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Gamma Value
A function for adjusting the overall brightness of an image. A gamma value is
the mathematical expression of how brightness data is converted from a
scanner (the input) to a monitor or printer (the output). With 1 as the base
value, a gamma value less than 1 makes an image darker, while a higher value
makes it brighter. The brightness handling characteristics of monitors vary
between manufacturers and models. A monitor’s gamma value explains the
degree to which its output (what you see on the screen) varies from the input
value.
Grayscale
An image mode that scans only the brightness data of an image and reproduces
the image in white, black and 254 shades of gray (256 tones or 8 bits).
Histogram
A graph indicating the distribution of brightness data in an image. A dot is
assigned a brightness value ranging from 0 (shadows) to 255 (highlights). The
histogram shows how much image data there is at each brightness value.
Adjusting the histogram changes the image contrast.
Image File
Images are expressed as collections of dots with varying color and brightness
values that are digitized in particular formats for processing by a computer. At
the most basic level, an image file contains bitmap information, which is the
color information for each dot in each column and row of an image. The
various file formats (TIFF, JPEG, BMP, etc.) use different methods of storing and
recalling this information.
JPEG
A file format developed by the Joint Photographic Experts Group. A standard
for storing color image data in a compressed format. The file extension is
“.jpg.”
Magnification
An expression of the relationship between the scanning resolution and the
output resolution stated as a percentage. If the output resolution is set to 720
dpi and the scanning resolution to 360 dpi, then the magnification rate is 50%.