L*a*b Color

Photoshop supports multiple color channel models. One of these is the L*a*b model. PS also allows the user to individually select channels and manipulate them.

PhotoImpact supports only the RGB model. There is not an easy way to access the individual channels.

One method for increasing saturation is the switch to the L*a*b color mode, and, on each of the a and b channels, increase the steepness of the diagonal curve. This can be done if the EasyFilter SmartCurve plugin is used.

Using that plugin, switch to L*a*b mode. Select first the a channel and then the b channel, and make the changes to the curves. Finally, accept the changes.