’Save Layer as Transparent PNG’ command can be saved the current layer as transparent PNG. You also can use this function if you want to save only the line drawing.
Prepare an illustration you would like to save a layer as a transparent PNG.
Open ①the Layer window, select ②the layer with the line drawing, tap ③’...’ button, select ④“Save Layer as Transparent PNG”.
The line drawing is saved with a transparent background in your camera roll.