Canon 4.1 - Manual (Page 68)

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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, BMP, etc.) use different methods of storing and
recalling this information.
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%.
Moiré
The patterns or lines created by overlapping dots in an image. This
phenomenon is found when photographs or pictures are scanned from books
and magazines at low resolutions. The Descreen function helps to eliminate
moiré patterns.
Optical Resolution
An expression of the volume of data per inch (dpi) that can be sampled by a
scanner.