问Bitmap.Save保持旧PixelFormat

EN

 public static string[] ConvertTiffToJpeg(string fileName)
        {
            using (Image imageFile = Image.FromFile(fileName))
            {
                var test = imageFile.PixelFormat;

                FrameDimension frameDimensions = new FrameDimension(
                    imageFile.FrameDimensionsList[0]);

                // Gets the number of pages from the tiff image (if multipage) 
                int frameNum = imageFile.GetFrameCount(frameDimensions);
                string[] jpegPaths = new string[frameNum];

                for (int frame = 0; frame < frameNum; frame++)
                {
                    // Selects one frame at a time and save as jpeg. 
                    imageFile.SelectActiveFrame(frameDimensions, frame);
                    using (Bitmap bmp = new Bitmap(imageFile))
                    {
                        jpegPaths[frame] = String.Format("{0}\\{1}{2}.jpg",
                            Path.GetDirectoryName(fileName),
                            Path.GetFileNameWithoutExtension(fileName),
                            frame);
                        bmp.Save(jpegPaths[frame], ImageFormat.Jpeg);
                    }
                }

                return jpegPaths;
            }
    }