The high quality of the images is often the cause for the large size of a PDF document. Compressing the high-quality images can dramatically reduce the file size by 50% to 90%. In this article, I am going to introduce how to compress PDF images in the following two aspects:
- Automatically compress high-quality images only
- Compress images to a certain extent
Installing Spire.Pdf.jar
If you use Maven, you can easily import the Spire.Pdf.jar in your application by adding the following code to your project’s pom.xml file. For non-Maven projects, download the jar file fromthis link and manually add it as a dependency in your application.
<repositories><repository><id>com.e-iceblue</id><name>e-iceblue</name><url>http://repo.e-iceblue.com/nexus/content/groups/public/</url></repository></repositories><dependencies><dependency><groupId>e-iceblue</groupId><artifactId>spire.pdf</artifactId><verson>4.8.7</version></dependency></dependencies>Example 1. Compress high-quality images only
Spire.PDF offers PdfPageBase.getImagesInfo() method to retrieve image information from a specific page. The image information includes the image index which is returned by PdfImageInfo.getIndex() method. Then, you can use PdfPageBase.tryCompressImage(int imgIndex) method to compress the specified image.
Kindly note that tryCompressImage() method will compress the high-resolution images only. Low-quality images will no longer be compressed.
importcom.spire.pdf.PdfDocument;importcom.spire.pdf.PdfPageBase;importcom.spire.pdf.exporting.PdfImageInfo;publicclassCompressHighQualityImage{publicstaticvoidmain(String[]args){//Load the sample PDF documentPdfDocumentdoc=newPdfDocument("C:\\Users\\Administrator\\Desktop\\Images.pdf");//Set IncrementalUpdate to falsedoc.getFileInfo().setIncrementalUpdate(false);//Declare a PdfPageBase variablePdfPageBasepage;//Loop through the pagesfor(inti=0;i<doc.getPages().getCount();i++){//Get the specific pagepage=doc.getPages().get(i);if(page!=null){if(page.getImagesInfo()!=null){//Loop through the images in the pagefor(PdfImageInfoinfo:page.getImagesInfo()){//Use tryCompressImage method the compress high-resolution imagespage.tryCompressImage(info.getIndex());}}}}//Save to filedoc.saveToFile("output/Compressed.pdf");}}
Example 2. Compress images to a certain extent
After the image information is obtained from a PDF page, we’re able to create a PdfBitmap object based on a specific image. Use the PdfBitmap.setQuality() method to reduce the image quality to a certain extent, and then use the PdfPageBase.replaceImage() method to replace the old image with the compressed image in your document.
importcom.spire.license.LicenseProvider;importcom.spire.pdf.*;importcom.spire.pdf.exporting.PdfImageInfo;importcom.spire.pdf.graphics.PdfBitmap;publicclassCompressAllImages{publicstaticvoidmain(String[]args){//Load the sample PDF documentPdfDocumentdoc=newPdfDocument("C:\\Users\\Administrator\\Desktop\\Images.pdf");//Set IncrementalUpdate to falsedoc.getFileInfo().setIncrementalUpdate(false);//Loop through the pagesfor(inti=0;i<doc.getPages().getCount();i++){//Get the specific pagePdfPageBasepage=doc.getPages().get(i);//Get image info from the pagePdfImageInfo[]images=page.getImagesInfo();//Determine if there is any image in the pgaeif(images!=null&&images.length>0)//Loop through the imagesfor(intj=0;j<images.length;j++){//Get the specific imagePdfImageInfoimage=images[j];PdfBitmapbp=newPdfBitmap(image.getImage());//Reset the image qualitybp.setQuality(40);//Replace the old image with the compressed imagepage.replaceImage(j,bp);}}//Save to filedoc.saveToFile("output/CompressAll.pdf",FileFormat.PDF);doc.close();}}
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