The Undo Brush Tool can be used to selectively undo modifications to individual pixels, restoring them to a previously targeted history state.
After setting a brush source, you can blend the image's current state back to a previous state, like painting backwards in time.
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.
Blend Mode—changes how the applied pixels interact with existing pixels on a layer. Select from the pop-up menu.
Blend—when enabled (default), pixels which do not overlap those in the selected history state are unaffected, allowing the blending of the current document state with the selected, previous state. If this option is off, all pixels are returned to the previous state when painted.
Protect Alpha—when enabled, you are not able to paint on the current layer's transparent regions.
Stabilizer—enables stroke stabilization using either a Rope stabilizer or Window stabilizer mode.
For rope mode—drag the stroke end by a 'rope' to smooth the stroke but introduce sharp corners at increasing rope Length (radius) values by redirecting the slackened rope. Set the value by toggling the Length vertical slider icon.
For window mode—smooths the stroke by averaging sampled input positions within a Window whose size is configurable. Set the value by toggling the Width vertical slider icon.
To paint from history:
Display the History panel.
Tap the Undo Brush Source camera icon on the history state you want to paint back to.