Resampling Images in Photoshop

Resampling means you are changing the pixel dimensions of an image. When you downsample (or resample down), you are eliminating pixels and therefore deleting information and detail from your image. When you resample up (or upsampling), you are adding pixels. Photoshop adds these pixels by using interpolation. Interpolation means Photoshop analyzes the colors of the original pixels and “manufactures” new ones, which are then added to the existing ones.

You can specify the interpolation method in the Image Size dialog box. The default that appears in the dialog box is based on the interpolation method you specified in your General Preferences dialog box. Here are your five choices:

-->Nearest Neighbor: This method is fast and provides for the smallest file size, but it is less precise and therefore of the lowest quality. This method works by copying the color of the nearest pixel. It can result in jagged edges, so use it only for images with non-anti-aliased edges (hard edges).

-->Bilinear: Considered a medium-quality method, it works by averaging the color of the pixel above, below, and to the right and left of each pixel.

-->Bicubic: This method is the slowest but most precise. It averages the color of the pixel above and below and the two on the right and left of each pixel. It provides a smoother transition between pixels but also increases the contrast between pixels to reduce blurriness.

-->Bicubic Smoother: Like Bicubic, but provides an even smoother transition between pixels and therefore increases the amount of blurriness. A good method to use when upsampling images. Can slightly affect the sharpness of the image.

-->Bicubic Sharper: Also similar to Bicubic, but applies less anti-aliasing and therefore less blurriness as well. This method applies just a little softening to pixel edges. This is a good method when downsampling an image. Bicubic Smoother and Bicubic Sharper are new to Photoshop CS.

If you really must resample, I recommend leaving the method set to Bicubic Smoother. Notice I said if you really must. Here are some reasons why you might choose to add or delete pixels:

-->You no longer have access to the original artwork, which you could rescan at the proper resolution and size.
-->You no longer have access to the original high-resolution version of the file.
-->You absolutely cannot substitute the low-resolution image with another of higher resolution.

Resampling isn’t a recommended activity, especially when it pertains to upsampling. I mean as smart as Photoshop is, having to manufacture pixels out of the blue is not an exact science. Your image tends to lose detail and sharpness and get blurry and mushy. The bottom line is your resampled image never looks as good as the original. Downsampling isn’t as scary. Even though you are deleting pixels, and therefore detail, the degradation is virtually undetectable with the eye.