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An example of a vector image (top) and bitmap image (bottom). |
Vector graphics and bitmap
graphics represent two different
methods for storing and displaying graphic images digitally. A TV screen
or computer monitor displays a "picture" using a sort of
bitmap, in which the bits are the individual pixels on the screen which
our eye sees not as dots but as a coherent image. Vector graphics use
math to describe the image and tell a computer how to use the math
to generate the image. Vector graphics are really x-y plots with lots
of points plotted. The bitmap file has extension like .bmp, .gif, .tiff,
or .jpeg while the .eps
extension usually marks a vector-graphic file.
Bitmap files can be very large, depending on the resolution chosen
(high resolution = many bits = big file), whereas vector-graphic files
are very compact.
Bitmap files are the best way to store and display photographic images.
When the subject or photograph (an analog depiction) is scanned to
make a digital file, the resolution of the scan must be carefully chosen
to be more than any intended use. The resolution is
usually described in pixels or,
in printing, by the dimension in inches related to the dpi in
the halftone. The resolution
chosen for the initial (conversion to digital) scan must be more than
needed for any subsequent use. For example, 72 dpi is a common choice
for web sites, but 300 dpi is common for print images. This means that
the digital camera taking the photo, or scanner scanning the image,
must have its resolution set accordingly if both print and web uses
are intended. Photo-editing software can reduce the size of a scanned
bitmap image easily (just delete un-needed pixels), but the bitmap
cannot be enlarged from a lower resolution without introducing artifacts
such as "stairstepped" lines
or letters, or "tiling" in photographic images, in which
the picture starts to look more like a mosaic.
The most common vector files are computer type-fonts. The letters
can be enlarged or reduced without any loss of image sharpness. Vector
files are a good choice for logos, line drawings, and simple illustrations.
The color rendition and graphic design can be re-sized up or down to
any size and still maintain sharp resolution, smooth edges, and complete
rendition of detail. Photographs, with their continually-changing color
and luminance, do not look their best as a vector graphic. Another
consideration is the choice of software used to manipulate the vector
graphic. It's a good idea to be using the same software throughout
the creative and print processes of manipulating the vector graphic.
Sometimes moving an .eps file through different graphic software results
in image distortion, the wrong font, or outright loss of the image.
Please contact Wood Printing Service for expert help in getting
the best print results from cost-effective use of graphic design software.
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