Introduction

PNG,[1] short for ``Portable Network Graphics,'' is a computer file format for storing, transmitting, and displaying images. Similar to the GIF and TIFF image formats--in fact, designed to replace them in many applications--PNG supports lossless compression, transparency information, and a range of color depths. PNG also supports more advanced features such as gamma correction and a standard color space for precise reproduction of image colors on a wide range of systems and embedded textual information for storing such things as a title, the author's name, and explicit copyright.

[1] PNG is officially pronounced ``ping'' (at least in English) but never spelled that way. Yes, this was a major topic of discussion during its design, and it is explicitly noted in the specification. Believe it or not, in November 1998 the issue once again came under discussion, this time with greater emphasis on non-English pronunciation. Though the ``three-letter'' approach (i.e., P-N-G spoken as three separate letters) was not approved for inclusion in the spec, it may be considered an acceptable unofficial alternative.

In this chapter, we'll consider PNG from the perspective of a user who has some familiarity with the process of creating and using computer images, but insufficient knowledge of the technical differences between various formats to be certain when to use what. I won't dwell on features that are mostly of concern to developers; where I do bring up programming issues, it is principally to explain to the user why some software may not perform as well as expected. I'll concentrate on two areas to which PNG is particularly well suited: as an intermediate editing format for repeatedly saving and restoring images without loss, and as a final display format for the World Wide Web. And I'll finish up with an in-depth look at one application that has particularly good PNG support: Macromedia's Fireworks 1.0, an image-editing program specifically designed for creating web images.