Work with Bitmaps


Vector graphic files save information by storing descriptions of paths and fills; raster image files save information by recording the character (color, brightness, transparency, and other attributes) and location of every single pixel in an illustration. Although raster files save images less efficiently (compared to vector files), the raster file logic makes it easier to fine-tune attributes such as color on a level not available with vectors. Therefore, photographs in particular are best edited in bitmap programs.

Sometimes bitmaps are the only show in town. This is still mainly the case on the Web, where vector-based illustrations must rely on plug-ins such as the Flash Player to be able to be viewed in browsers.

Open Bitmaps in Illustrator

There are three ways to open a bitmap image in Illustrator. Many bitmap file formats are supported by the File Open menu. Keep in mind, though, that when you save a file that was opened as a bitmap, you ll either save it as an Illustrator vector file or export it to a bitmap.

More typically, you ll place or paste a bitmap into an open Illustrator file. To place a bitmap within an Illustrator document, choose File Place and navigate to the file in the Place dialog box. The Place dialog box has a Link check box. A linked file is not embedded in the actual Illustrator document; the document simply remembers where that file is and displays it in the Illustrator document. If you don t check the Link check box when you place a file, it will be embedded in the Illustrator file.

Tip  

Link vs. embed ”if someone is providing you with Illustrator files, you might want to have placed bitmaps linked so you have the freedom to switch them or edit them more easily in a bitmap editor. If you are sending a file to a client, you should usually embed images so they don't get lost, or so that your client doesn't accidentally break links by moving, renaming, or deleting linked images.

Bring Photoshop Files into Illustrator

Photoshop s PSD file format is among those bitmap formats that you can open directly in Illustrator. Many attributes of Photoshop files are supported and maintained even after the file is opened in Illustrator.

Layers are explained in Chapter 20 in this book. They are a helpful tool for organizing and editing objects in Illustrator, but they re an even more essential feature in Photoshop since bitmap images are not composed of easily selectable objects as vector images are. When you open or place a Photoshop object in Illustrator, layers are maintained.

Type included in a Photoshop file is editable (and formatable) when you bring the Photoshop artwork into Illustrator.

Use Bitmap File Formats in Illustrator

If the size and color of the image are defined, the bitmap is ready to be imported. Illustrator can handle more than a dozen bitmap file formats, including the following:

  • BMP ( . bmp)    Bitmap, used with many Windows applications

  • GIF (.gif)    Graphics Interchange Format, used for web images

  • JPEG (.jpg)     Joint Photographic Experts Group, used for web photos

  • PCX (.pcx)     PC Paintbrush, used with some Windows applications

  • PDF (.pdf)    Portable Document Format, supports both vector and bitmap objects

  • PCD (.pcd)     Kodak Photo CD, supported by Kodak film developers

  • PSD (.psd)    Photoshop files, which come into Illustrator with layers and other features intact

  • PICT (.pict)     A Macintosh format, used with many Macintosh programs

  • PNG (.png)    Portable Network Graphics, similar to the GIF format for web-compatible graphics

  • PIXAR (.pxr)     Used for 3-D imaging

  • TGA (.tga)    Targa, supports enhanced gamma (intensity) settings and is used with the Truevision video board

  • TIFF (.tiff or .tif)     Tagged Image File Format, used by many scanners as a default image format

This list of bitmap formats supported by Illustrator is extensive , but not complete. So you should make sure that any bitmaps you are bringing into Illustrator have been saved to or exported to one of these formats.

Convert Vectors to Bitmaps

As noted, there are advantages to bitmap format, most notably the ability to edit the coloring of specific pixels or dots. You can convert a selected vector to a bitmap by choosing Object Rasterize from the menu.

Tip  

Just as bitmap and raster mean the same thing, pixel and dot mean pretty much the same thing. The smallest element of a printed bitmap is usually referred to as a dot (as in dots per inch in defining printer resolution), while the elements that make up a digital display (such as the one on your monitor) are referred to as pixels.

You can apply raster effects to vector objects that have been converted to raster objects. But don t confuse the Object Rasterize command with the rasterizing option available in the Effect menu. Objects that you have displayed as bitmaps by selecting Effect Rasterize cannot be used with bitmap filters. They aren t really raster objects; they just display that way.

Prepare Bitmaps for Illustrator

The most important thing you should know about working with bitmaps in Illustrator is that you cannot resize them or recolor them. OK, you can resize bitmaps in Illustrator, but you won t want to. The reason is that if you enlarge a bitmap in Illustrator it will get grainy and lose quality. If you reduce the size of a bitmap in Illustrator, it will get smaller without losing quality, but the file size will not be reduced.

Note  

Programs such as Photoshop do have resampling tools that enable you to reduce file size as you shrink a bitmap or enhance image quality when you make a bitmap bigger.

For example, Figure 19-2 shows an enlarged image containing both vector and bitmap objects. The bitmap ”the onion ”is obviously distorted and displays with jagged edges, while the vector-based type has no distortion at all ”even highly enlarged.

click to expand
Figure 19-2: Bitmap artwork degrades into visible pixels when enlarged, while the vector object (the type) does not.

You can alter the coloration of an entire bitmap image in Illustrator by choosing Filter Colors Adjust Colors and then tweaking the color of the entire selected bitmap. However, these color changes are applied to all colors in the bitmap image. Tinting coloration with a filter is a useful effect, but it doesn t serve as a coloring editor.

Since resizing and recoloring bitmaps is problematic in Illustrator, you should arrange to have photos or other bitmap artwork sized and colored before you bring it into Illustrator.




How to Do Everything with Illustrator CS
How to Do Everything with Adobe Illustrator CS
ISBN: 0072230924
EAN: 2147483647
Year: 2002
Pages: 175
Authors: David Karlins

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