When you are architecting a digital presentation on a macOS workstation, raw images often contain massive amounts of useless peripheral data (unwanted backgrounds, excessive borders). If you import an uncropped image into a layout, the dead pixels ruin the geometric symmetry of the document. To force the macOS neural engine to mathematically sever the unwanted edges and permanently redefine the image boundaries, you must use the native Crop tool within the Preview application.
Summoning the Selection Matrix
The Crop tool is a highly destructive geometric engine. It completely vaporizes any pixel that falls outside of your designated selection matrix.
- Locate your image file in Finder and double-click to open it in Preview.
- Look at the absolute top-right of the window and click the Show Markup Toolbar icon (it visually resembles a small marker pen).
- A secondary toolbar will instantly deploy. On the far left of this new toolbar, click the Selection Tool icon (it defaults to a dotted rectangle).
Executing the Geometric Obliteration
You must now mathematically define the exact zone of the image you wish to keep.
- Click and hold your left mouse button on the image, then drag diagonally to draw a pulsing selection box (marching ants) over the core subject.
- Release the mouse button. The exact dimensions of your selection are now locked. You can click and drag the blue dots on the corners of the box to fine-tune the boundaries down to the exact pixel.
- Once the selection matrix is perfect, press the Cmd + K keyboard shortcut, or click the Crop icon (which has just materialized on the Markup Toolbar).
The exact millisecond you execute the command, the macOS engine violently severs all pixels outside the selection box. The image instantly resizes to the new, highly optimized dimensions. Press Cmd + S to permanently commit the cropped architecture to the hard drive.