Abstract: Using a plurality of relatively narrowband light sensors having overlapping response characteristics, accurate and self-calibrating colour measurements may be carried out. With sufficient measurements, simultaneous equations may be solved to derive a light intensity measurement at portions of the spectrum at which the overlapping sensor responses intercept. Using LEDs as light sensors provides cheap narrowband sensors and provides the additional advantage that the LEDs may also be used to illuminate a source to provide additional cross-reference measurements. Using sensors and/or illumination sources directed at several angles may also be used to improve sensing accuracy by mitigating the effects of surface texture and/or fluorescence.

Abstract: A method of determining a value for a function which is particularly useful for mapping values from one colour space to another comprises a series of steps, as follows. The method is applicable to n-dimensional spaces, but is particularly described for three dimensions. The first step is to establish a three dimensional lattice, the function having values at the lattice points. The next step is to record values of the function for a subset of the lattice points, the lattice points of the subset being known value lattice points. These known value lattice points form a sparse lattice (preferably the sparse lattice points are regularly spaced along orthogonal axes). A value of the function for a given lattice point is established by returning a weighted average of the values of one or more of four known value lattice points defining a tetrahedron 42 touching or enclosing the given lattice point.

Abstract: A method of determining a value for a function that is particularly useful for mapping values from one color space to another includes a series of steps, as follows. The method is applicable to n-dimensional spaces, but is particularly described for three dimensions. The first step is to establish a three dimensional lattice, the function having values at the lattice points. The next step is to record values of the function for a subset of the lattice points, the lattice points of the subset known value lattice points. These known value lattice points from a sparse lattice (preferably the sparse lattice points ate regularly spaced along orthogonal axes). A values of the function for a given lattice point is established by returning a weighted average of the values of one or more of four known value lattice points defining a tetrahedron touching or enclosing the given lattice point.

Abstract: A graphics system is provided that utilizes a tree-structured organization of graphic segments (a-m) which potentially overlap when presented as a two-dimensional image. Each child segment in said organization inherits image-related spatial transformations to which its parent is subject. To increase flexibility of representation using such a tree organization, provision is made for associating parent and child segments (c;b,d) by an attachment relationship that determines that outside of the boundary of the parent (c) in said image, the child (b,d) is unrestricted by its parent. This relationship may either be an "above" or "below" attachment relationship (40,42) depending on whether the child or parent has a higher depth priority where the segments overlap.

Abstract: A graphics output system stores a collection of graphic segments that are intended for display, potentially in overlapping relation, in a two-dimensional output image. The stored graphic segments are converted into a representation of an output image. The stored graphic segments are specified by boundary inter-relationship data respectively determining the boundary of each segment and the relative depth priorities of the segments in the output image and any clipping of each said segment to the boundary of a lower-priority segment that it can potentially overwrite. The collection of graphic segments is modified, for example, by deleting or adding segments. A new image representation is not formed from the beginning each time the segment collection is modified. Instead, the output image representation is within a region delimited by the boundary of one or more segments associated with the modification.

Abstract: In inter-active computer graphics systems a pointing device, such as a mouse, is generally used to move a cursor over a displayed image to point to a particular image element. An action may then be initiated by clicking a mouse button. In order for an application (110) using the graphics system (11, 100) to understand what action is required, the graphics system must translate the image position pointed to by the mouse into the identity of the corresponding image element. To facilitate this translation, the present graphics system (11,100) in generating the output image from a stored group of graphic segments (20), also generates and stores a compact image representation (60) relating image position to the corresponding segment. This image representation (60) is then subsequently used to translate an input image position back into a segment identity.