【发布时间】：2019-02-18 09:27:19
【问题描述】：
我需要在 pdf 文件中找到（光栅）图像并调整它们的大小 （改变他们的分辨率）。
我的代码基于示例 PrintImageLocations。对于部分 那行得通，我扩展了 PDFStreamEngine 并对 “做”运算符：
我使用第一个参数获取原始 PDImageXObject 运营商和资源。
然后我从中创建一个 BufferedImage 并处理它以更改 像素数。
然后我通过 BufferedImage 创建一个新的 PDImageXObject 无损工厂
最后我使用 原始对象的名称
我尝试对内联图像做类似的事情，然后我到达 点我有一个 BufferedImage，但我不知道如何使用它 替换原来的内嵌图片。
也可以用 XObject 替换内联图像，但是 再次，我不知道如何替换这两个......
下面是我的代码；有趣的部分是函数“processOperator”。
// WIP!
// find raster images inside a pdf
// if their resolution is more than 900dpi
// then resize them
// reducing the resolution to 200dpi
// NB bug: fails on pdf files with more than one page
// ...DEBUG ScratchFileBuffer:516 - ScratchFileBuffer not closed!
// also fails on pdf with included pdf
// (e.g. latex \includegraphics{x.pdf})
// # to compile:
// apt install libpdfbox2-java
// export CLASSPATH=.:/usr/share/java/pdfbox2.jar:/usr/share/java/commons-logging.jar
// javac Resampleimages.java
// # to run:
// java Resampleimages x.pdf
// see
// https://pdfbox.apache.org/2.0/examples.html
// https://pdfbox.apache.org/docs/2.0.11/javadocs/
import org.apache.pdfbox.cos.COSBase;
import org.apache.pdfbox.cos.COSName;
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.PDImage;
import org.apache.pdfbox.pdmodel.graphics.image.PDImageXObject;
import org.apache.pdfbox.pdmodel.graphics.image.PDInlineImage;
import org.apache.pdfbox.util.Matrix;
import org.apache.pdfbox.contentstream.operator.DrawObject;
import org.apache.pdfbox.contentstream.operator.Operator;
import org.apache.pdfbox.contentstream.PDFStreamEngine;
import org.apache.pdfbox.pdmodel.PDResources;
import org.apache.pdfbox.pdmodel.graphics.image.LosslessFactory;
import java.io.File;
import java.io.IOException;
import java.util.List;
import java.awt.image.BufferedImage;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Color;
import org.apache.pdfbox.contentstream.operator.state.Concatenate;
import org.apache.pdfbox.contentstream.operator.state.Restore;
import org.apache.pdfbox.contentstream.operator.state.Save;
import org.apache.pdfbox.contentstream.operator.state.SetGraphicsStateParameters;
import org.apache.pdfbox.contentstream.operator.state.SetMatrix;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
public class ReplaceBigImages extends PDFStreamEngine
{
private static Log log = LogFactory.getLog(ReplaceBigImages.class);
public ReplaceBigImages() throws IOException
{
addOperator(new Concatenate());
addOperator(new DrawObject());
addOperator(new SetGraphicsStateParameters());
addOperator(new Save());
addOperator(new Restore());
addOperator(new SetMatrix());
}
public static PDDocument document;
public static void main( String[] args ) throws IOException
{
if( args.length != 1 )
{
usage();
}
else
{
try
{
document = PDDocument.load(new File(args[0]));
ReplaceBigImages printer = new ReplaceBigImages();
int pageNum = 0;
for( PDPage page : document.getPages() )
{
pageNum++;
log.info( "Processing page: " + pageNum );
printer.processPage(page);
}
}
finally {
if( document != null )
{
document.save(args[0].replace(".pdf", "_test.pdf"));
document.close();
}
}
}
}
protected void processOperator( Operator operator, List<COSBase> operands) throws IOException
{
String operation = operator.getName();
// log.debug(String.format("Operator %s", operation));
if( "Do".equals(operation) ) {
log.debug("### Found Do operator");
COSName objectName = (COSName) operands.get( 0 );
PDXObject xobject = getResources().getXObject( objectName );
// log.debug(String.format("%s isa %s", objectName, xobject.getClass().getSimpleName()));
if( xobject instanceof PDImageXObject)
{
log.debug(String.format("Looking at %s (%s)", objectName.getName(), xobject));
PDImageXObject image = (PDImageXObject)xobject;
BufferedImage scaledImage = changeImageResolution(image);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject replacement_img = LosslessFactory.createFromImage(document, scaledImage);
PDPage currentPage = getCurrentPage();
PDResources resources = currentPage.getResources();
resources.put(objectName, replacement_img);
}
}else if(xobject instanceof PDFormXObject)
{
PDFormXObject form = (PDFormXObject)xobject;
showForm(form);
}
} else if ("BI".equals(operation)) {
PDPage currentPage = getCurrentPage();
log.debug("### Found BI operator");
PDResources resources = currentPage.getResources();
PDInlineImage image = new PDInlineImage(operator.getImageParameters(),
operator.getImageData(),
resources);
BufferedImage scaledImage = changeImageResolution(image);
if (scaledImage != null) {
log.debug(String.format("Replacing with %s", scaledImage));
PDImageXObject replacement_img = LosslessFactory.createFromImage(document, scaledImage);
// ARGH!!! How do I replace the inline image???
resources.add(replacement_img, "pippo");
// operator.setImageParameters(scaledImage???)
// operator.setImageData(scaledImage???)
}
} else {
super.processOperator( operator, operands);
}
}
protected BufferedImage changeImageResolution( PDImage image)
throws IOException
{
int imageWidth = image.getWidth();
int imageHeight = image.getHeight();
Matrix ctmNew = getGraphicsState().getCurrentTransformationMatrix();
float imageXScale = Math.abs(ctmNew.getScalingFactorX());
float imageYScale = Math.abs(ctmNew.getScalingFactorY());
float resolution = imageWidth / ( imageXScale / 72 );
String stencil = "";
if (image.isStencil()) {
stencil = " (stencil)";
}
// TODO: take into consideration the size at which this file is included by TeX
log.debug("size: ("+imageWidth+","+imageHeight+")@("+imageXScale+","+imageYScale+") resolution = "+resolution+stencil);
// if ( resolution > 899f ) {
if ( resolution > 200f ) {
// what do the following two lines mean???
BufferedImage bImage = new BufferedImage(imageWidth,
imageHeight,
BufferedImage.TYPE_INT_ARGB);
if (image.isStencil()) {
log.warn("Is stencil; painting black.");
bImage = image.getStencilImage(Color.black);
} else {
bImage = image.getImage();
}
int desiredResolution = 200;
float xFactor = (imageXScale / 72) * desiredResolution / imageWidth;
float yFactor = (imageYScale / 72) * desiredResolution / imageHeight;
log.info("Scaling x to "+xFactor);
int dWidth = (int) (xFactor * imageWidth);
int dHeight = (int) (yFactor * imageHeight);
// the image type is from
// https://docs.oracle.com/javase/6/docs/api/constant-values.html#java.awt.image.
log.debug(String.format("Destination: %d x %d [%s]",
dWidth,
dHeight,
bImage.getType()));
BufferedImage scaledImage = new BufferedImage(dWidth,
dHeight,
bImage.getType());
Graphics2D graphics2D = scaledImage.createGraphics();
graphics2D.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
RenderingHints.VALUE_INTERPOLATION_BILINEAR);
graphics2D.setRenderingHint(RenderingHints.KEY_RENDERING,
RenderingHints.VALUE_RENDER_QUALITY);
graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
RenderingHints.VALUE_ANTIALIAS_ON);
graphics2D.drawImage(bImage, 0, 0, dWidth, dHeight, null);
graphics2D.dispose();
// see https://pdfbox.apache.org/docs/2.0.11/javadocs/org/apache/pdfbox/pdmodel/graphics/image/PDImageXObject.html#createFromByteArray-org.apache.pdfbox.pdmodel.PDDocument-byte:A-java.lang.String-
return scaledImage;
}
return null;
}
private static void usage()
{
System.err.println( "Usage: java " + ReplaceBigImages.class.getName() + " <input-pdf>" );
}
}
【问题讨论】：
-
你可以做的是用你的新图像创建一个 PDImageXObject，然后获取原始流并将这些字节分配给 setImageData()。还要确保使用相同的过滤器，但使用短名称（例如 FLATE_DECODE_ABBREVIATION 而不是 FLATE_DECODE）。或者使用解码后的流并从目标字典中删除所有过滤器（文件会更大，但可能是一种测试“某事”是否有效的方法）
-
代码PDInlineImageTest.java可以帮上忙，在源代码下载中搜索这个文件。这将创建一个完全从头开始的未压缩图像。