ImageData.java

/*************************************************************************
 *  Copyright 2012 Benedict J. Brown
 *
 *  Compilation:  javac ImageData.java
 *  Execution:    java ImageData imagename
 *
 *  Library for reading an image into a 2D array of ints, where each
 *  int represents a pixel in Java's ARGB format.
 *
 *  % java ImageData mandrill.jpg
 *
 *  Remarks
 *  -------
 *   - img[y][x] is row y, column x, where (0, 0) is upper left
 *
 *   - img stores each pixel in an int as 0RGB (i.e. alpha is forced to 0)
 *     in order to guarantee that pixel values are always positive
 *
 *   - relies on the Picture class from the introcs standard library
 *
 *   - note that Picture's pixel() accesses pixels as (col,row) or (x,y),
 *     which is the transpose of what load provides
 *
 *************************************************************************/

public class ImageData {
  /* Load an image from filename, and return it
   * as a 2D array of integers in row-major order
   *
   * and empty, 0x0 array is returned on errors
   */
  public static int[][] load(String filename) {
    try {
      Picture p = new Picture(filename);

      int[][] img = new int[p.height()][p.width()];
      for (int row = 0; row < p.height(); row++) {
        for (int col = 0; col < p.width(); col++) {
          img[row][col] = p.get(col, row).getRGB() & 0xFFFFFF;
        }
      }

      return img;
    } catch (RuntimeException e) {
      return new int[0][0];
    }
  }

  /* Create a Picture object from image data
   * in a 2D array of ints.  This is primarily
   * a helper method for show() and save(),
   * but is declared public because it is
   * useful in its own right.
   */
  public static Picture getPicture(int[][] img) {
    if (img == null) return null;
    if (img.length == 0) return null;
    if (img[0].length == 0) return null;

    Picture p = new Picture(img[0].length, img.length);

    for (int row = 0; row < img.length; row++) {
      for (int col = 0; col < img[0].length; col++) {
        p.set(col, row, new java.awt.Color(img[row][col]));
      }
    }

    return p;
  }

  /* Display img in a window
   */
  public static void show(int[][] img) {
    Picture p = getPicture(img);
    if (p != null) p.show();
  }

  /* Save img to filename.  The format is determined
   * by the file's extension.
   */
  public static void save(int[][] img, String filename) {
    Picture p = getPicture(img);
    if (p != null) p.save(filename);
  }

  /* Load an image, print its dimensions, and display
   * it for testing purposes and as a simple image viewer.
   */
  public static void main(String[] args) {
    int[][] img = load(args[0]);
    System.out.printf("Image %s: width = %d, height = %d\n",
                      args[0], img[0].length, img.length);
    show(img);
  }
}