A data conversion apparatus for converting index data to real data and an image generation apparatus for converting index texture data to real texture data by the data conversion to make it possible to suitably carry out texture mapping. A data conversion apparatus comprises a first memory and a second memory each for storing data having a n bit width and in which any data is stored, an address detecting means for detecting addresses of the first memory and the second memory based on input data, a data reading means for reading data stored at the detected addresses of the first memory and the second memory, a first data selecting means for selecting either of the data read from the first memory or the data read from the second memory, a data extending means for extending the selected data to data having a 2.times.n bits width, and a second data selecting means for selecting either of the first data formed by connecting the data output from the first memory and the data output from the second memory or the second data of the extended data.

In a bit mapped display environment which has n hardware color look-up tables (CLUTs) where n=1 or more, which also has a limited number of Display Attribute Identification Values, and which may operate under various window systems, such as the X Window System protocol, an apparatus and a method for installing and uninstalling hardware colormaps under the constraint of a finite number of Display Attribute Identification Values, whereby the most recently installed (MRI) policy of the X Window System is followed. The invention provides a scheme which gracefully degenerates to some "color flashing" when Display Attribute Identification Values are exhausted; which allows Display Attribute Identification Values to be uncoupled from colormap management and used for more graphics intensive functions when needed; and which dynamically regenerates when display attributes again become available. The invention also minimizes the rendering of the Display Attribute Planes when a new colormap is installed in a system containing multiple hardware color look-up tables.

A video register interface for a video processor in which each frame register has a first storage element which is written by a microprocessor interface independently from a second storage element which outputs control data to video processing circuitry. Since reading and writing are done independently to different storage elements, the contents of the register can be changed without adverse effects on a displayed image. The register interface is used in a CMOS video processor which in turn is used in a microprocessor based multimedia computing system.

An image display system comprises an area setting section, an area detecting section, an interrupt generating section, and a palette writing section. In order to divide a display screen into a plurality of small screen areas, the area setting section sets the head position of each of the areas. When the area detecting section detects the head position of a small screen area, the interrupt generating section generates an interrupt. In response to the interrupt, the palette writing section writes display color information for the small screen area into a palette. This system permits each of the small screen areas to be associated with a substantially different palette.

A gradation conversion system comprising: a plurality of gradation conversion devices for converting color display data into gradation display data by different gradation conversion methods, respectively; and switching device for selectively activating one of the plurality of graduation conversion device. Accordingly, if a number of different colors are to be displayed in the same number of gradations when converting multi-color display data into gradation display data, it is possible to perform this gradation conversion. On the other hand, if different colors are to be displayed in gradations as exact to the brightnesses of colors as possible, it is possible to select one of plural gradation conversion methods so as to carry out this gradation conversion.