as we are dealing with the mask of the thing we want to affect, the curve is rotated through 180°. Therefore the cut-off or compensation is applied to the top-right of the curve, not the lower left. However, it’s possible to flip the graph temporarily by clicking on the left/right double arrow button highlighted in the tint scale bar beneath the graph.

The image, above, also shows the live Effect curve has an arbitrary 10% cut-off level applied – where the shadow ends more abruptly.

Important: This method dictates the following best practices:

• Define a drop shadow color using only 100% tint of any ink (either a combination of CMYK or a spot color)
• The transparency defined in Drop Shadow or Inner/Outer Glow must be set to Darken or Multiply
• The opacity level defined in Drop Shadow or Inner/Outer Glow must be 100% (the final transparency level and profile can be adjusted with the Bitmap Alpha curve)

If, say, a color of 30% Cyan, 50% Magenta, 45% Yellow and 20% Black was used as the shadow or glow’s color, the curve applied to the Bitmap Alpha channel would affect this only proportionately. If a 10% Bitmap Alpha cut-off was applied to the afore-mentioned process CMYK color, then each ink would result in cut-offs of 3%, 5%, 4.5% and 2% and not the intended 10% for each channel.

It’s understood that apart from common pure black and spot color shadows and glows, that these best practices would impose too-great-a design restriction on most users. Therefore Astute Graphics has devised a series of instantly applicable Action sets which work around these limitations and allow operators to produce variable tint process CMYK shadows and glows with correct cut-off levels in a matter of seconds. This is covered in the dedicated article: Applying flexo cut-off curves to CMYK shadows and glows.

Other applied live Effects

This refers to any life Effects, especially other Phantasm CS color adjustments which may be applied on top of artwork being modified for ink drop-off simulation or compensation. If, for example, an embedded photo has a cut-off curve applied as a Filter, but that image also has a Bightness/Contrast live Effect applied, the curve will change the underlying image, but the live Effect will then update to adjust it once more. Depending on the settings being applied, the Brightness/Contrast adjustment could cause areas of the image to dip below the minimum threshold applied by the Filter.

It’s therefore advised that if a permanent flexo ink drop-off simulation or compensation curve has to be applied via the Phantasm CS Filter, that all effects are first expanded first via Object » Expand Appearance.

If you wish to maintain the live Effect to allow for future editing, the cut-off curve has to be applied as a live Effect and ensured that it remains at the bottom of the effects stack found in the Appearance panel.

Non-destructive flexo cut-off curves

If a cut-off curve which simulates or compensates for flexo ink drop-off is applied to artwork as a Filter, it is destructive. This means that the original artwork has been permanently adjusted and if the artwork is loaded in the future, it’s impossible to revert to original state without a secondary copy to call upon.

However, if the curves are applied as live Effects, the underlying artwork remains unaffected and the curve may be removed via the Appearance panel at any point in the design (unless the appearance is expanded). This has major obvious benefits, but it’s important to consider one side-effect; when measuring colors within Illustrator or through Phantasm CS’ edit embedded image tools and Photoshop, you will be measuring the original color levels and not the result following the live Effect.

In order to measure the result of a live Effect cut-off curve having been applied, temporarily expand the appearance (Object » Expand Appearance), make the measurement, and then Undo expansion to revert back to the live Effect.

Repeating common cut-off curves

Phantasm CS and Illustrator combined allow for several methods to quickly access common cut-off curves to either simulate or compensate for flexo ink drop-off:

1. Curves settings files: the Curves (and Levels) tools allow settings files to be saved and loaded. These settings files are compatible with Photoshop to ensure that changes made within Photoshop can be reflected in Illustrator.
2. Filter variants of the Phantasm CS tools can be incorporated into an Illustrator Action for quick replay. This technique is also covered in the dedicated article Applying flexo cut-off curves to CMYK shadows and glows, where it will used to apply correct adjustments to mixed tint process CMYK shadows and glows. [Also see Adobe Illustrator user manual reference for Actions]
3. Curves applied as live Effects can be turned into a Graphic Style which can be saved into the Graphic Style Library for future quick reference. [See Adobe Illustrator user manual reference for Graphic Styles Library]