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ImageIO plugin for reading and writing JPEG images via libjpeg-turbo/turbojpeg. Requires the libjpeg-turbo and turbojpeg shared native libraries to be installed on the system.

There is a newer version: 0.6.8

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package de.digitalcollections.turbojpeg;

import de.digitalcollections.turbojpeg.lib.structs.tjscalingfactor;

import java.awt.*;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.stream.Collectors;

public class Info {
  private int width;
  private int height;
  private int subsampling;
  List availableSizes;

  public int getWidth() {
    return width;
  }

  public int getHeight() {
    return height;
  }

  public int getSubsampling() {
    return subsampling;
  }

  public List getAvailableSizes() {
    return availableSizes;
  }

  private static int getScaled(int dim, int num, int denom) {
    return (dim * num + denom - 1) / denom;
  }

  public Info(int width, int height, int subsampling, tjscalingfactor[] factors) {
    this.width = width;
    this.height = height;
    this.subsampling = subsampling;
    // The available sizes are determined from the list of scaling factors.
    this.availableSizes = Arrays.stream(factors)
        .sorted(Comparator.comparing(f -> -getScaled(width, f.num.get(), f.denom.get())))
        .map(f -> new Dimension(getScaled(width, f.num.get(), f.denom.get()),
                                getScaled(height, f.num.get(), f.denom.get())))
        .filter(d -> d.width <= width && d.height <= height && d.width > 0 && d.height > 0)
        .distinct()
        .collect(Collectors.toList());
  }

  public Dimension getMCUSize() {
    switch (subsampling) {
      case 1:  // 4:2:2
        return new Dimension(16, 8);
      case 2:
        return new Dimension(16, 16);
      case 4:
        return new Dimension(8, 16);
      default:
        return new Dimension(8, 8);
    }
  }
}