ClassLibraryWeiBao/QR二维码/Windows/Render/ColorContrast.cs

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;


#if NETFX_CORE
using Windows.UI;
#elif SILVERLIGHT
using System.Windows.Media;
#else
using System.Drawing;

#endif


namespace Gma.QrCodeNet.Encoding.Windows.Render
{
    /// <summary>
    /// Port from Lea Vero's Contrast ratio javascript library.
    /// Formula that's on W3C
    /// http://www.w3.org/TR/2008/REC-WCAG20-20081211/#relativeluminancedef
    /// http://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrast-ratiodef
    /// Even though contrast ratio is used mainly for human eye. But decoder is very similar. Highest ratio for black and white is easiest to identify and decode.
    /// Where two same color is impossible, closest color is similar as well. 
    /// Decoder normally turn colored color to White Gray Black colors.
    /// Another important to note is proper decoder won't treat lighter color as 0, they will use pattern to match. Thus inverse color is possible.
    /// Pattern 1011101 << "w b w w w b w" is exactly same as "b w b b b w b"
    /// </summary>
    public static class ColorContrast
    {
#if NETFX_CORE || SILVERLIGHT
        private static double Luminance(Color color)
        {
#else
        private static double Luminance(GColor color)
        {
#endif

            double r, g, b;
            r = Colorspace(color.R);
            g = Colorspace(color.G);
            b = Colorspace(color.B);

            return 0.2126 * r + 0.7152 * g + 0.0722 * b;
        }

        private static double Colorspace(byte rgb)
        {
            double result = Convert.ToDouble(rgb) / Convert.ToDouble(byte.MaxValue);
            result = result < 0.03928 ? result / 12.92 : Math.Pow(((result + 0.055) / 1.055), 2.4);
            return result;
        }

#if NETFX_CORE || SILVERLIGHT
        private static Color InverseColor(Color color)
        {
            Color result = Color.FromArgb(color.A, ConvertByte(byte.MaxValue - color.R), ConvertByte(byte.MaxValue - color.G), ConvertByte(byte.MaxValue - color.B));
            return result;
        }