Graphic Formats

PNG:
Portable Network Graphics.  The Portable Network Graphics (PNG) format was designed to replace the older and simpler GIF format and, to some extent, the much more complex TIFF format. PNG provides a useful format for the storage of intermediate stages of editing. Since PNG's compression is made to prevent and loss of data--and since it supports up to 48-bit truecolor or 16-bit grayscale--saving, restoring and re-saving an image will not degrade its quality, unlike standard JPEG (even at its highest quality settings). PNG is a raster format, which is to say, it represents an image as a two-dimensional array of colored dots (pixels). PNG is explicitly not a vector format, i.e., one that can store shapes (lines, boxes, ellipses, etc.) and be scaled arbitrarily without any loss of quality.

From: http://www.libpng.org/pub/png/

GIF: 
The letters "GIF" actually stand for "Graphics Interchange Format". GIF is a compressed image file format. GIF images use a compression formula originally developed by CompuServe . GIFs are based on indexed colors, which is a palette of, at most, 256 colors. This helps greatly reduce their file size. These compressed image files can be quickly transmitted over a network or the Internet, which is why you often see them on Web pages. GIF files are great for small icons and animated images, but they lack the color range to be used for high-quality photos.

From: http://www.techterms.com/definition/gif

JPEG:  
(Joint Photographic Experts Group) An ISO/ITU standard for compressing still images.  JPEG format is very popular due to its variable compression range. For example, an image can be saved in high quality for photo printing, in medium quality for the Web and in low quality for attaching to e-mails, the latter providing the smallest file size for fastest transmission over slow connections. JPEG is a lossy compression method, wherein some data from the original image is lost. It depends on the image, but ratios of 10:1 to 20:1 may provide little noticeable loss. The more the loss can be tolerated, the more the image can be compressed. For text, it is recommended to compress the file and transform it into a GIF file.

From: http://www.pcmag.com/encyclopedia_term/0,1237,t=JPEG&i=45676,00.asp 

TIFF: 
TIFF or the Tagged Image File Format is a file format that is strictly used for bitmap data. TIFF files  don’t contain text or vector data, even though the file format theoretically would permit additional tags to handle such data. Despite being one of the earliest file formats for images, it is still very popular today. It is a highly flexible and platform-independent format which is supported by numerous image processing applications and virtually all prepress software on the market.

From: http://www.prepressure.com/library/file-formats/tiff