画像を白黒（グレースケール）にする方法

画像を白黒（グレースケール）にする方法
VB.NET

Public Shared Function CreateGrayscaleImage(ByVal img As Image) As Image
   
    Dim newImg As New Bitmap(img.Width, img.Height)
    
    Dim g As Graphics = Graphics.FromImage(newImg)

    Dim cm As New System.Drawing.Imaging.ColorMatrix( _
        New Single()() { _
            New Single() {0.299F, 0.299F, 0.299F, 0, 0}, _
            New Single() {0.587F, 0.587F, 0.587F, 0, 0}, _
            New Single() {0.114F, 0.114F, 0.114F, 0, 0}, _
            New Single() {0, 0, 0, 1, 0}, _
            New Single() {0, 0, 0, 0, 1} _
        })
    
    Dim ia As New System.Drawing.Imaging.ImageAttributes()
    
    ia.SetColorMatrix(cm)

    g.DrawImage(img, New Rectangle(0, 0, img.Width, img.Height), _
                0, 0, img.Width, img.Height, GraphicsUnit.Pixel, ia)

   
    g.Dispose()

    Return newImg
End Function

C#

public static Image CreateGrayscaleImage(Image img)
{
    
    Bitmap newImg = new Bitmap(img.Width, img.Height);
    
    Graphics g = Graphics.FromImage(newImg);

    System.Drawing.Imaging.ColorMatrix cm =
        new System.Drawing.Imaging.ColorMatrix(
            new float[][]{
                new float[]{0.299f, 0.299f, 0.299f, 0 ,0},
                new float[]{0.587f, 0.587f, 0.587f, 0, 0},
                new float[]{0.114f, 0.114f, 0.114f, 0, 0},
                new float[]{0, 0, 0, 1, 0},
                new float[]{0, 0, 0, 0, 1}
            });

    System.Drawing.Imaging.ImageAttributes ia =
        new System.Drawing.Imaging.ImageAttributes();

    ia.SetColorMatrix(cm);

    g.DrawImage(img,
        new Rectangle(0, 0, img.Width, img.Height),
        0, 0, img.Width, img.Height, GraphicsUnit.Pixel, ia);

    g.Dispose();

    return newImg;
}