text: /*-
   * sRGB.h
   *
   * Last changed in libpng 1.6.0 [February 14, 2013]
   *
   * COPYRIGHT: Written by John Cunningham Bowler, 2013.
   * To the extent possible under law, the author has waived all copyright and
   * related or neighboring rights to this work.  This work is published from:
   * United States.
   *
   * Utility file; not actually a header, this contains definitions of sRGB
   * calculation functions for inclusion in those test programs that need them.
   *
   * All routines take and return a floating point value in the range
   * 0 to 1.0, doing a calculation according to the sRGB specification
   * (in fact the source of the numbers is the wikipedia article at
   * https://en.wikipedia.org/wiki/SRGB).
   */
  static double
  sRGB_from_linear(double l)
  {
     if (l <= 0.0031308)
        l *= 12.92;
  
     else
        l = 1.055 * pow(l, 1/2.4) - 0.055;
  
     return l;
  }
  
  static double
  linear_from_sRGB(double s)
  {
     if (s <= 0.04045)
        return s / 12.92;
  
     else
        return pow((s+0.055)/1.055, 2.4);
  }
  
  static double
  YfromRGB(double r, double g, double b)
  {
     /* Use the sRGB (rounded) coefficients for Rlinear, Glinear, Blinear to get
      * the CIE Y value (also linear).
      */
     return 0.2126 * r + 0.7152 * g + 0.0722 * b;
  }
  