DICTIONARY.md

Dictionary

color perception

• wikipedia

Paradox / illusions

• Checker shadow illusion and Grey square optical illusion proof2

gamma correction

gamut

gradient/colourmap/palette

• color gradient is a set of colors arranged in a linear order ( ordered)
• palette : In computer graphics, a palette is a finite set of colors in no particular order
• Colorbar is a bar ( = broad shaft, or band, or stripe) that display the current colormap and indicate the mapping of data values into the colormap
• Color transfer function
  • a path through colour space
  • Color mapping ( map) is a function that maps (transforms) the colors of one (source) image to the colors of another (target) image

hue (dull to bright),

• single hue = monochromatic for the value of one numeric variable
• multiple hue (polichromatic ) for the data that aren’t based on the value of a single number ( categories)
• two hue = divergent

saturation ( chroma)

Lightness ( from black to white)

• How to Determine Lightness by Reda Lemeden
• stackoverflow question: formula-to-determine-brightness-of-rgb-color
• desaturation = Converting color to grayscale
  • Three algorithms for converting color to grayscale by John D. Cook
  • gimp 2.6 doc
  • stackoverflow question : Standard-rgb-to-grayscale-conversion
  • Conversion to grayscale by Jason Summers

Relative luminance is formed as a weighted sum of linear RGB components

//from function test_palette_subcommand from the file gnuplot/src/command.c
ntsc = 0.299 * rgb.r + 0.587 * rgb.g + 0.114 * rgb.b;

Photoshop

y = 0.30 * r + 0.59 * g + 0.11 * b;

Perceived brightness ( P from HSP ) by Darel Rex Finley

By playing around with Photoshop’s RGB-to-Greyscale mode conversion, I determined that it is doing something very close to this:

brightness = sqrt( .299 R^2 + .587 G^2 + .114 B^2 )

Cielab lightness

• RGB -> XYZ -> Celab
  • easyrgb
  • in OpenCV source /src/cv/cvcolor.cpp there are functions for color space conversions: icvBGRx2Lab_32f_CnC3R
  • python code by Manoj Pandey

Contrast

• https://en.wikipedia.org/wiki/Contrast_(vision)
• LUMINANCE CONTRAST IN COLOR GRAPHICS by NASA

colour spaces

• perceptualu uniform:
  • CIELAB color space for the characterization of colored surfaces and dyes
  • CIELUV color space for the characterization of color displays
    • HSLUV and hsluv-c
  • Kodak ProPhoto RGB, Adobe RGB (1998) and sRGB are examples of gray balanced and perceptually uniform RGB working color space
• Gray balanced means that equal RGB numbers always produce a neutral gray
• HSP by Darel Rex Finley

data types

• qualitative/quantitative
• ordered/non-ordered
• numerical/categorical(=non-numerical)
  • numerical data subtypes: discrete, continuous, interval, ratio

Qualitative/Quantitative

• Qualitative = can not be measured with a numerical result, needs discrete palette with distinctive colors
• Quantitative = can be measured with a numerical result. Needs continous palette ( sequential)

see also :

• descriptive like descriptive color palettes

ordered/not-ordered data

• ordered
  • continous ( numerical , real numbers)
  • sequential = discrete ( numerical, integer). See sequential palettes from Color Brewer
• not ordered = qualitative, discrete not ordered

Data and gradient relation:

• continous gradient for numeric real type data
• Sequential (discrete) color gradient for orderable or numeric integer data, like gradients from the Color Brewer library. "a series of ordered colors to represent ordinal or numerical data."
  • color scale
  • colour scheme is the choice of colors used in design for a range of media ( www, )
• Qualitative schemes: categorical differences in qualitative data