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CONTRAST
The difference between the black areas and white areas of an image. High contrast means the difference is great; low contrast, the difference is little (image is mostly made up of gray areas, lacking white whites and/or black blacks. Lineart has the ultimate contrast.

DOT GAIN
The extent to which halftone dots increase in size on the printed paper due to the fact the dots are squeezed between the offset blanket and the printing plate or the paper during the printing process.

GRAPHIC SCAN
The digitizing of a graphic image so that it can be saved in a number of graphic formats and further used, manipulated, or edited on a computer.

HALFTONE
A screened image that represents (with a series of dots) all the grays of a continuous tone image.

LINEART
Any B&W art made up of either black or white areas (no grays) or any color art that is made up of only solid colors.

LPI
(Lines Per Inch) Measurement of resolution for halftones, that is, lines or rows of halftone dots per inch.

SCALING FACTOR
Measurement (in percentage) of what the size of the final image will be in relation to the size of the orginal,
i.e. Size of Final Image ÷ Size of Original Image.

SPECULAR HIGHLIGHT
Those white areas in a photo that are reflections off of highly reflective surfaces.

TEXT SCAN
A file created using Optical Character Recognition (OCR) software. A hardcopy of text is scanned and converted to keystrokes that can be edited through the traditional word processing methods.

THRESHOLD
The cutoff point which determines if a portion of the original image is dark enough to become a pixel.

All scans are bitmap images. To convert scanned images to vecto images you must trace them in a vector graphics application like Illustrator.

Resolution (dpi) of the final scanned image
Size or Scale or Percentage (width by height or percentage of original) of final image see Scaling Factor
Scan type (bit depth you are using)
File size (what is too large)

Types of Scans

Line art (B&W) 1-bit
Halftone 1-bit
OCR 1-bit
Grayscale 8-bit
Color 24-bit

Controls

Threshold (for lineart, halftones, and OCR)
Brightness & Contrast (for grayscale/color)

Resolution

Resolution, Size, and Scan Type have a direct relationship to the final file size of the scan (increase any one>the file size increases)

The limits to how far you can enlarge an image during the scanning process and the resolution you can capture is determined by the scanning hardware and software you are using.

A physical limitation of a scanner is its ability to define the smallest pixel (or in other words, how many pieces per inch it can divide the original image). This resolution, pixels per inch (ppi) is the rating of the scanner (e.g. 600 x 300, 600 x 1200).

For example, considering a 600 dpi scanner:
each inch can be broken into 600 pixels @100% 600 dpi (max). If you enlarge the image (during or after the scan) to 200%, the same portion of the original is still be divided into 600 pixels, however, it is now spread out over two inches (or 200% of the original), therefore, each inch of the original is really represented by only 1/2 as many pixels (300).

Scanning software can compensate for this limiation by using a technique called interpolation, which introduces pseudo pixel data into your scanned file. The quality suffers, but you can get larger scans at higher resolution

Since the quality of the scan is related to the smoothness of the edges of the graphic, the higher the resolution, the greater the quality of the scanned image.

Since the quality of these scans are related to the resolution of the halftones created during the RIP portion of printing, you should follow this formula for the best quality scan without creating the file too big.

Halftone quality. The quality of a halftone is related to what the press can print. You must be aware of the following capabilities of the press on which your work will be reproduced:
•The smallest printable dot the press can print. (Dots below this size will not image and are said to blow out.)
•The largest printable dot the press can print. (Dots larger than this are said to fill in or print as solid ink.)
•The midtone dot gain. As the dots spread out, the picture looks darker. To compensate for the potential dot gain, extend the highlight-to-midtone range by decreasing the overall contrast.

What to look for in a halftone. Loss of detail from blown-out highlight dots and excessively large dots that create a dark or muddy appearance. Make sure that there are no dots in the specular highlights and that there are no shadow areas that have large areas of solid ink..