The Sponge Brush Tool can be used to selectively saturate or desaturate areas within an image.
Settings
The following settings can be adjusted from the context toolbar:
Width—the brush (stroke) size in pixels.
Opacity—how see through the brush is.
Flow—how fast the brush effect is applied (1% is very slow, 100% is immediate).
Hardness—how hard the edges of the brush are. The brush appears softer as the percentage decreases.
More—tap to display the Brushes dialog to access advanced brush settings.
Mode—choose from one of the following modes:
Saturate—when selected, brush strokes increase the saturation of the existing pixels.
Desaturate—when selected, brush strokes decrease the saturation of the existing pixels.
Force pressure—Toggle to control brush size with pressure if using a pressure-sensitive device. This overrides brush defaults.
Vibrance—tap to toggle between HSL Saturation and Vibrance modes. The former adjusts the colour intensity of all pixels; the latter adjusts the intensity of subtle coloured pixels, while minimizing clipping of highly saturated coloured pixels.
Symmetry—when the Lines setting is set to greater than 0, repeats the brush stroke around a number of axes (defined by the value). The centre axis point can be repositioned by dragging it.
Mirror—with symmetry enabled, causes brush strokes to be mirrored along the X and Y axis.
Lines—with symmetry enabled, defines the number of axes around which the brush stroke will be repeated.
Locked—when enabled, prevents the symmetry line from being moved.
Sponge Brush Tool
Force pressure—Toggle to control brush size with pressure if using a pressure-sensitive device. This overrides brush defaults.
Vibrance—tap to toggle between HSL Saturation and Vibrance modes. The former adjusts the colour intensity of all pixels; the latter adjusts the intensity of subtle coloured pixels, while minimizing clipping of highly saturated coloured pixels.