A method for displaying three dimensional imaging system data uses a modified Back To Front algorithm. With that algorithm, imaging system data are interpolated and converted into a series of vectors defined by a starting point in space and a length corresponding to consecutive non-zero imaging system data points. The vectors are transformed to an observer's viewpoint coordinate system and plotted on a CRT display.

An adaptive forward differencing apparatus wherein, when rendering curves, calculated x, y values are increased or decreased in order to create values which correspond to the next pixel of the display CRT, such that curves of substantially one pixel increments are continuously and uniformly generated. The apparatus of the present invention also provides circuitry for generating coordinates of display elements which approximate an ideal vector and to define curves, vectors or objects within maximum and minimum coordinates of the CRT display. The present invention also provides efficient circuitry for computing the value of 1/w of the homogenous coordinate w.

By an image processing method, a contour of a figure is represented with a series of clockwise outline vectors, a sense of each vector being set such that the figure be painted out by painting a left side of the vector, then, an outline is created from the outline vectors, and the figure is painted through a scanning operation in an x-axis direction by starting a painting operation at an odd-numbered intersection of the outline and a horizontal scanning line and suspending the painting operation at an even-numbered intersection thereof, thus painting pixels between the odd-numbered intersection and the even-numbered intersection, inclusive of the pixel at the odd-numbered intersection but exclusive of the pixel at the even-numbered intersection. In order to create the outline, plotting points for the outline are first calculating from the outline vectors through use of Bresenham algorithm. Then, a positional relation of a current plotting point to the previous one and the next one is obtained. A positional variation in the y-axis direction between the current plotting point and the previous one calculated based on the positional relation is stored in a flag. In creating the outline, outline components are plotted one after another based on the positional relation of the current plotting point to the previous one and to the next one, or based on the positional variation in the y-axis direction.

The present invention provides unique methods and apparatus for shading curves, polygons and patches, implementing Phong, Gouraud and other shading techniques in the rendering of images on a cathode ray tube or other display device. The present invention also includes a unique method and apparatus for shading patches by rendering a series of adjacent curves such that no pixel gaps exist between each rendered curve.

An image memory controller having a first address signal generation means for generating a first address signal in response to a state signal representing the operational state of a printer. The first address signal corresponds to a location in an image memory. A second address signal generation means generates a second address signal for refreshing the image memory and a third address signal generation means generates a third address signal used for rewriting at least part of data stored in the image memory. An address signal selection means selectively delivers any of the first, second, and third address signals to the image memory.