ava 将彩色pdf转换为灰度矢量pdf

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

import org.apache.pdfboxdmodel.PDDocument;
import org.apache.pdfbox.pdmodel.PDPage;
import org.apache.pdfbox.pdmodel.common.PDStream;
import org.apache.pdfbox.pdmodel.graphics.color.PDColorSpace;
import org.apache.pdfbox.pdmodel.graphics.color.PDDeviceGray;
import org.apache.pdfbox.pdmodel.graphics.image.PDImage;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImage;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImageCreator;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImageCreatorFromImage;
import org.apache.pdfbox.rendering.ImageType;
import org.apache.pdfbox.rendering.PDFRenderer;

import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;

public class ColorToGrayscalePDFConverter {
    public static void main(String[] args) {
        try {
            // 加载彩色 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，将彩色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);

                // 渲染当前页为图像
                BufferedImage image = pdfRenderer.renderImageWithDPI(pageIndex, 300, ImageType.RGB);

                // 将图像转换为灰度
                BufferedImage grayscaleImage = convertToGrayscale(image);

                // 创建灰度图像对象
                PDImageXObject grayscaleImageXObject = createImageXObject(document, grayscaleImage);

                // 替换原图像为灰度图像
                replaceImage(page, grayscaleImageXObject);
            }

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

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

    private static BufferedImage convertToGrayscale(BufferedImage colorImage) {
        BufferedImage grayscaleImage = new BufferedImage(colorImage.getWidth(), colorImage.getHeight(), BufferedImage.TYPE_BYTE_GRAY);
        grayscaleImage.getGraphics().drawImage(colorImage, 0, 0, null);
        return grayscaleImage;
    }

    private static PDImageXObject createImageXObject(PDDocument document, BufferedImage image) throws Exception {
        PDColorSpace colorSpace = PDDeviceGray.INSTANCE;
        PDImageXObject imageXObject;
        if (image.getType() == BufferedImage.TYPE_BYTE_GRAY) {
            imageXObject = LosslessFactory.createFromImage(document, image);
        } else {
            PDImage pdImage = LosslessFactory.createFromImage(document, image);
            PDImageXObject pdImageXObject = new PDImageXObject(pdImage, null);
            PDInlineImageCreator creator = new PDInlineImageCreatorFromImage(colorSpace, pdImageXObject);
            PDInlineImage inlineImage = creator.createInlineImage();
            imageXObject = inlineImage.createXObject(document);
        }
        return imageXObject;
    }

    private static void replaceImage(PDPage page, PDImageXObject grayscaleImageXObject) throws Exception {
        for (PDStream contentStream : page.getContentStreams()) {
            contentStream.getTokens().forEach(token -> {
                if (token instanceof PDImageXObject) {
                    PDImageXObject imageXObject = (PDImageXObject) token;
                    if (!imageXObject.getCOSObject().equals(grayscaleImageXObject.getCOSObject())) {
                        imageXObject.getCOSObject().setItem("Subtype", grayscaleImageXObject.getCOSObject().getItem("Subtype"));
                        imageXObject.getCOSObject().setItem("Width", grayscaleImageXObject.getCOSObject().getItem("Width"));
                        imageXObject.getCOSObject().setItem("Height", grayscaleImageXObject.getCOSObject().getItem("Height"));
                        imageXObject.getCOSObject().setItem("ColorSpace", grayscaleImageXObject.getCOSObject().getItem("ColorSpace"));
                        imageXObject.getCOSObject().setItem("BitsPerComponent", grayscaleImageXObject.getCOSObject().getItem("BitsPerComponent"));
                        imageXObject.getCOSObject().setItem("Filter", grayscaleImageXObject.getCOSObject().getItem("Filter"));
                        imageXObject.setSoftMask(null);
                    }
                }
            });
        }
    }
}

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" 的彩色 PDF 文件，将每一页的图像转换为灰度图像，并替换原始的彩色图像为灰度图像。最后，它保存为名为 "output.pdf" 的灰度矢量 PDF 文件。

请注意，此代码仅处理单页的彩色 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。