About Targets - NEC SpectraView II Guia Del Usuario

43 | NEC SPECTRAVIEW II - USER'S GUIDE

About Targets

SpectraView can also create custom Targets, which can then be exchanged with other SpectraView display users,
providing identical calibrated displays.
A Target consists of up to six specifications that describe the color characteristics of the display:
• Gamma or Tone Response Curve (TRC)
• White Point
• Intensity
• Contrast Ratio
• Color Gamut
• 6 Axis Color Trim
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. SpectraView uses the color
sensor to automatically measure the Tone Response Curves of the display.
Note:
If you are unsure what gamma value to use for a Target, try 2.2 which is the most popular on Windows, and on Macs for
most applications. A value of 1.8 is popular for some printing applications on Macs.
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 SpectraView, this correction is applied to the LUTs (Look Up Tables) inside the monitor. SpectraView 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.
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
location in a device-independent color space. SpectraView 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 black body 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 5000K, are reddish,
while higher color temperatures, such as 9300K, are bluish. A color temperature of 6500K is considered to be "neutral"
white.