Way back in Hour 1, we discussed the differences between vector and raster images. To quickly review, vector images are mathematically defined (Bézier) shapes that can be scaled to virtually any size without any loss in detail. Raster images are defined by individual pixels, which combine to create an image. Raster images, however, are bound by the resolution in which they were created, and scaling pixel images can produce jaggy or unclear results (see Figure 16.1). Although it is a vector program, Illustrator does have support for raster art. In this hour, we learn about:
Both have been enlarged 300%. Notice how the raster image becomes jaggy, whereas the vector image remains smooth.
There are basically two ways to get a raster image into Illustrator. The first way is to place the image. This command takes an existing raster image and places it into your document. The second way is to convert a vector object into a raster object by using Illustrator's Rasterize command. There is a really a third way--opening a raster file directly--but we'll get to that later in the chapter.
If you've used any page layout program, either PageMaker or QuarkXPress, you're familiar with the Place command. Place lets you import an image right into your Illustrator document. The image could either have been created in another application or it could have been exported from Illustrator in a raster format (see Hour 20, "Saving/Exporting Files").
To place a raster image, choose Place from the File menu (see Figure 16.2). You are then prompted with a dialog box asking you to find the file you want to place. After selecting the file, click Place. The image appears in the center of your screen (see Figure 16.3).
Choosing Place from the File menu.
The placed EPS file.
Notice that the image has a box with an "x" through it that shows the image is selected. Note that the "x" appears only on linked EPS images. All other placed images, whether linked or embedded, have just a box surrounding the image. You can only view placed images when in Preview mode. When you are in Artwork mode, you only see the surrounding box, not the image. EPS files are the one exception to this rule. In the View section of the Document Setup dialog box, there is a Show Placed EPS Artwork option that enables you to see a low resolution black and white preview of the EPS image when in Artwork mode.
Any object in Illustrator can be rasterized right inside Illustrator using the Rasterize command. Essentially, you are instructing Illustrator to convert a vector object into a raster. When an image is rasterized it becomes an embedded image (see "Linked and Embedded Images" later in this chapter).
2. Choose Rasterize from the Object menu (see Figure 16.4).
The Rasterize dialog box.
4. Next, choose a resolution. When Illustrator converts your selection to pixels, it needs to know how many pixels to create. For screen and web art, choose 72 dpi. If your art will be printed on an imagesetter, you need higher resolution--closer to 300 dpi for photographic images; 600 or more for bitmap and line art.
5. Finally, choose whether you want anti-aliasing or a mask. Both of these features are described in detail later in this chapter.
Time Saver: Everyone knows that you can use the Rasterize command on vector objects, but did you know that you can also apply the Rasterize command to raster art? This is most useful for converting color images to grayscale (select Grayscale from the Color Model pop-up menu) or for converting grayscale images into color (some Photoshop-compatible filters work only on RGB images).
One of the biggest advantages of vector art is the smooth lines you get when you print the file. Today's high-end imagesetters print at resolutions upwards of 2500 dpi, and we are used to seeing the clean sharp edges in our logos, type, and illustrations. Onscreen, however, things can appear jaggy because a monitor's resolution is only 72 dpi.
When your final art is printed, the images will be ultra-sharp, but what if your images won't be printed? What if you are designing for the Web or for a multimedia presentation, and the final art will be viewed onscreen? Do we have to live with jaggy art in these situations? That's where anti-aliasing comes in.
Anti-aliasing is the process of slightly blurring the edges of an image to give it a softer, smoother edge onscreen. Adobe's ATM (Adobe Type Manager) uses this technology to enable fonts to appear smooth onscreen at any size (see the following Just a Minute). Almost all images on the Web use anti-aliasing to give a clean and smooth appearance.
Just A Minute: You may notice that when in Preview mode, all type appears anti-aliased (assuming you enabled the Anti-alias Type option in the Keyboard Increments screen of the Preferences dialog box). When you switch to Artwork mode, the type is not anti-aliased. This anti-aliasing appears only onscreen, however--when you print the file, you still get the sharp lines you are used to. This is a great feature that Adobe added as of version 7. Of course, after you convert text to outlines, it does not appear anti-aliased onscreen.
When you use the Rasterize command to convert a vector object to raster, and the final image will appear onscreen at 72 dpi, anti-alias the object to give it that smooth appearance. To do so, simply check the Anti-Alias checkbox in the Rasterize dialog box (see Figure 16.5)
Checking the Anti-Alias box when invoking the Rasterize command ensures smooth edges.
A raster image always has a rectangular-shaped bounding box that defines the area of the image. Although vector files can have irregularly shaped edges, a raster requires a clipping path to achieve a different shaped border. When you rasterize an object in Illustrator, you have the option to create a mask for the image (see Figure 16.6). This allows you to place the rasterized image on a colored background without the white background box filling in around the rasterized art (see Figure 16.7).
Checking the Create Mask checkbox when invoking the Rasterize command.
The raster image on the left has no mask, whereas the raster image on the right was created using the Create Mask option.
To create a mask for an object at the time you rasterize it, simply check the Create Mask button in the Rasterize dialog box.
I mentioned earlier that there is a third way to bring a pixel image into Illustrator. Besides placing a file or using the Rasterize command, you can also use the Open command to directly open a raster image, which creates a new document with the raster image in it. Remember, however, that when you open a raster file, it automatically becomes embedded in the Illustrator document, and you cannot link it.
Illustrator 7 also sports a brand new and improved EPS parser. This means you can open just about any vector EPS (Encapsulated PostScript) file and edit it as if it were an Illustrator document. You can save a QuarkXPress document as an EPS, for example, and then open the file (not place it) and edit the document. It should be noted, however, that editing text may be difficult due to the way the text is imported.
Just A Minute: The EPS format, unlike any other, can support both raster and vector art--even within the same document. The parser in Illustrator can only convert vector EPS images (or the vector parts within an EPS) into editable art. Any art that is in raster format remains in raster form and can be edited only as a raster image.
As if things weren't already complicated enough, there are two ways Illustrator handles raster images. A raster image can either be linked, or embedded in an Illustrator document. Except for certain file formats, Illustrator links placed images by default.
A linked file resides outside of your Illustrator file, and Illustrator notes the location of that file, be it on your hard drive, on a Zip disk, or on a file server. The image in your document is simply a preview of that raster file. At print time, Illustrator goes to the original file and uses the high resolution information to print the image where it belongs in the illustration. You cannot print your file without that original raster image.
An embedded raster is actually part of your Illustrator document. After you embed a raster file, you no longer need the original raster file because the entire image is contained within your Illustrator document. Of course, this also means that your file size increases (if the file is a high-resolution one, your Illustrator file could grow to be extremely large).
If you decide not to link a file when you place it, uncheck Link when you import it (see Figure 16.8). The image will then be embedded.
Unchecking the Link box in the Place dialog box.
Time Saver: If you have a linked image in a file, and then you delete or remove the linked image from its directory, Illustrator can't access the image anymore. The next time you open the file, Illustrator alerts you and asks you where the file currently is. If you can't find it, Illustrator opens the document without the image in place.
Illustrator 7 supports a wide range of image formats. Depending on which platform you are using, Macintosh or Windows, you can open and place an array of different file formats. Some are specific to one particular program and others are specific to either the Macintosh or Windows platform, such as PICT and BMP.
There are, however, formats that can be used on either the Macintosh or Windows platforms. These formats include native Illustrator files, Acrobat PDF, TIFF, and EPS formats. PDF files can be viewed on any platform (even the World Wide Web) with the Acrobat Reader program.
Illustrator 7 sports a robust color management system that works in conjunction with either Apple ColorSync (Macintosh) or the Kodak Digital Science Color Management System (Windows). These are installed when you install Illustrator. You can edit the color settings in Illustrator by choosing Color Settings from the File menu (see Figure 16.9). You can fine-tune your options within the Color Settings dialog box (see Figure 16.10).
Choosing Color Settings from the File menu.
The Color Settings dialog box.
A color management system strives to keep colors consistent as you work with them--from scanning, to viewing onscreen, to proofing, to final output. Because each of these processes use different color technologies and even different color models, there can be a noticeable difference from what you see onscreen and what you actually get when the job is printed. Technologies such as ColorSync and Kodak Digital Science compensate for color differences by using color profiles from each device, such as your scanner, monitor, and printer, and try to make color consistent across the board.
A great feature of Illustrator is the ability to simulate print colors on display. This option lets you view files just like in Photoshop, when you want to view only certain color channels. It's also great when doing print work to get a better idea of how your file is going to print.
Notice also the checkbox marked Use ICC profiles with TIFF. With this option enabled (which it is by default), when you place a TIFF image, Illustrator prompts you with a dialog box to help calibrate the colors onscreen, making for more accurate color representation onscreen (see Figure 16.11). Of course, you can choose to leave everything as it is by clicking the Ignore Profile button.
The TIFF Color Management Options dialog box pops up when you place a TIFF file.
Placed raster images cannot be edited in Illustrator. You can, however, apply transformations to them, and you can also apply certain filters. You transform raster images just as you would any Illustrator object: select it and apply the transformation. This applies to all the transformation commands and tools--moving, scaling, rotating, reflecting, and shearing.
Illustrator has the capability to colorize 1-bit (black and white) TIFF images. After placing the image into your document, you can assign one color to the black part of the image by assigning a fill to the image.
One of the reasons why you would place a raster image into Illustrator is to trace it. Tracing a raster image creates a vector object that you can edit and scale without worrying about resolution. Illustrator's Autotrace tool was created with this in mind.
2. Choose the Autotrace tool from the Toolbox.
3. Click the edge of the image to trace.
The Curve Fitting Tolerance setting in Preferences determines how close and how smooth the traced object is in reference to the raster image. If you need more detail and accuracy for your tracing, you might look into Adobe Streamline, a software product geared specifically towards converting raster to vector art. For more information on tracing images, see Hour 21, "Working Smart in Illustrator."
Finally, one of the most exciting things you can do to raster images in Illustrator is apply Photoshop-compatible filters to them. Illustrator ships with several filters, including the entire Gallery Effects library of Photoshop-compatible filters. To use a filter, it must be present in Illustrator's Plug-ins folder when you launch Illustrator.
Photoshop-compatible filters can only be run on embedded raster images, not linked ones. Also, many Photoshop-compatible filters work only on images that are in RGB color mode. If you have an image that is not RGB, use the Rasterize command to convert to the RGB color space.
Photoshop-compatible filters can be found under the Filter menu. They look just like the other filters, but they are grayed-out unless you have an embedded raster image selected (see Figure 16.12).
Without an embedded raster image selected, all Photoshop-compatible filters are grayed out.
Have fun with the filters, and remember that you can always use the Rasterize command to convert vector art into a raster image, enabling you to apply Photoshop-compatible filters to it.
For more information on Photoshop-compatible filters, check out either Illustrator 7 Complete or Photoshop 4 Complete. These books do a great job of reviewing the filters, their settings, and the results you get.
Well, we learned to live with our pixel friends, and we proved that raster and vector images can coexist peacefully. We learned about linking and embedding, and also about Illustrator's powerful EPS parser. As if that weren't enough, we traced pixel images and even applied Photoshop-compatible filters to rasters within Illustrator. Next, we get back to the world of vector images and explore all of the filters we can apply to vector objects.
Color management--Software on a system level, such as Apple's ColorSync or Kodak's Digital Science, that assures consistent color on screens, scanners, printers and imagesetters.
Link--An external raster file that is referenced from within an Illustrator document.
Embed--A raster image that has been included within an Illustrator document.
Place--The act of importing an image or art into an Illustrator document.
1-bit--A raster image that contains only black and white pixels.
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