PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Understanding Image Formats
485
JPEG
JPEG (pronounced “jay-peg”) stands for Joint Photographic Experts Group and is really the
name of a standards body, not a specific format.The file format we mean when we refer
to JPEGs is officially called JFIF, which corresponds to one of the standards issued by
JPEG.
In case you are not familiar with them, JPEGs are usually used to store photographic
or other images with many colors or gradations of color.This format uses lossy compression;
that is, to squeeze a photograph into a smaller file, some image quality is lost.
Because JPEGs should contain what are essentially analog images, with gradations of
color, the human eye can tolerate some loss of quality.This format is not suitable for line
drawings, text, or solid blocks of color.
You can read more about JPEG/JFIF at the official JPEG site at http://www.jpeg.org/.
PNG
PNG (pronounced “ping”) stands for Portable Network Graphics.This file format is the
replacement for GIF (Graphics Interchange Format) for reasons we discuss shortly.The
PNG website describes it as “a turbo-studly image format with lossless compression.”
Because it is lossless, this image format is suitable for images that contain text, straight
lines, and blocks of color such as headings and website buttons—all the same purposes
for which you previously might have used GIFs. A PNG-compressed version of the same
image is generally similar in size to a GIF-compressed version. PNG also offers variable
transparency, gamma correction, and two-dimensional interlacing. It does not, however,
support animations; for this, you must use the extension format MNG, which is still in
development.
Lossless compression schemes are good for illustrations but not generally a good way
to store large photos because they tend to give large file sizes.
You can read more about PNG at the official PNG site at http://www.libpng.org/
pub/png/.
WBMP
WBMP, which stands for Wireless Bitmap, is a file format designed specifically for wireless
devices. It is not in wide use.
GIF
GIF stands for Graphics Interchange Format. It is a compressed lossless format widely
used on the Web for storing images containing text, straight lines, and blocks of single
color.
The GIF format uses a palette of up to 256 distinct colors from the 24-bit RGB
color space. It also supports animations, allowing a separate palette of 256 colors for each