WPF调节图片的对比度

public static class BitmapHelper
    {
        /// <summary>
        /// 调节图像的对比度
        /// </summary>
        /// <param name="sourceBitmap"></param>
        /// <param name="threshold">阈值，通过该参数控制调节</param>
        /// <returns></returns>
        public static Bitmap Contrast(this Bitmap sourceBitmap, int threshold)
        {
            BitmapData sourceData = sourceBitmap.LockBits(new System.Drawing.Rectangle(0, 0,
                                        sourceBitmap.Width, sourceBitmap.Height),
                                        ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);

            byte[] pixelBuffer = new byte[sourceData.Stride * sourceData.Height];

            Marshal.Copy(sourceData.Scan0, pixelBuffer, 0, pixelBuffer.Length);

            sourceBitmap.UnlockBits(sourceData);

            double contrastLevel = Math.Pow((100.0 + threshold) / 100.0, 2);

            double blue = 0;
            double green = 0;
            double red = 0;

            for (int k = 0; k + 4 < pixelBuffer.Length; k += 4)
            {
                blue = ((((pixelBuffer[k] / 255.0) - 0.5) *
                            contrastLevel) + 0.5) * 255.0;

                green = ((((pixelBuffer[k + 1] / 255.0) - 0.5) *
                            contrastLevel) + 0.5) * 255.0;

                red = ((((pixelBuffer[k + 2] / 255.0) - 0.5) *
                            contrastLevel) + 0.5) * 255.0;

                if (blue > 255)
                { blue = 255; }
                else if (blue < 0)
                { blue = 0; }

                if (green > 255)
                { green = 255; }
                else if (green < 0)
                { green = 0; }

                if (red > 255)
                { red = 255; }
                else if (red < 0)
                { red = 0; }

                pixelBuffer[k] = (byte)blue;
                pixelBuffer[k + 1] = (byte)green;
                pixelBuffer[k + 2] = (byte)red;
            }

            Bitmap resultBitmap = new Bitmap(sourceBitmap.Width, sourceBitmap.Height);

            BitmapData resultData = resultBitmap.LockBits(new System.Drawing.Rectangle(0, 0,
                                        resultBitmap.Width, resultBitmap.Height),
                                        ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format32bppArgb);

            Marshal.Copy(pixelBuffer, 0, resultData.Scan0, pixelBuffer.Length);
            resultBitmap.UnlockBits(resultData);

            return resultBitmap;
        }
    }