Description
Introduction
Ah, the life of being a teaching assistant at UGA. It’s a rewarding experience, but lacks the perks of some
more interesting jobs. The goal of this assignment is to help our illustrious head TA Sagar feel the
experience of traveling without him spending a dime!
To do this, we’re going to implement some trickery using Java. If you’ve ever watched a weather
forecast, you’ve seen some trickery in action, referred to commonly as a greenscreen. The weather
guesser stands in front of a large panel of green, and then software magically replaces the green space
with images of satellite imager, radar, etc. for viewers at home. Wait, it’s not magic, it’s science!
Computer science!
In this project, you will use Java to build a simple algorithm that you might see being used at a television
station, or even in the film special effects industry. You will write a program that processes an image
specified by the user, replacing the background with the background of another image, both of which
are specified by the user. Finally, you will save the image to a filename as specified by the user.
Figure 1. Example of a greenscreen in action
(source: http://www.gr8pix.biz/green-screenservice.php)
This lovely person is standing in front of a
greenscreen where the image is replaced with a
terrific shot of the Golden Gate Bridge.
Note, her positioning is mirrored; in this project,
you aren’t required to mirror an image.
Here are detailed instructions:
Part I: Swapping Colors
1. The program’s main class must be called GreenScreen.java
2. The main method of GreenScreen.java must handle these input parameters (in this particular
order):
args[0] (required) is the name of the .png image that you want to manipulate (input image 1)
args[1] (required) is the name of the .png image that you want to
args[2] (required) is the name of file that you will save with any modifications
args[3] (required) is the image filetype you will save (either “jpg” or “png”)
args[4] (required) is the color of the green screen *
* Args 3: the color of the green screen can be either green, or white, as defined by the color
constants in the Java API. For extra credit, you can implement a third option, “auto”, which
automatically selects the background color.
3. Implement as many helper functions as needed, but you should use at least two helper
functions: one to read in the image and perform the manipulations, and one to save the file of
the manipulated image.
4. Write your Java source code in emacs or vi on Nike.
Here is a sample of what a successful run of the program might look like:
cplaue% java GreenScreen sagar.png golden_gate.png modified png green
cplaue%
Note that the name of the output file “mod” does not contain the “.png” extension; since you are
specifying the type of image file, you know what extension to automatically tag on! (that is, the actual
file should be saved as mod.png).
Input File: sagar.png Input File: golden_gate.png Output File: modified.png
I will provide the sagar.png and golden_gate.png files on eLC that you may use as testers, each is a
resolution of 430×300. Feel free to come up with your own files to test using tasteful backgrounds!
You may be a bit worried at this point, wondering how the heck you’ll do this. Well, we structure this
assignment to help you—the key is to get started early and ask questions. Half of being a computer
scientist is not necessarily knowing the solution off the top of your head, but knowing where to look
and what questions to ask.
Here are some hints to help you out.
– Take a look in the Java API at the class Color. For the intents of this assignment, we will be using
colors in args[4] (valid colors specified earlier) as specified by the constants listed there.
– You will need to use try/catch blocks for anything involving File I/O
– There are many different ways to deal with Images. My suggestion is to take a look at the very
helpful class is BufferedImage
– Remember, the Java API and the Java Tutorials are valid resources to consult for this project.
Part II: Error Handling
Add error and exception handling to GreenScreen.java. Specifically, your program must:
• identify user input errors, and then print a meaningful error message identifying at least one of
the errors and a possible solution (i.e. If someone inputs “bmp” as the file type to save as, you
should print a message stating that the file type must be saved as a jpg or png).
• If an input parameter is missing or entered out-of-order, your program must detect this and
print out an appropriate error message.
• The program must terminate correctly after printing out an error message or successfully
processing an image. It is up to you to figure out what types of input errors and exceptions can
occur and how to correctly handle those errors and exceptions without having your program
crash, get stuck in a infinite loop, or have any other undesirable behavior.
• Capitalization should not matter for specifying colors.
• Your program should print out an error if the source and destination files are not the same
dimension (i.e. 200 x 200 pixels, each).
Part III: Submission Instructions
As discussed in class, this is a course to not only improve your skills as Java programmers, but also give
you experience in developing good software design habits. We have not formally taught design
specifications, but we still want you to reflect upon what you functions, libraries, and knowledge you’ll
need to build the program listed in Part 1.
Prepare a 1-page document that outlines just that: the functions you think you’ll need to write and the
associated knowledge you’ll need to implement these classes (libraries, math properties, etc). For this
project, we recommend you use an outline format. USE PLAIN ENGLISH TO DESCRIBE WHAT YOU THINK
YOU NEED TO DO. That’s all. Seriously.
You should work on this outline and submit it at least one week before you implement the code for the
project. Save this outline with your name, ID #, and “Project 1 Design Requirements” listed in the upper
right-hand corner of the document. Save it as a PDF labeled lastnameP1.pdf and upload it to this
assignment in eLC.
How to submit your source files to Nike
1. Create a folder in your Nike account called lastname_proj1 where lastname is your last name.
2. Copy all thoroughly commented Java source files into lastname_proj1.
3. Create a makefile and place it in lastname_proj1 that has three directives:
a. compile: compiles all of the source code
b. run: runs an example of your program
c. clean: removes all class files
4. Add a readme file to lastname_proj1 which has your name and clear instructions on how to
compile and run your program.
5. Also add a .txt file to lastname_proj1 which critiques your initial design document you previously
submitted. Specifically discuss if you needed to implement things in a different manner, use
different libraries, or make any compromises. Make sure this document also has your name.
5. Remove all class files before submitting.
6. Navigate to the parent directory of lastname_proj1 on Nike, and issue the command below
submit lastname_proj1 cs1302a
7. If the submission was successful, then you should see a file that begins with rec in your
lastname_proj1 folder.
Late Penalty:
This project is due by the 11PM on the date listed on eLC. There is a late penalty of 12% off the original
amount of points for each 24-hour period after the due date for a maximum of three days.
Points:
This project is worth 50 points to your course grade. Grading of this programming project will use the
appropriate rubric:
Proper documentation
(pre & post statements, commenting conditionals,
not excessive commenting)
5 points
Design Requirements & Reflection Documents
Includes thoroughness of the design requirements
and planning of the code, as well as the reflection
of the initial design specifications after the code
was implemented
10 points
Part I: Swapping Colors
Passing test cases
20 points
Part II: Exception Handling
Properly handling interesting data
15 points
Note, this grading rubric is to give you a rough idea of how we plan on evaluating your projects.
The extra credit part of this assignment is worth up to 10-extra points.
Collaboration Policy:
This project is to be worked on independently. You may not discuss code with any of your classmates.
You may post conceptual questions on Piazza, use your textbooks, the Java API, and the Java Tutorials.
PS:
If any of the “foreground” contains the background color, you can make it seem like a person has a hole
in him or her:
http://www.maniacworld.com/weatherman-with-a-green-tie.jpg
