PNG Format
The Portable Network Graphic (PNG, pronounced "ping") format is a newly designed format that is growing in acceptance. Although as of this writing the major web browsers do not have native (built-in) support for PNG formatted graphics, there are plug-ins available to extend the major browsers' functionality to display PNG images.
PNG Specifications:
The PNG format is the most robust of all of the graphics formats, so if it is universally accepted, it will raise the quality of Internet graphics. PNG supports 48-bit RGB color and 16-bit grayscale, and can use a variety of lossless compression algorithms, each of which is best suited to certain types of graphics. So, each pixel's colour is completely independent of every other pixel

Colour space information can be embedded within PNG files. If the web browsing software that displays the file supports colour management, it can compensate for the system gamma and other colour space parameters of the computer that is being used, so the image should appear correct regardless of the computer that is being used to display it.

The PNG format also supports transparency more fully than the simple transparency offered by the GIF89a format. Much as layered Photoshop images can have lowered opacity in areas, the PNG format allows for semi-transparent areas to be defined. It does this by allowing an alpha channel to indicate a transparency mask.

There are several other innovative features to the PNG format, such as the ability for the user of the web browsing software to change the brightness and sharpness on the fly, file integrity checks to prevent corruption during transfer, and two-dimensional interlacing. This interlacing allows for a graphic to be built in layers, instead of using a simple progressive display. However, this feature does not allow multiple- image support like the animated GIF format.

Best Uses for PNG Format
The PNG format should be, as of this writing, supported fully in version 5.0 of Microsoft Internet Explorer and in the final release version of Netscape Communicator. When the format is widely accepted, it should be more useful than the GIF format for illustrations. Although the colour support is stronger than that of the JPEG format, the file size cannot be reduced as far, because the compression algorithms are all lossless. Although Photoshop cannot currently create PNG files that utilize all of the features mentioned above, its support for PNG images includes several of the compression algorithms, alpha channel (transparency), and gamma embedding (however, the Ambient Light setting in the Monitor Set-up dialog box must be set to "Medium").

You can read more about this coming file format at the PNG Home Site, maintained by Greg Roelofs A

Updated last time March 22 Year 2002


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