C#

stor = ((rowTamplate[(h * pixelSize)] + rowTamplate[(h * pixelSize) + 1] + rowTamplate[(h * pixelSize) + 2]) / 3) - ((rowBitmap[(h * pixelSize)] + rowBitmap[(h * pixelSize) + 1] + rowBitmap[(h * pixelSize) + 2]) / 3);

BitmapData templateData = template.LockBits(new Rectangle(0, 0, 50, 70), System.Drawing.Imaging.ImageLockMode.WriteOnly, template.PixelFormat)
 bitmap = ImageResizer.ResizeImage(bitmap, 50, 70);//here bitmap is a region from original image where skin is present.and here I resize it to 50(width) by 70(height).
 BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, 50, 70), System.Drawing.Imaging.ImageLockMode.WriteOnly, bitmap.PixelFormat);
                       
double stor = 0;
for (int w = 0; w < 70; w++)
{
   Byte* rowTamplate = (byte*)templateData.Scan0 + (w * templateData.Stride);
   Byte* rowBitmap = (byte*)bitmapData.Scan0 + (w * bitmapData.Stride);
   for (int h = 0; h < 50; h++)
       {
             stor = 0;
//the exception is generated on the fllowing line
             stor = ((rowTamplate[(h * pixelSize)] + rowTamplate[(h * pixelSize) + 1] + rowTamplate[(h * pixelSize) + 2]) / 3) - ((rowBitmap[(h * pixelSize)] + rowBitmap[(h * pixelSize) + 1] + rowBitmap[(h * pixelSize) + 2]) / 3);
            if (stor < 0)
                                {
                                    stor *= -1;
                                }
                                PixelsCounter += (int)stor;
                                stor = 0;
                            }
                        }