var complex1 = new System.Numerics.Complex(Math.Sqrt(3), 1.0);
Console.WriteLine($"complex1.Magnitude = {complex1.Magnitude}");
Console.WriteLine($"complex1.Phase = {complex1.Phase * 180.0 / Math.PI}");

var complex2 = new System.Numerics.Complex(1.0, Math.Sqrt(3));
Console.WriteLine($"complex2.Magnitude = {complex2.Magnitude}");
Console.WriteLine($"complex2.Phase = {complex2.Phase * 180.0 / Math.PI}");

var complex3 = complex1 * complex2;
Console.WriteLine($"complex3.Magnitude = {complex3.Magnitude}");
Console.WriteLine($"complex3.Phase = {complex3.Phase * 180.0 / Math.PI}");

var complex4 = complex1 + complex2;
Console.WriteLine($"complex4.Magnitude = {complex4.Magnitude}");
Console.WriteLine($"complex4.Phase = {complex4.Phase * 180.0 / Math.PI}");

// 結果
//complex1.Magnitude = 2
//complex1.Phase = 30
//complex2.Magnitude = 2
//complex2.Phase = 60
//complex3.Magnitude = 4
//complex3.Phase = 90
//complex4.Magnitude = 3.86370330515627
//complex4.Phase = 45

for (int i = 0; i < N; i++)
{
    // 通常の処理
}

Parallel.For(0, N, i =>
{
    // この部分の処理が並列化される
});

private void ContrastImage(Bitmap bmp, double scale, double offset)
{
    var width = bmp.Width;
    var height = bmp.Height;

    // Bitmapをロック
    var bmpData = bmp.LockBits(
            new Rectangle(0, 0, width, height),
            System.Drawing.Imaging.ImageLockMode.ReadWrite,
            bmp.PixelFormat
        );

    // メモリの幅のバイト数を取得
    var stride = Math.Abs(bmpData.Stride);

    int channel = Bitmap.GetPixelFormatSize(bmp.PixelFormat) / 8;

    // 画像データ格納用配列
    var picData = new byte[stride * bmpData.Height];

    // Bitmapデータを配列へコピー
    System.Runtime.InteropServices.Marshal.Copy(
        bmpData.Scan0,
        picData,
        0,
        stride * bmpData.Height
        );

    for (int y = 0; y < height; y++)
    {
        int lineIndex = stride * y;

        for (int x = 0; x < width * channel; x++)
        {
            int value = picData[lineIndex + x];
            value = (int)(value * scale + offset);
            value = (value < 0) ? 0 : (value > 255) ? 255
                    : value
                    ;
            picData[lineIndex + x] = (byte)value;
        }
    }

    // 配列をBitmapデータへコピー
    System.Runtime.InteropServices.Marshal.Copy(
        picData,
        0,
        bmpData.Scan0,
        stride * bmpData.Height
        );

    // アンロック
    bmp.UnlockBits(bmpData);
}

for (int y = 0; y<height; y++)
{
    int lineIndex = stride * y;

    for (int x = 0; x<width* channel; x++)
    {
        int value = picData[lineIndex + x];
        value = (int)(value* scale + offset);
        value = (value< 0) ? 0 : (value > 255) ? 255
                : value
                ;
        picData[lineIndex + x] = (byte)value;
    }
}

Parallel.For(0, height, y =>
{
    int lineIndex = stride * y;

    for (int x = 0; x<width* channel; x++)
    {
        int value = picData[lineIndex + x];
        value = (int)(value* scale + offset);
        value = (value< 0) ? 0 : (value > 255) ? 255
                : value
                ;
        picData[lineIndex + x] = (byte)value;
    }
}
);