The issue of transparency can be very confusing to many users, because Draw 7,8 and 9 are capable of implementing many different types of transparent objects. This article and its related links will explain what transparency is. Tips are included to help you choose an appropriate transparency method for the job at hand. You will also find examples of how to create transparent objects and implement them in your designs.

The first step to creating transparencies is to identify what method of transparency your object needs. Ask yourself these general questions:

• What flavor of object am I creating--vector or bitmap?
• How high must the quality be--press quality or web graphic quality?
• What application will be used to output the final image--Draw, PhotoPaint or some other DTP program?
• What is the intended final output--laser/inkjet print, offset print or on-screen presentation?

The second step is to use the tools available in Draw and PhotoPaint to create the images.

Methods of transparency: clipping and masking
Just what is transparency, anyway? Seems like a simple question. But to understand how Draw and PhotoPaint (or any other publishing application, for that matter) render transparent objects, you need to know the two methods that are used by digital design software to make transparent objects.

Clipping: vector-based transparency
Clipping a bitmap inside a vector path is the traditional method for removing backgrounds from bitmapped images. There are several methods for creating clipped bitmaps. The most common method is to create a clipping path in your bitmap editing program. The vector path gets saved with the file, and when imported into a page layout application, the path cuts out the background, leaving your image visible in the middle.

Most professional graphics programs can handle clipped transparencies in at least one way. There are three ways to implement clipping in a Draw document:

• Clipping Path Saved with Bitmap
  The clipping path is created in an image editing program (i.e. PhotoPaint, Photoshop) and saved with the file. When imported into Draw, the clipping path is used to generate a custom crop outline.
• Manual Cropping
  Using the Shape (a.k.a Node) tool, you can add points to and reshape the rectangular cropping box that automatically surrounds a bitmap when it is imported into Draw.
• PowerClipping
  Bitmaps can be clipped into any closed path drawn or imported into Draw using the PowerClip feature. This is particularly advantagious because the path and the bitmap are separately editable.

Masking: bitmap-based transparency
Masking is not at all like clipping. Instead of cutting out the background along a path, masks filter the graphic through a grayscale image. Think of a mask as a screen. Dark areas on the mask represent blocked portions of the screen. The image can't seep through these clogged regions. Light areas in the mask simulate a clean screen. The image can flow freely through these unobstructed areas. Shades between light and dark represent varying levels of obstruction.

Advanced image editing programs like PhotoPaint and Photoshop use masking techniques to create layering and channel effects. Draw is unique among vector editing programs because it offers several ways to take advantage of masked transparencies. It is rivaled only by Corel Xara. Many of these features are taken from or inspired by Xara.

• Bitmap Color Mask
  Using this feature, Draw 9 lets you select ranges of color that you want to become transparent. Draw automatically creates a mask to block out these areas, making them transparent. You could use this technique to quickly remove a white background, for example.
• Interactive Transparency Tool
  This tool allows you to create a variety of transparency effects on vector and bitmap graphics, right in Draw. There are many settings available with this tool, but in the end, a hidden grayscale mask is created to render the effects. The power of this type of transparency is that it can be quickly and easily edited.
• Alpha Channel Transparency
  An alpha channel is an additional grayscale layer in a bitmap. In PhotoPaint and PhotoShop, channels represent selections of an image. When you import a bitmap containing an alpha channel into Draw 9, the information will be used to create a transperancy mask for the bitmap.
• GIF Transparency
  GIF files are the stuff the web is made of! When you import a GIF file into Draw, the transparency information is used to faithfully render your graphic, just is it would appear on a web page.

PostScript printing issues for transparent objects
Transparent objects can often be difficult to print. Here are a couple of keys that may open some doors to understanding.

Limitations of PostScript
Most designers--you, included--must eventually become familiar with the joys (and woes) of PostScript. If you ever have anything imaged by a service bureau or offset printer, your file will most definately be output to a PostScript device.

What does this have to do with transparency? PostScript Level 2 (the current common version of the PostScript language) has no built-in way of rendering masked transparencies. It can, however, handle clipped transparencies internally.When you print a clipped bitmap, Draw can easily generate PostScript code that tells the printer, "Here is a special shape. Draw the following objects inside this shape only."

To render masked transparencies, Draw must do something altogether different. Instead of telling the PostScript device how to print the object(s), Draw must render the area containing transparent objects as a rectangular bitmap image. This image (if aligned with all the objects around it and color-corrected properly) should blend seamlessly into the rest of the drawing when sent to the printer.

This doesn't always happen.

You should experiment with your equipment before trying to use any of the bitmap-based transparency effects described above. It is especially important to ask your service bureau or commercial printer about transparency effects in Draw 9 before sending them a file to be imaged. You'll upset yourself greatly (or your service bureau will curse your name) if you begin relying on these effects without testing them first.

Draw 9 supports output devices featuring the new PostScript 3 page description language. Support for masked transparency is built in to this new version of PostScript. This should greatly alieviate some of the printing problems experienced by some users.

Can I use Draw's transparency effects at all?
By all means! Most users will probably not experience major problems printing these effects. So use and abuse these features as much as you want! Even if you do have problems getting your printer or service bureau to print the effects properly, there are still lots of ways to use the images you generate using transparency effects.

The trick is to manually composite the objects involved in a transparency. You can do this in most cases by selecting the objects and converting them to a bitmap. You'll have to give this some thought, though. Once you convert an object to a bitmap, you won't be able to edit it as a vector object any more. It will only be as editable as any other bitmap.