In a pro camera app, what visual guide tells you exactly which parts of your picture are perfectly sharp when you are focusing by hand?

The visual guide in a pro camera app that tells you exactly which parts of your picture are perfectly sharp when focusing by hand is called Focus Peaking. This feature works by analyzing the live camera feed for areas of high contrast, which are direct indicators of sharpness. Contrast, in this context, refers to the difference in brightness or color between adjacent pixels, and sharp edges naturally exhibit high contrast. As you manually adjust the focus, the app overlays brightly colored lines or patterns, typically red, green, or blue (and often customizable), directly onto the edges of objects in the scene that are currently in sharp focus. For example, if you are focusing on a person’s eyes, as the eyes come into perfect focus, these colored highlights will appear on their edges, showing precisely that those specific parts are critically sharp. As you continue to adjust the focus, these highlights will shift to different parts of the scene, reflecting what is now in focus. When your desired subject is fully illuminated by these peaking highlights, it indicates that the subject is perfectly sharp, allowing for precise manual focus without relying solely on visual judgment of a small screen.