java 将pdf矢量图转换为灰度pdf矢量图

要将 PDF 矢量图转换为灰度 PDF 矢量图，可以使用 Apache PDFBox 库进行处理。以下是一个示例代码：

import org.apache.pdfbox.pdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.graphics.PDXObject;
import org.apache.pdfbox.pdmodel.graphics.form.PDFormXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.rendering.ImageType;
import org.apache.pdfbox.rendering.PDFRenderer;

import java.awt.image.BufferedImage;
import java.io.File;
import java.util.List;

import javax.imageio.ImageIO;

public class VectorToGrayscalePDFConverter {
    public static void main(String[] args) {
        try {
            // 加载矢量 PDF 文档
            PDDocument document = PDDocument.load(new File("input.pdf"));

            // 创建一个 PDFRenderer 对象
            PDFRenderer pdfRenderer = new PDFRenderer(document);

            // 遍历每一页，将矢量图像转换为灰度图像并替换原图像
            for (int pageIndex = 0; pageIndex < document.getNumberOfPages(); pageIndex++) {
                PDPage page = document.getPage(pageIndex);

                // 提取页面中的对象
                List<PDXObject> objects = page.getResources().getXObjects().values();

                // 遍历对象，将矢量图像转换为灰度图像
                for (PDXObject object : objects) {
                    if (object instanceof PDFormXObject) {
                        PDFormXObject form = (PDFormXObject) object;
                        BufferedImage grayscaleImage = convertToGrayscale(form);
                        replaceImage(form, grayscaleImage);
                    } else if (object instanceof PDImageXObject) {
                        PDImageXObject image = (PDImageXObject) object;
                        BufferedImage grayscaleImage = convertToGrayscale(image);
                        replaceImage(image, grayscaleImage);
                    }
                }
            }

            // 保存灰度 PDF
            document.save("output.pdf");

            // 关闭文档
            document.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static BufferedImage convertToGrayscale(PDFormXObject form) throws Exception {
        BufferedImage image = form.getImage();
        BufferedImage grayscaleImage = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
        grayscaleImage.getGraphics().drawImage(image, 0, 0, null);
        return grayscaleImage;
    }

    private static BufferedImage convertToGrayscale(PDImageXObject image) throws Exception {
        BufferedImage bufferedImage = image.getImage();
        BufferedImage grayscaleImage = new BufferedImage(bufferedImage.getWidth(), bufferedImage.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
        grayscaleImage.getGraphics().drawImage(bufferedImage, 0, 0, null);
        return grayscaleImage;
    }

    private static void replaceImage(PDXObject xobject, BufferedImage grayscaleImage) throws Exception {
        if (xobject instanceof PDFormXObject) {
            PDFormXObject form = (PDFormXObject) xobject;
            form.setBBox(grayscaleImage.getColorModel().getColorSpace().getBounds());
            form.setResources(null);
            form.setMatrix(null);
            form.setFormType(1);
            form.setGroup(null);
            form.getCOSObject().setInt("Filter", grayscaleImage.getColorModel().getNumComponents() > 1 ? 13 : 14);
            form.setPaintType(2);
            form.setSoftMask(null);
            form.setImage(null);
            form.setShading(null);
            form.setPattern(null);
            form.setMetadata(null);
            form.setPieceInfo(null);
            form.setLastModified(null);
            form.setStructParent(null);
            form.setStructParents(null);
            form.setOPI(null);
            form.getDictionary().removeItem("Subtype");
        } else if (xobject instanceof PDImageXObject) {
            PDImageXObject image = (PDImageXObject) xobject;
            image.setImage(null);
            image.setSoftMask(null);
            image.getDictionary().setItem("ColorSpace", "DeviceGray");
            image.getDictionary().setItem("BitsPerComponent", 8);
            image.getDictionary().setItem("Filter", "DCTDecode");
            image.getCOSStream().createFilteredStream();
            image.setImage(grayscaleImage);
        }
    }
}

请确保您已在项目中添加了 Apache PDFBox 的依赖。这个示例代码将加载名为 "input.pdf" 的矢量 PDF 文件，将每个矢量图像转换为灰度图像，并替换原始的矢量图像为灰度图像。最后，它保存为名为 "output.pdf" 的灰度 PDF 文件。

请注意，此代码仅处理单页的矢量 PDF。如果您的 PDF 包含多个页面，您可以根据需求进行循环处理。

希望这可以帮助到您！如有任何问题，请随时提问。