这些R，G和B系数值从何而来？

Question

https://rosettacode.org/wiki/Grayscale_image#C.23

Bitmap tImage = new Bitmap("spectrum.bmp");

for (int x = 0; x < tImage.Width; x++)
{
    for (int y = 0; y < tImage.Height; y++)
    {
        Color tCol = tImage.GetPixel(x, y);

        // L = 0.2126·R + 0.7152·G + 0.0722·B 
        double L = 0.2126 * tCol.R + 0.7152 * tCol.G + 0.0722 * tCol.B;
        tImage.SetPixel(x, y, Color.FromArgb(Convert.ToInt32(L),
 Convert.ToInt32(L), Convert.ToInt32(L)));
    }
}

// Save
tImage.Save("spectrum2.bmp");

Where do we find // L = 0.2126·R + 0.7152·G + 0.0722·B these values?

Answer 1

You can find that information in ITU (International Telecommunication Union) Recommendation ITU BT.709

Parameter values for the HDTV standards for production and international programme exchange

See page 4

You can see old versions here