CS 160, Fall 2013
Programming Assignment P7
Unscrambling 2D Images

Programming due Monday, Dec. 2 at noon; late deadline Dec. 2 at 10 p.m.

Using 2D Arrays to Write an Image Editor

This lab has the goal of teaching you how to:
  1. Implement a set of methods that allow a GUI object to use your class.
  2. Instantiate and call a supplied class to read and write images.
  3. Declare and use 2D arrays to store images.
  4. Manipulate the data in 2D arrays to unscramble images.

Description

The purpose of the assignment is to write a Java class that can be called by a user interface program to unscramble images in the Portable GreyMap (PGM) format. To do this you need to write a P7 object that instantiates and calls methods in Picture.java, and is in turn called from a graphical user interface (GUI) class called UserInterface.java. Both of these are supplied below.

Instructions

Part One

Create a project and class called P7, without a main method. Note: You may want to leverage code from the R21 recitation. At the top of the class declare the following instance (non-static) variables:
  1. An object of type Picture, set to null.
  2. An integer to store the image width, set to 0.
  3. An integer to store the image height, set to 0.
  4. A 2-dimensional array of integers to store the image data, not allocated.
You can name your variables whatever you like.

Part Two

Import Picture.java from here, and UserInterface.java from here into the P7 project. Create a constructor for the P7 class as shown below that instantiates an object of type Picture into the associated class instance variable. 
public P7() {
    // Instantiate Picture
}

Part Three

Write the following public (non-static) methods, which will be described below in more detail:

public void readImage(String inFile) {}

public void writeImage(String outFile) { }

public int[][] imageData() { }

public void invert() { }

public void exchange() { }

public void decode() { }

public void swap() { }

The readImage method should call the readPGM method in the Picture object, passing the input file name, then it should call the getHeight, getWidth, and getData methods to fill in the class instance data defined above. The writeImage method should call the setData method in the Picture object with the image data, then call the writePGM method passing the output file name. The parameters and return types of the methods in Picture.java are not documented here, so you must look at the file to find them. The calls to readImage and writeImage should be wrapped in a try catch block as follows: 
try {
	// Calls to readPGM or writePGM and associated code here
} catch (Exception e) {
	System.out.println(e.getMessage());
}
Implement imageData by simply returning a copy of the image array. The remaining methods manipulate the image data in some way or another to restore an image that has been scrambled.

Part Four

Make sure that all methods exist in your P7.java, even though some of the transformations may not do anything. You should now be able to run the main program in UserInterface.java to read and write PGM files. If you are having trouble integrating with the provided files, check that your method names and parameters match. We have provided a test file called Cam.pgm that you can download to the P7 project directory (not into the /src or /bin subdirectories).

Part Five

Implement the remaining methods as follows: NOTE: The maximum value of a pixel (Picture.MAXVAL) is 255, so only 8 bits are valid for each pixel. These are numbered bits 0-7, where bit 0 is equal to 1 and bit 7 is equal to 128. There are no negative values allowed.

Testing

The invert method can be tested with Invert.pgm. The exchange method can be tested with Exchange.pgm. The decode method can be tested with Decode.pgm. The swap method can be tested with Swap.pgm. In all cases except decode, the restored image should be identical to Cam.pgm. After unscrambling an image you can write it to the disk, and compare it to Cam.pgm using the Linux diff command, thus all students can verify that their code is perfect before submission! As stated above, this does not apply to the image from decode. Why do you think this is the case? NOTE: We may test your code with an image file that has a different size and contents than the provided test file, so do not hardcode anything.

Grading Criteria

Note: Do not modify the provided files in any way, or your program will not compile in our test system! Please follow the usual rules for submitting Java programs.

Submission

Submit your modified source file named P7.java to the the Checkin tab on the course web site.

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