function colorsRGBtoLin ( $chan )
        {
#-k     color
#-      Send this function a decimal sRGB gamma encoded color value between 0.0 and 1.0
#-p     $chan   - req   - color channel, 0-255
#-p             - ret   - a linearized value.
#-c     Myindex response 2019-06-19 on https://stackoverflow.com/questions/596216/formula-to-determine-brightness-of-rgb-color
#-d     2/19/21 - Added

        if ( $chan <= 0.04045 ) { return $chan / 12.92; }
        else                    { return pow(( $chan + 0.055)/1.055,2.4); }
        }

?>