为什么用gid+生成的图片PS打不开??

Question

为什么用gid+生成的图片PS打不开?代码如下,用PS CS4打开它提示:不能完成请求,因为找到不知名或无效的JPEG标识符类型
 Bitmap bt = new Bitmap(1244, 1769);
         
            Graphics g = Graphics.FromImage(bt);
            if (this.pictureBox1.Image != null && this.pictureBox2.Image != null)
            {
                g.DrawImage(this.pictureBox1.Image, new RectangleF(70, 70, this.pictureBox1.Image.Width, this.pictureBox1.Image.Height));
                g.DrawImage(this.pictureBox2.Image, new RectangleF(70 + this.pictureBox2.Image.Width + 35, 70, this.pictureBox2.Image.Width, this.pictureBox2.Image.Height));
            }
            if (this.pictureBox3.Image != null && this.pictureBox4.Image != null)
            {
                g.DrawImage(this.pictureBox3.Image, new RectangleF(70, this.pictureBox3.Image.Height + 35+70, this.pictureBox3.Image.Width, this.pictureBox3.Image.Height));
                g.DrawImage(this.pictureBox4.Image, new RectangleF(70 + this.pictureBox4.Image.Width + 35, 35 + this.pictureBox4.Image.Height+70, this.pictureBox4.Image.Width, this.pictureBox4.Image.Height));
            }            if (this.pictureBox5.Image != null && this.pictureBox6.Image != null)
            {
                g.DrawImage(this.pictureBox5.Image, new RectangleF(70, (this.pictureBox5.Image.Height + 35) * 2+70, this.pictureBox5.Image.Width, this.pictureBox5.Image.Height));
                g.DrawImage(this.pictureBox6.Image, new RectangleF(70 + this.pictureBox6.Image.Width + 35, (35 + this.pictureBox6.Image.Height) * 2+70, this.pictureBox6.Image.Width, this.pictureBox6.Image.Height));
            }            if (this.pictureBox7.Image != null && this.pictureBox8.Image != null)
            {
                g.DrawImage(this.pictureBox7.Image, new RectangleF(70, (this.pictureBox7.Image.Height + 35) * 3+70, this.pictureBox7.Image.Width, this.pictureBox7.Image.Height));
                g.DrawImage(this.pictureBox8.Image, new RectangleF(70 + this.pictureBox8.Image.Width + 35, (this.pictureBox8.Image.Height + 35) * 3+70, this.pictureBox8.Image.Width, this.pictureBox8.Image.Height));
            }
            string aaa=Guid.NewGuid().ToString();
            bt.Save("d://xrprint//" + aaa + ".jpg");
            System.Diagnostics.Process.Start("d://xrprint//");

Answer 1

bt.Save("d://xrprint//" + aaa + ".jpg", System.Drawing.Imaging.ImageFormat.Jpeg);

Answer 2

Graphics g = Graphics.FromImage(bt);
g.Clear(Color.White);