将 PDF 转换为具有透明度的 png 文件（保留 alpha）

Question

我一直在尝试将 PDF 转换为具有透明度的 png 文件，但没有成功。 我试图用很多方法解决它，但我没有成功。 我正在写我的方式，希望有人能找到问题所在：

1.

try (final PDDocument document = PDDocument.load(new File(srcpath))){
                PDFRenderer pdfRenderer = new PDFRenderer(document);
                for (int page = 0; page < document.getNumberOfPages(); ++page)
                {
                    BufferedImage bim = pdfRenderer.renderImageWithDPI(page, 300, ImageType.RGB);
                    String fileName = imageConverted;

                    boolean hasAlpha = bim.getColorModel().hasAlpha();
                System.out.println(hasAlpha);

                    ImageIOUtil.writeImage(bim, fileName, 300);
                }
                document.close();
            } catch (IOException e){
                System.err.println("Exception while trying to create pdf document - " + e);
            }

1. RandomAccessFile raf; 尝试 { raf = new RandomAccessFile(file, "r");

           FileChannel channel = raf.getChannel();
           ByteBuffer buf = channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
           PDFFile pdffile = new PDFFile(buf);
           // draw the first page to an image
           int num=pdffile.getNumPages();
           for(int i=0;i<num;i++)
           {
               PDFPage page = pdffile.getPage(i);
   
               //get the width and height for the doc at the default zoom              
               int width=(int)page.getBBox().getWidth();
               int height=(int)page.getBBox().getHeight();             
   
               Rectangle rect = new Rectangle(0,0,width,height);
               int rotation=page.getRotation();
               Rectangle rect1=rect;
               if(rotation==90 || rotation==270)
                   rect1=new Rectangle(0,0,rect.height,rect.width);
   
               //generate the image
               BufferedImage img = (BufferedImage)page.getImage(
                           rect.width, rect.height, //width & height
                           rect1, // clip rect
                           null, // null for the ImageObserver
                           true, // fill background with white
                           true  // block until drawing is done
                   );
                Graphics2D graphics = (Graphics2D)img.getGraphics();
                graphics.setBackground( new Color( 255, 255, 255, 0 ) );
   
               ImageIO.write(img, "png", new File(imageConverted));
           }
       } 
       catch (FileNotFoundException e1) {
           System.err.println(e1.getLocalizedMessage());
       } catch (IOException e) {
           System.err.println(e.getLocalizedMessage());
       }
   

3.

// Instantiating the PDFRenderer class
        PDFRenderer renderer = new PDFRenderer(document);

        // Rendering an image from the PDF document
        BufferedImage image = null;
        try {
             image= renderer.renderImage(0);
        } catch (IOException e1) {
            return "N/A";
        }

        // Writing the image to a file
        try {
            ImageIO.write(image, "png", new File(imageConverted));
        } catch (IOException e) {
            return "N/A";
        }

但我得到的是白色背景的 png ...... 任何想法？ 提前谢谢！！！

Answer 1

改变这一行

BufferedImage bim = pdfRenderer.renderImageWithDPI(page, 300, ImageType.RGB);

到

BufferedImage bim = pdfRenderer.renderImageWithDPI(page, 300, ImageType.RGBA);

这会给你一个透明的图像。