Great article from CNet
One of the unsung heroes of Apple’s Mac OS X is the simple, yet incredibly powerful, Preview application. Using Preview, you can easily adjust your photos and get them ready for print, projects, and sharing. And best of all, it comes free on every Mac, bundled with OS X.
Many tips floating around the Internet will suggest using Adobe’s Photoshop or Photoshop Elements to accomplish tasks like resizing and adjusting image resolution. Though these applications are great solutions, they can also be costly and somewhat complicated for new users. Photoshop can run as high as $199 for the latest version, and Elements still costs about $69.
Using Preview to resize an image:
- Select the image you wish to resize. Preview handles nearly all popular image formats including JPEG, TIFF, PNG, and GIF. If the image you want to open is associated with another program (like Photoshop), right-click the image file and mouse over “Open With” and choose Preview from the list.
- From the Preview menu bar select Tools > Adjust Size.
- In the size adjustment box that appears, you will notice you have several options.
- To adjust the dimensions of your image, you can set a custom height or width, or constrain your image to fit into common sizes. Keep in mind that you will want to keep your image proportions locked so stretching does not occur.
- You can also adjust the resolution (pixels per inch) that your photo contains. Adding pixels does not necessarily mean you will have a higher-resolution photograph, however, and some distortion can occur when resampling.
- For images that will only be seen on a screen, make the resolution 72 pixels/inch. If you need to print at a low fidelity or your image contains a lot of text, set the resolution to 150 or 300 pixels/inch. Also keep in mind that higher-resolution images are bigger files.
Preview is also a great tool for doing all kinds of other simple adjustments on images. If you need to take out a background on an image, you can use Preview’s Instant Alpha feature to quickly and easily complete the task. The Instant Alpha tool is located in Preview’s tool bar, under the Select menu.
Once you have the tool selected, click on part of the background you wish to delete and begin dragging. The red overlay that appears represents the area that can be deleted. Drag until the space is covered and let go. Press delete on your keyboard and the area will be removed.
In order to keep the image with the background deleted, you must save it as a PNG or GIF file with the alpha check box selected.
Now you know how to quickly resize a photograph and create images with alpha backgrounds. But, what if the color on your image is off slightly? Well, Preview can fix that, too.
From the Preview menu bar, select Tools > Adjust Color. You may recognize the semitransparent HUD that appears from programs like iPhoto or Pages. The color adjustment tool allows you to tinker with your image’s levels, the exposure and contrast, saturation, temperature, and tint. You can also add a sepia tone or extra sharpness to your image.
Of course Preview only offers the very basic features for adjusting colors and resizing images. For more-advanced photo-editing capabilities, check out the editing functions in iPhoto, which also comes free on every new Mac.