Absolute Beginner's Guide to Digital Photography

CHAPTER 12 THE IMPORTANCE OF RESOLUTION 187

technique is essentially JPEG technology in reverse. JPEG compression performs a

series of steps to compress an image: initial input, discrete cosine transform, quanti-

zation, and encoding.

FIGURE 12.6
Interpolation
options in
Photoshop.

Cameras, scanners, and image editors provide interpolation technology to increase

the resolution of an image. For example, Photoshop includes several algorithms that

enable you to increase the resolution or physical size of an image. To access these

options (listed here), choose Image, Image Size:

■ Nearest neighbor. Nearest neighbor interpolation is a simple interpolation

method. Each interpolated pixel is assigned the value of the nearest pixel of

the input image. If more than one pixel has the same distance to the pixel to

be interpolated, one of these is chosen. The drawback to this method is the

poor quality of the interpolated image.

■ Bilinear. Uses four adjacent pixels to calculate the interpolated pixel value.

Bilinear interpolation is a relatively simple interpolation method. However,

image quality is better than if you use nearest neighbor interpolation.

■ Cubic. Cubic convolution uses adjacent pixels to determine the value of the

interpolated pixel. The number of adjacent pixels the cubic algorithm uses is

not fixed. Instead, the algorithm approximates and optimizes the sine/cosine

function.

Cubic convolution provides the highest-quality interpolated image, but requires the

most processing power (and time). For image processing, the bilinear interpolation is

a fine compromise between quality and time. Avoid the nearest neighbor interpola-

tion method unless you’re in a hurry.