You can Copy these selected pixels, or choose Invert Selection from the Edit menu then hit Delete so you get a file that just contains the thing you selected. Once you're done, release the mouse button and if the contrast is reasonable Preview will snap to the outline. Pick it, then draw carefully around the outline of the object you want to isolate. The newer feature is called Smart Lasso, and you access it from the selection drop-down at the left of the tools toolbar in Preview. It’s likely you won't get all the background on the first go, and there's no way to add to a selection like in Photoshop, but all this means is that you do it in stages select a bit, hit Delete, select the next bit, Delete, and so on. Click and drag on the background, keeping an eye on the edge of the thing you're trying to cut out. Then, if you also want a 'set to Auto color' keystroke, select the Color: command in the Format list. Open your image in Preview, and click the toolbox icon top right then the magic wand tool. 1 I dont think there is a standard key, but you can assign one via Tools->Customize keyboard., select Format in the left column, locate and select FontColor in the right column, then assign a key (make sure you actually click the Assign button. The first is Instant Alpha, used for removing backgrounds handy when you've been given a flat JPEG of a logo on white, say, but need to put it on a coloured background.

In fact, its two tools can actually be surprisingly effective on not-too-challenging files. Of course Photoshop and its competitors are the daddy when it comes to isolating portions of images, but if you don't have one of these, or if you're just doing a quick-and-dirty job for a mock-up, say, then reach for Preview.

Preview can be surprisingly effective on not-too-challenging files

Edit color in preview mac os x