1. Creative Commons Attribution Non-Commercial Share Alike License
Original Developer: Beth Simon, 2009

2. THIS LECTURE GOT WRITTEN OVER!
Re develop from older ones – there were some new slides in Fa 2009, so get those from UP.

3. CSE8A Lecture 15
Read next class: read pg
Quizzes pick up

4. About group quizzes and learning
Group quizzes are great, I really learn a lot
Group quizzes are good, it helps me solidify my learning to discuss the questions with others
Group quizzes are OK, I’m not sure how much I learn by doing them
Group quizzes are not helpful to my learning at all.

5. By the end of today’s class you should be able to…
LG30: Write and read code that either loops over a subset of pixels or loops over all pixels and controls changes to pixels with and if statement
LG31: Use parameters to control looping in conditional setting of pixels
LG32: Identify the flow of control in the three types of Java if statements: if, if-else, and if-else if-else
LG34: Compare and contrast two solutions to a problem using for loops and if statements

6. Changing pixels all over, conditionally
//Inside loop over all pixels
topP = this.getPixel(x,y);
botP = this.getPixel(x,y+1);
topAvg = topP.getAverage();
botAvg = botP.getAverage();
if (Math.abs(topAv – botAv) < 10)
topP.setColor(Color.WHITE);
else
topP.setColor(Color.BLACK);
What is it doing?
Comparing 2 pixels side by side and, if they are similar make the pixel white, otherwise black
Comparing 2 pixels one on top of the other and, if they are similar make the pixel white, otherwise black
Comparing 2 pixels side by side and, if they are different make the pixel white, otherwise black
Comparing 2 pixels one on top of the other and, if they are different make the pixel white, otherwise black

7. What’s the result of running that code on this input?

8. A DIFFERENT edgeDetect
//Inside loop over all pixels
topP = this.getPixel(x,y);
botP = this.getPixel(x+1,y); // was (x,y+1)
topAvg = topP.getAverage();
botAvg = botP.getAverage();
if (Math.abs(topAv – botAv) < 10)
topP.setColor(Color.WHITE);
else
topP.setColor(Color.BLACK);

9. A DIFFERENT edgeDetect
//Inside loop over all pixels
topP = this.getPixel(x,y);
botP = this.getPixel(x+1,y); // was (x,y+1)
topAvg = topP.getAverage();
botAvg = botP.getAverage();
if (Math.abs(topAv – botAv) < 10)
topP.setColor(Color.WHITE);
else
topP.setColor(Color.BLACK);

10. Which is most true about ONE execution of this code (for a specific diffValue)
int diffValue = Math.abs(topAv – botAv);
if (diffValue < 10)
topP.setColor(Color.WHITE);
else
topP.setColor(Color.BLACK);
Section A AND Section B may BOTH be executed
If Section B is executed then Section A is not executed
Neither Section is ever executed
It is possible neither Section will be executed (but sometimes one might be).

11. Which is most true about ONE execution of this code (for a specific diffValue)
int diffValue = Math.abs(topAv – botAv);
if (diffValue < 10)
topP.setColor(Color.WHITE);
else if (diffValue < 50)
topP.setColor(Color.GREY);
else
topP.setColor(Color.BLACK);
Section A can be executed AND Section B may BOTH be executed but then C can’t be executed
If Section A is executed then neither Section B nor C can be
All sections can be executed for a single diffValue
It’s possible no section is executed for a given diffValue
Confused? See page 187 for execution flow diagram

12. In Lab 5: Which best describes the conditions under which we change pixel color?
public void makeConvict() {
for (int x = 0; x < this.getWidth(); x++)
for (int y = 0; y < this.getHeight(); y++)
Pixel currentPix = this.getPixel(x,y);
if ( (currentPix.getGreen() > 200) && (y%2==0))
currentPix.setColor(Color.BLACK); }
else if( (currentPix.getGreen() > 200) && y%2 == 1)
currentPix.setColor(Color.WHITE);
Based on the coordinates of the Pixel
Based on the color of the Pixel
Based on the coordinates for some Pixels, the color for other Pixels
Based on a compound condition of color and coordinates of the Pixel