LAB 13 - Modifying Pictures in a Matrix (part 1 - Copying Pixels)

Topics

n To copy pixels in a matrix using nested loops

5.1 Copying Pixels

Type in the following code in the Program window (changing the comments):

/* Program that modifies pictures using nested loops

 * Picture and Pixel classes are defined in bookClasses developed

 * at Georgia Tech by Mark Guzdial / Barbara Ericson

 *

 * @author Wayne Summers

 * @date   Sept. 19, 2007

 */

public class ModifyPictures

{

  public static void main(String[] args)

  {

    String fileName;

    fileName = FileChooser.pickAFile();  // note that this pops up a window to select a jpg file

    Picture pic;

    pic = new Picture(fileName);

// calls to methods that manipulate images go here

    pic.show(); 

  }

}

5.1.1 Looping Across the Pixels with a Nested Loop

5.1.2 Mirroring a Picture (vertical)

i) Type in the following code in the Program window below the main method and before the last }:

/**

  * Method that mirrors the leftside of a picture to the rightside

  * @param pict - picture Object to be modified

 */

public static void mirrorVertical(Picture pict)

 {

   int mirrorPoint = pict.getWidth() / 2;

Pixel leftPixel = null;

   Pixel rightPixel = null;

// loop through the rows

   for (int y = 0; y < pict.getHeight(); y++)

   {

     // loop from 0 to just before the mirror point

     for (int x = 0; x < mirrorPoint; x++)

     {

            leftPixel = pict.getPixel(x, y);

            rightPixel = pict.getPixel(pict.getWidth() – 1 – x, y);

            rightPixel.setColor(leftPixel.getColor());

     }

   }

 }

ii) Type in the following code in the Program window in the main method and before the pic.show();

mirrorVertical(pic);

iii) Test your program.

5.1.2 Mirroring a Picture (horizontal)

i) Type in the following code in the Program window below the main method and before the last }:

  /**

  * Method that mirrors the top of a picture to the bottom

  * @param pict - picture Object to be modified

 */

public static void mirrorHorizontal(Picture pict)

 {

  int height = pict.getHeight();

  int width = pict.getWidth();

  int mirrorPoint = height / 2;

  Pixel topPixel = null;

  Pixel bottomPixel = null;

   // loop through the columns

   for (int x = 0; x < width; x++)

   {

     // loop from 0 to just before the mirror point

     for (int y = 0; y < mirrorPoint; y++)

     {

        topPixel = pict.getPixel(x, y);

        bottomPixel = pict.getPixel(x, height - 1 - y);

        bottomPixel.setColor(topPixel.getColor());

     }

   }

 }

ii) Type in the following code in the Program window in the main method and before the pic.show();

mirrorHorizontal (pic);

iii) Test your program.

QUESTIONS:

Write a program that uses a method that calls both mirrorHorizontal and mirrorVertical.

Does it matter which order you call the two methods?

CHALLENGE: Write a method that mirrors across the diagonal.

Submit the .java file and the answer to the question through the DropBox in WebCT.