Before we look at Affinity Photo, here’s how to install extensions in El Capitan (after you’ve purchased and downloaded them): Open System Preferences on your Mac and click Extensions. Click Photos in the left sidebar. Click the check boxes to enable the extensions you want to use in Photos.

To use an extension in Photos, double-click a photo in your library to open it in single view, then click Edit. Click Extensions. You can find it at the bottom of the Photos editing tools on the right-hand side of the window.

Okay, back to Affinity Photo. The software isn’t inexpensive, but it offers Photoshop-level features for 50 bucks — and six extensions that are accessible from within Photos.

One of the limitations of the OS X app is that its adjustment tools apply to an entire image, not areas you select. The Affinity Retouch extension rectifies that. It also offers Dodge, Burn, Blur, and Sharpen tools. It packs a Healing tool and an Inpainting tool, which lets you remove objects from a scene and “intelligently” replace them.

The Affinity Haze Removal tool removes haze and mist from backgrounds. Affinity Liquify lets you, well, liquify images by warping and distorting them. You can “smear” things around.

Affinity Monochrome allows you to change your pics to black-and-white. Affinity Develop allows you to tweak a variety of aspects of a photograph, including exposure, contrast, clarify, saturation, vibrance, temperature, tint, shadows, highlights, color, and luminosity.