What technical benefit does focus peaking provide in a third-party camera app that enables critical sharpness in near-dark conditions where autofocus typically fails?

Autofocus (AF) systems, particularly contrast-detection AF common in many cameras, determine focus by analyzing the differences in light intensity, or contrast, across the image sensor. In near-dark conditions, there is insufficient light for the sensor to capture strong contrast information. The resulting weak and noisy signal makes it difficult for the AF algorithm to accurately identify sharp edges, causing it to "hunt" (move the lens back and forth trying to find focus) or fail to lock focus. Focus peaking provides a technical solution by visually highlighting areas of the live view feed that are in sharp focus, enabling precise manual focusing. The third-party camera app continuously analyzes the real-time video stream from the camera's sensor. It applies a digital processing algorithm, such as a high-pass filter or an edge detection algorithm, to identify rapid changes in pixel luminance (brightness) and chrominance (color). These rapid changes signify sharp edges, which are characteristic of in-focus areas. When the algorithm detects these sharp transitions, it overlays a brightly colored highlight directly onto these edges on the camera's display. For example, a red outline might appear on the subject's eye when it is critically in focus. This visual feedback is independent of the autofocus system's operation. Even if the overall scene is dim, the focus peaking algorithm is specifically designed to computationally detect and amplify the subtle high-frequency details that still exist in the image data, which the human eye or the autofocus system struggles to discern naturally in low light. The critical technical benefit is that focus peaking bypasses the light-gathering limitations that cripple autofocus in low light. It transforms the challenging task of focusing in near-darkness into a clear, visual process. By manually adjusting the lens until the desired subject shows the most intense and widespread colored highlights, the user can achieve critical sharpness based on directly observed digital edge detection, ensuring precise focus where the camera's automatic systems would otherwise fail due to lack of sufficient light for reliable contrast measurement.