UMAX Technologies Astra 2000U Owner's Manual page 110

Continuous Tone-An image that has enough tonal range so that the
human eye can't detect obvious "jumps" or "steps" between gray or
color levels. A photograph is an example of a contone image. A
computerized contone image can only be represented as a bitmap
image.
Descreen-The process of removing a moiré.
Dmin-The lightest area of an image that a device can reproduce and
still have detail. A Dmin value of 0.0 would be considered perfect.
Dmax (-) Dmin=Dynamic range.
Dmax-The darkest area of an image that a device can reproduce
and still have detail. A Dmax value of 4.0 would be considered
perfect. Dmax (-) Dmin=Dynamic range.
DPI (Dots Per Inch)-A standard unit of measurement for scanners
and printers. Scanners are given a DPI rating even though they
create pixels not dots. DPI is also a scanner's measure of it's
enlargement capabilities. DPI is not a good measure of a scanner's
overall image quality.
Dynamic Range-An instruments range, such as a scanner, of
measurable values. The range is from the lowest value it can detect
to the highest value. A perfect dynamic range for a scanner is
considered to be 4.0 or Dmin=O and Dmax=4. The dynamic range
of a scanner is most indicative of it's overall image quality with 3.0
being a minimum rating for prepress capable scanners.
Gamma-The range of colors and gray tones that can be interpreted
by a color model, or is generated by a specific device.
Grayscale-The depiction or measurement of all values between
white and black.
Halftone-A combination of spots and dots that create the illusion of
tonality - both for color and continuous tone Black & White. A
newspaper picture is a good example of an image that has been
halftoned.
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