if you need some simple smoothness effect you can simple pick the color of the surrounding pixels of each pixel and use the average as your pixel color .
this actually simulates Paint.NET's built-in Median effect , and it gives a nice smooth for your effects .
this might be coded like so:
ColorBgra CurrentPixel,pxl1,pxl2,pxl3,pxl4,pxl5,pxl6,pxl7,pxl8;
CurrentPixel = src[x,y];
pxl1= src[Math.Min(x+1,rect.Right-1),y];
pxl2= src[Math.Max(x-1,rect.Left),y];
pxl3= src[x,Math.Min(y+1,rect.Bottom-1)];
pxl4= src[x,Math.Max(y-1,rect.Top)];
pxl5= src[Math.Min(x+1,rect.Right-1),Math.Min(y+1,rect.Bottom-1)];
pxl6= src[Math.Min(x+1,rect.Right-1),Math.Max(y-1,rect.Top)];
pxl7= src[Math.Max(x-1,rect.Left),Math.Min(y+1,rect.Bottom-1)];
pxl8= src[Math.Max(x-1,rect.Left),Math.Max(y-1,rect.Top)];
CurrentPixel.R=(byte)((CurrentPixel.R+pxl1.R+pxl2.R+pxl3.R+pxl4.R+pxl5.R+pxl6.R+pxl7.R+pxl8.R)/9);
CurrentPixel.G=(byte)((CurrentPixel.G+pxl1.G+pxl2.G+pxl3.G+pxl4.G+pxl5.G+pxl6.G+pxl7.G+pxl8.G)/9);
CurrentPixel.B=(byte)((CurrentPixel.B+pxl1.B+pxl2.B+pxl3.B+pxl4.B+pxl5.B+pxl6.B+pxl7.B+pxl8.B)/9);
Hope you find this helpful .
Ahmed.