Glossary

Application Programming Interface. The API is the set of subroutine calls that is available for use by an application programmer.

The undisplayed buffer in a double-buffer pair. See double-buffering; compare with front buffer.

A rectangular array of bits mapped one-to-one with pixels. The frame buffer is a stack of bitplanes.

IVL state that is not stored in the rendering context. For example, the current drawable and the current rendering context.

Eliminating (e.g., not displaying) some portion of the image that is being rendered. For example, images may be clipped because some portions fall outside the current window or current scissor box.

A logical set of bitplanes. The color buffer may consist of a number of buffers depending on whether it is single-buffered, double-buffered, stereo, or stereo double-buffered. The components of a color buffer are therefore referred to as the front and back buffers. For devices that support stereo buffers, the color buffer is made up of the front left buffer, front right buffer, back left buffer, and back right buffer.

A hardware implementation of a color look-up table. The frame buffer hardware uses each 8-bit pixel value as an index into this table when refreshing the physical display.

The set of rules for manipulating color values in a processing system. IVL can be described as using an RGBA color model since it is based on processing pixel values with red, green, blue, and alpha components.

An array that is used in a color look-up operation. Each incoming pixel component value is used as an index into this array. The value stored in the array at the indexed location is extracted and becomes the pixel component for subsequent processing.

A common image-processing operation that can be used to filter an image. The filtering is accomplished by computing the sum of products between the source image and a smaller image or matrix called the convolution filter or convolution kernel. The convolution filter can be loaded with different values to achieve effects like sharpening, blurring, and edge detection.

An attribute that defines how IVL treats image borders during the convolution process. The border mode you choose may cause the output image to be a different size than the source image.

A two-dimensional image that is used during convolution to achieve effects like sharpening, blurring, and edge detection.

Another name for convolution filter.

A coefficient that provides additional control over the bicubic interpolation operation. The weighting factor biases the cubic curve used to perform the interpolation. Cubic weighting factors typically assume values from -1.0 to 0.0.

The buffer that is the target of all subsequent pixel-write operations. This term is sometimes shortened to "draw buffer".

The X window or GLX pixmap that contains the buffers that will be used for all subsequent rendering operations.

The location at which to draw a pixel rectangle. This value is in window coordinates. This term is sometimes shortened to "raster position".

The buffer from which pixels will be obtained during all subsequent pixel-read operations. This term is sometimes shortened to "read buffer".

A connection that bypasses the X network transport mechanism in order to access the rendering hardware directly.

The process of using two buffers to provide smooth animation. This is done by drawing into the back buffer while the front buffer is displayed. Once drawing is complete, the contents of the back buffer are moved to the front buffer. See also front buffer and back buffer; compare with single-buffering.

The buffer that is the target of all subsequent pixel-write operations.

An X window or a GLX pixmap.

Capabilities that are not yet part of the OpenGL standard. The "EXT" suffix indicates OpenGL extensions that are supported by two or more vendors. The "HP" suffix indicates OpenGL extensions that are currently supported only by Hewlett-Packard.

Another name for Convolution Filter.

A data structure containing pixel information which is a product of the pixel rasterization operation. A fragment consists of a color value and the coordinate of the frame buffer location at which that color value is to be written.

Operations that are applied to a fragment prior to writing the fragment's color value into the frame buffer. The two fragment operations that are currently defined for IVL are the pixel ownership test and the scissor test.

A two-dimensional array of memory locations that stores pixel values. Some of these locations correspond to the pixels that are visible on the display screen. Other locations are used for non-displayed pixel values, such as the back buffer of a double-buffered window.

The displayed buffer in a double-buffer pair. See double-buffering; compare with back buffer.

The OpenGL extension to X. An X server extension that allows IVL to coordinate its rendering operations with those of X and other extensions.

An X pixmap that has been enabled to support rendering via IVL. GLX pixmaps have an associated visual type, so they can contain the extended visual attributes defined by IVL.

A rectangular array of pixel values, either in client memory or in the frame buffer.

A term used to describe the organization of the pixel components in an image. IVL currently supports two formats: GL_LUMINANCE, which indicates that pixel values are stored as luminance (one-component) values, and GL_RGBA, which indicates that pixel values are stored as red, green, blue, and alpha (four-component) values.

The stage of the IVL pixel processing pipeline that provides support for image scaling (zoom), rotating, translation (pan), and interpolation.

The storage unit for each component of a pixel. Pixel components may be either GL_UNSIGNED_BYTE or GL_UNSIGNED_SHORT.

Another name for resampling.

Image Visualization Library. A 2D API for image processing with a programming interface very similar to the imaging portions of the OpenGL API together with several defined imaging extensions.

Image Visualization Accelerator. Optional graphics hardware that accelerates many of IVL's capabilities.

Bitplanes are grouped into logical buffers. The only logical buffer that is supported in this release of IVL is the color buffer.

See color table.

A term used to describe images that contain only one pixel component per pixel. A one-component image is sometimes called a "grayscale" or "intensity" image.

A one-component pixel format that contains only luminance pixel component values.

The data types that are "natural" for a computer architecture. The machine data types for a workstation may include signed and unsigned 8-bit values, signed and unsigned 16-bit values, signed and unsigned 32-bit values, 32-bit floating point values, and 64-bit floating point values.

The distance between two points on a grid addressed by integer coordinates. This distance is the sum of the horizontal distance plus the vertical distance between the two points.

A window that is not stereoscopic, i.e., does not support stereo viewing.

A 3D graphics API that includes capabilities for 2D imaging.

Extensions to OpenGL that support common image processing and display operations. See also Extensions.

A set of bitplanes that lie on top of the bitplanes for a color buffer. Applications can render into the overlay planes without disturbing the contents of the color buffer. The resulting display shows the contents of the overlay planes superimposed on the contents of the color buffer. Not all frame buffers include overlay planes.

The fundamental element of a pixel. An RGBA pixel has four components: red, green, blue, and alpha. A luminance pixel has just one component (luminance).

The test performed by IVL to determine if the pixel location at which the fragment is to be written is part of the current drawable. If it is not, the fragment is discarded.

The process by which the pixels of an image are converted to fragments, each corresponding to a pixel in the frame buffer.

A rectangular array of pixels, either in client memory or in the frame buffer. Used synonymously with "image".

A set of operations that are applied whenever pixels are transferred from one place to another in the IVL environment. The operations include color table lookup, convolution, and image transformation.

The process of reading pixel values from host memory using the type and format parameters and the state values defined by glPixelStore.

A non-displayable region of the frame buffer into which rendering may occur. In the X Window System, a pixmap is defined to be very similar to a window. The X notion of a pixmap has to be extended in order to use pixmaps for IVL rendering. See GLX pixmap.

The color look-up table that immediately follows the image transformation stage of the pixel processing pipeline.

Rendering an image using multiple passes, with improved interpolation quality in each pass.

The location at which to draw a pixel rectangle. This value is in window coordinates.

The buffer from which pixels will be obtained during subsequent pixel-read operations.

The process that maps the discrete image samples computed by resampling into a continuous surface. In this process, pixel values between the sample points are computed using a method such as bilinear or bicubic interpolation. Compare with Resampling.

The data structure that encapsulates server state information. The majority of IVL state is stored in the rendering context.

The process of transforming a sampled image from one coordinate system to another. The two coordinate systems are related by the mapping function of the transformation. Using the inverse of the transformation, the regular grid corresponding to the pixel locations in the output image is mapped onto the input image. The input image is then sampled at each of these points, and the sampled values are assigned to their respective output locations in the output image. Compare with Reconstruction.

A term used to describe images that contain four pixel components per pixel (red, green, blue, and alpha).

A four-component pixel format that contains red, green, blue, and alpha pixel component values.

A rectangular clipping region, defined in window coordinates. When the scissor test is enabled, only pixel locations within the scissor box can be modified.

A clipping operation that eliminates any pixels that would be drawn outside of the current scissor box.

State that resides in the server and controls the rendering process. The current rendering context and the current drawable are among the few state values that are not part of server state.

A mode in which the same buffer is used simultaneously for drawing and displaying an image. In this mode, animations may reveal slight halting between frames. Compare with double-buffering.

A window that contains both a left eye view and a right eye view to support stereo viewing. When the proper viewing equipment is used, the user will see a three-dimensional, stereo image.

A rectangular portion of a larger image.

The X Visual that defines the display attributes of a window. There are six visual types in X: TrueColor, DirectColor, PseudoColor, StaticColor, GrayScale, and StaticGray.

An image processing term that defines a continuous transfer function specifying the input to output intensity-value mapping. The window defines the width or range of input intensity values that will be mapped from black to white. The level defines where the center of the window range will fall with respect to the input intensity value domain. In IVL, support for window-level mapping is implemented as a color look-up table.

The mechanism by which frame buffer features are exposed and software portability is defined in the X Window System. The XVisualInfo structure in X defines the visual type, screen, and depth of the window, as well as the number of bits of red, green, and blue information in a pixel.