C# 72dpi的图片怎么转换为300dpi

C# 72dpi的图片怎么转换为300dpi，要求图片无损，不仅仅是修改下图片的dpi参数就好了。修改后的图片大小应该和原图片大小一样，但是尺寸会变小。类似于在ps中图像大小更改里的取消重定图像像素，更改dpi的方法 
if (this.pbMain.Image.VerticalResolution <200||this.pbMain.Image.HorizontalResolution < 200)
{
//System.Drawing.Image img = System.Drawing.Image.FromHbitmap(((Bitmap)this.images[0]).GetHbitmap());
//float x = img.VerticalResolution;
//float y = img.HorizontalResolution;
int width = ((Bitmap)this.images[0]).Width;
int height = ((Bitmap)this.images[0]).Height;
if (height > width)
{
height = 2338;
width = 1653;

}
else if (width > height)
{
height = 1653;
width = 2338;
}
Bitmap bmpSource = new Bitmap(((Bitmap)this.images[0]), width, height);
//Bitmap bmpSource = new Bitmap(((Bitmap)this.images[0]));
int iSourceWidth = bmpSource.Width;
int iSourceHeight = bmpSource.Height;
float fSourceHorResolution = bmpSource.HorizontalResolution;
float fSourceVerResolution = bmpSource.VerticalResolution;
//图象dpi
float fTargetHorResolution = 200;
float fTargetVerResolution = 200;
Bitmap bmpTarget = new Bitmap(width, height);
Graphics g = Graphics.FromImage(bmpTarget);
g.DrawImage(bmpSource, 0, 0, iSourceWidth, iSourceHeight);
bmpTarget.SetResolution(fTargetHorResolution, fTargetVerResolution);
bmpTarget = TiffManager.KiSharpen(bmpTarget, (float)0.7);
bmpTarget = TiffManager.ConvertTo1bbpIndexed(bmpTarget, (float)0.8);
bmpTarget.Save(filename, info, ep);
}