Web Design in a Nutshell, 3rd Edition

PNG transparency in Fireworks

Start with a layered image that has transparent areas (the checkerboard pattern shows through). To apply true alpha-channel transparency to a 24-bit PNG, choose 32-bit PNG in the Optimize palette. To save variable levels of transparency in an 8-bit PNG, check Transparency, and then select Alpha Transparency from the pull-down menu. If you view the color table for the image, you will see that it is full of colors that are marked with transparent areas. Choosing Index Transparency results in on/off binary transparency, similar to GIF transparency.

The GIMP

The GIMP (GNU Image Manipulation Program) is a free, Photoshop-like image-editing tool that runs on the X Window System under Unix. There is also a Microsoft Windows port available. The GIMP is virtually unknown by most professional graphic designers, but it bears mention here due to its superior implementation of the PNG format.

The GIMP offers excellent compression, full transparency support, gamma correction, and embedded text entry. You can apply compression incrementally using the deflate compression level knob (a sophisticated tool that no other image program offers). For more information, see http://www.gimp.org.

Figure 31-3 shows the available transparency options and resulting images for 32- and 8-bit PNGs in Fireworks. Notice that the cells in the 8-bit indexed color table give an indication that they contain transparency information.