Graphics
 

Adobe Illustrator CS5 : Learning the Truth About Transparency (part 1) - Understanding Transparency Flattening

11/18/2011 4:36:00 PM
Illustrator contains several features that use transparency, including the ability to specify blending modes and opacity masks with the Transparency panel and via effects such as Feather and Drop Shadow. Transparency as a feature in Illustrator (and InDesign as well) requires closer attention when it comes to printing documents. In fact, Illustrator, InDesign, and Adobe Acrobat all use the same methods to print with transparency, so the concepts you learn here apply to all those applications as well.

You may have heard that printing with transparency is problematic, but a lot has changed since transparency was first introduced in Illustrator 9. Once you understand what happens to a file with transparency and you learn about a few simple settings, you won’t have to worry about printing issues when you’re using transparency features.

In truth, transparency has always been around—in raster form—in Photoshop. The only difference now is that you can apply these effects in vector form and still edit them late in your workflow. At the end of the day, these transparency effects will become rasterized, leaving you with the same result as if you had done everything in Photoshop. In any case, let’s take a closer look at what transparency is and how it works.

Understanding Transparency Flattening

Let’s start with a simple fact: PostScript doesn’t understand transparency. As you probably know, PostScript is the language that printers and RIPs speak. Native transparency is understood only by PDF language version 1.4 or newer (first present in Acrobat 5 and Illustrator 9).

Note

If you’ve used Photoshop before, you may be familiar with the term flattening, which combines all layers in a document. Although similar in concept, transparency flattening is different.


To print objects with transparency, Illustrator must “translate” any transparent artwork into a language that PostScript understands. This translation process is called transparency flattening.

The process of flattening is simple, and Illustrator follows two cardinal rules when performing flattening on a file:

1.
All transparency in the file must be removed.

2.
While performing rule #1, the appearance of the file cannot change.

Both of these rules are followed during the flattening process, with no exception. Obviously, all transparency has to be removed because PostScript doesn’t know what transparency is. Additionally, if removing the transparency would result in your file changing in appearance, that would mean you could design something in Illustrator that couldn’t be printed, which doesn’t make sense either. If you think about it, if you’re removing transparency from the file and you’re also keeping the visual appearance of the object, something has to give, and that something is the editability of your file. Let’s take a look at an example of this.

Flattening Artwork

Let’s try an example of flattening:

1.
Draw two different-colored circles, one overlapping the other.

2.
Set the top circle to Multiply (Figure 1).

Figure 1. By setting the top circle to the Multiply blending mode, you can see through it to the circle below, even with Opacity set to 100%.


The nice feature of transparency is that you can move the top circle around or change its color, and any overlapping areas will simply multiply. The problem is that PostScript doesn’t know what transparency is and doesn’t know how to print that overlapping area, so transparency flattening is required.

3.
Select both circles, choose Object > Flatten Transparency, and click OK (don’t worry about the dialog box, which we’ll get to later).

The file is now flattened. Does it look any different? It can’t, because of rule #2, but the file now no longer contains any transparency and can be printed on a PostScript device. The difference is that the file is no longer editable as it was before it was flattened. Upon selecting the circles, you’ll find that the two transparent circles have now been broken up into three individual opaque shapes (Figure 2).

Figure 2. Once the objects are flattened, the artwork is split up into individual opaque pieces, called atomic regions.


This flattening process happens every time you print something with transparency. However, the flattening happens in the print stream, not to your actual Illustrator file. When you choose to print a file, Illustrator flattens a copy of your file and sends the flattened file to the printer, while leaving your document intact. It wouldn’t be good if simply printing a file rendered it uneditable. In our example, we specifically flattened the file using the flatten transparency function to see the results, but under normal circumstances, you would not flatten the transparency manually—Illustrator would do that for you automatically at print time.

Note

Flattening also happens whenever you save or export your file to a format that doesn’t understand transparency. For example, EPS (which is PostScript) and PDF 1.3 do not support transparency.


So, when you print a file with transparency, this flattening process occurs so that a PostScript printer can print the file correctly, and this process happens on the way to the printer, so your Illustrator file is not affected in any way.

The example of the two overlapping circles is a simple case of flattening. But other examples can display certain side effects. Let’s explore such a case.

Flattening with Rasterization

Let’s create another example:

1.
As in the previous example, create two overlapping circles.

2.
Set the top circle to Multiply.

3.
Fill each circle with a linear gradient, but in one of the circles, apply the gradient on a 45-degree angle.

The result is two circles with gradients, but the area in which these two shapes overlap appears as two gradients traveling in different directions (Figure 3).

Figure 3. This figure shows two overlapping circles, each filled with a gradient on a different angle.


When this file is flattened, you know that the result will be three separate shapes as in the previous example; however, this example is a bit different. Although gradients can be preserved in vector form, there’s no way to describe a crisscross gradient, like you see in the overlapping area, as a vector. Because of rule #2, Illustrator is not allowed to change the appearance of your file during flattening, so the only course of action Illustrator can take is to turn that overlapping area into a raster image.

4.
Select both circles, choose Object > Flatten Transparency, and click OK.

You’ll find that although the file looks the same, it now consists of two vector shapes and a raster image in the middle. Illustrator creates a vector mask for the middle shape so that the file will print correctly (raster images are always rectangular in shape). It’s important to point out that Illustrator didn’t raster the entire file; it merely rasterized the portion of the file that could not be preserved in vector form (Figure 4).

Figure 4. Where appearance can’t be preserved in vector form, Illustrator converts parts of a file into a raster.


At this point, a question should be forming in your mind: If part of the file is now a raster image, what is the resolution of that raster? Patience, young Padawan; we’ll get to that soon. Here’s a review of what you’ve learned to this point:

  • Transparency flattening is required to correctly print a file with transparency to a PostScript device.

  • Transparency flattening happens automatically, in the print stream, when you print a file with transparency from Illustrator, InDesign, Acrobat, or Adobe Reader.

  • Transparency flattening may cause certain parts of a vector file to become rasterized to prevent a file from changing in appearance.

Using the Two Levels of Rasterization

In the previous example, where two vector shapes resulted in a portion of that file becoming rasterized, Illustrator had no choice but to rasterize the middle region because there was simply no other way to preserve the appearance in vector form. This is one level of rasterization.

However, in some cases a second level of rasterization may occur, even if the appearance of a file could be preserved in vector form. Before printing a file, Illustrator analyzes the entire document and looks for complex regions containing many overlapping objects (which would result in a large number of atomic regions). Illustrator may then choose to rasterize those complex regions for performance reasons. Although we’ve been trained to think vector objects are simpler than their bitmapped counterparts, try to imagine an Illustrator graphic filled with many overlapping objects with transparency applied (Figure 5, on the next page). Although it may seem like only several objects at first glance, once those objects are broken up into atomic regions, you may be looking at thousands of vector shapes, which can take a long time to process and print (Figure 6, on the next page). In those cases, Illustrator can save precious RIP and processing time by rasterizing these complex regions.

Figure 5. Using the Symbol Sprayer tool, you can easily create a file that contains many overlapping shapes. You can also make some of these symbols transparent with the same tool.


Figure 6. Even though you may have started with a small number of objects, the resulting number of atomic regions can be extremely large because of flattening.


As far as the first level of rasterization goes, you really have no choice but to allow Illustrator to rasterize objects where it needs to do so. What you can do, however, is learn how to build files that work around this issue . With regard to the second level of rasterization, you can control how liberal Illustrator is when looking for complex regions. In fact, you can even disable this second level of rasterization altogether. Finally, with either level of rasterization, Illustrator always gives you total control over how these areas are rasterized.

Understanding the Transparency Flattener Settings

Illustrator has three transparency flattener presets that you can choose from in the Advanced panel of the Print dialog box. These settings control how files with transparency are flattened at print time. To access these settings, choose Edit > Transparency Flattener Presets, and click the New button to define a new preset. Let’s explore the settings in the Transparency Flattener Preset Options dialog box (Figure 7).

Figure 7. You can define your own custom flattener settings, or your printer or service provider can define them for you.

  • Raster/Vector Balance. This slider is what controls how liberal Illustrator is when looking for complex regions to rasterize (what we defined previously as the second level of rasterization). A number closer to zero (0) gives Illustrator more freedom to rasterize at will, resulting in faster print times. Moving the slider closer to 100 results in fewer rasterized areas but longer print times. At the 100 setting, Illustrator does not rasterize any parts of the file for performance reasons, effectively disabling the second level of rasterization. The High Resolution flattener preset uses this setting. In cases where files are taking extremely long to print (or crashing the RIP altogether), adjusting this slider to a slightly lower setting helps.

  • Line Art and Text Resolution. In cases where Illustrator is going to rasterize line art or text, you can specify a resolution that results in good-looking, sharp output. You’ll notice that the High Resolution flattener setting specifies a resolution of 1200 ppi, ensuring that text elements and vector objects still have nice, clean, sharp edges in final output.

    Note

    The two resolution settings in the flattener controls are used whenever vector objects are forced to become rasters during the flattening process. However, live effects, such as Feather and Drop Shadow, use the Document Raster Effects Resolution setting to determine their resolutions.


  • Gradient and Mesh Resolution. Because gradients and meshes are continuous tones in nature, they don’t require a resolution as high as line art or text. In fact, anything twice your line screen is probably getting thrown out anyway. Therefore, Illustrator uses this setting to rasterize elements that can afford to be set at a lower resolution. You’ll notice that the High Resolution flattener preset uses a value of 300 ppi.

  • Convert All Text to Outlines. In cases where text is going to be rasterized, chances are that the rasterized text looks a bit chunkier than regular vector text. To compensate for this, you can turn on this option to convert all text to outlines, giving a consistent chunkier look to all of your text.

  • Convert All Strokes to Outlines. Similar to the previous setting, this compensates for disparities between vector and rasterized strokes by converting all strokes to outlines.

  • Clip Complex Regions. We mentioned that Illustrator can look for complex areas of a file and rasterize them for performance reasons. However, we know that raster images are always rectangular in shape, which means it’s possible for “innocent” parts of your file to become rasterized simply because they fall into the rectangular bounding box of the area that is complex. More often than not, this results in stitching, or noticeable boxes and color shifts. The Clip Complex Regions option avoids this issue by creating a clipping mask around any rasterized complex region (so the rectangular-shaped raster is masked by the vector outline of the object). As you can probably understand, this makes for even more complex files and can result in longer print times as well. This option is turned on by default but isn’t applicable in the High Resolution preset because no complex regions are rasterized at all with that setting (because it has a Raster/Vector Balance setting of 100).

Understanding Object Stacking Order and Transparency Flattening

When rasterization occurs during transparency flattening, the last thing you want to see turning into a raster is text. That’s because you always want text to be clean and sharp in your printouts. Even at the High Resolution setting, where text is rasterized at 1200 ppi, that resolution is still less than half of what most imagesetters set text with—usually upward of 2400 ppi.

Although it’s true that under certain circumstances rasterization must occur in order to print a file and maintain its appearance, the way you build your files can affect how often this happens. Let’s look at a simple example that clarifies this:

1.
Draw a circle, and add a drop shadow to it by choosing Effect > Stylize > Drop Shadow.



2.
Switch to the Type tool, create some text, and position the text near the drop shadow (Figure 8).

Figure 8. Placing text near an object is common, especially when you’re adding captions or credit text near photographs.


3.
With the text still selected, choose Object > Arrange > Send to Back.

4.
Now select both the circle and the text, choose Object > Flatten Transparency, and click OK.

Upon close inspection, you’ll see that a portion of the text was rasterized. This happened because the text was below the drop shadow in the stacking order, and to maintain the file’s appearance when the drop shadow was rasterized, Illustrator had to include part of the text in the drop shadow’s bounding area (Figure 9).

Figure 9. To maintain the appearance of the file, Illustrator rasterized the text that was behind the drop shadow.


5.
Choose Edit > Undo to go back to the version before you applied the Flatten Transparency function, and select the text object.

6.
Choose Object > Arrange > Bring to Front.

7.
Select the circle and the text, choose Object > Flatten Transparency, and click OK.

In this case, the text, which was above the drop shadow in the stacking order, was not affected at all and was not rasterized (Figure 10).

Figure 10. If the text appears above the shadow in the stacking order, the text is not rasterized during flattening.


When using transparency features in Illustrator (or InDesign, for that matter), it’s important to make sure that text always appears above objects with transparency to avoid unwanted rasterized text issues. Of course, some designs call for text to appear beneath transparent objects, and in those cases, you don’t have much of a choice.

 
Others
 
- Dreamweaver CS5 : Using Dreamweaver Templates - Adding Content to Template Documents
- Dreamweaver CS5 : Using Dreamweaver Templates - Using Editable Regions
- Adobe Photoshop CS5 : Fixing Depth-of-Field Problems
- Adobe Photoshop CS5 : Using the Dodge and Burn Tools
- QuarkXPress 8 : Combining type and graphics
- QuarkXPress 8 : Fine-tuning typography
- Adobe After Effects CS5 : Curves: Gamma and Contrast
- Adobe After Effects CS5 : Levels: Histograms and Channels
- Adobe Fireworks CS5 : Adjusting tonal range & Using the Align panel
- Adobe Fireworks CS5 : Importing images & Distortion-free bitmap scaling
- CorelDraw 10 : Naming a Web Page
- CorelDraw 10 : Adding a Page Background
- Adobe Flash Professional CS5 : Sampling and Switching Fills and Strokes (part 2)
- Adobe Flash Professional CS5 : Sampling and Switching Fills and Strokes (part 1)
- Adobe InDesign CS5 : Adding and Deleting Anchor Points
- Adobe InDesign CS5 : Converting Points
- Adobe Flash Catalyst CS5 : Creating a Data List component (part 2) - Convert the sample record into a Data List component & Define the repeated item
- Adobe Flash Catalyst CS5 : Creating a Data List component (part 1) - Design a sample record
- Adobe Flash Catalyst CS5 : Flash Catalyst data lists
- Adobe Illustrator CS5 : Printing from Illustrator (part 3) - Specifying Color Separations
 
 
Most View
 
- Windows Phone 8 : Walking Through the Bookshop Sample Application (part 5) - Overview of the Sample Bookshop WCF Service
- Windows 8 : Using the Control Panel Items (part 10) - Programs and Features, Recovery, Region and Language
- Microsoft PowerPoint 2010 : Preparing a Slide Show - Triggering Animations
- Sharepoint 2013 : Managing and Configuring Profile Synchronization (part 9) - Audiences - Audience Targeting Rules and Logic, Targeting Content to Audiences
- Windows 8 : Sharing files and folders (part 4) - Understanding NTFS permissions - Modifying file or folder permissions
- Microsoft Lync Server 2013 Edge Server : Edge Server Installation (part 5) - Creating Certificates
- Windows 8 : Using the Control Panel Items (part 9) - Power Options
- Windows 8 Explorer : Working with Files
- Microsoft Visio 2010 : Adding Structure to Your Diagrams - Comparing Containers and Groups
- Creating Extended Events Sessions in SQL Server 2012 (part 2) - Monitoring Server Logins
 
 
Top 10
 
- Microsoft Project 2010 : Setting Up Project for Your Use - Defining Project Information (part 2) - Defining Project Properties
- Microsoft Project 2010 : Setting Up Project for Your Use - Defining Project Information (part 1) - Understanding the Project Information Dialog Box
- Microsoft Project 2010 : Setting Up Project for Your Use - Setting the Task Mode
- Securing an Exchange Server 2007 Environment : Securing Outlook Web Access
- Securing an Exchange Server 2007 Environment : Protecting Against Spam (part 2) - Filtering Junk Mail
- Securing an Exchange Server 2007 Environment : Protecting Against Spam (part 2) - Filtering Junk Mail
- Securing an Exchange Server 2007 Environment : Protecting Against Spam (part 1) - Protecting Against Web Beaconing
- Securing an Exchange Server 2007 Environment : Securing Outlook 2007 (part 2) - Encrypting Communications Between Outlook and Exchange , Blocking Attachments
- Securing an Exchange Server 2007 Environment : Securing Outlook 2007 (part 1) - Outlook Anywhere
- Securing an Exchange Server 2007 Environment : Securing Your Windows Environment (part 3) - Keeping Up with Security Patches and Updates