Image img = Image.FromFile(filename);
// Assumes myImage is the PNG you are converting
using (var b = new Bitmap(img.Width, img.Height)) {
    b.SetResolution(img.HorizontalResolution, img.VerticalResolution);

    using (var g = Graphics.FromImage(b)) {
        g.Clear(Color.White);
        g.DrawImageUnscaled(img, 0, 0);
    }

    // Now save b as a JPEG like you normally would
    b.Save(@路徑, System.Drawing.Imaging.ImageFormat.Jpeg);
}
 

原文連結 https://stackoverflow.com/questions/6513633/convert-transparent-png-to-jpg-with-non-black-background-color