Creating PNG Files 299PNGCreating PNG FilesWeb Design in a Nutshell, eMatter EditionThere are two ways to create an alpha channel:
- Save a selection.Select the area of the image that you’d like to remain visible.
Save the selection to a channel (SelectÝ Save Selection). - Create a new channel.Activate the Channels Palette by selecting WindowsÝ
Show Channels. Select “New Channel...” from the pop-up menu in the upper-
right corner. Make sure that “Color Indicates” is set to “Masked Areas.”
You can use any of the image-editing tools (paintbrushes, selections, fills) to edit
the alpha channel information. When all channels are visible, the channel will act
as a mask and your image will show through.
When you are finished creating the Alpha Channel, save the PNG file with a.png
suffix.
Macromedia Fireworks 1.0
Macromedia Fireworks uses PNG as its native file format because of its lossless
compression. It also allows you to export PNG files, including both Alpha Channel
and 8-bit varible transparency.
The various PNG settings are accessed in the Export Preview dialog box (FileÝ
Export) by selecting PNG from the Format menu (see Figure 16-3). Choose either
“Indexed (8-bit),” “Millions (24-bit),” or “Millions + Alpha (32-bit)” from the Bit
Depth menu.
When 8-bit is selected, controls similar to those for GIFs appear for setting the
palette, number of colors, and dither amount. There are no extra controls for a
straightforward 24-bit or 32-bit export.
To add variable levels of transparency to a 24-bit image, simply select “Millions +
Alpha (32-bit)” from the pull-down menu and your work is done.
For 8-bit images, there are three transparency options:
None
This option adds no transparency information to the PNG image.
Figure 16-2: PNG options in Adobe Photoshop 4.0 and higher