This function allows you to draw Parallel Gradation. You can also use it to apply even gradation, or create striped patterns, by adjusting the contrast and number.
Prepare an illustration you want to add gradation to.
Open ① the Layer window, and add to the top ② a new layer.
Tap ②Color Burn from ①Blend Mode . Drag the slider of ③Opacity to adjust as you like.
Tap ②Filter from ①Tool Selection window .
Tap ①Parallel Gradation .
Drag the ①Sliders to adjust Wave Length and Angle and etc.
Tap the ① Knob twice to open the Color Picker. Drag the ②Slider to adjust the color.
When finished, return to the canvas with ①✓ button.
And you're finished.