Apache POI, converting powerpoint slides to images, images are low quality

Question

Here is my code

import lombok.RequiredArgsConstructor;
import lombok.extern.slf4j.Slf4j;
import org.apache.poi.hslf.usermodel.HSLFSlide;
import org.apache.poi.hslf.usermodel.HSLFSlideShow;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.awt.*;
import java.awt.geom.Rectangle2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

@Service
@Slf4j
@RequiredArgsConstructor(onConstructor = @__(@Autowired))
public class FileConverterService {
  public void convertPptToImages() throws Exception {
    ClassLoader classLoader = getClass().getClassLoader();
    File file = new File(classLoader.getResource("Sylon_GuidedPath_Sprint22Deck.ppt").getFile());

    Document pdfDocument = new Document();
    //    PdfWriter pdfWriter = PdfWriter.getInstance(pdfDocument, new FileOutputStream(""));
    FileInputStream is = new FileInputStream(file);
    HSLFSlideShow ppt = new HSLFSlideShow(is);
    is.close();
    Dimension pgsize = ppt.getPageSize();
    pdfDocument.setPageSize(new Rectangle((float) pgsize.getWidth(), (float) pgsize.getHeight()));
    // convert to images
    int idx = 1;
    for (HSLFSlide slide : ppt.getSlides()) {
      BufferedImage img =
          new BufferedImage(pgsize.width, pgsize.height, BufferedImage.TYPE_INT_RGB);
      Graphics2D graphics = img.createGraphics();
      graphics.setRenderingHint(
          RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
      graphics.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
      graphics.setRenderingHint(
          RenderingHints.KEY_TEXT_ANTIALIASING, RenderingHints.VALUE_TEXT_ANTIALIAS_ON);
      graphics.setRenderingHint(RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
      graphics.setRenderingHint(
          RenderingHints.KEY_INTERPOLATION, RenderingHints.VALUE_INTERPOLATION_BICUBIC);
      graphics.setRenderingHint(
          RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
      // clear the drawing area
      graphics.setPaint(Color.white);
      graphics.fill(new Rectangle2D.Float(0, 0, pgsize.width, pgsize.height));
      // render
      slide.draw(graphics);
      // save the output
      ImageWriter jpgWriter = ImageIO.getImageWritersByFormatName("jpg").next();
      ImageWriteParam jpgWriteParam = jpgWriter.getDefaultWriteParam();
      jpgWriteParam.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
      jpgWriteParam.setCompressionQuality(1f);
      jpgWriter.setOutput(new FileImageOutputStream(
        new File("slide-" + idx + ".jpg")));
      IIOImage outputImage = new IIOImage(img, null, null);
      jpgWriter.write(null, outputImage, jpgWriteParam);
      jpgWriter.dispose();
      idx++;
    }
  }

I based my code off this documentation, http://poi.apache.org/components/slideshow/how-to-shapes.html#Render

I have tried both jpeg and png, and the image seems to be fairly low resolution and the text is difficult to read compared to the original .ppt. Is there any way to increase the resolution/quality of the images?

Answer 1

What you can try

1. Applying RenderingHints to the graphics, below is a sample I created comparing the image with/without rendering hint. You can see that the character looks better with rendering hint.
2. Increase the compression quality for the jpeg image.

---

Following program demonstrates how to generate image with/without rendering hint and create image with 100% compression quality.

import java.awt.Dimension;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileInputStream;

import javax.imageio.IIOImage;
import javax.imageio.ImageIO;
import javax.imageio.ImageWriteParam;
import javax.imageio.ImageWriter;
import javax.imageio.plugins.jpeg.JPEGImageWriteParam;
import javax.imageio.stream.FileImageOutputStream;

import org.apache.poi.hslf.usermodel.HSLFSlide;
import org.apache.poi.hslf.usermodel.HSLFSlideShow;

public class ImproveSlideConvertToImageQuality {
    public static void main(String[] args) throws Exception {
        convertPptToImages(true);
        convertPptToImages(false);
    }

    public static void convertPptToImages(boolean withRenderHint) throws Exception {
        File file = new File("test.ppt");
        String suffix = withRenderHint ? "-with-hint" : "-without-hint";
        try (FileInputStream is = new FileInputStream(file); HSLFSlideShow ppt = new HSLFSlideShow(is)) {
            Dimension pgsize = ppt.getPageSize();
            int idx = 1;
            for (HSLFSlide slide : ppt.getSlides()) {
                BufferedImage img = new BufferedImage(pgsize.width, pgsize.height, BufferedImage.TYPE_INT_RGB);
                Graphics2D graphics = img.createGraphics();
                if (withRenderHint) {
                    graphics.setRenderingHint(RenderingHints.KEY_INTERPOLATION,
                            RenderingHints.VALUE_INTERPOLATION_BILINEAR);
                    graphics.setRenderingHint(
                            RenderingHints.KEY_ALPHA_INTERPOLATION, RenderingHints.VALUE_ALPHA_INTERPOLATION_QUALITY);
                    graphics.setRenderingHint(
                            RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
                    graphics.setRenderingHint(
                            RenderingHints.KEY_FRACTIONALMETRICS, RenderingHints.VALUE_FRACTIONALMETRICS_ON);
                    graphics.setRenderingHint(
                            RenderingHints.KEY_RENDERING, RenderingHints.VALUE_RENDER_QUALITY);
                    graphics.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                            RenderingHints.VALUE_TEXT_ANTIALIAS_GASP);
                }
                // render
                slide.draw(graphics);
                final ImageWriter writer = ImageIO.getImageWritersByFormatName("jpg").next();
                writer.setOutput(new FileImageOutputStream(
                        new File("slide-" + idx + suffix + ".jpeg")));
                JPEGImageWriteParam jpegParams = new JPEGImageWriteParam(null);
                jpegParams.setCompressionMode(ImageWriteParam.MODE_EXPLICIT);
                jpegParams.setCompressionQuality(1f);
                // writes the file with given compression level
                // from your JPEGImageWriteParam instance
                IIOImage image = new IIOImage(img, null, null);
                writer.write(null, image, jpegParams);
                writer.dispose();
                idx++;
            }
        }
    }
}

References:
Controlling Rendering Quality
Setting jpg compression level with ImageIO in Java