What are some alternatives?
When comparing Adobe Photoshop and Pixelmator, you can also consider the following products
GIMP - GIMP is a multiplatform photo manipulation tool.
Affinity Photo - Affinity is the imaging and design suite for creative professionals exclusively for Mac.
Sketch - Professional digital design for Mac.
Krita - Krita is a professional FREE and open source painting program. It is made by artists that want to seaffordable art tools for everyone. Concept art. texture and matte painters, illustrations and comics.
Pixlr - Pixlr® makes it easy to transform everyday images into stunning works of art.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.