GDI+中位图颜色替换

GDI+中的著名烂函数-setpixel & getpixel

作用是获得一个象素点的颜色和设置一个象素点的颜色。

下面是一个代码片断(为了把位图的某种颜色替换为另一种颜色)，测试中在100x100位图中试验了以下代码，竟然消耗了500ms左右，这函数写的真是垃圾的可以。

 

for (int x = 0; x < image.Width; x++)
            {
                for (int y = 0; y < image.Height; y++)
                {
                    Color pixelColor = ((Bitmap)image).GetPixel(x, y);
                    if ((pixelColor.R == oldColor.R) && (pixelColor.G == oldColor.G) && (pixelColor.B == oldColor.B))
                        ((Bitmap)image).SetPixel(x, y, newColor);
                }
            }

还好，C#可以通过unsafe直接访问内存，自己重写了一下，速度竟然有非常大的改进->0ms。看来DotNet某些函数的效率真是……

unsafe
            {
                Bitmap bmp = (Bitmap)image;
                int width = bmp.Width;
                int height = bmp.Height;
                BitmapData bmdata = bmp.LockBits(new Rectangle(0, 0, width, height), ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
                byte* p = (byte*)bmdata.Scan0;
                int offset = bmdata.Stride - width * 3;

                for (int j = 0; j < height; j++)
                {
                    for (int i = 0; i < width; i++)
                    {
                        if ((p[0] == oldColor.R) && (p[1] == oldColor.G) && (p[2] == oldColor.B))
                        {
                            p[0] = newColor.B;
                            p[1] = newColor.G;
                            p[2] = newColor.R;
                        }
                        p += 3;
                    }
                    p += offset;
                }
                bmp.UnlockBits(bmdata);
                image = bmp;
            }