Epson Perfection 640U Series Manuel - Page 6

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Image Quality—Dynamic Range

Dynamic range measures the difference between the lightest highlights and darkest shadows that a scanner

can perceive (on a scale of 3.0 to 4.0). The maximum density rating is referred to as Dmax.

A dynamic range measurement is important for

designers who scan transparent media (such as slides,

transparencies, and negatives) because the media

itself generally has a dynamic range of 3.2. Reﬂective

media, such as a photograph, generally does not have

a dynamic range greater than 2.0.

A high dynamic range results in scanned images



with superior detail in highlights and in shadows—

especially when scanning transparent media.

Image Quality—Focus Method

Epson scanners use a ﬁxed focus system, AutoFocus optics system, or a Dual-Focus mechanism.

1. Fixed Focus: With this type of focus system, the lens is set to record everything sharply from a ﬁxed

distance—from the lens to the glass scanning bed. The Epson Perfection and GT series scanners use a

ﬁxed focus optics system. The newest Epson scanners have a ﬁxed focal point just above the surface of the

glass for optimized ﬁlm scanning.

2. AutoFocus optics system: Epson highest-end graphic

arts scanners use an AutoFocus optics system that can

be used in AutoFocus mode or manual mode. This

system offers these beneﬁts:

The Epson manual/automatic focus optics system



gives you precised sharpness control, especially

when scanning three-dimensional objects and

transparencies.

With three-dimensional images, you can pick



your point of focus so that background items are

captured with sharp detail, as shown in the glove

and towel in the images to the right.

For super sharpness when scanning transparencies



or slides mounted in holders, you can set the focus

to compensate for the 2.5mm distance between the

glass and the slide.

3. Dual-Focus mechanism: One of the Epson Expression series scanners uses a

Dual-Focus mechanism. When using the scanner's custom ﬁlm holders to scan

transparent media, you can set the scanner's focal distance to compensate for the

2.5mm distance between the glass and the media. This method eliminates the

"Newton Ring" problem that plagues less sophisticated scanners. Newton Rings are the circular rainbow-

colored patterns that appear in a scanned image, caused by surface tension. This effect is similar to the

rainbows that appear in soap bubbles.

Scanner Technical Brief—Page 6

Superior detail

in highlights

Superior detail

in shadows

Epson automatic/manual focus

Standard ﬁxed focus

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