This invention pertains to the field of color displays and more particularly, to a color display system and a method of color display using multiple primary colors.
Color can be defined in terms of three essential parameters: hue, saturation, and brightness. These three parameters will now be explained in further detail with respect to the well-known Newton color circle, which is shown in
Hue is related to a wavelength for spectral colors. The terms “red” and “blue” are primarily describing hue. It is convenient to arrange the saturated hues around the circumference of Newton color circle as shown in
Saturation relates to the purity of the color. In
Brightness has been defined as exhibiting more or less light. In
So, it can be seen that two different colors may have an identical hue, but different saturation and/or brightness values.
In view of the foregoing, it will be understood that as the term is used herein, a color is a unique combination of hue, saturation, and brightness values. Further understanding if these terms may be had by reference to “CIE Colorimetry,” Publication 15.2 of the Commission Internationale d'Eclairage (International Commission on Illumination) (CIE) (1986). Another good reference for explaining these terms is “Measuring Colour,” R. W. G. Hunt, 2nd Edition (1991).
This ensemble of rods 110 in some respects has the characteristics of a high-speed, black and white film (such as Tri-X). The rods 110 are exceedingly sensitive, performing in light too dim for the cones 120 to respond to, yet they are unable to distinguish color. Also, the images relayed to the brain by the rods 110 are not well defined. That is, the rods 110 are more sensitive to detect light at lower intensity levels than the cones 120, but do not distinguish between colors. The rods 120 are the primary source of vision at night.
In contrast, the ensemble of cones can be imagined as a separate, but overlapping, low-speed color film. They perform well in bright light, giving detailed colored views, but they are fairly insensitive at low light levels. That is, the cones 120 have a higher light threshold for activation than the rods 110 (they are less sensitive to overall light intensity).
There are three different types of cones 120, each one of which process different colors of the spectrum differently. The three types of cones 120 are generally referred to as cyanolabes, chlorolabes, and erytholabes. Cyanolabes are most sensitive to blue light, chlorolabes are most sensitive to green light, and erytholabes are most sensitive to red light. The chlorolabes and erytholabes are mostly packed into the fovea centralis region of the eye. The cyanolabes are mostly found outside the fovea. It is currently believed, based on measured response curves, that the 6 to 7 million cones 120 are divided as follows: 64% erytholabes, 32% chlorolabes, and 2% cyanolabes.
Color matching studies carried out in the 1920s showed that colored samples could be matched by combinations of monochromatic primary colors Red (700 nm), Green (546.1 nm) and Blue (435.8 nm). The average responses of a large group of observers can be reproduced by a set of three color matching functions. One set of commonly used color matching functions are CIE color matching functions.
Any set of three colors which, when added in appropriate combination can yield white, are called “primary colors.” It is useful to map a color space with a set of primary colors, such as blue, green, and red. If unit amounts of B, G, and R colors produce white light, then theses three colors can be used like unit vectors to define the color space.
The CIE color space uses a parameter Y to measure brightness, and parameters x and y to specify the chromaticity which covers the properties hue and saturation on a two dimensional chromaticity diagram.
Based on the fact that the human eye has three different types of color sensitive cones, as discussed above, the response of the eye is best described in terms of three “tristimulus values,” usually denoted as X, Y and Z. From the color matching functions, one can derive tristimulus values that specify the chromaticity. However, once this is accomplished, it is found that the colors can be expressed in terms of the two color coordinates x and y.
In general existing color display systems display images using a set of only three primary colors, typically red, green, and blue. An existing display system combines the three primary colors with appropriate weightings to produce all of the various colors to be displayed.
However, one cannot display the entire range of human color perception by combinations of only three primary colors (e.g., RGB). The colors which can be matched by combining a given set of three primary colors (such as the blue, green, and red of a color television screen) are represented on the chromaticity diagram by a triangle joining the coordinates for the three colors, the interior of which is referred to as its gamut.
It is important for many displays to be able to fully reproduce the entire EBU color gamut, as this is a widely-adopted standard for video displays. However, it is also desired to provide a display which can not only reproduce all colors within the EBU color gamut, but which can do so with high brightness levels.
From the discussion above, it can be seen that the three primary color elements in existing displays simultaneously need to be able to cover a large color gamut and to generate the high brightness levels that are required at certain color points in the color space.
These fundamental requirements limit the choice of materials and components which are available to produce a display device. For example, with phosphor-based display systems, phosphors must be selected that can provided saturated colors and also can handle the high loads to generate a desired brightness level. Due to the high load and desire for a long-lived phosphor, the choice of phosphor materials is rather limited. Similarly, with laser projection displays the existing three-primary-color systems require high-powered lasers having good color points and long lifetimes. Such lasers are not available at this time.
In an attempt to address some of these requirements, some digital light processing (DLP) projectors add a fourth white color element to the three standard primary color elements for red, green and blue. The white color element has a color point at or very close to the desired white color point for the system (e.g., D65, 9200K, etc.). However, such an approach does not expand the color gamut, or permit increased intensity for highly saturated colors that are located far away from the white color point.
Accordingly, it would be desirable to provide to a color display system and a method of color display that can simultaneously meet color saturation and brightness requirements. It would also be desirable to provide such a color display system that can utilize a wider range of materials, including longer-lived materials. The present invention is directed to addressing one or more of the preceding concerns.
In one aspect of the invention, a color display system comprises a plurality of pixels, and means for controlling the plurality of pixels to display an image. Each pixel comprises a first set of three primary color elements and a second set of three primary color elements. Each of the primary color elements of the first set has a different color than any of the other primary color elements of the first set, and each of the primary color elements of the second set has a different color than any of the other primary color elements of the second set and the first set.
In another aspect of the invention, a color display system comprises first, second, third, and fourth primary color elements. Each first through fourth primary color elements has a different color. The first through third primary color elements together span a first color gamut. The fourth primary color element is capable of producing a substantially greater brightness level than the one of the first through third primary color elements whose color is closest to the color of the fourth primary color element.
In yet another aspect of the invention, a method of displaying a pixel of an image, comprises: providing first, second, and third primary color elements, the first through third primary color elements having three corresponding colors that are different from each other, and said first through third primary color elements together spanning a first color gamut; providing a fourth primary color element having a different color than any of the first through third primary color elements, wherein the fourth primary color element is capable of producing a substantially greater brightness level than a one of the first through third primary color elements having a color closest to the color of the fourth primary color element; and proportionately combining the colors produced the first through fourth color elements to produce a desired pixel color.
Further and other aspects will become evident from the description to follow.
The first set of primary colors, labeled 1110, 1112, and 1114 (e.g., R1, G1, and B1), are located relatively close to the locus of the 1931 CIE standard chromaticity diagram. The first set of primary colors 1110, 1112, and 1114 can cover a large area within the color space, and are able to generate very saturated colors. The first set of primary colors 1110, 1112, and 1114 defines a first color gamut.
Meanwhile, the second set of primary colors, labeled 1120, 1122, and 1124 (e.g., R2, G2, and B2), are located inside the first color gamut. The second set of primary colors 1120, 1122, and 1124 defines a second color gamut. Beneficially, the second color gamut is located entirely within the first color gamut. In general, the second set of primary colors 1120, 1122, and 1124 are all less saturated than the first set of primary colors. However, in general, the second set of primary colors 1120, 1122, and 1124 can generate very high brightness levels compared to the first set of primary colors.
In practice, then, a color display system can use two sets of three primary color elements corresponding to the two sets of three primary colors.
In such a color display system, all colors that are located within the second color gamut of the second set of primary colors 1120, 1122, and 1124 can be obtained using the second set of color elements. Accordingly, high brightness levels can be achieved as desired. Optionally, colors that are located within the second color gamut can be obtained by mixing all six primary colors.
Meanwhile, all colors outside the second color gamut, but within the first color gamut of the first set of primary colors 1110, 1112, and 1114, can be produced using the first set of primary color elements.
These principles illustrated with respect to
Of course, other embodiments are possible using the principles described above, including electroluminescent devices (ELD), light emitting diode (LED) displays, LCD and liquid crystal on silicon (LCOS) projection displays, color plasma displays, raser base displays and poly-LED devices, etc.
As before, a color display system operating with four colors according to these principles may comprise a CRT, an LCD, an ELD, a color plasma display, etc. A concrete example will now be provided in the context of a laser color projection display system.
A blue (B) channel for such a system might comprise two lasers: (1) a deep blue (453 nm) laser for producing the blue saturated colors, but outputting light with a low number of lumens; and (2) a high-lumen blue (473 nm) laser for producing the bright blue light contributions. Advantageously, it is easier to make a 473 nm laser with higher lumen levels and a sufficient life time, than to do so with a 453 nm laser.
Furthermore, such a system might use only a single laser for the green (G) channel, and only a single laser for the red (R) channel, e.g., a green (532 nm) laser for producing the green saturated colors and the bright green light contributions, and a red (630 nm) laser for producing the red saturated colors and the bright red light contributions. In that case, the green (G) laser and the red (R) laser each need to individually provide the combined color saturation, brightness and lifetime requirements.
Meanwhile, for the blue (B) channel, the 453 nm laser is used to generate the highly saturated blue colors of a desired color gamut (e.g., the EBU color gamut), while the 473 nm laser is used to generate high-lumen (bright) blue light fluxes when brighter images are displayed. That is, the 453 nm, 532 nm, and 630 nm lasers together can span a desired color gamut (e.g., the EBU color gamut), but together they cannot achieve a desired brightness level. Conversely, the 473 nm, 532 nm, and 630 nm lasers together can produce a high brightness level, but together they cannot span all of a desired color gamut (e.g., the EBU color gamut). For example, the 473 nm, 532 nm, and 630 nm lasers together are not capable of covering the lower left region of the EBU color gamut.
Thus, the combination of a 453 nm laser and a 473 nm laser to span the entire EBU standard color gamut, and to achieve high brightness levels, is a technically feasible solution to covering the entire desired color gamut and achieving desired brightness levels, at a lower cost. Similarly, two lasers could be used to generate the green (G) and/or the red (R) channels.
Variations of the example above are possible within the principles disclosed herein. For example, the first through third colors may span the entire desired color gamut, and the fourth color may lie inside the first color gamut, only being used to increase to increase brightness. Furthermore, another variation is possible where the first through third colors together cannot span a desired color gamut, and the fourth laser not only increases the brightness level, but also provides a missing range of color to span the desired color gamut.
While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB04/51871 | 9/27/2004 | WO | 3/10/2006 |
Number | Date | Country | |
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60507140 | Sep 2003 | US |