Method and apparatus for visually measuring the chromatic characteristics of a display

#The present invention relates in general to a method and apparatus for measuring the chromatic characteristics of a display. In particular, the present invention relates to a method and apparatus for visually measuring the chromatic characteristics and without the use of color matching cards or the hardware meters such as calorimeter, spectroradiometer, and photometer. More particularly, the present invention relates to a method and apparatus for measuring the tonal response curves (TRCs) of the primary colors, where the TRC model can be described by any kind of function, and accurate white point of a display if the provided chromaticity characteristics of the primaries are accurate.

#A color display usually consists of red, green, and blue primaries. High-fidelity color picture can be re-generated with the display if the chromatic characteristics of the display are well understood. The chromatic characteristics include the chromaticity coordinates and TRCs of the primaries, and white point. A color display shows white color when its RGB video inputs are of the same value. The chromaticity coordinate of the white color is called the white point. The white point is determined by the relative luminance among the primaries. For example the standard ITU-R BT.709 for color displays designates the white point as x=0.3127 and y=0.3291. However, usually several white point options are provided for a computer monitor. The TRC is the relation of the luminance of a primary color and the video voltage. For example, the TRC of a CRT display can be described by a power function, which is known as gamma model and can be expressed as Luminance=[Video Voltage]γ, where gamma γ is a constant.

#The chromaticity coordinates of the primaries of a CRT display are fixed if there is no crosstalk among the primaries. If its tube type, e.g. Sony Trinitron, or phosphor, e.g. P22, is known, the chromaticity coordinates of primaries can be known. Usually the chromaticity coordinate of the white point of a display either follows a standard or can be known by the color temperature setting of the monitor. However in practice different display manufacturers usually set different chromaticity coordinates for the same so called color temperature, such as 6500K and 9300K. Nowadays, the chromaticity characteristics of a display are recorded in the extended display identification data (EDID) memory embedded in most computer monitors. EDID is a standard of Video Electronics Standards Association (VESA). The white point recorded in EDID is the default setting of the monitor. There is a gamma value of TRC stored in EDID. However, the value it is usually incorrect because the change of brightness and contrast setting of the display may change the gamma value; besides the three gamma values of the red, green, and blue primaries may not be the same.

#FIG. 1 illustrates an example of NULR with two different kinds of luminance levels.

#FIG. 2 illustrates the cases of (a) ULR 3 is surrounded by NULR 4 and (b) NULR 4 is surrounded by ULR 3.

#FIG. 3 illustrates (a) the chromaticity triangle and (b) a portion within the triangle.

#This invention discloses a method and apparatus for visually measuring the TRCs of primaries and the white point of a display without the help of hardware meters. The methods for measuring the TRCs and white point are separately described in detail in the followings. The apparatus for implementing the disclosed methods is also described. The present invention is described hereinafter with reference to the accompanying drawings, in which a preferred embodiment of the invention is shown. This invention may be embodied in many different forms and should not be constructed as limited to the embodiments set forth herein.

#TRC Measurement

#The TRC of a primary is designated as R(v), where v is video voltage and the maximum video voltage is V. In a computer apparatus the video voltage is digitized as 1 v = m ⁢ V 2 ″ - 1 , ⁢ m = 0 , ⁢ 1 , ⁢ 2 , ⁢ … ⁢ , ⁢ ⁢ 2 n - 1 , ⁢ ( 1 )