用 iText 读取图像签名流/对象..是黑色背景和白色前景，如何反转

Question

I am trying to read image objects from a PDF document. The image comes out as black background and white text. How can I reverse that. the image in the pdf, is white foreground and black background.

Here is the code, main piece for loading the image component

import java.awt.image.BufferedImage;
import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.IOException;

import javax.imageio.ImageIO;

import com.itextpdf.text.DocumentException;
import com.itextpdf.text.Image;
import com.itextpdf.text.pdf.PRStream;
import com.itextpdf.text.pdf.PdfDictionary;
import com.itextpdf.text.pdf.PdfName;
import com.itextpdf.text.pdf.parser.ImageRenderInfo;
import com.itextpdf.text.pdf.parser.PdfImageObject;
import com.itextpdf.text.pdf.parser.RenderListener;
import com.itextpdf.text.pdf.parser.TextRenderInfo;

public class MyImageRenderListener implements RenderListener {

    /**
     * The new document to which we've added a border rectangle.
     */
    protected String path = "";

    /**
     * Creates a RenderListener that will look for images.
     */
    public MyImageRenderListener(String path) {
        this.path = path;
    }

    /**
     * @see com.itextpdf.text.pdf.parser.RenderListener#beginTextBlock()
     */
    public void beginTextBlock() {
    }

    /**
     * @see com.itextpdf.text.pdf.parser.RenderListener#endTextBlock()
     */
    public void endTextBlock() {
    }

    /**
     * @see com.itextpdf.text.pdf.parser.RenderListener#renderImage(
     *com.itextpdf.text.pdf.parser.ImageRenderInfo)
     */
    public void renderImage(final ImageRenderInfo renderInfo) {
        try {
            String filename;
            FileOutputStream os;
            PdfImageObject image = renderInfo.getImage();
            PdfImageObject tmp = null;
            PdfName filter = (PdfName) image.get(PdfName.FILTER);

            ///
            PdfDictionary imageDictionary = image.getDictionary();
            // Try SMASK, SMASKINDATA
            PRStream maskStream = (PRStream) imageDictionary.getAsStream(PdfName.SMASK);

            // todo - required - black white - fix
            PdfImageObject maskImage = new PdfImageObject(maskStream);
            image = maskImage;
            if (PdfName.DCTDECODE.equals(filter)) {
                filename = String.format(path, renderInfo.getRef().getNumber(), "jpg");
                os = new FileOutputStream(filename);
                os.write(image.getImageAsBytes());
                os.flush();
                os.close();
            } else if (PdfName.JPXDECODE.equals(filter)) {
                filename = String.format(path, renderInfo.getRef().getNumber(), "jp2");
                os = new FileOutputStream(filename);
                os.write(image.getImageAsBytes());
                os.flush();
                os.close();
            } else if (PdfName.JBIG2DECODE.equals(filter)) {
                // ignore: filter not supported.
            } else {
                BufferedImage awtimage = renderInfo.getImage().getBufferedImage();
                if (awtimage != null) {
                    filename = String.format(path, renderInfo.getRef().getNumber(), "png");
                    ImageIO.write(awtimage, "png", new FileOutputStream(filename));
                }
            }

            try {
                final String newfile = String.format(path, renderInfo.getRef().getNumber(), ".x.", "png");

                BufferedImage bi = image.getBufferedImage();
                BufferedImage newBi = new BufferedImage(bi.getWidth(), bi.getHeight(), BufferedImage.TYPE_USHORT_GRAY);
                newBi.getGraphics().drawImage(bi, 0, 0, null);
                ImageIO.write(newBi, "png", new FileOutputStream(newfile));
            } catch(final Exception e) {
                e.printStackTrace();;
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static Image makeBlackAndWhitePng(PdfImageObject image) throws IOException, DocumentException {
        BufferedImage bi = image.getBufferedImage();
        BufferedImage newBi = new BufferedImage(bi.getWidth(), bi.getHeight(), BufferedImage.TYPE_USHORT_GRAY);
        newBi.getGraphics().drawImage(bi, 0, 0, null);
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(newBi, "png", baos);
        return Image.getInstance(baos.toByteArray());
    }

    /**
     * @see com.itextpdf.text.pdf.parser.RenderListener#renderText(
     *com.itextpdf.text.pdf.parser.TextRenderInfo)
     */
    public void renderText(TextRenderInfo renderInfo) {
    }
}

And code around loading the pages

 public static void readImages(final PdfReader reader, final File filex) throws IOException {
        for (int i = 0; i < reader.getXrefSize(); i++) {
            PdfObject pdfobj = reader.getPdfObject(i);
            if (pdfobj == null || !pdfobj.isStream()) {
                continue;
            }
            PdfStream stream = (PdfStream) pdfobj;
            PdfObject pdfsubtype = stream.get(PdfName.SUBTYPE);
            if (pdfsubtype != null && pdfsubtype.toString().equals(PdfName.IMAGE.toString())) {
                byte[] img = PdfReader.getStreamBytesRaw((PRStream) stream);
                FileOutputStream out = new FileOutputStream(new File(filex.getParentFile(), String.format("%1$05d", i) + ".jpg"));
                out.write(img);
                out.flush();
                out.close();
            }
        }
    }

Answer 1

To combine my comments:

What you see, merely is the soft mask of the image which contains transparency information, white = opaque, black = transparent. The base image actually is all black but only where the mask indicates opaque, that image black is drawn. Thus it looks like reversed.

You can use image manipulation libraries to invert a bitmap. Simply googl'ing for "imageio invert image" returns this , this , and numerous other interesting matches.