Understanding File Formats

(C) Mustek, 1996

All rights reserved. This document may not be reprinted,reproduced or distributed in anyway without the express written permissionof Mustek.

All graphic image file formats fall into two categories, either Bitmapformats or Vector formats.

Vector formats use mathematical formulas to recreate graphics. If thegraphic is a circle, the file format will have the location of the circle’scenter, it’s radius and other pertinent information such as what colorto draw the circle. Vector formats are easily scalable without creatingjagged edges, but they are only suitable for simple drawings with a fewcolors. Scanners do not use vector file formats.

Bitmap formats store the actual color of each dot in the image. Theyare more suitable for scanned images due to the large number of colorsand complex tonal variations in a photograph. A disadvantage to Bitmapformats is that they create large files that take lots of drive space tostore. This problem is over come by several bitmap file formats which compressthe data prior to storage on disk.

Most scanning programs, including iPhoto Plus and Picture Publisher,use the *.TIF file format as their default. *.TIF files use compressionbut it does not shrink the file sizes significantly unless the image isblack and white (Scanned in Line Art Mode).

Another popular file format is the *.BMP file. This is the format Microsoftuses for Windows Wallpaper. So if you want to use your own photos as Wallpaper,save them in the Windows directory in the *.BMP format.

The two most popular bitmap file formats today are *.GIF and *.JPG.Both of these formats are popular on the Internet because of their highcompression ratios.

*.GIF compression uses an algorithm similar to ZIP files. It also reducesthe number of colors in the image. A scanned image can have up to 16.7million colors. A *.GIF file reduces this down to a maximum of 256colors. With appropriate utilities, you can reduce this even further to16 colors. Obviously you wouldn’t want to do that with a photograph though.

*.JPG does not reduce color depth. It merely uses compression algorithmssimilar to ZIP files. This is the most popular format for scannedimages on the Internet and for sending pictures as attachments to e-mail.

For more help with scanning graphics for the Internet, see our InternetGraphics Tutorial.