Epson 1000 ICS, CX3200, CX5200, Stylus 2000, Stylus 2500 Technical Brief
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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.)
Optical resolution and
Precision stepper motor
for high quality sub-scan
resolution
Dynamic range control
Type of lamp system used
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
The Epson Expression
Optic system
®
and GT series scanners are Epson’s professional series scanners designed for excellence with respect to image quality, speed, usability, versatility, and durability. These scanners include the
highest quality components.
The Epson Perfection® series scanners are designed for home and entry-level corporate and graphics arts
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).
1200 dpi
2400 dpi
Scanner Technical Brief—Page 1 6/07
Image Quality—Resolution (cont.)
3. Interpolated resolution: Interpolation is a method to increase the resolution of an image. It uses a
complex algorithm to “add” pixels to an image based on the mathematical probability of surrounding
pixels.
For example, if a scanner has a hardware resolution of 1200 x 2400 dpi, and a maximum resolution of
9600 x 9600 dpi, the scanning software uses interpolation to create scanned images with resolutions
greater than the hardware resolution.
4. Benefits of higher optical resolution: Higher resolution allows you to scan the following types of im
ages without using interpolation. Using actual image data instead of interpolated data results in more
accurate images.
Line Art
When scanning black and white line art, image pixels translate exactly
to the printed dots. Therefore, high resolution is required to capture
and print the sharp lines and edges of an image.
2 x 2.5 inch
image scanned
at 1200 dpi
If enlarged to 8 x
10 inches, effective
resolution: 300 dpi
Enlarging a small original
In order to capture enough detail to enlarge an image, you must
increase the scanned resolution in proportion to the increase in image
size. If you don’t, then you will have to interpolate image data to
maintain the same resolution in the larger image.
-
Precise pixel editing
Many graphic artists scan images at high resolutions for precise pixel
editing. It is always better to capture the image data when the image
is being scanned and use true image data than to use interpolation if
more data is needed later.
Image Quality—Pixel depth
Pixel depth refers to the number of bits of data captured for each picture element (pixel). Each pixel can
have two states (On or Off); therefore the number of colors or gray scales that a scanner can recognize is
computed by taking the pizel depth as an exponent of two. The following charts lists the number of colors
recognized for each different scan mode.
Scan mode Number of colors recognized
Bi-level (1 bit per pixel)
8-bit gray scale
10-bit gray scale
8-bit color (indexed color)
24-bit RGB (8 bits per pixel, per color)
36-bit RGB (12 bits per pixel, per color
48-bit RGB (16 bits per pixel, per color)
21 = 2 colors (black and white)
28 = 256 shades of gray
210 = 1,024 shades of gray
28 = 256 colors
224 = 16.7 millions colors
236 = Over 68 billion colors
248 = Over 250 trillion colors
Scanner Technical Brief—Page 2 6/07
Image Quality—Pixel depth (cont.)
Photoshop
With a 48-bit image fi le, you always have
All Epson scanners have a 42-bit or 48-bit color depth. but some of the models support 24-bit external color
depth, which is the data that is sent from the scanner to the computer. Here are the differences between
output color depth:
48-bit capture
48-bit capture
24-bit transfer
A greater color bit depth generally results in more accurate color reproduction, smoother gradations with
fewer sudden shifts in color, and detailed shadows and highlights.
48-bit transfer
Image Quality—Epson ColorTrue® Imaging System
Epson scanners use the Epson ColorTrue II Imaging System which is made up of three main elements
(hardware, optics, and processing) and result in superior image quality with fast processing speeds.
Precise scan carriage
Simultaneous RGB scanning
High resolution CCD
Custom glass lenses
Pixel optimization
Custom ASIC
Scanner Technical Brief—Page 3 6/07
Image Quality—Epson ColorTrue® Imaging System (cont.)
Through a combination of these hardware, optics, and processing features, the Epson ColorTrue Imaging
System and Epson ColorTrue II Imaging System deliver scanned images with:
Smooth gradations
Smooth edges and
minimal color fringing
Greater detail in shadows
Accurate colors
Greater detail in
highlights
Sharp image quality
without distortion
1. Hardware components: Epson scanners use a precise scan carriage with better motors to achieve subscan
resolutions that are double or quadruple the scanner’s optical resolution. Additionally, Epson scanners
capture Red, Green, and Blue simultaneously, versus other scanners that use one-pass scanning but
alternate Red, Green, and Blue lights for each line of a scan. Epson advantages are:
Better color registration
Faster scanning speeds
Higher quality sub-scan resolutions
Epson Method
(1/2 or 1/4 step carriage movement)
Simultaneous RGB Capture
One pass
Single-Pass Alternate RGB Method
(1/2 step carriage movement)
Red Capture
Green Capture
Blue Capture
One pass
2. Optics: Epson scanners use custom lenses that are designed specifically to work with Epson technology
and the scanner’s CCD. These lenses feature:
Larger “sweet spot” and precision lenses for reduced distortion
Accurately aligned lens elements to control sharpness
Glass lenses (versus plastic lenses used by many competitors)
which offer better reflective qualities, providing greater image
quality.
Better image quality than competitive off-the-shelf lenses
because Epson scanners feature custom-made lenses that
match the CCD.
Scanner Technical Brief—Page 4 6/07
Small “sweet spot”
can allow edge
distortion
Larger “sweet
spot” minimizes
distortion
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