CS 101 - Intro to Computing, Spring 2008

Lab 14

In class we discussed an example that rotated an image 90 degrees in a clockwise direction.

For this lab, you are to write

• one program that will rotate an image 90 degrees in a counterclockwise directions and
• another program that will rotate an image 180 degrees (in either the clockwise or countereclockwise direction).

Some key issues to think about are

• What is the size of the new rotated image based on the width and height of the original image?
• What are the X and Y coordinates of a pixel in the new rotated images based on the X and Y coordinates of the pixel in the original image?

We will need to determine the formulas for the counter clockwise rotation. Consider the following 5x3 "image":

a	b	c	d	e
f	g	h	i	j
k	l	m	n	o

When rotated counter clockwise 90 degrees, it will become:

e	j	o
d	i	n
c	h	m
b	g	l
a	f	k

We can (hopefully) notice a pattern between the original X and Y positions and the rotated X and Y positions by inspecting the following summary once it is filled in with the pixel position information.

pixel	Original X	Original Y	Rotated X	Rotated Y
a
b
c
d
e
f
g
h
i
...
o

The same will need to be done with the image rotated 180 degrees. The above image would be as follows once rotated:

o	n	m	l	k
j	i	h	g	f
e	d	c	b	a

Lab Assignment 14

Write two Java programs that will do the following:

1. Program 1: Rotate 90 Counter Clockwise

   1. The program is to be named: Lab14a
   2. Print out your name and your net-id
   3. Allow the user to select a picture from a file stored on the local machine
   4. Create an image that has been rotated 90 degrees counter clockwise.
   5. Display the modified image
   6. Save the modfied image to a file on the local machine

2. Program 2: Rotate 180

   1. The function is to be named: Lab14b
   2. Print out your name and your net-id
   3. Allow the user to select a picture from a file stored on the local machine
   4. Create an image that has been rotated 180 degrees
   5. Display the modified image
   6. Save the modfied image to a file on the local machine

   Be sure to change comment with the name of the author to contain the following:

   • your name
   • day and time of your CS 101 lab section (i.e. Wednesday at 9:00)
   • A description of the project.

3. You are also to submit the Java file electronically by using the UNIX turnin command.

   To use the UNIX turnin command to electronically hand-in your html file using the project name of lab14. To submit the files in lab14a.java and lab14b.java for lab14, the turnin command is entered as:

        turnin -c cs101 -p lab14 lab14a.java lab14b.java
   

   To verify what you submitted using the turnin command type:

        turnin -c cs101 -p lab14 -v
   

Grading Criteria

• Identifying Info - 10
• Rotating an image 90 degrees - 45
• Rotating an image 180 degrees - 45