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1 | NEC Display Wall Calibrator - UsEr's GUiDE
The choice of Intensity adjustment method will depend on the particular application and viewing environment.
If the displays are being used in a bright environment, then the Intensity would generally need to be the maximum
possible. So either Maximum Possible Matching or Maximum Possible Per Display would be used.
White Point
The White Point specifies the color of pure "white" on a display. Since there is no unique perceptual or physical
definition of what "white" is, it must be defined in terms of a standard or device-independent color space to be
measured and reproduced.
There are several methods of specifying a white point, including using a blackbody radiator color temperature or
as a point in a device-independent color space. NEC Display Wall Calibrator allows the white point to be specified
either as a black body radiator color temperature in Kelvin, as a CIE standard illuminant, or as CIE xy chromaticity
coordinates.
A White Point expressed as a blackbody radiator color temperature in Kelvin represents the light given off by an
object, known as a blackbody, as it is heated to a given temperature. Low color temperatures, such as 2500K, are
reddish, while higher color temperatures, such as 9300K, are bluish. A color temperature of 6500K is considered to
be "neutral" white.
A CIE Standard Illuminant is a defined white color based on a known light source. In NEC Display Wall Calibrator
the D or Daylight Illuminant series can be used to specify a white point. Daylight Illuminants are named according
to their corresponding correlated color temperature. For example, D50 is very close in color to a 5000K blackbody
radiator.
Since adjusting the White Point away from the native value of the display involves reducing the level of at least one
color (red, green, or blue), the brightest possible display will be when least amount of correction is made. Choosing
a White Point that is very different from the native White Point will mean that a large correction must be applied, and
the maximum brightness will be impacted.
If the application the video wall is being used for does not need a specific White Point, and the brightest possible
display is required, a White Point that will achieve the highest possible overall Intensity after calibrating can be
automatically calculated. This calculation factors in the native Intensity and White Points of each display in order to
determine the resulting White Point. This function is available in the White Point group in the Edit Calibration Target
dialog.
Gamma and Tone Response Curves (TRC)
The Gamma or Tone Response Curve of a display is the relationship between the video input signal level and the
light output ("brightness") displayed on the monitor. The display monitor is a nonlinear display device. In simple
terms, this means that doubling the level of the video input signal to the display does not double the light output. For
CRT based displays, the light output follows a mathematical power function of the input video signal. This power
function has an exponent called gamma, which is commonly used to describe the relationship between the video
input signal and light output of the screen.
A gamma value of 1 would result in a perfectly linear display (doubling the signal level doubles the light output)
and the Tone Response Curves would be straight lines. The particular Tone Response Curves of a display will
change with the display color settings and may vary from one display to the next. If accurate color matching is to be
performed, the display's Tone Response Curves must be accurately measured and compensated for. NEC Display
Wall Calibrator uses the color sensor to automatically measure the Tone Response Curves of the display.
Normally, a standard Gamma value is required when working with images. For example, the sRGB standard color
space target specifies a display Gamma value of 2.2. Since the Gamma value of the display may be different than
the required Gamma value, a correction needs to be applied so that the apparent display Gamma matches that of
the required Target. In NEC Display Wall Calibrator, this correction is applied to the LUTs (Look Up Tables) inside
the monitor. The software also uses the monitor's LUTs for Targets that have Tone Response Curves which do not
follow a normal Gamma curve. An example is DICOM, which uses a curve that changes shape based on how bright
the display is.
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