How to Resample Images in Photoshop CS6
When using Photoshop Creative Suite 6, there may come a time when you will need to resample your image. Although this is usually not the best option, sometimes, you are left with no choice.
Resampling means you’re changing the pixel dimensions of an image. When you downsample, you’re eliminating pixels and therefore deleting information and detail from your image. When you upsample, you’re 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 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 six choices:
Nearest Neighbor: This method is fast and provides for the smallest file size, but it’s less precise and therefore the lowest quality.
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.
Bicubic Smoother: A good method to use when you must upsample images, but it can slightly affect the sharpness of the image.
Bicubic Sharper: This is a good method when downsampling an image.
Bicubic Automatic: This new method detects whether you are upsampling or downsampling and chooses the best algorithm, either Bicubic Smoother or Bicubic Sharper. Unless you have a good reason not to do so, leave it on this default setting.
If you really must resample, especially when upsampling, you should leave the method set to Bicubic Automatic or Bicubic Smoother. 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 otherwise rescan at the proper resolution and size.
You no longer have access to the original high-resolution version of the file.
You want to print a photo at a specific dimension, but the image’s current resolution won’t allow for decent-quality output.
You absolutely can’t replace the low-resolution image with another of higher resolution.
Here are some tips and tricks to keep in mind when you’re messing around with image size and resolution settings:
Use the Smart Sharpen or Unsharp Mask filter after you resample. Choose Filter→Sharpen→Smart Sharpen or Unsharp Mask. These filters heighten the contrast between pixels to give the illusion of sharpening or forcing the image more into focus.
Don’t change your settings — just print. If you want to leave the size and resolution settings untouched, but you need to print your image at a different size, use the Scaled Print Size option in the Print dialog box.
Start out with the proper dimensions. Try to enter the proper dimensions and resolution when creating a new document. Be sure you scan images at a high-enough resolution, too. Finally, if you’re shooting a digital photo, ensure that you are using the highest megapixel setting your camera is capable of capturing.
Don’t use a higher resolution than you need. All you do is create an unnecessarily huge file with a slower print time. In some cases, it may actually make your printout look darker and muddier.
Resampling isn’t a recommended activity, especially upsampling. As smart as Photoshop is, having to manufacture pixels isn’t an exact science. Your image tends to lose detail and sharpness. Your resampled image never looks as good as the original and may be blurry. Downsampling isn’t as scary. You’re deleting pixels, and therefore detail, but the degradation is virtually undetectable to the eye.