OIS uses a movable lens or sensor to physically counter hand shake, sharpening photos and videos. Critical for low-light photography and zoomed video.
OIS senses motion via gyroscope and shifts the lens (lens-OIS) or sensor (sensor-shift OIS) to compensate. Allows 2–4 stops slower shutter speeds (i.e., 1/15s instead of 1/120s) without blur.
EIS (Electronic Image Stabilization) is digital — crops the image and shifts frames to align. Effective for video but reduces resolution and adds processing artifacts.
Flagship phones typically combine OIS + EIS for hybrid stabilization. Sensor-shift OIS (iPhone 15 Pro Max, Pixel 9 Pro XL) generally beats lens-OIS by stabilizing the entire imaging plane.