在线等一个改变图片对比度的算法

/// <summary>

        /// 图像亮度变化

        /// value大于0图像变亮，value小于0图像变暗

        /// value的取值范围是-255~255

        /// </summary>

        /// <param name="bitmap">原始图像</param>

        /// <param name="value">亮度变化值：大于0图像变亮，小于0图像变暗value的取值范围是-255~255</param>

        /// <returns>亮度变化后的图像</returns>

        public static Bitmap Lightness(Bitmap bitmap, int value)

        {



            if (bitmap == null)

            {

                return null;

            }



            int width = bitmap.Width;

            int height = bitmap.Height;



            try

            {



                Bitmap bmpReturn = new Bitmap(width, height, PixelFormat.Format24bppRgb);



                BitmapData srcBits = bitmap.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);

                BitmapData targetBits = bmpReturn.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.WriteOnly, PixelFormat.Format24bppRgb);



                unsafe

                {

                    byte* pSrcBits = (byte*)srcBits.Scan0.ToPointer();

                    byte* pTargetBits = (byte*)targetBits.Scan0.ToPointer();

                    int stride = srcBits.Stride;

                    byte* pTemp;



                    for (int h = 0; h < height - 1; h++)

                    {

                        for (int w = 0; w < width - 1; w++)

                        {

                            int r, g, b;

                            int r1, g1, b1;

                            int r2, g2, b2;

                            pTemp = pSrcBits;

                            r = pTemp[2];

                            g = pTemp[1];

                            b = pTemp[0];

                            if (value >= 0)

                            {

                                r1 = r + ((255 - r) * value) / 255;

                                g1 = g + ((255 - g) * value) / 255;

                                b1 = b + ((255 - b) * value) / 255;

                            }

                            else

                            {

                                r1 = r + (r * value) / 255;

                                g1 = g + (g * value) / 255;

                                b1 = b + (b * value) / 255;

                            }



                            pTargetBits[2] = (byte)r1;

                            pTargetBits[1] = (byte)g1;

                            pTargetBits[0] = (byte)b1;



                            pSrcBits += 3;

                            pTargetBits += 3;

                        }



                        pSrcBits += srcBits.Stride - width * 3;

                        pTargetBits += srcBits.Stride - width * 3;

                    }

                }

                bitmap.UnlockBits(srcBits);

                bmpReturn.UnlockBits(targetBits);



                return bmpReturn;

            }

            catch

            {

                return null;

            }

        }