The Sponge Brush Tool can be used to selectively saturate or desaturate areas within an image.
Settings
The following settings can be adjusted using vertical tool sliders:
Opacity/Accumulation toggle—how see-through the brush is or the extent of deviation in the opacity or visibility of the stroke as it is painted, respectively. Tap to toggle the setting, then slide up or down to set the value.
Flow/Hardness toggle—how fast the brush effect is applied (1% is very slow, 100% is immediate) or how hard edged the brush is, respectively.
Width—controls the width of the stroke using a vertical slider next to the tool's location. Slide up or down to set the width.
The following settings can be adjusted from the context toolbar:
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 color intensity of all pixels; the latter adjusts the intensity of subtle colored pixels, while minimizing clipping of highly saturated colored pixels.
Stabilizer—choose from the following options:
Rope stabilizer—drag the stroke end by a 'rope' that smooths the stroke but lets you introduce sharp corners at increasing Length (radius) values by redirecting the slackened rope.
Window stabilizer—smooths the stroke by averaging the stroke's position over a Window whose size is configurable.