The present invention relates to a light-emitting diode (xe2x80x9cLEDxe2x80x9d) display apparatus. More particularly this invention relates to a light-emitting diode display apparatus used for a display such as a type of a standing signboard and methods for controlling same.
In conventional LED displays three well-chosen primary colors are used to produce a wide range of colors. The three well-chosen primary colors, when added together in the appropriate proportions, can approximate many of the colors that a human can perceive. This is a thoroughly studied area of human perception that is explained by the fact that the human eye perceives color using three different types of sensors called cones. A human perceives color when any or all of these three types of cones are stimulated. Theoretically, if three light sources, in this case LEDs, can individually stimulate these three different kinds of cones, all human perceivable colors could be duplicated. In practice, however, light sources because of certain deficiencies, cannot produce the stimuli needed to reproduce all colors.
An LED display is typically made up of various dots arranged in a matrix pattern having rows and columns. The dots are usually called pixels where the pixels are made up of several LEDs. The individual LEDs emit light of three basic colors: red, green and blue. Typically, each pixel is composed of at least one LED of each color. The intensity of the LEDs is usually controlled by controlling the current to the individual LEDs. This is sometimes referred to as controlling the drive to an LED. A pixel can produce a specific perceived color by varying the drive to the three colors of LEDs that comprise the pixel. Thus, by controlling the current drive to each of the LEDs that makes up a pixel and in turn controlling each of the pixels that make up a matrix of pixels, an LED display device is capable of displaying a plurality of colors and light intensities so as to realize, for example, a multi-color display. A large LED display can contain hundreds of thousands of pixels and millions of LEDs.
In an LED display, each of the pixels and each of the LEDs must be controlled. Accordingly, prior art systems utilize a display driver in conjunction with a decoder and microprocessor for controlling the drive to each LED of a display. U.S. Pat. No. 5,612,711 (the xe2x80x9c711 patentxe2x80x9d), entitled xe2x80x9cDisplay System,xe2x80x9d describes an example of such a prior art system. The ""711 patent discloses an apparatus and method for driving LEDs of different colors in a matrix of pixels. Differently colored LEDs are commonly connected so that a voltage applied to one LED is applied to all the commonly connected LEDs. Drivers provide different voltages to different color LEDs in the matrix of LEDs. A processor controls the overall operation of the LED display.
Prior art displays, however, suffer from several deficiencies. Prior art LED displays that use three color of LEDs have a limited color gamut, significantly less than that able to be perceived by humans. Furthermore, prior art systems suffer from poor quality control in the transferring of original artwork to a display medium such as an LED display.
Prior art systems also suffer from undesirable artifacts such as contouring due to inappropriate luminance control at low brightness. Undesirable artifacts due to increments in dynamic range are called xe2x80x9ccontouringxe2x80x9d because the increments in intensity produce what looks like flat regions in brightness with jumps or increments that look like contour lines.
A light-emitting diode display according to the present invention is generally comprised of light-emitting diodes (xe2x80x9cLEDsxe2x80x9d), which use a plurality of colors including blues, reds, and greens arranged in a specific pattern such as a matrix pattern. The display is appropriate, inter alia, for displaying moving or stationary images by powering the LEDs so that light from individual LEDs combine to produce the desired color, brightness and spatial pattern of light.
One aspect of the invention is a method for displaying an image on a light-emitting diode (LED) display. In the embodiment, the display comprising a matrix of pixels, each pixel made up of at least four LEDs each capable of emitting light at an individual chromacity. The method specifies a color to be displayed at a pixel and at least one desired operating characteristic for said pixel is selected. The method identifies a plurality of color gamuts containing said specified color, each color gamut being defined by a different set of said at least four LEDs of said pixel and being associated with at least one operating parameter. The method further selects from said plurality of color gamuts the color gamut having at least one operating parameter most closely corresponding to said at least one desired operating characteristic. The method then generates said specified color within said selected color gamut.
In alternative embodiments one of said plurality of color gamuts is defined by at least four LEDs. Also, the desired operating characteristic includes at least one of minimized power consumption, minimized current draw, minimized time usage and maximized brilliance. In another embodiment, the at least one desired operating parameter includes at least one of power consumption, current draw, on/off state and brilliance. And in still another alternative embodiment, the method selects a specific LED within a pixel for which an operating parameter is to be optimized and selects the color gamut most closely associated with said optimized operating parameter.
Another aspect of the invention is a method for displaying an image on a light-emitting diode display. In this method the display has a first set of light-emitting diodes capable of emitting light having a first set of chromacities and the first set of chromacities is equal to or greater than four. The method of the invention includes identifying at least one light-emitting diode capable of emitting light having a at least one chromacity for which an operating parameter is to be minimized. The method then identifies a first region of chromacity with a first boundary available through operation of the at least one light-emitting diode and a first subset of said first set of light emitting diodes capable of emitting light having a first subset of chromacities. The method further identifies a second region of chromacity with a second boundary available through operation of a second subset of light emitting diodes capable of emitting light having a second subset of chromacities. When a color is specified, the method determines whether the desired color resides within the second boundary. If the desired color resides within the second boundary, the method generates the desired color using the second subset of light-emitting diodes, thereby minimizing the operating parameter. Alternatively, if the desired color does not reside within the second boundary, the method generates the desired color using said at least one light-emitting diode and the second set of light-emitting diodes.
According to another embodiment of the invention, a light-emitting diode display is described. The light-emitting diode display includes a plurality of pixels arranged in a plurality of rows and columns to display a predetermined image. The plurality of pixels is composed of a first set of light-emitting diodes capable of emitting light having a first set of chromacities which are equal to or greater than four. The light-emitting diode display also includes digital input circuitry to input a digital signal for a desired color and a desired luminance. A digital-to-analog then capable of converting the digital signal to an analog signal. Control electronics is then capable of driving the plurality of pixels. The invention further includes a threshold operator capable of determining whether the desired color is within a first region of chromacity with a first boundary. The first region is available through operation of at least one light-emitting diode capable of emitting light having a first chromacity and a second set of light emitting diodes capable of emitting light having a second set of chromacities. The threshold operator is further capable of determining whether the desired color is within a second region of chromacity with a second boundary available through operation of third set of light emitting diodes having a third set of chromacities. The third set does not include the first light-emitting diode and, wherein the third set of light-emitting diodes is less than or equal to the first set.
In an alternative embodiment of the invention, the desired color is within the first region of chromacity and the control electronics drives the at least one light-emitting diode and the second set of light-emitting diodes to generate the desired color. In another embodiment, the desired color is within the second region of chromacity and the control electronics drives the third set of light-emitting diodes to generate the desired color. In yet another embodiment, the control electronics implements a non-linear control function which may include polynomial, exponential, or piece-wise linear function.
According to another embodiment, the invention is an image transfer interface that includes calibrating a workstation display and developing an image on said workstation display. The method then converts the image to a digitally specified image, wherein the digitally specified image is in accordance with a standard. The digital image is then transferred to a recipient that maps the digitally specified image to an light-emitting diode display.
In alternative embodiments, the standard is a CIE standard including the CIELAB standard. In another embodiment, the light-emitting diode display is calibrated. A computer network may be used for transferring the digitally specified image.
Alternative embodiments of the invention include implementing the methods of the invention on a computer having a memory and a processor. Other embodiments implement the methods of the present invention using more than one distributed computer.
The present invention further includes a fault tolerant method for displaying images on an light-emitting diode display. The method includes inputting a first image, displaying the first image. Upon detecting the absence of a second image, the method inputs a default image; and displays the default image. In another embodiment, the default image is a set of default images.