Vector and Bitmap Images

Bitmap images (also known as raster images) are made up of pixels in a grid. Pixels are picture elements; tiny dots of individual color that make up what you see on your screen.

Bitmap images are resolution dependent. Resolution refers to the number of pixels in an image and is usually stated as dpi (dots per inch) or ppi (pixels per inch). Bitmap images are displayed on your computer screen at screen resolution: 72 or 96 ppi.

Because bitmaps are resolution dependent, it's difficult to increase or decrease their size without sacrificing a degree of image quality. When you reduce the size of a bitmap image through your software's resample or resize command, you must throw away pixels. When you increase the size of a bitmap image through your software's resample or resize command, the software has to create new pixels. When creating pixels, the software must estimate the color values of the new pixels based on the surrounding pixels. This process is called interpolation.

Common bitmap formats include:
• BMP
• GIF
• JPEG, JPG
• PNG
• PICT (Macintosh)
• PCX
• TIFF
• PSD (Adobe Photoshop)

Popular bitmap editing programs are:
• Microsoft Paint
• Adobe Photoshop
• Corel Photo-Paint
• Jasc Paint Shop Pro
• Ulead PhotoImpact

Vector images are made up of many individual, scalable objects. These objects are defined by mathematical equations rather than pixels, so they always render at the highest quality. Objects may consist of lines, curves, and shapes with editable attributes such as color, fill, and outline.

Because they're scalable, vector-based images are resolution independent. You can increase and decrease the size of vector images to any degree and your lines will remain crisp and sharp, both on screen and in print. Fonts are a type of vector object.

Another advantage of vector images is that they're not restricted to a rectangular shape like bitmaps. Vector objects can be placed over other objects, and the object below will show through. See the example images on this page. The vector circle and bitmap circle appear to be exactly the same when seen on a white background. But when you place the bitmap circle over another color, it has a rectangular box around it, from the white pixels in the image.

Vector images have many advantages, but the primary disadvantage is that they're unsuitable for producing photo-realistic imagery. Vector images are usually made up of solid areas of color or gradients, but they cannot depict the continuous subtle tones of a photograph. That's why most of the vector images you see tend to have a cartoon-like appearance.

The most common reason for wanting to convert a vector to a bitmap would be for use on the Web. At this time, the most common and accepted format for vector images on the Web is Shockwave Flash (SWF). Another standard for vector images on the Web is SVG, a graphics programming language based on XML. Due to the nature of vector images, they are best converted to GIF or PNG format for use on the Web.

Common vector formats include:
• AI (Adobe Illustrator)
• CDR (CorelDRAW)
• CMX (Corel Exchange)
• CGM Computer Graphics Metafile
• DXF AutoCAD
• WMF Windows Metafile

Popular vector drawing programs are:
• Adobe Illustrator
• CorelDRAW
• Macromedia Freehand
• Xara X

http://graphicssoft.about.com/od/aboutgraphics/a/bitmapvector.htm