Chapter 2. Scanning Concepts

2.4 File Formats and Compression
Depending on the contents of your documents, basically, we can classify them into three image types.

2.4.1 File Formats
Determine the kind of information to be saved in a file, the compatibility with various software applications and the exchanging of data in the production process. There are some influential factors in saving a scanned image. What program you'll use to post-process the image? How much disk storage is available? Will you exchange the file with others during production process and the eventual output mediums?

Please refer to the following table.
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 files.
  • PCX .pcx Multimedia, Presentation, Video Used by most software application.
    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 application
  • Targa .tga Multimedia, Presentation, Video
  • Can save alpha channel information
  • JPEG .jpg Multimedia, Presentation, Video
  • With the best compression ratio (40:1)
  • 2.4.2 Compression
    File compression schemes fall into two general categories: lossy and lossless. Lossless compression schemes pack the data in a file without actually deleting information, so there is no loss to image detail, color or output quality. The lossless compression options include the disk and file compression utilities (for example, DiskDoubler, PKZIP, ARJ or LHARC) and another type of TIFF format with LZW (Lempel-Ziv-Welch) compression.

    If the 2:1 compression ratios are not high 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 ratios are user selectable in the host software and range from 2:1 to about 40:1.