如何将位图图像保存为 JPEG

Question

The problem is that the file is not saving as JPEG. Just a normal file.

This is my code so far:

private void btnSave_Click(object sender, EventArgs e)
{
    saveDialog.FileName = txtModelName.Text;

    if (saveDialog.ShowDialog() == DialogResult.OK)
    {
        Bitmap bmp = new Bitmap(pnlDraw.Width, pnlDraw.Height);

        pnlDraw.DrawToBitmap(bmp, new Rectangle(0, 0,
            pnlDraw.Width, pnlDraw.Height));

        bmp.Save(saveDialog.FileName, System.Drawing.Imaging.ImageFormat.Jpeg);
    }
}

Answer 1

How about checking if file name has .jpg extension before saving it?

You can also change saveDialog to only allow user selecting .jpg images.

private void btnSave_Click(object sender, EventArgs e)
{
    saveDialog.FileName = txtModelName.Text;
    saveDialog.DefaultExt = "jpg";
    saveDialog.Filter = "JPG images (*.jpg)|*.jpg";    

    if (saveDialog.ShowDialog() == DialogResult.OK)
    {
        Bitmap bmp = new Bitmap(pnlDraw.Width, pnlDraw.Height);

        pnlDraw.DrawToBitmap(bmp, new Rectangle(0, 0,
            pnlDraw.Width, pnlDraw.Height));

        var fileName = saveDialog.FileName;
        if(!System.IO.Path.HasExtension(fileName) || System.IO.Path.GetExtension(fileName) != "jpg")
            fileName = fileName + ".jpg";

        bmp.Save(fileName, System.Drawing.Imaging.ImageFormat.Jpeg);
    }
}

Answer 2

int width;
int height;
int stride;
int x;
int y;
string filename;

Bitmap bitmap = new Bitmap(width,height,stride,PixelFormat.Format32bppArgb,new IntPtr());

//then set the pixel;
bitmap.SetPixel(x,y,Colors.Black);
bitmap.Save(filename);