When you need to remove an unwanted background from a photograph or extract a specific object—like a person or a product—you might think you need a complex photo editing suite like Adobe Photoshop. However, the native Preview application included with macOS contains a highly advanced, AI-driven selection tool called the “Smart Lasso.” This tool allows you to trace the rough outline of a complex object, and the software will automatically snap the selection perfectly to the object’s edges, allowing you to crop it out cleanly.
How to Activate the Smart Lasso
The Smart Lasso is hidden by default inside Preview’s markup toolbar.
- Double-click your image (JPEG, PNG, HEIC) to open it in Preview.
- Click the Markup Toolbar icon in the top right corner of the window (it looks like a small pencil tip inside a circle).
- A new toolbar will appear just below the main menu. On the far left side of this new toolbar, click the Selection Tools icon (it usually looks like a dotted rectangle).
- From the drop-down menu that appears, select Smart Lasso.
How to Trace and Extract an Object
Unlike a traditional, manual lasso tool where you must trace perfectly with a shaky mouse, the Smart Lasso requires very little precision.
- Ensure the Smart Lasso is active. Your mouse cursor will change to a crosshair.
- Click and hold your mouse button down. Trace a rough line around the outer edge of the object you want to keep. You do not need to be perfect; just ensure the thick, red tracing line you are drawing overlaps the boundary between the object and the background.
- Continue tracing until you connect the line back to your starting point, forming a complete loop.
- Release your mouse button.
The moment you release the mouse, the thick red line will disappear and be replaced by “marching ants” (a moving dotted line). Preview’s AI will analyze the contrasting pixels and automatically shrink-wrap the selection line so it perfectly hugs the contours of your object.
How to Finalize the Crop
Now that your object is perfectly selected, you must extract it.
- Look at the top menu bar (next to the Apple logo) and click Edit.
- Select Invert Selection. The marching ants will move to select everything except your object (the entire background).
- Press the Delete key on your keyboard.
- If your image was originally a JPEG, Preview will warn you that it must convert the image to a PNG to support a transparent background. Click Convert.
The messy background will vanish instantly, leaving your perfectly extracted object sitting on a clean, transparent canvas.