When you take a screenshot on your Mac or download an image from the internet, the file often contains massive amounts of useless background data—such as messy desktop icons or irrelevant website borders. You do not need to download massive, expensive suites like Adobe Photoshop to surgically isolate the subject of an image. The native macOS Preview application contains a highly advanced graphic isolation engine that allows you to instantly crop images and mathematically remove solid backgrounds.
Executing a Basic Crop
If you simply want to slice off the edges of an image to change its aspect ratio or remove a messy border, the basic crop tool is highly efficient.
- Double-click your image to open it in Preview.
- Click and drag your mouse cursor directly across the image. The engine will instantly draw a mathematically precise, dashed rectangular selection box.
- Look closely at the edges of the box; you will see small blue dots (handles). Click and drag these handles to perfectly align the box around the exact subject you want to keep.
- Once the box is perfect, look at the absolute top of the screen and press the keyboard shortcut Command + K (or click Tools > Crop).
The Preview engine instantly executes a destructive surgical strike. It violently deletes every single pixel that exists outside of your designated box, instantly shrinking the image down to your exact specifications.
Using the Instant Alpha Engine (Removing Backgrounds)
If you have a logo on a solid white background and you need to make that white background completely transparent (so you can paste the logo over a dark presentation slide), the standard square crop tool is useless. You must use Preview’s hidden “Instant Alpha” engine.
- Open the image in Preview.
- Click the Show Markup Toolbar button (the pencil tip icon) at the top of the window.
- Look for the Instant Alpha icon on the far left side of the new toolbar (it looks like a magic wand). Click it.
- Move your mouse cursor directly over the solid white background you want to destroy.
- Click and hold the mouse button, and slowly drag your mouse slightly.
The exact millisecond you drag, the neural engine mathematically analyzes the pixel color you clicked on (white) and instantly highlights every single adjacent white pixel in the entire image with a bright red overlay.
Once the entire white background is highlighted in red, release the mouse button. The red overlay turns into a complex selection border. Press the Delete key on your keyboard.
The Preview engine violently rips the background pixels out of the image architecture, replacing them with a mathematically perfect transparent void (represented by a gray-and-white checkerboard pattern). The logo is now perfectly isolated and ready for professional use.