Issues Relating to Digital Image Compression and File Formats
Scientific Working Group on Imaging Technology (SWGIT)
See also the instructional videos on "Crime Scene and Evidence Photography"
Introduction
This document provides a foundation of knowledge of compression algorithms and file formats utilized in digital imaging, including photography and scanning. It does not cover video compression algorithms or file formats. Understanding these processes and their advantages and disadvantages will allow agencies to make informed decisions for the appropriate application of file formats and compression algorithms. For a comprehensive understanding, the reader is encouraged to seek out other sources.
Compression
Compression is the process of reducing the size of a data file utilizing algorithms to rearrange the way data is organized within the file. Compression can be used to facilitate the storage and transfer of large files. The resulting file may retain all of the data or there may be data, including visual information, that is lost. Compression algorithms that retain all of the original data are “lossless,” and those in which data is lost are “lossy.” By setting the camera or software to the least amount of compression (or the fewest amount of pictures you can store), you will significantly decrease the amount of data lost. The decision to use lossy or lossless compression will be dictated by the intended use of the image.