Select “PNG” from the pulldown menu, and check the box next to “Alpha” to insure the image maintains it’s transparency.PNG files are much higher quality than GIF, and for most uses you’ll want to use a transparent PNG, but we’ll cover both how to create and save as either transparent GIF or PNG anyway. Exporting the Image as a Transparent PNG or GIF

Instead, you can save the newly transparent image as a copy by using “Export” or “Save As”.

If the original file was a PNG or GIF and you are satisfied you can just save as usual, but in a lot of cases you may not want to overwrite the original file. To get the finer details transparent it can help to zoom in and out of the image using Command+Plus and Command+Minus keys. Repeat as necessary for other parts of the image you want to become transparent.Hit the Delete key, or go to the Edit menu and select “Cut” to remove everything that was highlighted red with the Alpha tool (note: if the original image was a format that does not support transparency, you will be asked to convert the document, choose “Convert” to proceed” as expected.

Click and hold on the part of the image you want to turn transparent, and while still holding move the cursor up or down to either select more or less of the image to turn transparent – anything that is red is what will become transparent.Select the “Instant Alpha” tool, which looks like a magic wand in the Editing Tools menu bar (in earlier Preview versions it is contained under the Selection pulldown menu if the image is smaller than certain widths).For earlier Mac OS X Preview versions: Click the little pen icon in the toolbar to reveal the image editing tools.Click the Toolbox icon in the toolbar of Preview app to reveal the image editing tools.You can turn any image transparent with Preview, though you’ll find the resulting image must be saved as an image format that supports transparency. How to Make a Transparent Image on Mac with Preview

Mac os image editor