绘图操作时报错“无法从带有索引像素格式的图像创建 Graphics 对象”

如下代码会出现“无法从带有索引像素格式的图像创建 Graphics 对象”异常

Bitmap bitmap = new Bitmap(fileName);

Graphics graphics = Graphics.FromImage(bitmap);

解决方法为DrawImage到一个空的图片。

OpenFileDialog dialog = new OpenFileDialog
{
Filter = "Image|*.bmp;*.png;*.jpg;*.jpeg",
FilterIndex = 1
};
if (dialog.ShowDialog() == DialogResult.OK)
{
string fileName = dialog.FileName;
Bitmap bitmap = new Bitmap(dialog.FileName);

Bitmap image = new Bitmap(bitmap.Width, bitmap.Height);// 将原图片DrawImage到新图片image，然后在image上进行绘图操作
using (Graphics graphics = Graphics.FromImage(image))
{
Rectangle destRect = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
Rectangle srcRect = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
graphics.DrawImage(bitmap, destRect, srcRect, GraphicsUnit.Pixel);
graphics.Dispose();
}

Graphics graphicsNew = Graphics.FromImage(image);
Pen pen = new Pen(Color.Red);
graphicsNew.DrawRectangle(pen, 0, 0, image.Width - 3,image.Height - 3);// 在图片上绘制矩形框

this.pictureBox1.Image = image;
}