It's often nice to be able to take the best part of a photo, for display on a particular device.

For example:

  • Desktop wallpapers / screensavers
  • Mobile phone backgrounds
  • Viewing photo albums on a PSP / iPod / iPhone etc
  • Sending an MMS picture message

Now you can just resize your image to the correct resolution for the screen - but there are often surplus parts to a photo that you'd rather not waste space on, especially for a small device like a mobile phone.

Take the photo below for example. This is a snap of my cousin's baby, and it looks great on a computer monitor - when you're sat right in front of it.  On a digital photo frame the baby would be harder to see though, as it would be viewed at a distance. The same applies if it were to be viewed on a mobile phone, where the low resolution would mean only a small number of pixels would be used to show the important part of the photo.  In this example then, I will crop the photo to remove the bottom and right edges, for display on a mobile phone with a screen resolution of 240x320 pixels.

When cropping, the important thing is to ensure that the new image is in the correct proportions to fit on the target display - in this case 3:4 aspect ratio for diaplay in "portrait" mode. (for normal computer monitors, 4:3 would be needed).

Now one way of doing this is to roughly select the area you need in Photoshop, and then resize the image so one dimension is correct, and then perform another crop. eg: I might resize the image I need to 320 pixels high and see that the new image is actually 250 pixels wide, meaning I'd have to shave another 10 pixels off to get the photo to fit my phone's screen.  This method works, but is obviously time consuming and prone to errors.

A much nicer way of doing it is to use Photoshop's Rectangular Marquee Tool, with the Fixed Aspect Ratio option selected. In the screenshot below, you see the settings I've used to crop the photo to 3:4 aspect ratio. Now, when I draw the rectangle on the photo, whatever I do it will always be constrained to the right dimensions.  For 4:3 I would just change the width to 4 and the height to 3.

Fixed Aspect crop example in Photoshop

 Once the image is cropped all that is needed to do is resize it to the correct size.

Written by Celerity Design, on July 31, 2008
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