Understanding interpolation

Interpolation is the process of increasing the resolution of an image (or a section of an image) when cropping to increase the number of pixels per inch. A

6-megapixel digital camera should be able to produce 8x10 prints without a problem, even if you have to do some cropping.

If you print large prints — say, 11x14, or 13x19 — your digital camera can produce more resolution without interpolation, and that's a better result. Larger prints require a larger amount of image information, however; for larger prints, the more megapixels, the better. Though you can get acceptable large prints from 5-megapixel cameras (or even some photos shot with a 3- or 4-megapixel camera), you're usually limited to prints no larger than 8x10 inches.

If you do a lot of cropping, and still maintain image sizes of 5x7 or 8x10, the image quality may noticeably decrease at that print size — unless you tell Photoshop to interpolate by indicating a higher resolution in the Crop tool's Option bar when you crop.

I'll often crop out small portions of a photograph — it's sort of like creating a photo from a photo — but indicating a higher resolution in the Option bar may degrade the quality somewhat, depending on how much of the image you're eliminating in your crop. Images from 7- or 8-megapixel cameras can still provide enough resolution to produce high-quality large prints even if you do some extreme cropping — as I've done in the example shown in Figure 12-5.

Original as 360ppi Extreme crop at 360ppi

Figure 12-5: Extreme cropping at the same ppi setting.

Original as 360ppi Extreme crop at 360ppi

Figure 12-5: Extreme cropping at the same ppi setting.

A great Photoshop plug-in to use to further interpolate images is Genuine Fractals. You can enlarge an image up to 700 percent without image degradation, a perfect solution for extreme cropping or when you want to enlarge your digital images to poster-size prints. For more information on Genuine Fractals, visit its Web site at www.ononesoftware.com.

When you choose a resample method, Photoshop actually assigns an interpolation method — which assigns color values to the new pixels that are created when you enlarge an image. Photoshop bases those color values on a sample of neighboring pixels (hence the term sampling). The resampling method you choose helps preserve the quality of the image when you size an image larger than its native (original) resolution.

Here's your range of resampling choices:

I Nearest Neighbor: Used for basic illustrations when quality isn't an issue. Not recommended for photos.

I Bilinear: Another method not recommended for use with photos, but still useful for some illustrations.

I Bicubic: The preferred method of resampling photos. This method uses the values of surrounding pixels to interpolate. Leave Bicubic as your default resampling method because it provides the highest quality interpolation method in Photoshop.

I Bicubic Smoother: This method (similar to the bicubic resampling method) increases the size of an image — with smoother results than with other resampling methods. May be good for some images and portraits.

I Bicubic Sharper: This resampling method is used for reducing the size of an image while enhancing sharpness.

Note: Because sharpening is a step that should come after resizing, the Bicubic Sharper option really isn't needed.

Understanding Adobe Photoshop Features You Will Use

Understanding Adobe Photoshop Features You Will Use

Adobe Photoshop can be a complex tool only because you can do so much with it, however for in this video series, we're going to keep it as simple as possible. In fact, in this video you'll see an overview of the few tools and Adobe Photoshop features we will use. When you see this video, you'll see how you can do so much with so few features, but you'll learn how to use them in depth in the future videos.

Get My Free Video

Post a comment