图片转换，把bmp图片转换为jpg图片

using System.IO;
using System.Drawing.Imaging;

public class imgConvert
{
        private void BMPToJPG(string bmpFileName,string jpgFileName)
        {
                        
            
            System.Drawing.Image img;
            img=ReturnPhoto(bmpFileName);
    
            img.Save(jpgFileName,ImageFormat.Jpeg);
        }

        private Image ReturnPhoto(string bmpFileName)
        {
            System.IO.FileStream stream ;
            stream=File.OpenRead(bmpFileName);
            Bitmap bmp = new Bitmap(stream);
            System.Drawing.Image image = bmp;//得到原图
            //创建指定大小的图
            System.Drawing.Image newImage = image.GetThumbnailImage(bmp.Width, bmp.Height, null, new IntPtr());
            Graphics g=Graphics.FromImage(newImage);
            g.DrawImage(newImage,0,0, newImage.Width, newImage.Height); //将原图画到指定的图上
            g.Dispose();
            stream.Close();
            return newImage;
        }
}