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Additive Primary Colors: Red, Green, Blue; the 3 colors used to create all other colors when direct, or transmitted, light is used (as in a video monitor). They are called additive primaries, because when these three colors are superimposed they produce white.

Anti-Aliasing: A method of filling in data which has been missed due to under-sampling. In imaging this usually takes on the process of removing jagged edges by interpolating values in-between pixels of contrast. These methods are most often used to remove or reduce the stair-stepping artifact found in digital high contrast images.

Aspect Ratio: The proportion of an image's size given in terms of the horizontal length verses the vertical height. An aspect ratio of 4:3 indicates that the image is 4/3 times as wide as it is high.

Bitmap: An image is called a bit map if it contains a value for each of its pixels. This is the opposite of vector images where a small set of values can generate an object.

BMP: File format extension for bitmap images. Format originator: Microsoft Corporation 16011 NE 36th Way, Box 97917/Redmond, WA 98073

Brightness: The value of a pixel in an electronic image, representing its lightness value from black to white. Usually defined as brightness levels ranging in value from 0 (black) to 255 (white).

CMY & CMYK: Cyan, Magenta, Yellow, (K) black: Computer monitors are additive, but color printers are subtractive. Instead of combining light from monitor phosphors, printers coat paper with colored pigment, which remove specific colors from the illumination light. CMY is the subtractive color model that corresponds to the additive RGB model. Cyan, magenta, and yellow are the color complements of red, green, and blue. Due to the difficulties of manufacturing pigments that will produce black when mixed together, a separate black ink is often used and is referred to as K ('B' is already used for blue).

Contrast: A measure of rate of change of brightness in an image.

Crop: An image processing method of removing the region near the edge of the image, but keeping a central area.

DPI (Dots per Inch): The number of printer dots that can be printed in one inch, or the number of pixels a scanner can physically distinguish in each vertical and horizontal inch of an original image.

Exif (Exchangeable ImageFile Format) Information: The Image files produced by nearly all Digital cameras are created as JPEG files containing Exif header information. Exif files are primarily JPEG files that have a different header block than regular JPEG’s. These headers contain additional data sections with camera settings and information, as well as a preview thumbnail picture as part of the Exif header.

File Extensions: The file extension is two or three letters that follow a file name and is separated from the file name with a period. File extensions are most commonly used with PC computers to help the computer know which program will open the file.

GIF (file format extension): Graphics Interchange File Format. Format originator: CompuServe Inc. 500 Arlington Center Blvd./Columbus, OH 43220. Uses the LZW compression created by Unisys, which requires special licensing. It is the same as the LZW compression used in the TIFF file format, except that the bytes are reversed and the string table is upside-down. All GIF files have a palette. Some GIF files can be interlaced in that the raster lines can appear as every 4 lines, then every 8 lines, then every other line. This is due to GIF files usually being received from a modem.

Histogram: A tabulation of pixel value populations usually displayed as a bar chart where the x-axis represents all the possible pixel values and the y-axis is the total image count of each given pixel value. That is, a histogram counts how many pixels in the image have a given intensity value or range of values. Each histogram intensity value or range of values is called a bin. Each bin contains a positive number, which represents the number of pixels in the image that fall within the bin's range. A typical 8-bit gray-scale histogram contains 256 bins. Each bin has a range of a single intensity values. Thus, bin 0 contains the number of pixels in the image that have a gray-scale value of 0 or black. Likewise, bin 255 contains the number of white (255) pixels. When the collection of bins are sorted (0-255) and charted, the graph displays the intensity distributions of all the images pixels.

HSL (Hue Saturation, and Lightness): A method of describing any color as a triplet of real values. The hue represents the color or wavelength of the color. It is sometimes called tone and is what most people think of as color.

Image Format: Refers to the specification under which an image has been saved to disk or in which it resides in computer memory. There are many commonly used digital image formats in use. Some of the most used are TIFF, DIB, GIF, and JPEG. The image format specification dictates what image information is present and how it is organized in memory. Many formats support various sub-formats or 'flavors'.

Interpolation: Refers to the methods used to artificially increase image resolution. Interpolation creates new pixels from those that exist and inserts them in-between the existing pixels to increase the image's overall resolution. Though interpolation can improve picture quality when enlarged, interpolated images tend to look fuzzy when enlarged further.

JPEG (image compression): Joint Photographic Experts Group. A collaborative specification by the CCITT and the ISO for image compression. JPEG is usually a lossy compression.

JPG (file format extension): Format originator: Joint Photographics Experts Group

Pixel: Short for the mostly obsolete term Picture (X) Element. This is the most fundamental element of a digital image. A digital image is made up of rows and columns of points of light. Each indivisible point of light is called a pixel. Each pixel in an image is addressed by its column (x) and its row (y) usually written as the coordinate pair (x,y). An 8-bit pixel can take on one of 256 values. A 24-bit pixel has 3, 8-bit components for each of the primary colors, red, green, and blue.

Resolution: Indicates the number of dots, often measured in dpi, that make up an image on a screen or printer. The larger the number of dots, and thus the higher the resolution, the finer and smoother images can appear when displayed at a given size. Low resolution causes jagged characters. The ideal resolution is a trade-off between quality and the overhead in storage power and processing strength requuired to use it.

RGB: Red, Green, Blue. A triplet of numeric values that are used to describe a color.

TIFF (file format): Tagged Image File Format.

TIF (file format extension): Format originator: Aldus Corp and Microsoft Corp; 411 First Ave South Seattle, WA 98104; 16011 NE 36th Way Redmond, WA 98073

Unsharp Mask: Unsharp masking is used to sharpen the edges of an image. The Unsharp Mask filter corrects blurring created during photographing or scanning. Unsharp Mask identifies pixels that differ from surrounding pixels by the Threshold you specify and increases the pixels' contrast by the Strength you specify. In addition, you specify the Radius of the region to which each pixel is compared.