NEC SpectraView 2190 User Manual

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NEC SpectraView 2190 User Manual Manual pdf 36 page image

| SPECTRAVIEW II - USER’S GUIDEAbout TargetsSpectraView 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 four specifications that describe the color characteristics of the display:Gamma or Tone Response Curve (TRC)White PointIntensityContrast RatioGamma and Tone Response Curves (TRC)The Gamma or Tone Response Curve of a display is the relationship between the video input signal level and thelight output (“brightness”) displayed on the monitor. The display monitor is a nonlinear display device. In simpleterms, this means that doubling the level of the video input signal to the display does not double the light output. ForCRT based displays, the light output follows a mathematical power function of the input video signal. This powerfunction has an exponent called gamma, which is commonly used to describe the relationship between the videoinput 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 willchange with the display color settings and may vary from one display to the next. If accurate color matching is to beperformed, the display’s Tone Response Curves must be accurately measured and compensated for. SpectraViewuses 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, andon 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 colorspace target specifies a display Gamma value of 2.2. Since the Gamma value of the display may be different thanthe required Gamma value, a correction needs to be applied so that the apparent display Gamma matches thatof 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 normalGamma curve. An example is DICOM, which uses a curve that changes shape based on how bright the display is.White PointThe White Point specifies the color of pure “white” on a display. Since there is no unique perceptual or physicaldefinition of what “white” is, it must be defined in terms of a standard or device-independent color space to bemeasured and reproduced.There are several methods of specifying a white point, including using a blackbody radiator color temperature or asa location in a device-independent color space. SpectraView allows the white point to be specified either as a blackbody 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 anobject, known as a blackbody, as it is heated to a given temperature. Low color temperatures, such as 5000K, arereddish, while higher color temperatures, such as 9300K, are bluish. A color temperature of 6500K is considered tobe “neutral” white.A CIE Standard Illuminant is a defined white color based on a known light source. In SpectraView the D or DaylightIlluminant series can be used to specify a white point. Daylight Illuminants are named according to their correspondingcorrelated color temperature. For example, D50 is very close in color to a 5000K blackbody radiator.••••