By default, DigiCap is applied to the entire surface of the 1-bit TIFF used to image the plate. At a microscopic level, every halftone dot is a solid area. When DigiCap is applied to a surface, it will show up in solid areas and in halftone dots.
Applying DigiCap in all areas is often beneficial, because it can adjust ink film thickness at a very precise level in all solid areas, no matter how small. However, ink film thickness tends to decrease as dots get smaller. This is because reduced surface tension causes smaller areas to carry proportionately less ink. There may be a point where DigiCap is detrimental to the laydown of ink in tonal areas. In these cases, you can use the Keepaway setting to control the appearance of DigiCap in halftone dots.
Keepaway places a black outline around the edges of all solid areas. DigiCap will not appear in the Keepaway areas. As Keepaway is increased, there are more halftone dots whose diameters are too small to allow the appearance of DigiCap.
100-80-60-40-20 with Keepaway disabled—DigiCap throughout
Figure 2. 100-80-60-40-20 with Keepaway of 2 enabled—DigiCap kept out of 20%
Figure 3. 100-80-60-40-20 with Keepaway of 5 enabled—DigiCap kept out of anything less than 75%
The Keepaway feature also helps to ensure that edges of solids and reverse type print cleanly.