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On a typical standard 2.2-gamma CRT display, an input intensity RGB value of (0.5, 0.5, 0.5) only outputs about 22% of full brightness (1.0, 1.0, 1.0), instead of 50%. [19] To obtain the correct response, a gamma correction is used in encoding the image data, and possibly further corrections as part of the color calibration process of the device.
The first three numbers are the white point to use, then the average surround lighting, in this case 200 cd/m², then the relative luminance of the surround on the same scale as the white point, in this case 18%, then the surround conditions, where 1 = average, 2 = dim and 3 = dark, and then XYZ coordinates of the color to check.
No one color model is necessarily "better" than another. Typically, the choice of a color model is dictated by external factors, such as a graphics tool or the need to specify colors according to the CSS2 or CSS3 standard. The following discussion only describes how the models function, centered on the concepts of hue, shade, tint, and tone.
"HCL" designed in 2005 by Sarifuddin and Missaou, which is a transformation of whatever type of RGB color space is in use. [5] HCT with tone as a synonym for luminance is then used within Material Design for its color system, using value ranges of 0–360°, 0–120+ and 0–100%, respectively. [6]
N bb is a fudge factor that is normally 1; it's only of concern when comparing brightness judgements based on slightly different reference whites. Here Y is the relative luminance compared to white on a scale of 0 to 1 and L A is the average luminance of the adapting visual field as a whole, measured in cd/m 2.
A comparison between a typical normalized M cone's spectral sensitivity and the CIE 1931 luminosity function for a standard observer in photopic vision. In the CIE 1931 model, Y is the luminance, Z is quasi-equal to blue (of CIE RGB), and X is a mix of the three CIE RGB curves chosen to be nonnegative (see § Definition of the CIE XYZ color space).
For each 8-bit RGB octet triple contained in each 24-bit color value in the input image, the NTSC luminance is computed using the following formula: [1] [2] [3] = + + The image is now subdivided into 4-pixel by 4-pixel blocks, and, the arithmetic mean of the luminance of each pixel in the block is used to select a representative luminance value.
Judd was the first to employ this type of transformation, and many others were to follow. Converting this RGB space to chromaticities one finds [4] [clarification needed The following formulae do not agree with u=R/(R+G+B) and v=G/(R+G+B)] Judd's UCS, with the Planckian locus and the isotherms from 1,000K to 10,000K, perpendicular to the locus.