Removing the background from an image is a common task when creating presentations, designing logos, or making memes. Traditionally, you would need to open a heavy, expensive application like Adobe Photoshop to carefully erase the background pixels. However, if you are using a Mac, you can instantly remove solid backgrounds and make them perfectly transparent using a hidden tool built directly into the native macOS Preview application.
How to Use the Instant Alpha Tool
The “Instant Alpha” tool works best on images that have a relatively solid, uniform background color (like a person standing in front of a white wall or a blue sky).
- Double-click your image file to open it in the default macOS Preview app.
- Look at the toolbar at the very top of the window and click the Markup Toolbar icon. (It looks like a small pen tip enclosed in a circle, located just to the left of the search bar).
- A second toolbar will appear directly below the first one.
- Click the Instant Alpha icon. (It looks like a magic wand).
- Move your mouse pointer over the solid background color you want to remove.
- Click and hold your mouse button, and slowly drag your cursor slightly outward.
As you drag, you will see a red overlay expanding across the background. This red overlay represents the pixels that are about to be deleted. The further you drag, the more aggressively the tool will select similar colors.
- Once the red overlay perfectly covers the background (without bleeding onto the main subject of your image), release your mouse button. The background will now be outlined with a moving dashed line (a “marching ants” selection).
- Press the Delete key on your keyboard.
Converting File Formats for Transparency
If your original image was a JPEG (.jpg), macOS will display a warning dialog box when you press the Delete key. It will state: “Convert this document to PNG?”
The standard JPEG file format is physically incapable of supporting transparency. If you delete a background in a JPEG, it will simply turn solid white. The PNG file format, however, fully supports an “alpha channel” (transparent pixels).
Click the Convert button on the warning dialog. Preview will automatically convert the file to a PNG, delete the selected background, and replace it with a checkered pattern (which is the universal symbol for a transparent background).
You can now drag and drop this new PNG file directly into a Keynote presentation or a Word document, and whatever is behind the image will show through perfectly.