# Glossary

This glossary contains descriptions of significant terms that appear in this book.

**affine transformation**- Geometric image transformation, such as translation, scaling, or rotation.
**band**- The set of all samples of one type in an image, such as all red samples or all green samples.
**box filter**- A low-pass spatial filter composed of uniformly-weighted convolution coefficients.
**bicubic interpolation**- Two-dimensional cubic interpolation of pixel values based on the 16 pixels in a 4 x 4 pixel neighborhood. See also
*bilinear interpolation*,*nearest-neighbor interpolation*. **bilinear interpolation**- Two-dimensional linear interpolation of pixel values based on the four pixels in a 2 x 2 pixel neighborhood. See also
*bicubic interpolation*,*nearest-neighbor interpolation*. **binary image**- An image that consists of only two brightness levels: black and white.
**chain code**- A pixel-by-pixel direction code that defines boundaries of objects within an image. The chain code records an object boundary as a series of direction codes.
**cobble**- To assemble multiple tile regions into a single contiguous region.
**color space conversion**- The conversion of a color using one space to another color space, such as RGB to CMYK.
**components**- Values of samples independent of color interpretation.
**compression ratio**- In image compression, the ratio of an uncompressed image data file size to its compressed counterpart.
**data element**- Primitive types used as units of storage of image data. Data elements are individual members of a
`DataBuffer`

array. **directed graph (digraph)**- A graph with one-way edges. See also
*directed acyclic graph (DAG)*. **directed acyclic graph (DAG)**- A directed graph containing no cycles. This means that if there is a route from node A to node B then there is no way back.
**first-order interpolation**- See
*bilinear interpolation*. **high-pass filter**- A spatial filter that accentuates an image's high-frequency detail or attenuates the low-frequency detail. Contrast with
*low-pass filter*,*median filter*. **histogram**- A measure of the amplitude distribution of pixels within an image.
**Lempel-Ziv-Welch (LZW) compression**- A lossless image coding method that scans the image for repeating patterns of blocks of pixels and codes the patterns into a code list.
**low-pass filter**- A spatial filter that attenuates an image's high-frequency detail or accentuates the low-frequency detail. Contrast with
*high-pass filter*,*median filter*. **median filter**- A non-linear spatial filter used to remove noise spikes from an image.
**nearest-neighbor interpolation**- Two-dimensional interpolation of pixel values in which the amplitude of the interpolated sample is the amplitude of its nearest neighbor. See also
*bicubic interpolation*,*bilinear interpolation*. **perspective warp**- An image distortion in which objects appear trapezoidal due to foreshortening.
**projective warp**- See
*perspective warp*. **quantization**- The conversion of discrete image samples to digital quantities.
**ROI**- Abbreviation for
*region of interest*. An area or pixel group within an image that has been selected for processing. **run-length coding**- A type of lossless image data compression that scans for sequences of pixels with the same brightness level and codes them into a reduced description.
**Sobel edge detection**- A spatial edge detection filter that detects edges by finding the gradient of an image.
**square pixel**- A pixel with equal height and width.
**thresholding**- A point operation that maps all the pixel values of an image that fall within a given range to one of a set of per-band constants.
**transform coding**- A form of lossy block coding that transforms blocks of an image from the spatial domain to the frequency domain.
**trapping**- An image manipulation technique used in printing that uses dilation and erosion to compensation for misregistration of colors.
**unsharp masking**- An image enhancement technique using a high-frequency accentuating filter.
**zero-order interpolation**- See
*nearest-neighbor interpolation*.