Openpdf: Convert pdf to images

[sabraMa]

Hello
I have some questions:
1 Could I convert my pdf document( multipages) to png images with OpenPDF ?
2 Is it possible to generate pdfA format ?
3 there is any way to compress exsiting pdf ?

thank you a lot for your help

[doobo]

This is my method of rewriting. I hope it will be useful！

     /**
     * 根据总页数,按照perSize页生成一张长图片的逻辑, 进行拆分
     * @param in
     * @param perSize
     * @return
     */
    public static List<byte[]> pdfToImage(byte[] in, Integer perSize) {
        List<byte[]> bms = new ArrayList<>();
        try {
            /*图像合并使用参数*/
            // 定义宽度
            int width = 0;
            // 保存一张图片中的RGB数据
            int[] singleImgRGB;
            // 定义高度，后面用于叠加
            int shiftHeight = 0;
            //保存每张图片的像素值
            BufferedImage imageResult = null;
            // 利用PdfBox生成图像
            PDDocument pdDocument = PDDocument.load(in);
            PDFRenderer renderer = new PDFRenderer(pdDocument);
            /*根据总页数, 按照50页生成一张长图片的逻辑, 进行拆分*/
            // 每50页转成1张图片
            perSize = perSize == null? 1: perSize;
            // 总计循环的次数
            int totalCount = getPages(pdDocument.getNumberOfPages(), perSize);
            for (int m = 0; m < totalCount; m++) {
                for (int i = 0; i < perSize; i++) {
                    int pageIndex = i + (m * perSize);
                    if (pageIndex == pdDocument.getNumberOfPages()) {
                        break;
                    }
                    // 144为图片的dpi，dpi越大，则图片越清晰，图片越大，转换耗费的时间也越多
                    BufferedImage image = renderer.renderImageWithDPI(pageIndex, 144, ImageType.RGB);
                    int imageHeight = image.getHeight();
                    int imageWidth = image.getWidth();
                    if (i == 0) {
                        //计算高度和偏移量
                        //使用第一张图片宽度;
                        width = imageWidth;
                        // 保存每页图片的像素值
                        // 加个判断：如果m次循环后所剩的图片总数小于pageLength，则图片高度按剩余的张数绘制，否则会出现长图片下面全是黑色的情况
                        if ((pdDocument.getNumberOfPages() - m * perSize) < perSize) {
                            imageResult = new BufferedImage(width, imageHeight * (pdDocument.getNumberOfPages() - m * perSize), BufferedImage.TYPE_INT_RGB);
                        } else {
                            imageResult = new BufferedImage(width, imageHeight * perSize, BufferedImage.TYPE_INT_RGB);
                        }
                    } else {
                        // 将高度不断累加
                        shiftHeight += imageHeight;
                    }
                    singleImgRGB = image.getRGB(0, 0, width, imageHeight, null, 0, width);
                    imageResult.setRGB(0, shiftHeight, width, imageHeight, singleImgRGB, 0, width);
                }
                // image转byte[]
                ByteArrayOutputStream byteArrayOutputStream = new  ByteArrayOutputStream();
                ImageIO.write(imageResult, "png", byteArrayOutputStream);
                byteArrayOutputStream.flush();
                bms.add(byteArrayOutputStream.toByteArray());
                byteArrayOutputStream.close();
                // 写图片
                //File outFile = new File(pdfPath.replace(".pdf", "_" + m + ".jpg"));
                //ImageIO.write(imageResult, "jpg", outFile);
                shiftHeight = 0;
            }
            pdDocument.close();
        } catch (Exception e) {
            log.error("pdf转图片异常", e);
        }
        return bms;
    }

        /*
     * 计算总页数
     */
    private static int getPages(int counts, int pageSize) {
        if(counts == 0) {
            return 0;
        } else if (counts <= pageSize) {
            return 1;
        } else if (counts%pageSize!=0) {
            return counts / pageSize + 1;
        } else {
            return counts / pageSize;
        }
    }

[andreasrosdal]

Thanks for sharing! Can you please submit this code as a pull request to OpenPDF? Create a new Java class for it. Then we can add this as a new useful high-level function in the library.

[asturio]

This is a nice one for anybody wanting to contribute.

• Grab the code of https://github.com/LibrePDF/OpenPDF/issues/346#issuecomment-651729163
• Create some new utility class for that method
• clean the code a little bit (my chinese is not that good :-) )
• write some Unit-Test
• Create a Pull Request

[GreenToad]

This code uses Apache PDFBox not LibrePDF

[asturio]

Just answering 2 questions:

1. Yes, OpenPDF can generate PDF/A
2. I'm not aware of any part of OpenPDF for compressing existing PDFs. There are some other nice (non-Java) tools which can manipulate Postscript and PDF. Maybe Ghostscript is a away to do so.