Editing and Saving an Image Using Mac OS X Preview

Not everybody has access to a professional image editing software, such as Adobe Photoshop. However, you can still perform basic image editing tasks (cropping, rotating, re-sizing, colour correction, adding text, saving to a new file format) with Preview, which is installed on every Apple Mac computer.

Opening an image with Preview

Preview is the default image viewing/editing application on new Macs. If you haven’t installed an image editor like Photoshop, double clicking the file will open the image in Preview. Alternatively, if you right click the file and choose 'Open with’, you will find Preview in the list of applications shown.

Cropping an image in Preview

To crop an image you need to select the 'Edit’ button (No.1) at the top of the window. This reveals a new tool bar with a variety of drawing tools and selection tools. When you select 'Edit’ the 'Rectangular Selection’ tool (No.2) is selected automatically by default. Use this tool to draw a rectangle (No.3) over the area of the image you wish to retain. Then select the 'Crop to Selection’ tool (No.4). Your image should now be cropped to area of your rectangle.

Re-sizing an image in Preview

To re-size an image you need to select the 'Tools’ menu at the top of the screen, then choose 'Adjust Size…’ from the menu. This will present you with a dialogue box and a series of options. The first of these, 'Fit into:’ (No.1) allows you to select from a list of pre-defined sizes – these correspond to various computer screen sizes. Your image will not end up the same size as one of the options unless you uncheck 'Scale proportionally’ (No.5); however this would result in a distorted image. It’s more likely that you will require a size not in this list, so choose 'Custom’. Next you should enter the size you wish the image to be (No.2). If you are using the image online you must work in pixels, if you intend to print it use cm or mm (No.3). Next set the 'Resolution’ (No.4), for use on a screen this should be 72 pixels/inch. For print you will want a higher resolution of 150 or 300 pixels/inch; N.B. You can only adjust the 'Resolution’ downwards without making the image smaller or making it look worse. Finally, always leave the 'Scale proportionally’ and 'Resample image’ options (No.5) checked. If you adjust the size of an image disproportionally you will end up with an image that is stretched or squashed, leaving people looking strange and text illegible. The panel below these options (No.6) provides information about the effect on the size of your image (as a percentage) and its file size.

Advanced image editing in Preview

Preview allows you to perform more advanced image editing tasks, such as drawing rectangles, ellipses and lines, adding text, making irregularly shaped selections and adjusting the colour of the image. These tutorials will show you how to accomplish these tasks:

Mac Basics: Preview app views and edits images and PDFs

Preview: OS X’s Secret Weapon Image Editor

Saving an image in Preview

By default Preview will save the image in it’s original format, simply choose 'Save’ from the 'File’ menu. It is often sensible to keep an original copy of the image you are editing; you may wish to re-use it later for a different purpose and require an un-edited version. To save the image as different file, choose 'Duplicate’ from the 'File’ menu, assign the file a new name and choose a location to save the file to. Occasionally, it will be necessary to save the image in a different file format. Photos should always be saved as JPEGs, graphic images – like clip art – should be saved as PNGs. If you wish to use transparency in your image you will have to save the file as a PNG. To save the image in a different file format choose 'Export…’ from the 'File’ menu. Then choose the appropriate file format from the 'Format’ drop-down menu. Set the file name, choose a location and select 'Save’.