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Leon Davis
Leon Davis

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Converting PDF to Various Image Formats in Java

#java #imagetopdf #pngtopdf #svgtopdf

In practical development, PDF files are widely used for storing contracts, reports, invoices, and technical documents. However, there are times when we need to convert PDF files into image formats for purposes such as displaying them on web pages, generating thumbnails, performing image processing, or printing. For example:

  • Displaying PDF page previews in web applications or systems.
  • Converting invoices or reports to PNG/JPG for easy printing or embedding into other documents.
  • Performing OCR or image processing on PDF pages.

Using programming to batch convert PDF files into images can greatly improve efficiency and ensure consistent output. This guide will detail how to convert PDFs into PNG, JPG, TIFF, and SVG formats using Java, with complete example code and explanations.

Environment Setup

Importing Spire.PDF for Java

Spire.PDF for Java is a powerful PDF manipulation library that supports reading, editing, and converting PDFs.

If your project uses Maven, add the following to your pom.xml:

<repositories>
    <repository>
        <id>com.e-iceblue</id>
        <name>e-iceblue</name>
        <url>https://repo.e-iceblue.cn/repository/maven-public/</url>
    </repository>
</repositories>

<dependencies>
    <dependency>
        <groupId>e-iceblue</groupId>
        <artifactId>spire.pdf</artifactId>
        <version>11.8.3</version>
    </dependency>
</dependencies>
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For non-Maven projects, download the JAR package and import it into your project. After importing, you can use import com.spire.pdf.* to work with PDF documents.

Converting PDF to PNG/JPG

When you need to display PDF page previews on web pages or systems, or generate thumbnails for reports, invoices, etc., converting PDFs into bitmap formats like PNG or JPG is a common choice. PNG supports transparent backgrounds and is ideal for web display, while JPG has a high compression rate, making it suitable for printing or storing large numbers of images. Below is an example that shows how to convert each page of a PDF into a high-resolution image and save it as a separate file.

import com.spire.pdf.*;
import com.spire.pdf.graphics.PdfImageType;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class PDFtoImage {
    public static void main(String[] args) throws IOException {
        // Instantiate PdfDocument
        PdfDocument pdf = new PdfDocument();

        // Load the PDF document
        pdf.loadFromFile("example.pdf");

        // Loop through each page of the PDF
        for (int i = 0; i < pdf.getPages().getCount(); i++) {
            // Convert page to Bitmap image and set horizontal and vertical resolution
            BufferedImage image = pdf.saveAsImage(i, PdfImageType.Bitmap, 500, 500);

            // Save as PNG file
            File file = new File(String.format("ConvertedImage-%d.png", i));
            ImageIO.write(image, "PNG", file);
        }

        // Close the document
        pdf.close();
    }
}
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Explanation:

  • PdfDocument pdf = new PdfDocument();: Creates a PDF document object.
  • pdf.loadFromFile("example.pdf");: Loads the PDF file to be processed.
  • pdf.saveAsImage(i, PdfImageType.Bitmap, 500, 500);: Converts the ith page to a Bitmap image with 500x500 DPI.
  • ImageIO.write(image, "PNG", file);: Saves the BufferedImage as a PNG file. Change "PNG" to "JPEG" to save as a JPG image.

Converting PDF to SVG

If you want to display a vector preview on a web page or in an application without distortion, SVG is the best choice. Unlike bitmap images, vector graphics can be scaled arbitrarily without losing clarity. Using PDF to SVG conversion allows you to directly convert PDF pages into vector graphics that can be embedded into HTML, making it suitable for dynamic scaling or frontend rendering.

import com.spire.pdf.*;

public class PDFToSVG {
    public static void main(String[] args) {
        // Create a PdfDocument object
        PdfDocument pdf = new PdfDocument();

        // Load the PDF document
        pdf.loadFromFile("example.pdf");

        // Save the PDF as SVG
        pdf.saveToFile("ConvertedResult.svg", FileFormat.SVG);
    }
}
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Explanation:

  • FileFormat.SVG: Specifies that the output format is SVG.
  • This method saves the PDF document pages as multiple SVG files, suitable for vector previews or embedding into web pages.

Converting PDF to TIFF

TIFF is commonly used for printing, archiving, and multi-page image processing. Unlike PNG/JPG, TIFF supports multi-page documents, allowing you to save an entire PDF or specific pages as a single TIFF file. This method is ideal for generating multi-page print documents, archiving, or further processing in image editing software.

import com.spire.pdf.*;

public class PDFtoTiff {
    public static void main(String[] args) {
        // Load the PDF document
        PdfDocument pdf = new PdfDocument();
        pdf.loadFromFile("example.pdf");

        // Save the entire document as TIFF
        pdf.saveToTiff("ConvertedResult.tiff");

        // Save a specific page range as TIFF (pages 2 to 3, set DPI)
        pdf.saveToTiff("ConvertedResult_Part.tiff", 1, 2, 400, 600);
    }
}
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Explanation:

  • saveToTiff(String fileName): Converts the entire PDF to a TIFF file.
  • saveToTiff(String fileName, int startPage, int endPage, int xDpi, int yDpi): Converts a specific page range to TIFF, setting horizontal and vertical DPI.

Batch Converting PDF to Images

In real-world projects, you often need to process a large number of PDF files, such as generating report previews, invoice images, or image backups. Manual processing is inefficient and error-prone, while using a program to handle batch processing can greatly improve efficiency and maintain consistent output.

import com.spire.pdf.*;
import com.spire.pdf.graphics.PdfImageType;
import javax.imageio.ImageIO;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class BatchPDFtoImage {
    public static void main(String[] args) throws IOException {
        // Specify the PDF folder
        File folder = new File("pdf_folder");
        File[] files = folder.listFiles((dir, name) -> name.endsWith(".pdf"));

        for (File file : files) {
            // Load PDF
            PdfDocument pdf = new PdfDocument();
            pdf.loadFromFile(file.getAbsolutePath());

            // Loop through each page and save as PNG
            for (int i = 0; i < pdf.getPages().getCount(); i++) {
                BufferedImage image = pdf.saveAsImage(i, PdfImageType.Bitmap, 300, 300);
                String outputFile = "ImageOutput/" + file.getName().replace(".pdf", "_Page_" + (i + 1) + ".png");
                ImageIO.write(image, "PNG", new File(outputFile));
            }

            System.out.println(file.getName() + " has been successfully converted to images.");
            pdf.close();
        }
    }
}
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Explanation:

  • Loops through all PDF files in the specified folder and processes them one by one.
  • Saves each PDF page as a PNG file, automatically generating filenames.
  • Sets 300x300 DPI, suitable for general display and printing.

Conclusion

This guide has detailed how to use Java to convert PDF documents to various image formats, including PNG, JPG, TIFF, and SVG. By setting resolution, specifying page ranges, and performing batch processing, you can meet different application scenarios such as web previews, printing, and image processing.

Mastering PDF to image conversion through programming improves development efficiency, ensures consistent output, and is a common skill in PDF automation processing for developers.

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