Picture Lab Student Guide Act6
User Manual: Pdf
Open the PDF directly: View PDF 
.
Page Count: 9
| Download | |
| Open PDF In Browser | View PDF |
AP® Computer Science A
Picture Lab
Student Guide
The AP Program wishes to acknowledge and thank
Barbara Ericson of the Georgia Institute of Technology, who developed
this lab and the accompanying documentation.
A6: Mirroring pictures
Car designers at General Motors Research Labs only sculpt half of a car out of clay and then use a
vertical mirror to reflect that half to see the whole car. What if we want to see what a picture would look
like if we placed a mirror on a vertical line in the center of the width of the picture to reflect the left side
(Figure 6)?
Figure 6: Original picture (left) and picture after mirroring (right)
How can we write a method to mirror a picture in this way? One way to figure out the algorithm, which
is a description of the steps for solving a problem, is to try it on smaller and simpler data. Figure 7 shows
the result of mirroring a two-dimensional array of numbers from left to right vertically.
Figure 7: Two-Dimensional array of numbers (left) and mirrored result (right)
Can you figure out the algorithm for this process? Test your algorithm on different sizes of twodimensional arrays of integers. Will it work for 2D arrays with an odd number of columns? Will it work
for 2D arrays with an even number of columns?
One algorithm is to loop through all the rows and half the columns. You need to get a pixel from the left
side of the picture and a pixel from the right side of the picture, which is the same distance from the
right end as the left pixel is from the left end. Set the color of the right pixel to the color of the left pixel.
The column number at the right end is the number of columns, also known as the width, minus one. So
assuming there are at least 3 pixels in a row, the first left pixel will be at row=0, col=0 and the first right
pixel will be at row=0, col=width-1. The second left pixel will be at row=0, col=1 and the corresponding
right pixel will be at row=0, col=width-1-1. The third left pixel will be at row=0, col=2 and its right pixel
will be at row=0, col=width-1-2. Each time the left pixel is at (current row value, current column value),
the corresponding right pixel is at (current row value, width - 1 - (current column value)).
14
The following method implements this algorithm. Note that, because the method is not looping through
all the pixels, it cannot use a nested for-each loop.
public void mirrorVertical()
{
Pixel[][] pixels = this.getPixels2D();
Pixel leftPixel = null;
Pixel rightPixel = null;
int width = pixels[0].length;
for (int row = 0; row < pixels.length; row++)
{
for (int col = 0; col < width / 2; col++)
{
leftPixel = pixels[row][col];
rightPixel = pixels[row][width – 1 - col];
rightPixel.setColor(leftPixel.getColor());
}
}
}
You can test this with the testMirrorVertical method in PictureTester.
Exercises
1. Write the method mirrorVerticalRightToLeft that mirrors a picture around a mirror
placed vertically from right to left. Hint: you can copy the body of mirrorVertical and
only change one line in the body of the method to accomplish this. Write a class (static) test
method called testMirrorVerticalRightToLeft in PictureTester to test this
new method and call it in the main method.
2. Write the method mirrorHorizontal that mirrors a picture around a mirror placed
horizontally at the middle of the height of the picture. Mirror from top to bottom as shown in the
pictures below (Figure 8). Write a class (static) test method in PictureTester to test this
new method and call it in the main method.
Figure 8: Original picture (left) and mirrored from top to bottom (right)
15
3. Write the method mirrorHorizontalBotToTop that mirrors the picture around a mirror
placed horizontally from bottom to top. Hint: you can copy the body of mirrorHorizontal
and only change one line to accomplish this. Write a class (static) test method in
PictureTester to test this new method and call it in the main method.
4. Challenge — Work in groups to figure out the algorithm for the method mirrorDiagonal
that mirrors just a square part of the picture from bottom left to top right around a mirror placed
on the diagonal line (the diagonal line is the one where the row index equals the column index).
This will copy the triangular area to the left and below the diagonal line as shown below. This is
like folding a square piece of paper from the bottom left to the top right, painting just the bottom
left triangle and then (while the paint is still wet) folding the paper up to the top right again. The
paint would be copied from the bottom left to the top right as shown in the pictures below
(Figure 9). Write a class (static) test method in PictureTester to test this new method and
call it in the main method.
Figure 9: Original picture (left) and mirrored around the diagonal line with copying from
bottom left to top right (right)
16
How image processing is related to new scientific breakthroughs
Many of today’s important scientific breakthroughs are being made by large, interdisciplinary
collaborations of scientists working in geographically widely distributed locations, producing, collecting,
and analyzing vast and complex datasets.
One of the computer scientists who works on a large interdisciplinary
scientific team is Dr. Cecilia Aragon. She is an associate professor in the
Department of Human Centered Design & Engineering and the eScience
Institute at the University of Washington, where she directs the Scientific
Collaboration and Creativity Lab. Previously, she was a computer scientist in
the Computational Research Division at Lawrence Berkeley National
Laboratory for six years, after earning her Ph.D. in Computer Science from
UC Berkeley in 2004. She earned her B.S. in mathematics from the California
Institute of Technology.
Her current research focuses on human-computer interaction (HCI) and computer-supported
cooperative work (CSCW) in scientific collaborations, distributed creativity, information visualization,
and the visual understanding of very large data sets. She is interested in how social media and new
methods of computer-mediated communication are changing scientific practice. She has developed
novel visual interfaces for collaborative exploration of very large scientific data sets, and has authored
or co-authored many papers in the areas of computer-supported cooperative work, human-computer
interaction, visualization, visual analytics, image processing, machine learning, cyberinfrastructure,
and astrophysics.
In 2008, she received the Presidential Early Career Award for Scientists and Engineers (PECASE) for her
work in collaborative data-intensive science. Her research has been recognized with four Best Paper
awards since 2004, and she was named one of the Top 25 Women of 2009 by Hispanic Business
Magazine. She was the architect of the Sunfall data visualization and workflow management system for
the Nearby Supernova Factory, which helped advance the study of supernovae in order to reduce the
statistical uncertainties on key cosmological parameters that categorize dark energy, one of the grand
challenges in physics today.
Cecilia Aragon is also one of the most skilled aerobatic pilots flying today.
A two-time member of the U.S. Aerobatic Team, she was a medalist at the
1993 U.S. National Championships and the 1994 World Aerobatic
Championships, and was the California State Aerobatic Champion.
23
Glossary
1. Abstract class — You cannot create an object of an abstract class type. But, you can create an
object of a subclass of an abstract class (as long as the subclass is not also an abstract class).
2. Abstract method — An abstract method cannot have a method body in the class where the
method is declared to be abstract.
3. Algorithm — A step-by-step description of how to solve a problem.
4. AWT — The Abstract Windowing Toolkit. It is the package that contains the original Graphical
User Interface (GUI) classes developed for Java.
5. Binary number — A binary number contains only the digits 0 and 1. Each place is a power of 2
starting with 20 on the right. The decimal number 6 would be 110 in binary. That would be
0 * 20 + 1 * 21 + 1 * 22 = 6.
6. Bit — A binary digit, which means that it has a value of either 0 or 1.
7. Byte — A consecutive group of 8 bits.
8. Column-major order — An order for storing two-dimensional array data in a one-dimensional
array, so that all the data for the first column is stored before all the data for the second column
and so on. In a two-dimensional array represented using an array of arrays (like in Java) this
means that the outer array represents the columns and the inner arrays represent the rows.
9. Digital camera — A camera that can take digital pictures.
10. Digital picture — A picture that can be stored on a computer.
11. Inheritance — In Java, a class can specify the parent class from which it inherits instance
variables (object fields) and object methods. Even though instance variables may be inherited, if
they are declared to be private they cannot be directly accessed using dot notation in the
inheriting class. Private methods that are inherited can also not be directly called in an
inheriting class.
12. Inner loop — In a nested loop (a loop inside of another loop) the loop that is inside of another
loop is considered the inner loop.
13. Interface — A special type of class that can only have public abstract methods in it and/or static
constants.
14. Lossy compression — Lossy compression means that the amount of data that is stored is much
smaller than the available data, but the part that is not stored is data that humans would not
miss.
15. Media computation — A method of teaching programming by having students write programs
that manipulate media: pictures, sounds, text, movies. This approach was developed by Dr.
Mark Guzdial at Georgia Tech.
16. Megapixel — One million pixels.
17. Nested loop — One loop inside of another loop.
18. Outer loop — In a nested loop (a loop inside of another loop) the loop that is outside of another
loop is considered the outer loop.
19. Package — A package in Java is a group of related classes.
20. Pixel — A picture (abbreviated pix) element.
21. RGB model — Represents color as amounts of red, green, and blue light. It sometimes also
includes alpha, which is the amount of transparency.
24
22. Row-major order — An order for storing two-dimensional array data in a one-dimensional
array, so that all the data for the first row is stored before all the data for the second row, and so
on. In a two-dimensional array represented using an array of arrays (like in Java) this means
that the outer array represents the rows and the inner arrays represent the columns.
23. Subclass — A class that has inherited from another class.
24. Superclass — A class that another class has inherited from.
25. UML —Unified Modeling Language. It is a general purpose modeling language used in objectoriented software development.
25
References
Dann, W., Cooper, S., & Ericson, B. (2009) Exploring Wonderland: Java Programming Using Alice
and Media Computation. Englewood, NJ: Prentice-Hall.
Guzdial, M., & Ericson B. (2006) Introduction to Computing and Programming in Java: A Multimedia
Approach. Englewood, NJ: Prentice-Hall.
Guzdial, M., & Ericson, B. (2009) Introduction to Computing and Programming in Python:
A Multimedia Approach. (2nd ed.). Englewood, NJ: Prentice-Hall.
Guzdial, M., & Ericson, B. (2010) Problem Solving with Data Structures using Java: A Multimedia
Approach. Englewood, NJ: Prentice-Hall.
26
Quick Reference
DigitalPicture Interface
Pixel[][] getPixels2D()
// implemented in SimplePicture
void explore()
// implemented in SimplePicture
boolean write(String fileName) // implemented in SimplePicture
SimplePicture Class (implements Digital Picture)
public SimplePicture()
public SimplePicture(int width, int height)
public SimplePicture(SimplePicture copyPicture)
public SimplePicture(String fileName)
public Pixel[][] getPixels2D()
public void explore()
public boolean write(String fileName)
Picture Class (extends SimplePicture)
public Picture()
public Picture(int height, int width)
public Picture(Picture copyPicture)
public Picture(String fileName)
public Pixel[][] getPixels2D()
// from SimplePicture
public void explore()
// from SimplePicture
public boolean write(String fileName) // from SimplePicture
Pixel Class
public double colorDistance(Color testColor)
public double getAverage()
public int getRed()
public int getGreen()
public int getBlue()
public Color getColor()
public int getRow()
public int getCol()
public void setRed(int value)
public void setGreen(int value)
public void setBlue(int value)
public void setColor(Color newColor)
java.awt.Color Class
public Color(int r, int g, int b)
public int getRed()
public int getGreen()
public int getBlue()
27
Source Exif Data:
File Type : PDF File Type Extension : pdf MIME Type : application/pdf Linearized : No XMP Toolkit : XMP Core 5.4.0 Company : Georgia Institute of Technology Source Modified : D:20140924205053 Title : Creator : Barb Ericson Format : application/pdf Metadata Date : 2014:09:24 16:51:04-04:00 Create Date : 2014:09:24 16:50:58-04:00 Modify Date : 2014:09:24 16:51:04-04:00 Creator Tool : Acrobat PDFMaker 9.1 for Word Instance ID : uuid:9584e36b-2bbd-43f0-8e7e-429b696e2129 Subject : 5 Document ID : uuid:450c018e-e2cc-4e59-bb31-4baca6115fda Producer : Adobe PDF Library 9.0 Page Count : 9 PDF Version : 1.4 Author : Barb EricsonEXIF Metadata provided by EXIF.tools