Epson 4870 - Perfection Pro Manual

This technical brief provides detailed information on the Image Quality, Performance, and Flexibility of Epson

Scanners.

Image Quality—Factors affecting image quality

When comparing scanners, hardware resolution and color pixel depth are two features often used to gauge

image quality. These two features are important, but there are a number of factors that determine image

quality in a scanner, such as the following: (Many of these elements will be discussed in detail in upcoming

sections of this document.)

Precision stepper motor

for high quality sub-scan

Type of lamp system used

The Epson Expression

lence with respect to image quality, speed, usability, versatility, and durability. These scanners include the

highest quality components.

The Epson Perfection

users, and are designed with the highest quality components in their price class.

Image Quality—Resolution

A scanner's resolution determines the amount of data that is read by the scanner. As resolution increases, so

does the ﬁle size. Resolution is measured in a variety of ways.

1. Optical resolution: This is the actual number of pixels read by the CCD (Charge Coupled Device), which

measures the intensity of the light that is reﬂected from the image to be scanned, and converts it to an

analog voltage. If a scanner has a resolution of 600 x 2400 dpi, its optical resolution is 600 dpi, which

means that it can resolve 600 bits of data per inch.

2. Hardware resolution: Using a precision stepper motor to double-step or

quadruple-step the carriage, the scanner's sub-scanner resolution can be

increased. For example, a scanner can have an optical resolution of 1200

dpi, but a hardware resolution of 1200 x 2400 dpi (because it double-steps

the carriage to increase the vertical resolution).

Scanner Technical Brief—Page 1

resolution

Dynamic range control

Optic system

and GT series scanners are Epson's professional series scanners designed for excel-

series scanners are designed for home and entry-level corporate and graphics arts

Optical resolution and

color bit depth

Quality of the Analog to Digital con-

verter (ADC); Epson scanners have

optimum performance for minimal

noise and tight color registration.

Type of focus method

Color vs. monochrome CCD

1200 dpi

6/07