Popular Types of Graphical Files

This list describes several popular types of file with some of their characteristics and uses.

.jpeg or .jpg     
Defined by the joint photographic experts group. Intended for photogrpahic images in a compressed form. Not as good for print, line graphics, or iconic images with few distinct colors. Uses 24 bit RGB color (8 bits represent each color intensity, Red, Green, Blue). Can compress files size 10 to 20 times or more compared with uncompressed 24 bit RGB such as tiff. Image quality is degraded every time the file is processed then compressed again. Can select trade-off between amount of compression and quality of image.

.gif
Developed by Compuserv (a computer sevices company) in 1987 for saving files in a small space and called the graphics interchange format. Uses a total of 8 bits per pixel to represent 256 colors from the full 24-bit RGB space (colors used are determined by the image). Consequently, this format is good for line drawings and graphics with limited colors (up to 256) such as icons, but not for photographs which have colors ranging over a much larger space. Uses LZW (Lempel-Ziv-Welch) loss-less compression, so images are reproduced exactly as saved.

.tiff or .tif
Developed in the mid-1980's and now owned by Adobe systems the tagged image file format evolved into a format that can store scanned or photgraphic images. This is a full file format that does not lose quality in storage. There is some loss-less compression using the LZW algorithm. It stores either 32-bit CMYK format or 24-bit RGB format images (CMYK is the typical format used for printing images, RGB for projecting images on a screen.)

.png
This format is called portable network graphics and is intended to give a good means of transtering images on the network. It uses 24-bit RGB representation and loss-less compression that results in files smaller than .tif files.

.psd
This is the photoshop file format with support for most of the image options in photoshop. This means that it is a more complex file structure than simpler ones like .jpeg and .gif, but it retains much of the editing information from photoshop such as layers, masks, cropping information, transparency, etc. A newer version (.psb) is intended for very large files, 2 GB+.

.pdf
Adobe systems developed this portable document format in 1992 for documents that include print and images. It has been updated often since. It is an ISO standard and licensed for free by Adobe. It can include graphical images as well as print in various forms. The .pdf format is used to transport documents so they reproduce identically on any system and is the one used by Adobe Reader/Writer.

Camera Raw
This category includes many formats. Each digital camera manufacturer has their own proprietary raw format that records all the information recorded by the camera sensors. This means that the files are very large but with full information they can be manipulated more accurately than any other format, then saved to another format such as .tiff or .jpeg. Some of the fancier cameras allow in camera editing of files to some extend. Here are some of the specific file formats:

.nef        Nikon
.crw
.raf
.orf
.dcr
.mrw       <to be supplied>
.dng
.ptx
.arw
.erf
.bay

Exercise: Find out the file types supported by your camera (if you have one, or a friend's if you do not). Find out the file types for one other camera that has a raw format (other than Nikon).

.dng
This is a standard camera raw format that is used in photoshop and lightroom -- Adobe products. For example, Lightroom can convert most proprietary camera raw formats, such as .nef, to .dng without loss of information. It has the advantage that as the image is processed in raw format, the changes are kept in the same file, rather than a separate file. Some camera manufacturers have also adopted the .dng format.