Patent Application
20100302273
Liquid crystal display (LCD) display devices are widely used in desktop and other computing environments. An LCD display device (or “LCD device”) includes a liquid crystal panel, a backlight, and associated drive electronics. An LCD device can include an LCD module and associated front end electronics that may include video inputs, peripheral inputs (e.g. USB), scaler, processor, power supply electronics, etc. Color critical LCD devices are widely used in professional photography, video and/or graphics environments, or other environments in which color critical displays may be desired. Color critical LCD devices can be designed to conform to a particular standardized color space or output device specification.
Color management systems in the video source (e.g., a PC or workstation) typically rely on certain identification data provided by the LCD device in order to configure correctly and to provide the proper transform of the image data based on the particular standardized color space or output device specification. However, if the LCD device characteristics cannot be identified by the source, or if the data provided by the LCD device does not match current characteristics, the color management system may not recognize that the LCD device is performing per the intended standard and that no further color management is needed.
If this should occur, the color management system may process the image data in such a way that the resulting image on the display is actually be less accurate than would otherwise be the case. Therefore, it is desirable that the display correctly identifies itself and properly describes the current color characteristics to produce an accurate image.
In color critical LCD devices (e.g., the LP2480zx LCD monitor, commercially available from Hewlett-Packard Company, Palo Alto, Calif.), the LCD device can change performance in terms of color gamut, tone response (or gamma curve), white point, and brightness through by a user selecting one of a number of color space presets. The color information within each preset may also be selected and changed by the user, e.g., using the on-screen display (OSD) controls and a separate calibration tool (e.g., a colorimeter and associated software, used to characterize the display's color performance and then program the color presets as desired).
In this manner, the LCD device may be configured such that the performance matches desired output characteristics. Output characteristics may include, but are not limited to various standard specifications such as, sRGB, AdobeRGB, etc. This ability makes color management by the video source unnecessary, as source images encoded per a given standard may be sent unprocessed to the display, where these images are correctly displayed on the LCD device.
For example, the Adobe® RGB color space is defined by the first triangle 102. In other words, the first triangle 102 defines the color gamut of a LCD device conforming to the Adobe® RGB output device specification within the depicted 1976 CIE u′v′ color space. The second triangle 104 can define defines a sRGB/Rec. 709 output device specification. The third triangle 106 can define a SMPTE-C output device specification. Other output device specifications can also be plotted without the 1976 CIE u′v′ color space depicted in the chromaticity chart 100 as can be appreciated. It should also be appreciated that the depicted color gamuts on the chromaticity chart 100 are not necessarily to scale, and are shown to illustrate that various output device specifications have varying color gamuts within the 1976 u′v′ CIE color space 101.
These standard output device specifications represent an expected response by a display that is designed to comply with such a specification. In other words, for a given input value for a particular pixel on such a display, any display conforming to a particular standard output device specification is expected to emit substantially the same luminance at substantially the same perceived color. Stated another way, any display conforming to the particular standard output device specification is expected to have substantially the same transfer function or gamma response curve. In addition, these specifications also specify RGB primaries, white point, and white luminance with which a conforming display must comply. The RGB primary requirements of a standard output device specification specify the nominal chromaticity coordinates and/or tristimulus values of the red, green, and/or blue primary colors produced by that device at the maximum red, green, and/or blue input value. Likewise, a white point specified by a standard output device specification define tristimulus values and/or chromaticity coordinates that serve to define a target white or reference white of a conforming display.
In addition, an LED backlight is employed, as opposed to a cold cathode fluorescent lamp (CCFL) backlight, which permits white point control via the backlight without adjusting red, green, and/or blue maximum levels of the subpixels of the panel itself. In other words, because the red, green, and blue channels of the backlight can be independently controlled, a whitepoint can be chosen and/or varied according to various standard output device specifications without compensating the maximum subpixel values assignable for red, green, and blue subpixels, which can often be a compromise employed in a display employing a CCFL backlight.
It should be appreciated that various standard output device specifications can define varying color gamuts, each having a varying definition of a whitepoint. Accordingly, as noted above, the RGB LED backlight 304 permits an adjustable whitepoint depending on a standard output device specification chosen, which can be employed without adjusting the maximum subpixel values assignable for red, green, and blue subpixels of the LCD panel 306 in order to compensate for a non-white output of an alternative backlight.
Because the native color gamut of the LCD panel “encloses” various gamuts corresponding to standard output device specifications used in the art, the adjusted input values can be generated by the color gamut mapping engine 502 cause the LCD device 200 to emulate a standard output device specification. In other words, as noted with respect to the discussion regarding
The color gamut mapping engine 502 can also allow a user to select from among various standard output device specifications that can be preprogrammed in the color gamut mapping engine 502. In one embodiment, the color gamut mapping engine 502 or other memory accessible to the LCD device 200 can be configured to store the various color space properties of various standard output device specifications, including, but not limited to, sRGB, SMPTE-C, Adobe® RGB, and SMPTE-431-2. In another embodiment, the color gamut mapping engine 502 or other memory can be configured to store settings that direct how input values and/or the RGB LED backlight should be adjusted in order to compensate for the native properties of the LCD panel such that the LCD device 200 complies with various standard output device specifications.
Accordingly, a user may select a standard output device specification that the user wishes the LCD device 200 to emulate. Additionally, the user may switch between various specifications that the LCD device 200 can emulate, which provides the ability for a user to view content in various output device specifications on a single LCD device 200 without having to recalibrate the monitor for each specification. The color gamut mapping engine 502 can be configurable in this way by commands sent via an input/output interface to the LCD device 200. An input/output interface can include, but is not limited to, a Universal Serial Bus (USB) interface, Ethernet interface, a Data Display Channel/Command Interface (DDC/CI), and other input/output interfaces as can be appreciated.
Additionally, a user may also configure the color gamut mapping engine and/or the RGB LED backlight via the input/output interface to achieve various settings for RGB primaries, whitepoint, gamma, luminance, and other monitor properties that may vary from standard output device specifications for which LCD device 200 is preprogrammed. Accordingly, a user interface to facilitate such functionality can be provided on a personal computer via color calibration software or within the LCD device 200 itself via an on screen display (OSD). These user defined settings can be stored within the color gamut mapping engine 502 or other memory accessible to the LCD device 2001. In this way, a user to create, calibrate, and store these various monitor settings and switch between user defined settings and/or standard output device specifications without a complete recalibration of the monitor.
The LCD device may implement the program code 500 to change performance by the user selecting one of a number of color presets defining color gamut, tone response (or gamma curve), white point, and brightness. The color information within each preset may also be selected and changed by the user, e.g., using the on-screen display (OSD) controls and a separate calibration tool (e.g., a colorimeter and associated software, used to characterize the display's color performance and then program the color presets as desired).
Because the color information may be changed at the LCD device, the updated color information needs to be provided to the host system. In an exemplary embodiment, identification data may be communicated to the host system in a standardized format. One such format is as Extended Display Identification Data (or EDID) file. The EDID format is an industry standard established by the Video Electronics Standards Association (VESA). However, the LCD device is not limited to any particular file format. By way of example, VESA has published a standard currently known as “DisplayID.” DisplayID is similar in structure and function to the EDID format. For purposes of this discussion, however, the EDID format will be used for purposes of illustration.
Typically, the EDID data is fixed at the time of the manufacture for a conventional monitor, and therefore can be stored in nonvolatile memory (e.g., an EPROM) at the monitor and provided to the host system, e.g., at startup. However, in exemplary implementations of the LCD device, the EDID contents may be modified dynamically or “on the fly” as different color presets are selected by the user.
In an exemplary embodiment, EDID data may be provided to the host system as follows. All EDID information which is “generic” to all presets (or static) is stored within the monitor storage 501 (e.g., programmed at the factory). Static information may include, for example, the model number, serial number, supported timings, date of manufacture, etc.
In addition, information specific to each color preset (such as primary chromaticities, “gamma” value, white point, etc.) is stored separately for each preset. A working file generator 503 may produce a working file by merging the static information with the preset-specific (or user-selected) data.
In alternative embodiment, complete preset-specific information files may be generated and stored on the LCD device instead of dynamically generating the working file. These preset-specific information files may then be “swapped in” when each preset is selected by the user.
In operation 701, user input is received at the LCD device, e.g., via the OSD. The user input specifies color information (e.g., primary chromaticities, gamma value, and white point) for each of a plurality of color presets (e.g., sRGB, Adobe RGB, SMPTE-C, and SMPTE-431-2) selected by the user. In operation 702, the color information is merged with static information for the LCD device (e.g., model number, serial number, supported timings, and date of manufacture). Merging may occur each time the user changes color information for each of the plurality of color presets selected by the user. In operation 703, the merged color information and static information is communicated to the host system in a standardized format (e.g., EDID or DisplayID).
The operations shown and described herein are provided to illustrate exemplary implementations of providing user-selected color characteristics for an LCD device to a host system. It is noted that the operations are not limited to the ordering shown. Still other operations may also be implemented.
It is noted that the exemplary embodiments shown and described are provided for purposes of illustration and are not intended to be limiting. Still other embodiments are also contemplated for providing user-selected color characteristics for an LCD device to a host system.
