File Formats and Compression

File Formats
File format determines the structure of information to be saved in a file; the compatibility with various software applications and the data exchange in the image processing duration. There are some factors affecting the saving of a scanned image. What application will you use to process the image? How much disk space is available? Will you exchange the image data with others during the production ? And what are the eventual output mediums?

Please refer to the following table to obtain better performance.

File Format File Extension Recommended
Output Media		 Advantages
TIFF .tif Print
  • Efficient file size
  • Can save color separations in a single channel
EPS .eps, .epsf Print
  • Can save duotone information
  • Can save clipping path
  • Can save color separations in 1 or 5 channels
PCX .pcx Multimedia, Presentation, Video Used by most software applications
PICT .pict, pct Multimedia, Presentation, Video
  • Compact file size
  • Can include both raster and vector information
BMP .bmp Multimedia, Presentation, Video
  • Used by most software applications
Targa .tga Multimedia, Presentation, Video
  • Can save alpha channel information
JPEG .jpg Multimedia, Presentation, Video
  • With the best compression ratio (40:1)

Compression
File compression schemes fall into two general categories: lossy and lossless. Lossless compression schemes pack data in a file without deleting information, that is, no loss of  image details, color or output quality. The lossless compression options include the disk and file compression utilities (e.g., DiskDoubler, PKZIP, ARJ or LHARC) and  TIFF formats with LZW (Lempel-Ziv-Welch) compression.

If the 2:1 compression ratio is  not enough, lossy compression has to be considered. The most popular lossy compression option is JPEG. JPEG stands for the Joint Photographic Experts Group, which developed the compression standard.  JPEG compression ratio is selectable in the host software and ranges from 2:1 up  to   40:1.