Floor coverings comprise important interior design elements that are frequently relied upon to unify and enhance a specific interior design concept.  Over the last decade, modular carpeting—i.e., the use of carpet tiles or panels—has become a favorite of interior designers, particularly in commercial spaces, due to its potential to mimic the appearance of conventional broadloom carpeting while, at the same time, provide a practical means by which localized portions of the carpeting can be easily removed to access under-floor wiring or can be easily replaced in the event of damage, excessive wear, staining, and the like.  One specific application of the techniques disclosed herein is to automate the creation of a large number of individual carpet tiles that, when installed, produce a non-repeating, multiple-tile pattern sufficient to generate high visual interest and that disguise, to a large degree, any patterning artifacts that would otherwise be visually objectionable, yet provide one or more common design elements that visually unify the multiple tile pattern. 
One of the generally acknowledged key attributes of a successful modular carpet tile installation, and one that may be helpful in achieving the look of broadloom carpet, is the inconspicuousness of the seams between contiguous carpet tiles.  Where design elements within a single tile are duplicated in adjacent tiles and/or extend into adjacent tiles, and those design elements are not perfectly duplicated within each tile, the region around the seam can become visually obtrusive due to pattern discontinuities between adjacent tiles and can draw attention to any imperfections in the form of mismatched color or misaligned design elements.  This condition, which shall be referred to as “seam discontinuity,” occurs frequently when there are design elements—for example, a simple band of color—that extend across the boundary separating adjacent tiles and that tend to emphasize the transition from one tile to a contiguous tile.  Somewhat counter-intuitively, one way to make such transitions as unobtrusive as possible is to apply a pattern to the individual carpet tiles that provides such visual variety across the installation as a whole that the transition between individual adjacent tiles becomes relatively less important.  To the viewer, the non-regular nature of the overall pattern formed by multiple tiles visually overwhelms the discontinuities at the boundaries, with each tile in a series (but not necessarily in a collection, or installation) having a unique pattern but one that is aesthetically consistent, in terms of color and individual pattern elements, with all other tiles in the installation. 
Another key attribute of a successful modular carpet installation, or any carpet installation, for that matter, is the ability of the selected pattern to provide an unobtrusive complement to the overall interior design.  Floor covering patterns are frequently based on a relatively small pattern, i.e., one in which at least one complete pattern repeat may be defined completely within the area of a single carpet tile.  Such patterns, however, carry a significant potential disadvantage.  In many cases, otherwise well-placed design elements appear to align into rows when viewed along relatively shallow viewing angles, resulting in large-scale pattern anomalies that involve multiple carpet tiles and that extend over large areas of installed carpet.  Such pattern anomalies (which are sometimes referred to as “design lines”) can be sufficiently severe as to become visually prominent and overwhelm the intended overall pattern. 
Added to such inherent design-based problems is the fact that the patterning process can occasionally cause slight periodic non-uniformities to occur within the pattern, such as the uneven application of dye within a pattern element or background area, resulting in a localized streak or band.  When viewed as individual tiles, such periodic non-uniformities can be relatively unobtrusive, but when a series of such tiles carrying the same non-uniformity are installed over a larger area, such non-uniformities can become aligned, thereby emphasizing these manufacturing artifacts and forming visually conspicuous streaks or bands that extend over many carpet tiles.  For purposes herein, these pattern anomalies, design lines, and manufacturing artifacts shall be collectively referred to as “patterning artifacts.” 
It is believed that both seam discontinuities and patterning artifacts can be emphasized by the incorrect choice of the size of the pattern repeat, coupled with a subconscious expectation of uniformity or symmetry that is generated by seeing a relatively large expanse of carpet tiles, all having the same pattern.  Accordingly, in order to minimize or eliminate such discontinuities and artifacts, the use of a non-repeating design, but one which shares common colors and design elements among adjacent tiles, has been found to be effective in eliminating the subconscious expectation of uniformity or symmetry, thereby minimizing the visual impact of patterning artifacts as well as seam discontinuities. 
A challenge in implementing this technique is developing a system by which a series of such composite patterns can be generated and printed at the time of manufacture.  It is possible to achieve a pseudo-random appearance using a relatively small number of different design elements on individual carpet tiles, and then rotating the tiles during installation to produce a more random-appearing overall pattern.  However, because this involves turning the tiles to orient them in different directions during installation, the pile orientation of the individual tiles is also turned, which may result in a variety of problems, including watermarking or sheen (difference in light reflectivity from tile to tile) and seam problems (dramatic pile lay changes at boundaries).  Accordingly, the techniques disclosed herein are believed superior, as these problems are generally avoided. 
At least one of the techniques described herein provides a series of carpet tiles, each of which carries a unique pattern that is pre-defined, using design elements that preferably coordinate with a base layer and with other patterns in the series.  Optionally, the orientation of the overlay pattern may also be altered before printing on the carpet tile, thereby introducing a greater number of unique composite patterns while allowing for an installation that preserves a single direction for pile lay (i.e., a “unidirectional” installation).  Additionally, this technique allows for certain geometric operations to be performed on the pattern to enhance the appearance of pattern randomness, if desired. 
As an additional advantage of the pattern generation system disclosed herein, in at least one embodiment, at least one common design element or motif (for example, the background) is incorporated into the composite pattern to serve as a visually unifying element across all tiles in the installation.  Accordingly, the composite patterns generated in accordance with the teachings herein and carried by the carpet tiles exhibit a distinct “random” or “pseudo-random” appearance when installed, although these patterns have at least one integrating design motif that is coordinated across all generated patterns, thus imparting an underlying visual uniformity to the carpet tile installation.  As an additional benefit, the random or pseudo-random elements incorporated into the design tend to mask any visually obtrusive, large-scale design lines that can appear as the unintended artifacts of the design or manufacturing process, as well as any unintended mis-matching of patterns or colors at the boundaries of the individual tiles. 
By use of the design systems described herein, the designer has at his or her disposal automated techniques that, with minimal designer input, can generate a series of patterns that share a common artistic theme or motif and that are suitable for use in patterning carpet tiles or other floor coverings, as well as other textile products.  In particular, the systems disclosed herein are especially suited for use in patterning carpet tiles or other textiles using the application of interruptible dye streams and electronically-controlled dye applicators that are actuated in accordance with digitally-defined patterns.  In such applications in which electronically-defined patterns are accessed and processed as part of the patterning process, the system disclosed herein effectively re-locates a portion of the design process to the actual patterning step in the manufacturing process, where it can proceed without designer intervention. 
While the techniques and systems described herein are especially well-suited for printing or dyeing carpet tiles, it is contemplated that similar designs may be computer generated using pre-dyed yarns on graphic tufted machines. 
Definitions
To facilitate the discussion that follows, the explanations will assume that the substrates to be patterned are carpet tiles of uniform size, but not necessarily of uniform pile height.  It should be understood, however, that the concepts may be applied to patterning other substrates, and particularly other textile substrates (including broadloom carpets), with appropriate modifications with respect to the size and nature of the substrate and the pattern effect to be desired.  Additionally, it should be understood that the following terms shall have the meanings indicated below, unless the context clearly dictates otherwise.  These definitions will serve as an introduction to some of the concepts explained in more detail further below. 
The term “layer” refers to a separately configurable virtual data space which stores a pattern or design that is intended to be superimposed upon (or be superimposed by) other patterns or designs (each of which would constitute a separate layer) to form a composite pattern.  The pattern for each layer is capable of being independently selected and, optionally, independently oriented (that is, rotated or mirrored).  For example, a first layer could be comprised of a set of spaced vertical parallel lines and a second layer could be comprised of a pattern of geometric shapes.  Inhabiting separate data files within the design software, the first layer, for example, may act as the background layer, while the second layer's geometric shapes could be positioned over the background stripes as the superimposed layer to form a new composite pattern.  Optionally, the superimposed pattern may be rotated (for example, 90 degrees), mirror-imaged, rotated and mirror-imaged, or repositioned (that is, “translated”), to create additional composite patterns.  Also optionally, the background layer may similarly be geometrically altered (for example, by rotating, mirror-imaging, etc.). 
As used herein, one layer—the background layer—will be referred to as the “base” layer (which is comprised of the base pattern, as defined below), and all other layers—the superimposed layers—will be referred to as “overlay” layers (comprised of one or more overlay patterns, as defined below), although this nomenclature does not necessarily imply any specific number of layers or any order in which the layers are placed on the substrate.  In fact, as contemplated herein, these terms are merely used to describe the pattern generation process, and not the process or sequence through which the pattern is actually applied to the substrate.  This distinction may be important in certain printing operations where, for example, the application of yellow and blue in the same area of the substrate, in that order, yields a different shade of green than the corresponding application of blue and yellow, due to “masking,” dye saturation, and other effects.  Typically, it is believed the designer will choose the base layer to be that layer that most nearly covers the surface of the substrate to be patterned and onto which one or more overlay patterns are applied, in order to maximize the visually unifying aspect of the base layer, but this is not required by the processes described herein. 
The term “host” refers to a master pattern, preferably in virtual form and preferably non-repeating in nature, from which small, template-sized pattern subsets or samples may be defined.  If applied to a floor covering context, in one embodiment the host could be thought of as a non-repeating pattern on a virtual large substrate (say, for example, a virtual substrate dimensioned to be twenty feet square), onto which may be superimposed a tile-sized virtual template (for example, eighteen or thirty-six inches square) at various locations randomly (or non-randomly) positioned within the large virtual substrate.  At each position, the template defines a tile-sized pattern “sample” of the master host.  If the host pattern is non-repeating and sufficiently large, and each template position within the host is unique (i.e., the template position is not exactly repeated within a given tile series), then every host pattern sample defined by the template for a given tile series will also be unique.  Conversely, if the position of the template within the host is repeated, then the resulting host pattern sample will also be repeated.  In one embodiment, hosts may be used to define infinite, unique base patterns.  Alternately, the position of the template within the host may be repeated to produce composite patterns having the same base pattern for all tiles in the series.  In yet another embodiment, the position of the template within the host may be repeated, but the host pattern sample may subsequently be manipulated (e.g., by rotating, mirror imaging, stretching, shrinking and repeating, etc.)  before being incorporated into the composite pattern, thereby defining unique, but related, base pattern layers. 
The term “template” refers to a closed geometric shape that defines the borders of the pattern sample to be extracted from the host pattern to form a base pattern.  The template may be any shape or size, depending upon the desired design effect, although templates having the dimensions of the tile to be printed are most often contemplated herein.  It is also contemplated (but not required) that separate templates may be defined for use as base layers. 
The term “base layer pattern” or “base pattern” refers to a pattern layer that acts as the background onto which design overlays are superimposed.  In one embodiment described herein, the base pattern remains consistent for all of the tiles in a given collection.  Alternately, the base pattern may be manipulated before being digitally combined with the overlay pattern to form a composite pattern.  It is contemplated, in one embodiment, that the base layer host pattern will be sized to match, or nearly match, the size of the substrate to be patterned (e.g., a 36-inch square for patterning a 36-inch carpet tile), and the base pattern template will simply be the same size as the base layer host pattern.  This means that, in this embodiment, every base pattern will be identical—the same pattern element(s) expressed in the same location(s)—for each composite pattern, and therefore every composite pattern will have the same unifying design element(s) in the same location(s), whereas the overlay pattern will vary for each composite pattern within the design series. 
In yet another embodiment contemplated herein, each base pattern is selected from a host pattern using a template (the “base pattern template”), such that the base patterns of a collection of tiles are unique but related by the same design motifs and elements.  In this instance, unique base patterns are individually printed on a single substrate (e.g., a single carpet tile), resulting in a series of printed substrates that are uniquely patterned (although all substrates will share whatever design similarities that exist within the host pattern that was used, after any pattern manipulation is accounted for). 
As made clear above, an objective of the processes disclosed herein is the automated generation of a series of patterns to be randomly placed on a respective series of carpet tiles, with the resulting carpet tiles exhibiting a random or pseudo-random pattern when installed, but also exhibiting one or more unifying pattern elements (typically, from the base pattern host) that visually integrate the various tiles and provide overall pattern coherence to the floor covering installation.  To facilitate the discussion below, it will be assumed that the random or pseudo-random component of the composite pattern is assigned to one or more overlay patterns, and the unifying pattern elements are assigned to the base pattern layers, either of which may be manipulated before being combined into composite patterns. 
A primary purpose of the base pattern is to provide common pattern elements or colors that are shared by all carpet tiles (or at least the suggestion of such elements or colors), thereby providing a unifying pattern motif across multiple carpet tiles that may carry dramatically different overlay patterns and thereby form a visually integrated or coherent interior space despite the “random” appearance of the overall pattern when installed.  In one embodiment, the base pattern host is larger than the base pattern template and can, through varying the placement of the template at different locations within the host and/or the geometric manipulation (e.g., rotating, mirror-imagining, etc.)  of the resulting host “sample”, generate base patterns that are themselves unique.  It is also contemplated that, where the base pattern template is not larger than the base pattern host, the template can be positioned at the same location within the host, thereby generating a repeating pattern that can be placed at different locations within the composite pattern. 
The term “overlay pattern” refers to a pattern layer, separate from the base pattern layer, which is selected from a collection of pre-defined overlay patterns (“the overlay pattern collection”).  The overlay pattern collection is a set of pre-defined patterns that visually coordinate with a particular base pattern and with other overlay patterns within the set.  In one embodiment, each overlay pattern in a tile series incorporates design elements and colors of the base pattern, with no two overlay patterns in a series being identical.  In the embodiments described herein, it will be assumed (as a simplifying, non-limiting example) that all of the overlay patterns from a particular overlay pattern collection (including desired manipulations to the overlay patterns) are printed in random order to create a first tile series before randomized printing of the overlay patterns (and their desired manipulations) begins again to create subsequent tile series.  While it is contemplated that multiple overlay layers may be used on a single tile, with each layer representing a different pattern from the series, it is anticipated that, in many cases, a single overlay layer will be sufficient, if the corresponding pattern series available for use as an overlay layer is sufficiently varied. 
Among the design elements contemplated for use as overlay pattern components are letters, words, trademarks, logos (for instance, commercial or school logos), and the like, which may be proprietary to the users of such patterned carpet tiles.  In instances where such proprietary design elements are used, the manipulation algorithms described herein are modified to prevent the design element (e.g., the logo) from being mirror-imaged, or otherwise distorted, or from being truncated by being placed too close to a tile edge.  Thus, the integrity of the proprietary design element is preserved. 
The term “composite pattern” refers to the superposition of a base pattern and at least one overlay pattern, as created prior to any actual patterning step. 
The term “tile series” refers to a plurality of tiles, each of which has been printed with a base pattern and one of the pre-defined overlay patterns from the overlay pattern collection.  The tile series contains at least the same number of tiles as there are overlay patterns (that is, if there are twelve unique overlay patterns, then the tile series has a minimum of twelve tiles).  If each of the twelve unique overlay patterns is manipulated, for example, in one of eight ways, as will be discussed further herein, then the tile series may contain 96 tiles.  Using computer algorithms, the order in which the tiles within a tile series are printed varies from one tile series to the next, creating a random order for printing and installation.  It should be understood that where the base pattern is randomly selected from a much larger base pattern host, thereby resulting in unique base pattern layers, the tile series may be, as a practical matter, infinitely large, particularly if the base pattern is subject to geometric manipulation prior to printing. 
The term “tile collection” refers to sets of tiles that share a unifying base pattern, but hat have overlay layers that are derived from a given tile series intended for use with that base pattern.  Because the tiles in each tile series are produced with overlay patterns that are randomly ordered, the tile collection will similarly contain tiles whose patterns are randomly ordered.  In at least one embodiment, it is potentially preferred that the tiles of a collection are installed so that no two identical tiles are positioned adjacent to one another, in the same row with one another, in the same column with one another, in the same diagonal with one another, or the like, to maintain the random appearance of the installation. 
The term “geometrically manipulated” or “geometric manipulation” refers to processes of altering the appearance of a pattern by techniques such as rotating, mirror-imaging (either along an edge or some selected axis), rotating and mirror-imaging, re-scaling (that is, expansions or contractions of all or portions of a pattern), shifting or translating (that is, moving a design element from one location to another), and the use of more complex, multi-step techniques.  In the case of overlay patterns, the preferred manipulation steps are rotation (preferably in 90-degree increments), mirror-imaging along an edge, rotation and mirror-imaging, and translating.  In terms of multi-step techniques, which are typically more suitable for use with base patterns, multiple patterns may be extracted, or otherwise generated, either from the original extracted pattern or in combination with one or more other pattern(s) extracted from the host pattern.  In the latter case, where multiple patterns are to be used, the various patterns may be electronically “stitched,” collaged, or otherwise combined to form a pattern that is aesthetically pleasing for use on the face of the carpet tile.