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PART I1 THE PAGE
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BITMAPS VS. VECTORS
Bitmaps and vectors are the two fundamentally different ways that computers create, store, and manipulate images.
vector graphics
In the practical world of computer graphics, bitmap and vec- tor images bump happily along with each other. You could work for years without needing to differentiate between the two. But that’s not to say you should remain in the dark.
Vector graphics are images that are composed by mathematical formulas.
Adobe Photoshop manipulates photographic images. Adobe Illustrator makes graphic images. They are sister ap- plications that dominate the worlds of still images. Whereas many sisters grow apart as they grow old, these have grown closer. With each new version of Adobe’s Creative Suite,
the interfaces of both applications become more and more alike.
Don’t think of vectors as being relatively simple shapes, like letterforms (which are almost always created with vectors.) Vector graphics can be extremely complicated and produce images with hand-drawn qualities. The vector format is best suited for solid colors, lines, curves, charts, logos, and fonts. In vector graphics, a mathematical formula provides instructions to the entire grid. Fortunately, you don’t need to know how vectors work in order to put them to work.
Photoshop and Illustrator may be sisters, but they are quite different. Photoshop works with pixels and bitmaps. Illustrator works with something called vectors.
While “math” may be an accurate description of the com- puter code that generates Illustrator images, the reference makes it hard to get a concrete grasp of how vectors work. It’s easier if you think of vectors as being a few specific points that are connected by paths. As you will see, points and paths become the very tangible engine by which you will create within Illustrator.
bitmap graphics
There are two advantages of vectors over bitmaps. First, a vector image allows any geometric shape, even a com- plex series of curves and lines, to be described in very little space. Vector graphics are highly compact and don’t hog computer hard drives. The illustration here provides an example.
At a glance you can see that the amount of data required for a vector is far less than the data required for a bitmap. The vector formula is written out in words. Its mathematical version would be even shorter. The bitmap data would consist of binary information about whether each and every pixel was to be blue or white. As with words, the code would fill pages. Joe Maidenberg
Bitmap graphics are images made up of a grid of pixels.
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CHAPTER 4: ILLUSTRATION
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Visualize the computer image as a mosaic, made up of mil- lions of square blocks, or pixels. A bitmap is the image “seen from above.” The bitmap format (which is sometimes called a raster format) lends itself to continuous tone, photo-realistic images.
I created a bitmap stick figure (top left) using a drawing tablet and working in a 4 x 6–inch space. My hand is a bit shaky using the Pencil tool. I created the vector stick figure (bottom left) in Illustrator. using the Brush tool with settings that smoothed out my drawing. (Both draw- ings on the top and bottom left have been scaled down to fit into the book’s layout). In terms of resolution, the two figures on the left top and bottom look pretty much the same.
The second huge advantage of vectors over bitmaps can be understood at a glance: Vectors allow you to resize with- out any loss of quality. This ability to keep an image sharp no matter how big or small it is called resolution independence.
The human eye reads the evenly distributed pixels of a bitmap’s surface as if it were a coherent, smooth image.
A standard size for a computer image is 640 x 480 pixels. This area contains roughly 300,000 pixels laid out in rows.
With bitmaps, size matters. If you try to expand them too much, the image breaks down and artifacting occurs. Bitmaps are thus resolution dependent.
The close-ups (right, both rows) compare the stick figures’ shoulders. Both these shots are enlarged 1200 percent, meaning they are twelve times bigger than the originals. The vector drawing (bottom right) shows the brushstroke in perfect clarity. The detail of the raster drawing (top right) shows individual pixels.