March 26, 2007 HelpLine

Interpreting Interpolation
Q) When I’m resizing my images, I’m given several different options for interpolation. People tell me to use bicubic, but there are two sub-options. Which should I be using?

M. Stewart
Via the Internet

A) Anytime you resize your image using interpolation-whether increasing or decreasing image size-your software creates new pixels. Bicubic interpolation in image-editing software creates new pixels by doing mathematical calculations on the immediately surrounding 16 pixels. By using this method, the software makes a fairly accurate guess as to what the new pixel should look like. Unfortunately, there can be some sharpness issues raised by using this interpolation, so there are the two options you mention: Bicubic Sharper and Bicubic Smoother.

The general rule is that if you reduce the size of the image you should use Bicubic Sharper and if you increase the size of the image you should use Bicubic Smoother. To remember which is which, think about “sharpening a pencil down to a fine point.”

Whichever way you choose, you should examine the results at full size to see if you’ve chosen the best method. There may be times when it works better to use a regular bicubic interpolation and then sharpen manually.

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