Absolute Beginner's Guide to Digital Photography

■ dpi. Dots per inchis used by inkjet printers,

dye-sublimation printers, and laser printers to

define their output resolution. For example,

some printers have 600 dpi output resolu-

tion; photo inkjet printers will have any-

where from 1440 dpi to 5760 dpi. This is not

the same as ppi. The two do not go hand-in-

hand.

■ lpi. Lines per inchis used by printers who

print magazines and newspapers. Their

printing equipment prints a specific number

of halftone dots per inch (called line screen,

or lines per inch). A newspaper is 85 lpi and

a glossy magazine is 130 lpi.

■ Samples per inch. This term is used with

scanners to represent the number of bits of

information that are created per inch when scanning. The scanner “samples”

an image as it runs along it with a bright light. The sampling rate, such as

72, 100, 300, or 600, is the number of samples the scanner grabs per inch

and then converts into pixels. Scanner sampling turns into ppi after the

image is scanned into image-editing software. As such, “samples per inch”

and ppi are interchangeable.

■ Megapixels. Digital cameras currently define resolution using the term

megapixels. A digital camera that takes pictures at VGA resolution (640× 480

pixels) is called a 0.3-megapixel camera. Cell phones use this resolution. A

high-end camera, such as a Nikon 6-megapixel camera, will generate an

image that contains 3000×2000 pixels. Quite a difference!

These terms are all used to describe resolution. Resolution is what you need to deter-
mine when working with images on a computer. The digital camera will record the
image at a set resolution. When you import it into an image editor, you can change
this resolution. What you decide to change it to depends on the output. For printing
on fine photo paper, you need one resolution; for a quick thumbnail on a Web site
or even an email, a smaller resolution is needed.

Here is a simple rule that will help you understand resolution:

ppi is used for input, and dpi is used for output.

CHAPTER 12 THE IMPORTANCE OF RESOLUTION 175

Some scanners use the

term dpito represent reso-

lution. Scanners “sample” an

image, so either term is essentially

correct. A sample turns into a

pixel; a sample can also be called

a dot.