Convert image to sepia, gray scale and vice versa using C# in ASP.Net

Please refer below link

http://www.codeproject.com/Articles/31120/Image-Transformation-Grayscale-to-Color

also you can refer below code Using Aforge do this:

var filter = new GrayscaleToRGB();
var RGBBitmap = filter.Apply(AForge.Imaging.Image.Convert16bppTo8bpp(bitmap));

GrayscaleToRGB is in AForge.Imaging.Filters

http://www.aforgenet.com/framework/docs/html/503a43b9-d98b-a19f-b74e-44767916ad65.htm