image - 使用 PdfSharp 从 pdf 中提取 "FLATEDECODE"类型的图像

Question

我正在尝试从 pdf 中提取图像。图像是过滤器“FlateDecode”。我得到了图像，但它只是一条黑色路径。我是这方面的新手，请帮助我。代码是:

int width = xObject.Elements.GetInteger(PdfImage.Keys.Width);
int height = xObject.Elements.GetInteger(PdfImage.Keys.Height);
int bitsPerComponent = xObject.Elements.GetInteger  (PdfSharp.Pdf.Advanced.PdfImage.Keys.BitsPerComponent);
System.Drawing.Imaging.PixelFormat pixelFormat = new   System.Drawing.Imaging.PixelFormat();
switch (bitsPerComponent)
{   
            case 1:
                pixelFormat = System.Drawing.Imaging.PixelFormat.Format1bppIndexed;
                break;
            case 8:
                pixelFormat = System.Drawing.Imaging.PixelFormat.Format8bppIndexed;
                break;
            case 24:
                pixelFormat = System.Drawing.Imaging.PixelFormat.Format24bppRgb;
                break;
            default:
                throw new Exception("Unknown pixel format " + bitsPerComponent);
 }
 Bitmap bitmap = new Bitmap(width, height, pixelFormat);
 byte[] raw = xObject.Stream.Value;
 BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, width, height),      ImageLockMode.WriteOnly, pixelFormat);
 Marshal.Copy(raw, 0, bitmapData.Scan0, raw.Length);
 bitmap.UnlockBits(bitmapData);
 using (MemoryStream imageStream = new MemoryStream())
 {
            bitmap.Save(imageStream, ImageFormat.png);
            System.Drawing.Image img = System.Drawing.Image.FromStream(imageStream);

            img.Save("D:\\trial.png", System.Drawing.Imaging.ImageFormat.png);
 }

Answer 1

img.Save("D:\\trial.png", System.Drawing.Imaging.ImageFormat.Jpeg);

不应该是.PNG吗？