graphics can be created as either raster (bitmap) or vector images.
Adobe Photoshop is a design program that works with raster (bitmap) images and is used for fixing photos and using textures. A bitmap is a grid of individual pixels that
collectively compose an image. Raster graphics render images as a
collection of countless tiny squares. Each square, or pixel, is coded in
a specific hue or shade. Individually, these pixels are worthless... together, they're worth a thousand words. Raster graphics are
best used for non-line art images; specifically digitized photographs,
scanned artwork or detailed graphics. Non-line art images are best
represented in raster form because these typically include subtle
chromatic gradations, undefined lines and shapes, and complex
Because raster images are pixel-based,
they can exhibit image degradation. Just like photographic
images that get blurry and imprecise when blown up, a raster image gets
jagged and rough. When looked at close enough, the individual pixels that comprise the image can be seen. Hence, your
raster-based image of Wayne Newton, magnified to 1000%, becomes
bit-mapped before you can isolate that ravenous glint in his eye.
Although raster images can be scaled down easily, smaller versions
often appear less crisp, or "softer" than the original.
maximize raster image quality, keep in mind that
raster format is "resolution-specific", meaning that raster images are
defined and displayed at one specific resolution. Resolution in raster
graphics is measured in dpi, or dots per inch. The higher the dpi, the
better the resolution. The resolution actually
observed on any output device is not a function of the file's own
internal specifications, but the output capacity of the device itself.
Thus, high resolution images should only be used if your equipment has
the capability to display them at high resolution.
Overall, as compared to vector graphics, raster graphics are less
economical, slower to display and print, less versatile and more
unwieldy to work with. Some images, like
photographs, are still best displayed in raster format. Common raster
formats include TIFF, JPEG, GIF, PCX and BMP files.
Adobe Illustrator is a design program
that uses vector artwork and is used for artwork that requires a cleaner
look, such as logos. Vector graphics are based on mathematical formulas more versatile,
flexible and easy to use. The most obvious advantage of vector images
over raster graphics is that vector images are quickly and perfectly
scalable. There is no upper or lower limit for sizing vector images.
Just as the rules of mathematics apply identically to computations
involving two-digit numbers or two-hundred-digit numbers, the formulas
that govern the rendering of vector images apply identically to graphics
of any size.
Vector images are
not resolution-dependent, rather they display at the resolution capability of whatever
output device (monitor, printer) is rendering them. Vector graphics tend to be considerably smaller than their raster
counterparts, making them more efficient and versatile.
Common vector formats include AI, EPS, CGM, WMF and PICT (Mac).