The option you choose in this tab determines which area of the image becomes transparent. To create a transparency from a selection, make the selection before opening the PNG Optimizer dialog.
For the type of transparency, choose from these options:
No transparency Saves the image without transparency.
Single color transparency Makes one color transparent. If the image contains transparency, then you can then select the Existing Image or Layer Transparency option (described below). If the image does not contain a transparency, then select the Areas that Match this Color option. The Single Color Transparency option usually creates a smaller file than the Alpha Channel Transparency option, but selecting it causes the image to lose existing alpha channel transparency.
Alpha channel transparency Uses the image’s alpha channel transparency. Because paletted images cannot contain alpha channels, this option is available only when you select Greyscale or 16 million color option on the Colors tab.
For the areas of the image to be transparent, choose from these options:
Existing image or layer transparency Uses the current transparency information. For paletted transparency and alpha transparency images, the alpha channel is used to create transparency
Inside the current selection For images with a selection, this option makes transparent everything within the selection.
Outside the current selection For images with a selection, this option makes transparent everything outside the selection.
Areas that match this color Click the color box to select any color. Or, to choose a color from the image, move the cursor over the image, and click the color. In the Tolerance edit box, set a tolerance factor that indicates how closely colors must match the selected color before they become transparent.
Previewing images in a Web Browser