AP Computer Science Name: Michael Metz Picture Lab - Hullo

AP Computer Science Name: Michael Metz
Picture Lab

A1: Introduction to digital pictures and color
Questions:

1. How many bits does it take to represent the values from 0 to 255?
➢
8 bits

2. How many bytes does it take to represent a color in the RBG color
model?
➢
3 bytes

3. How many pixels are in a picture that is 640 pixels wide and 480
pixels high?
➢
640 * 480 = 307200 pixels

A2: Picking a color
Questions:

1. How can you make pink?
➢ R: 255 G: 0 B: 255

2. How can you make yellow?
➢ R: 255 G: 255 B: 0

3. How can you make purple?
➢ R: 115 G: 0 B: 255

4. How can you make white?
➢ R: 255 G: 255 B: 255

5. How can you make dark gray?
➢ R: 75 G: 75 B: 75

A3: Exploring a picture
Questions:

1. What is the row index for the top left corner of the picture?
➢0

2. What is the column index for the top left corner of the picture?
➢0

3. The width of this picture is 640. What is the right most column
index?
➢639

4. The height of this picture is 480. What is the bottom most row
index?
➢479

5. Does the row index increase from left to right or top to bottom?
➢top to bottom

6. Does the column index increase from left to right of top to bottom?
➢left to right

7. Set the zoom to 500%. Can you see squares of color? This is called
pixelation. Pixelation means displaying a picture so magnified that
the individual pixels look like small squares.
➢yes

Exercises:
1. Copy the line(s) in the main() method that you changed and paste
them here. Run the main method again, take a screen shot of your
computer screen (press the [ctrl] and [Print Scrn] buttons at the
same time) and paste the screen shot below your line(s) of code.
public static void main( String args[])
{
/*Picture pix = new Picture("beach.jpg");
pix.explore();*/
Picture pix = new Picture("wall.jpg");
pix.explore();
}



A4: Two-dimensional arrays in Java
Exercises:

1. Copy the lines of code from your getCount() method and paste them
here.
public int getCount(int a){
int num = a;
int x = 0;
for(int m = 0; m < matrix.length; m++)
for(int n = 0; n < matrix[0].length; n++)
if(num == matrix[m][n])
x++;
return x;
}
After uncommenting the testGetCount() method and the call to it in
the main() method of IntArrayWorkerTest, what is printed? Copy
and past the output shown in your terminal window here:

Count should be 6 and count is 6
2. Copy the lines of code from your getLargest() method and paste

them here.
public int getLargest(){
int num = 0;
for(int x = 0; x < matrix.length; x++)
for(int z = 0; z < matrix[0].length; z++)
if(num < matrix[x][z])
num = matrix[x][z];
return num;
}
After uncommenting the testGetLargest() method and the call to it
in the main() method of IntArrayWorkerTest, what is printed? Copy
and past the output shown in your terminal window here:
Largest should be 6 and is 6
Largest should be 6 and is 6
Largest should be 6 and is 6
Largest should be 6 and is 6

3. Copy the lines of code from your getColTotal() method and paste
them here.

public int getColTotal(int r){
int num = 0;
for(int x = 0; x < matrix.length; x++)
num += matrix[x][r];
return num;

}

After uncommenting the testGetColTotal() method and the call to it
in the main() method of IntArrayWorkerTest, what is printed? Copy
and past the output shown in your terminal window here:

Total for column 0 should be 5 and is 5
Total for column 1 should be 7 and is 7
Total for column 2 should be 9 and is 9


A5: Modifying a picture
Questions:

1. Open Picture.java and look for the method getPixels2D. Is it there?
➢No

2. Open SimplePicture.java and look for the method getPixels2D. Is
it there?
➢Yes

3. Does the following code compile? EXPLAIN.
DigitalPicture p = new DigitalPicture();

➢NO, you cannot instantiate a object from a interface, A interface
can be a pointer but you cannot instantiate it!

4. Assuming that a no-argument constructor exists for SimplePicture,
would the following code compile? EXPLAIN.
DigitalPicture p = new SimplePicture();
➢Yes, like I said in the above answer, “A interface can be a pointer
but you cannot instantiate it!”. The interface DigitalPicture is
pointing to a SimplePicture object, and SimplePicture implements
the DigitalPicture interface.

5. Assuming that a no-argument constructor exists for Picture, does
the following code compile? EXPLAIN.
DigitalPicture p = new Picture();
➢Yes, like I said in the above answer, “A interface can be a pointer
but you cannot instantiate it!”. The interface DigitalPicture is
pointing to a Picture object, and Picture extends SimplePicture
which implements the DigitalPicture interface.

6. Assuming that a no-argument constructor exists for Picture, does
the following code compile? EXPLAIN.
SimplePicture p = new Picture();





5. Copy the lines of code from your grayscale() method and paste them
here.

public void grayscale(){
Pixel[][] pixels = this.getPixels2D();
for (Pixel[] rowArray : pixels)
for (Pixel pixelObj : rowArray)
{
double average = ((pixelObj.getGreen()) + (pixelObj.getBlue())

+ (pixelObj.getRed())) / 3.0;
pixelObj.setRed((int) average);
pixelObj.setGreen((int) average);
pixelObj.setBlue((int) average);

}
}
Copy the lines of code from your new static tester method in the
PictureTester class and paste them here.
public static void testGrayscale(){

Picture beach = new Picture("beach.jpg");
beach.explore();
beach.grayscale();
beach.explore();
}
After calling this tester method in the main() method of PictureTester,
take a screen shot, and paste your image here:









3. Copy the lines of code from your mirrorHorizontlBotToTop() method
and paste them here.
public void mirrorHorizontalBotToTop()
{
Pixel[][] pixels = this.getPixels2D();
Pixel topPixel = null;
Pixel bottomPixel = null;
int height = pixels.length;
for (int row = 0; row < height / 2; row++)
for (int col = 0; col < pixels[0].length; col++){
topPixel = pixels[row][col];
bottomPixel = pixels[height - 1 - row][col];
topPixel.setColor(bottomPixel.getColor());
}
}

Copy the lines of code from your new static tester method in the
PictureTester class and paste them here.

public static void testMirrorHorizontalBotToTop()
{

Picture caterpillar = new Picture("caterpillar.jpg");
caterpillar.explore();
caterpillar.mirrorHorizontalBotToTop();
caterpillar.explore();
}
After calling this tester method in the main() method of
PictureTester, take a screen shot, and paste your image here: