Electric lamp and discharge devices: systems – Plural power supplies – Plural cathode and/or anode load device
Reexamination Certificate
2000-06-09
2002-03-19
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Plural power supplies
Plural cathode and/or anode load device
C315S169300, C315S169400, C345S058000, C345S060000
Reexamination Certificate
active
06359389
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to the field of display devices. More specifically, the present invention relates to the field of flat panel display devices having adjustable gamma responses.
(2) Background
Flat panel or liquid crystal displays (LCDs) are popular display devices and are used in computer systems, multi-media systems and other consumer electronic devices. Many types of flat panel displays are typically back-lit or edge-lit. That is, a source of illumination is placed behind the LCD layers to facilitate visualization of the resultant image. The LCD material acts as a regulator of light passing through color filters and to the eye, thereby forming an image. Flat panel LCD units are used today in many applications including the computer component industry and the computer peripheral industry where flat panel LCD units are an excellent display choice for lap-top computers and other portable electronic devices. Flat panel LCD displays are also being used in the high end graphic arts industry where display quality and realistic image quality are very important consumer goals.
In the field of flat panel LCD devices, much like conventional cathode ray tube (CRT) displays, a pixel is composed of a red, a green and a blue color point or “spot.” When each color point of the pixel is illuminated simultaneously, and with the appropriate intensity, white can be perceived by the viewer at the pixel's screen position. To produce different colors at the pixel, the intensities (e.g., brightness) to which the red, green and blue points are driven are altered in well known fashions. The separate red, green and blue data that correspond to the color intensities of a particular pixel are called the pixel's color data. Color data is often called gray scale data. The degree to which different colors can be achieved by a pixel is referred to as gray scale resolution. Gray scale resolution is directly related to the amount of different intensities (e.g., luminosities) to which each red, green and blue point can be driven.
All color systems must accurately reproduce the color tones of the original scene. Since no known reproduction process can exactly capture the original elements in a given situation (e.g., the brightness of the sun shining down on a landscape), the basic goal of reproduction is to capture the relative differences between objects in the original view. The ratio of the whitest point to the blackest point in a scene is know as its dynamic range, which must be reproduced on some medium such as film, a CRT, an LCD, or paper. The characteristics of this medium, or its “native response,” will determine the level of success a given reproduction achieves.
The number of steps, or gray scale, into which this dynamic range can be subdivided determines the resolution of a particular primary color. A typical monitor system will have the ability to display 8-bits, or 256 shades per primary color for a total of over 16.7 million colors (256×256×256). This is known as the color depth or image palette of the display system.
These display mediums, especially CRTs, although they behave in a fairly linear fashion, introduce some amount of distortion which has to be corrected to make the reproduced image look “proper.” Human eyes see logarithmically. To compensate for this, monitors are made to mimic the eye's viewing so that the display shows the eye information in a way people are used to seeing. The resulting response curve varies in an exponential manner known as the “gamma curve,” which is a polynomial equation describing any point on a brightness curve being displayed by a particular monitor. Its function is to correct for the non-linearity of the input signal and its corresponding luminance. Using CRTs as an example, the brightness changes very little at the lower energy gray levels causing some compression of the shadow detail where our eyes are the most sensitive. So instead of a straight-line, linear response where there is a equal amount of output change for a given input change, the gamma curve has a long, shallow beginning before it begins to climb.
Traditionally, display management systems manipulate the shape of the gamma curve through the use of color lookup tables (“LUTs”) in a memory location some where in the data information path on the host computer or graphics card. The LUT contains one entry, typically, per gray scale level. The information bits that make up an image are converted from one value to another, as in the following equation, on their way to the display device. This method has farther reaching applications.
RGBc=RGBc
−max[[−
kop
+(
RGB
in/(
RGB
in−max))
(1/×)
]/Kgp]
where:
RGBc=corrected RGB value
RGBc−max=maximum of corrected RGB values (2
n
−1)
RGBin=RGB input value
RGBin−max=maximum of RGB input values (2
n
−1)
Kop, Kpg, x=fitted parameters of display primary channel
By using LUTs to alter the gamma curve, the host computer system or graphics card can impact the luminance (brightness) as well as the color temperature of the monitor.
There are strong historical reasons why particular gamma responses have been selected by different display customer segments. For instance, different displays may have different gamma responses. In some instances, however, the gamma response of a display is based on the type of work for which display is used. For instance, a digital television (TV) or web based TV may use a different gamma response than a high end graphics computer aided design system, etc. Further, print media may select 1.8 gamma and film media may use 2.2 gamma. Further, the gamma response of a display device may be altered depending on the environment in which the screen is used, e.g., the lighting characteristics of the office, etc. The displays available today solve these issues on an independent, case-by-case basis. Different displays may have different gamma responses. Therefore, it is advantageous to provide a display device that has an adjustable gamma response. It is further advantageous to provide a display device that could give the display added flexibility to solve all such applications well.
There is a disadvantage in using LUTs to correct the normal gamma setting, the color temperature, and the brightness at which a particular display operates: the overall luminance and color resolution (e.g., the “color depth”) of the displayed data can be compromised by using LUTs to correct the normal gamma setting. Adjusting these three image elements in this manner can use up to 2 bits of information in a memory register that would normally be applied toward describing the tonal qualities of the image itself. Loss of 2 bits of color depth in an 8-bit system means that the user is being deprived of 16.52 million colors (2
8
×2
8
×2
8
−2
6
×2
6
×2
6
) out of a possible palette of 16.78 million. Traditional solutions increase the addressable memory depth in the host or the graphics card to 10-bits in order to over-sample the RGB input, apply the correction, and then down-sample to preserve the original column information. However, this is costly and difficult to implement. Therefore, using LUTs to correct the normal gamma setting can lead to a degradation of the overall gray scale resolution of a monitor. Therefore, it is advantageous to provide a display device that has an adjustable gamma response without an incidental degradation of gray scale resolution.
SUMMARY OF THE INVENTION
Accordingly, it would be advantageous to provide a display that allows its gamma response to be altered without any incidental loss in gray scale resolution. It would also be advantageous to provide a display that allows its gamma response to be altered, via software control, without any incidental loss in gray scale resolution. It would also be advantageous to provide a flat panel LCD display that allows its gamma response to be altered, via software contro
Evanicky Daniel E.
Medina Oscar I.
Mendelson Jonathan D.
Silicon Graphics Inc.
Vu Jimmy T.
Wagner , Murabito & Hao LLP
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