Using masks to modify dithering

When you use masks to optimize the amount of dithering in a GIF, PNG-8, or WBMP image, white areas of the masks yield the most dithering, and black areas of the masks yield the least dithering. You can adjust the maximum and minimum levels of dithering in the Modify Quality Setting dialog box.

To use masks to modify dithering:

1. In the Optimize panel/palette, choose a GIF or PNG-8 setting from the Settings menu, or choose GIF or PNG-8 from the file format menu.
2. Click the mask button to the right of the Dither text box.
3. Choose which masks to use:
• All Text Layers to use the masks from all text layers in the image.
• All Vector Shape Layers to use the masks from all shape layers in the image.
• Channel to choose an alpha from the menu. In ImageReady, you can choose Save Selection to create a new alpha channel based on the current selection.
4. To preview the results of the weighted optimization, select the Preview option.
5. Define the dithering range:
• To set the highest percentage of dithering, drag the right (white) tab on the slider, enter a value in the Maximum text box, or use the arrows to change the current percentage.
• To set the lowest percentage of dithering, drag the left (black) tab on the slider, enter a value in the Minimum text box, or use the arrows to change the current percentage.
6. Click OK.