Start with high-confidence image processing books, then narrow by subgenre or adjacent topics.
Photoshop Elements 13 for Dummies
Barbara Obermeier, Ted Padova
Photoshop Elements 14 for Dummies
Adobe Photoshop CC for Dummies
Peter Bauer
Photoshop CS5: the Missing Manual
Lesa Snider
Principles of Digital Image Processing
Wilhelm Burger, Mark J. Burge
