The PNG Tab

PNG images have similar options to the GIF image, so we will go over only the differences. First is the Bit Depth (see Figure 7.10). Because PNG images are built on a bit-depth system, they can have transparency in the image itself. This is very useful when doing "cutout" images and shapes. The only way to get transparency in the PNG is to set its Bit Depth to 24-bit with Alpha (the default choice). If you do not need your image to have transparency in it, choose either 24-bit or 8-bit for a smaller file size.

Figure 7.10. The PNG tab in publish settings.

The other major difference in the GIF tab and the PNG tab is the capability to use filters with PNGs. This option attempts to compress the file further by going line by line through the image to see where it can make adjustments. Like many of the settings, you will have to play with them to get the desired result. Here are the choices for this option:

• None This default choice does not apply any filter.

• Sub This choice evaluates the following and preceding pixel of each pixel to create a set value.

• Up This choice evaluates the current pixel and the one above it to gain a pixel value.

• Average This choice evaluates the pixel to the left and the one above to gain a pixel value.

• Path This choice creates a function to evaluate the top, top-left, and left pixels to gain a pixel value.

• Adaptive This choice evaluates all the colors necessary to create the highest quality image.