Image Formats

Image Format = the way we describe the image:

• size = # rows, # coloumns
• color/greyscale/binary
• number bits/pixel
• compression standard used if any.
• any related text/message want to tie to it.

This information usually at the head or top of the file.

There are several different formats, created by different standards or manufactures to solve different problems. Each standard has different limitations e.g. what kinds of images they can represent (binary, color, etc). Some provide compression of the image others just store the image.

The following describes the tradeoff when considering whether or not to use a particular format and whether or not to compress the image.

Tradeoff = Quality versus Size

More Info versus Less

BMP = BitMap format.

• up to 16.7 million color
• No compression
• Microsoft Windows
• Common use Windows background screens and screen saver programs

GIF = Graphics Interchange Format

• Pronounced "jiff"
• up to 256 colors
• Built in File compression (don't attempt to apply additional compression to a GIF picture).

PNG = Portable Network Graphics

• up to 16.7 million colors (full color)
• Built in File compression.
• Extension of GIF format to allow full color
• Not as good compression as JPEG

JPEG = Joint Photographic Experts Group

• also JIFFY, JAG
• up to 16.7 million colors
• Compression (loose) based on HAS responses to frequencies
• Best on Natural images
• Not as good for images with well-defined edges such as cartoons, or black and white images.

PBM,PGM,PPM = Portable BitMap format

• used by PBMPlus tools suit.
• upto 16.7 million colors
• No Compression

PCX = Microsoft Paintbrush app. format

• up to 16.7 million colors
• No compression
• only Mac

TGA = TrueVision Targa files from Amiga

• up to 16.7 million colors
• these files sometimes fed into programs that generate factals and animation.

TIF, TIFF = Tagged image File Format

• as many colors as can be utilized by program that creates the picture file
• Most detail information about image in this format (can even attach comments about the picture which are not viewed with the image but with the utility can be read).
• TIFF 5.0 allows for four different compression schemes including no compression.
• TIFF 6.0 also supports JPEG compression.

XBM = X BitMaps

• format for Xwindows graphic user interface system for UNIX.
• two colors
• not compressed

Raw = no header information, just the image data