Patent Application
20090128543
The present invention generally relates to display devices, and more particularly relates to methods and systems for improving performance in field sequential color (FSC) display devices.
In recent years, liquid crystal displays (LCDs), and other flat panel display devices, have become increasingly popular as mechanisms for displaying information to operators of vehicles, such as aircraft. One of the reasons for this is that LCDs are capable of providing very bright and clear images that are easily seen by the user, even in high ambient light situations, such as daytime flight.
Conventional active matrix (AM) LCDs use spatial averaging of the pixels to generate full color from three different colors (e.g., red, green, and blue (RGB)) of light emitters, such as light emitting diodes (LEDs), along with an array of color filters. However, approximately two-thirds of the available backlight power is often absorbed by a color filter array which significantly impairs power efficiency. This loss of power efficiency leads to thermal management being a significant issue in conventional LCD displays for applications requiring high display luminance.
Recently, field sequential color (FSC) displays have been developed for use with various image sources, such as LCDs, cathode ray tubes (CRTs), liquid crystal on silicon (LCOS), and digital micro-mirrors (DMMs). FSC displays do not use color filters and yet generate full color by sequentially writing each pixel in the display in conjunction with sequentially switching RGB emitters in the backlight. Full color is generated at each pixel by temporally averaging the RGB emissions of each pixel. Because color filters are not required, the power consumption is greatly reduced, which often eliminates the need for active cooling of the display in high luminance applications. Additionally, display resolution is effectively tripled when compared with conventional LCDs, as full color may be generated at each individual pixel, rather than using multiple pixels in combination.
However, there still are several limitations to FSC displays, such as FSC LCDs, with respect to maximizing luminance and a propensity for color breakup that adversely affects image quality. In a conventional FSC LCD, each video frame is subdivided into three equal sub-frames, each for refreshing the display with one of the RGB data. Thus, a 60 Hertz (Hz) video refresh rate used in a conventional RGB pixel LCD leads to a 180 Hz refresh rate for an FSC LCD. The RGB LED backlight operation is synchronized with writing the RGB data for the FSC LCD and, in order to avoid unintentional color mixing from one sub-frame to the next, the duty cycle of the RGB emitters has to be reduced to much less than the sub-frame period. The RGB emitters are turned “on” only after all the rows in the display are addressed and the pixels have switched to the demanded state, which reduces the duty cycle of the LED emitters to as low as, for example, 20% of the sub-frame time. This in turn reduces the maximum achievable display luminance using a given RGB backlight. Furthermore, to reduce color breakup in FSC LCDs, the refresh rate is often increased to, for example, 240 Hz, further restricting the duty cycles of the RGB emitters in the backlight, and thus the maximum achievable display luminance.
Accordingly, it is desirable to provide a method and system for improving performance in a FSC display device, such as increasing display luminance and power efficiency and decreasing color breakup. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.
A method for displaying an image on a display device having first and second light sources is provided. A video signal is provided to the display device. The video signal includes a plurality of frames, and each frame includes first and second sub-frames corresponding to the respective first and second light sources. The first light source is operated for a first duration during the first sub-frame of each of the plurality of frames. The second light source is operated for a second duration during the second sub-frame of each of the plurality of frames. The second duration is different than the first duration.
A method for displaying an image on a display device having first, second, and third light emitters and an imaging device is provided. A video signal is provided to the display device. The video signal includes a plurality of frames, and each frame includes first, second, and third sub-frames corresponding to the respective first, second, and third light emitters. The first light emitter is operated for a first duration during the first sub-frame of each of the plurality of frames. The second light emitter is operated for a second duration during the second sub-frame of each of the plurality of frames. The second duration is different than the first duration. The third light emitter is operated for a third duration during the third sub-frame of each of the plurality of frames. The third duration is different than the first and second durations. An image is generated with the light emitted from the first, second, and third light emitters during the respective first, second, and third durations with the imaging device.
A display device system is provided. The display device system includes a backlight comprising first and second light emitters, an image source coupled to the backlight and configured to generate an image with light emitted from the first and second light emitters, and a controller coupled to the backlight and the image source. The controller is configured to provide a video signal to the backlight and the image source. The video signal includes a plurality of frames, each frame comprising first and second sub-frames corresponding to the respective first and second light emitters of the backlight. The controller is further configured to operate the first light emitter for a first duration during the first sub-frame of each of the plurality of frames and operate the second light emitter for a second duration during the second sub-frame of each of the plurality of frames. The second duration is different than the first duration.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, and brief summary or the following detailed description. It should also be noted that
Exemplary embodiments of the invention also provide a display comprising a FSC backlight coupled to a FSC LCD module. Furthermore, the backlight system controller receives and processes brightness data for red, green, and blue light emitters, and video timing signals that synchronize FSC backlight operation with FSC LCD operation. Furthermore, the backlight system controller may be implemented using a plurality of digital controls, including field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), discrete logic, microprocessors, microcontrollers, and digital signal processors (DSPs), or combinations thereof.
The LCD panel 12 is in operable communication with the LCD system controller 16 and the power supply 22.
Referring again to
Referring again to
During operation, the LCD system controller 16 provides video data, or a video signal, to the LCD panel 12 in the form of color and brightness. In one embodiment, and in accordance with FSC display operation, the video data is applied in sequential frames (full or partial video frames), with each frame including multiple (e.g., three) sub-frames, each corresponding only to a particular color (e.g., red, green, or blue). For example, the first sub-frame includes only red data for each display pixel 38 (
The LCD system controller 16 provides a synchronization signal to the backlight subsystem controller 18 to ensure that the red video sub-frame provided by the LCD system controller 16 is synchronized with the activation of the red LEDs 48 (
Referring to
The LCD system controller 16 provides an image synchronization signal to the backlight subsystem controller 18, which may occur at one-third of the sub-frame rate, at the sub-frame rate, or at an alternate rate which ensures synchronized operation between the LCD panel 12 and the backlight 14, depending upon the point of origin for the image synchronization signal. For example, if the sub-frame rate is 180 Hz, then the image synchronization signal may be provided at 60 Hz or 180 Hz.
Thus, within a single frame 56, the operation of the backlight 14 and the LCD panel 12 includes configuring the pixels 38 three times (i.e., once for each of the colors of LEDs) and emitting light through the LCD panel 12 three times (i.e., each of the colors of LEDs being activated once). During the red sub-frame 58, the pixels 38 are appropriately configured for red light within the inactive portion 64, and the red LEDs 48 are operated within the active portion 66. During the green sub-frame 60, the pixels 38 are appropriately reconfigured for green light within the inactive portion 64, and the green LEDs 50 are operated within the active portion 66. During the blue sub-frame 62, the pixels 38 are again appropriately reconfigured for blue light within the inactive portion 64, and the blue LEDs 52 are operated within the active portion 66.
In the depicted embodiment, the time required to configure the pixels 38, or the inactive portions 64 (i.e., LCD data address time period), for each color (or within each sub-frame 58, 60, and 62) is approximately the same (as it involves using the same active matrix LCD for each color). However, as shown, the active portions 66 of the sub-frames 58, 60, and 62 differ considerably. That is, although the time taken to configure the pixels 38 is approximately the same in each sub-frame 58, 60, and 62, the “on-time” for each color is unique. This asymmetry results in the differing durations of the sub-frames 58, 60, and 62 as described above.
The on-times for each color (and thus the sub-frame durations) are optimized based on the required luminance from each of the colors and the relative performance characteristics (i.e., differences in radiant properties) of the individual emitters as described above, as well as perception of the different colors of light by the viewer's eye 54. For example, when the blue luminance requirement is low, the blue LEDs 52 backlight duty cycle, and thus the blue sub-frame 62 time, is decreased in relation to the green sub-frame 60 time and the red sub-frame 58 time. Increasing the on-times for the green and red LEDs 48 and 50 by increasing their duty cycle (and thus increasing their sub-frame times) increases the display luminance for those colors.
One advantage is that display luminance may be increased by as much as 33% compared to a conventional FSC LCD module. In addition to increasing the display luminance, this asymmetric sub-frame operation also allows operation of the FSC LCD system under conditions where the RGB emitters operate more efficiently, thereby reducing the display power consumption. Another advantage is the reduction of the propensity for color breakup image artifact, thereby increasing the image quality of the display. By selectively increasing the duty cycle of the green and red emitters which have higher photopic sensitivity than the blue emitter, the separation between the green-to-green and red-to-red is decreased during saccadic movements, which in turn reduces the propensity for color break-up artifact.
Referring now to
As shown in
During operation the LCD panel 68 and the backlight 70 are arranged such that the upper, mid-, and lower sections 74, 76, and 78 of the LCD panel 68 are aligned with the respective upper, mid-, and lower groups 88, 90, and 92 of the backlight 70. The LCD panel 68 and the backlight 70 may be driven using similar signal to those depicted in
Of particular interest in this embodiment is that the upper section 74 of the LCD panel 68 and the upper group 88 of the backlight 70 continue to carry out the operation as dictated by the green and blue sub-frames 60 and 62 while the other sections and groups are still operating under the red sub-frame 58.
With respect to construction, the LCD 96, may be similar to the one used in the previous embodiments. As with the embodiment shown in
The RGB luminance values for each region 112-118 of the LED backlight 98 are calculated from the image data to be displayed. In essence, the LED backlight 98 shown in
Other embodiments may utilize different numbers and arrangements of light sources (e.g. LEDs). The numbers and arrangements, along with the sizes and shapes of the LEDs may be varied. Additionally, the overall size and shape of the LCD panel (or other image source) used may be varied. For example, a LCD panel with a substantially rectangular shape may have a length of between 3 and 15 inches and a width of between 1.5 and 12 inches. Furthermore, although not described in detail, the backlight power controller 20 (or other control component of the system 10) may include a “dimming” function in which power to the LEDs is reduced for instances with lower luminance requirements, such as nighttime operation.
The flight deck 202 includes a user interface 206, display devices 208 (e.g., a primary flight display (PFD)), a communications radio 210, a navigational radio 212, and an audio device 214. The user interface 206 is configured to receive input from the user 211 (e.g., the pilot) and, in response to the user input, supply command signals to the avionics/flight system 204. The user interface 206 may include flight controls and any one of, or combination of, various known user interface devices including, but not limited to, a cursor control device (CCD), such as a mouse, a trackball, or joystick, and/or a keyboard, one or more buttons, switches, or knobs. In the depicted embodiment, the user interface 206 includes a CCD 216 and a keyboard 218. The user 211 uses the CCD 216 to, among other things, move a cursor symbol on the display devices 208, and may use the keyboard 218 to, among other things, input textual data.
Still referring to
The communication radio 210 is used, as is commonly understood, to communicate with entities outside the vehicle 200, such as air-traffic controllers and pilots of other aircraft. The navigational radio 212 is used to receive from outside sources and communicate to the user various types of information regarding the location of the vehicle, such as Global Positioning Satellite (GPS) system and Automatic Direction Finder (ADF) (as described below). The audio device 214 is, in one embodiment, an audio speaker mounted within the flight deck 202.
The avionics/flight system 204 includes a runway awareness and advisory system (RAAS) 220, an instrument landing system (ILS) 222, a flight director 224, a weather data source 226, a terrain avoidance warning system (TAWS) 228, a traffic and collision avoidance system (TCAS) 230, a plurality of sensors 232 (e.g., a barometric pressure sensor, a thermometer, and a wind speed sensor), one or more terrain databases 234, one or more navigation databases 236, a navigation and control system (or navigation computer) 238, and a processor 240. The various components of the avionics/flight system 204 are in operable communication via a data bus 242 (or avionics bus). Although not illustrated, the navigation and control system 238 may include a flight management system (FMS), a control display unit (CDU), an autopilot or automated guidance system, multiple flight control surfaces (e.g., ailerons, elevators, and a rudder), an Air Data Computer (ADC), an altimeter, an Air Data System (ADS), a Global Positioning Satellite (GPS) system, an automatic direction finder (ADF), a compass, at least one engine, and gear (i.e., landing gear).
The processor 240 may be any one of numerous known general-purpose microprocessors or an application specific processor that operates in response to program instructions. In the depicted embodiment, the processor 240 includes on-board RAM (random access memory) 244 and on-board ROM (read only memory) 246. The program instructions that control the processor 240 may be stored in either or both the RAM 244 and the ROM 246. For example, the operating system software may be stored in the ROM 246, whereas various operating mode software routines and various operational parameters may be stored in the RAM 244. It will be appreciated that this is merely exemplary of one scheme for storing operating system software and software routines, and that various other storage schemes may be implemented. It will also be appreciated that the processor 240 may be implemented using various other circuits, not just a programmable processor. For example, digital logic circuits and analog signal processing circuits could also be used.
While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes can be made in the function and arrangement of elements without departing from the scope of the invention as set forth in the appended claims and the legal equivalents thereof.
