Web Graphic File Formats: GIF, JPG & PNG
High quality graphic images can be
quite large, with file sizes that would make displaying them on a web page prohibitatively
time consumming. When discussing web graphics, we need to discuss file
compression techniques. There are basically two types of compression
methods: lossy and lossless. Lossy
compression creates smaller files by discarding some information about the
original image. It removes details and color changes it deems too small for the human eye
to differentiate. Lossless compression, on the other hand, never
discards any information about the original file.
GIF
Graphics Interchange Format.
A lossless compression format for images developed by CompuServe in the late 1980s,
using the compression algorithm patented by UNISYS. The LZW compression routine used
in Gifs is the same one found in zip files. The most common types
of images used on the Web are Gifs. The biggest limitation of GIFs is
that they can only contain up to 256 different colors. The GIF 89a
format allows for the creation of transparent, interlaced and animated gifs.
JPEG graphic format:
JPEG or JPG is a graphics file
format that was devised by a committee called the Joint Photographic Expert's
Group. It refers to a set of formats that support full-color images and stores
them in a compressed from. JPEG is a 24-bit storage formats that allow for 16,777,216
Colors. It is a standardized image compression mechanism, designed
for compressing either full-color or gray-scale images of natural, real-world
scenes. It works well on photographs, artwork but not so well on line
drawings, cartoons and lettering.
Using JPEG compression, most images
can be compressed up to 20:1 without noticeable loss of quality; some can be compressed as
much as 50:1. The JPG format is a lossy compression, but the
user may to choose how much trade-off of quality for storage space they wish.
That is a JPeg image can be saved in low, medium, high and maximum resolution.
PNG format:
PNG stands for Portabel Network
Graphics, and the format was devised in 1995 by the W3C and CompuServe in response to
controversies over GIF licensing. PNG provides a patent-free
replacement for GIF and can also replace many common uses of TIFF. Indexed-color,
grayscale, and true color images are supported, plus an optional alpha channel for
transparency. Sample depths range from 1 to 16 bits. The Internet Media Type image/png was
approved on 14 October 1996. The PNG
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Last updated on 11/23/2004 by L.M. Hicks |