I have the following code for changing the DPI of an image:

```
public void changeDPI(string imagePathSource,string imagePathDestination,float DPIx,float DPIy)
        {
            Bitmap bitmap = new Bitmap(imagePathSource);
            Bitmap newBitmap = new Bitmap(bitmap);
            newBitmap.SetResolution(DPIx,DPIy);
            newBitmap.Save(imagePathDestination);
        }

```

However, this ends up changing the memory size of the file. An example test image started at 267 KB, and the `newBitmap` version of the file ended up as 1.51 MB. How can I change the DPI without changing the file size?