Working with PNG files

The PNG Optimizer dialog box contains three tabbed areas where you can configure the color, transparency, and format options of the file. The fourth page displays estimated download times of the image at various modem speeds.

You can choose the color depth for the PNG file — the greater the color depth, the longer it takes to download the image. The controls under the Colors tab of the PNG Optimizer dialog box let you select a color depth for your PNG image. For paletted images, you can select the method of color reduction, number of colors, and amount of dithering.

PNG images contain a gAMA chunk, which controls gamma levels of an image. The gamma setting helps the image appear consistent across multiple display devices. If in doubt, you should use the default PC value.

You can choose to base transparency on existing image or layer transparency, or you can sample the color in the image that you want to make transparent. If you have a selection in your image, you can base the transparency on the selection. You can also base transparency on the alpha channel.

PNG images can be interlaced or non-interlaced, which affects how the image is displayed on a computer with a slow Internet connection.

The size of the compressed file and an estimate of the download time at four modem speeds are displayed under the Download Times tab of the PNG Optimizer dialog box.

You can open the PNG wizard from the PNG Optimizer dialog box. The wizard guides you through the steps of optimizing a PNG file.

The PNG Optimizer dialog box appears. The preview areas show the current image on the left and the resulting PNG file on the right.

If you choose the Palette-Based method, you can choose the number of colors in the image and the amount of dithering applied.

• Single color transparency — lets you make one color transparent by clicking a color swatch or clicking a color in the image, and entering a value in the Tolerance control.

• Alpha channel transparency — uses the current selection or alpha channel transparency of the image. You can choose which part of the image will be transparent by choosing Existing image or layer transparency, Existing alpha channel transparency, Inside the current selection, or Outside the current selection option.

4 Click the Gamma tab, and set or type a value in the Gamma control if you want to change the default value.

• Interlaced — the image is displayed incrementally in several passes; detail is added with each pass. Use this option with larger images so that the viewer can get an idea of how the image looks while waiting for it to download

6 Click OK to open the Save As dialog box, navigate to the folder in which you want to save the new image, type a name for the file, and click Save.

You can click the Download Times tab to preview the file size of the compressed file and an estimate of the download time at four modem speeds.

3 Click Finish to close the wizard and open the Save As dialog box, where you type a name and select a location for saving the GIF file.

To	Do the following
Choose a color within the image	On page 2 or 3 of the wizard, move the cursor over the image, and click a color. The color swatch displays the color you clicked.
Choose a color using the Color dialog box.	On page 2 or 3 of the wizard, click the color swatch to open the Color dialog box.
Change a setting	On page 6 of the wizard, click Back to return to the previous pages. Then, change the settings you want, and return to page 6 to view the results.