anyone please tell me the fast execting c# code for sobel edge detect..I am new to image processing

Have you looked at OpenCV? opencv.willowgarage.com

Not C#, but a great resource. Rather than trying to redo things in C#, I'd probably consider using the native C/C++ OpenCV stuff and import / link to the DLL APIs from C# as required. Might not be quite as friendly as if it was all in C#, but I'd trust it to be fast and reliable.

thanks for reply...
can anyone tell me how to convert below code into unsafe code...

Bitmap box1,box2;
int fxr,fyr,rr;

fxr = -1 * box1.GetPixel(i, j - 1).R + box1.GetPixel(i, j).R - box1.GetPixel(i + 1, j).R + box1.GetPixel(i - 1, j - 1).R - box1.GetPixel(i - 1, j + 1).R +
box1.GetPixel(i + 1, j + 1).R;

fyr = box1.GetPixel(i, j - 1).R + box1.GetPixel(i - 1, j).R + box1.GetPixel(i, j).R - box1.GetPixel(i - 1, j + 1).R - box1.GetPixel(i + 1, j - 1).R - box1.GetPixel(i + 1, j + 1).R;

rr = Math.Sqrt(Math.Abs(fxr * fxr) + Math.Abs(fyr * fyr));
if (rr < 0) rr = 0;
if (rr > 255) rr = 255;
Color cc = Color.FromArgb(Convert.ToInt32(rr), Convert.ToInt32(rr), Convert.ToInt32(rr));
box2.SetPixel(i, j, cc);