1. Week 2

2. Homework Are you collaborating effectively? Are you starting early?
Are you running your homework code to see if it works?
Homework 2 is now posted.
Due this coming Friday night at midnite!

3. Prequiz
Are you collaborating effectively?

4. What have we learned so far?
Basics of writing a computer program in Jython using JES
Names
Quantities (Numbers)
Things (Pictures, strings)
Functions
Files

5. Have you actually written a computer program?
Yes?/No?
Why doesn't it look like a computer program?

6. JES commands def pickAFile() picture = makePicture(filename)
thePixels = getPixels(picture)
getRed(pixel), getGreen(pixel), getBlue(pixel)
setRed(pix, col), setGreen..., setBlue...
color = makeColor(r, g, b)
setColor(pixel, color)
show(picture)
showVars()

7. Can a function call a function?

8. Can a function that you write call a function that you write?

9. Example def grayScale(picture): for px in getPixels(picture):
r = getRed(px) * 0.299
g = getGreen(px) * 0.587
b = getBlue(px) * 0.114
lum = r + g + b
setColor(px, makeColor(lum, lum, lum)
def grayPicker():
pic = makePicture(pickAFile())
grayScale(pic)
show(pic)
# Should this function return something?

10. New Material

11. MediaPath
As a convenience, Jython contains a name called MediaPath. You don't use this name directly. Instead you use two functions:
setMediaPath()
Opens a file chooser window
Allows you to choose a directory!
Sets MediaPath to the value of that directory path which is a string
getMediaPath("filename")
returns the value of MediaPath concatenated with the "filename"

12. range()
The "for loop" in JES allows you to create a loop structure and have a "loop variable" take on all of the different value in a collection
for px in getPixels(picture):
You can even make up a collection:
for loopvar in [1, 3, "apple", 7000]
But sometimes you just want to have a loop run with the loop variable having an increasing (or decreasing) sequence of integers
Enter the range function!

13. Individual Pixel Manipulation
So far we have seen operations on a whole collection of pixels ( i.e. getPixels(picture) )
But sometimes we would like to be able to be more selective in out manipulation of pixels
pixel = getPixel(picture, x, y)

14. Picture Size
With getPixels we basically had a collection of pixels we could go through one at a time
With getPixel things get a little more complex. Now we have to specifiy the x and y of the pixel.
How do we even know the size of a picture?
width = getWidth(picture)
height = getHeight(picture)

15. Nested for Loops

16. Selective Manipulation
(x1,y1)
(x2,y2)

17. Nested for Loops def nested(pict):
for x in range(1, getWidth(pict)+1):
for y in range(1, getHeight(pict)+1):
pix = getPixel(pict, x, y)
# Do whatever processing you want
# to the pixel here!

18. Homework 2 Template def hw2(): mypic =
makePicture(getMediaPath('myPicFile.jpg'))
# Call your function that will modify the pic
# Just as an example
nested(mypic)
show(mypic)

19. Homework 2 Checklist
Write a function (or functions) that will manipulate a picture.
Make sure that your program uses getMediaPath
Put the program and file in the same folder
Using WebWork turn BOTH files in as hw2
Make sure to retrieve the submission and run it just like the grader will run it!!!

20. Translating
Can we put a picture wherever we want it?

21. Another Useful Tool makeEmptyPicture(width, height)
Can you guess what it does?
Can you guess what it returns?

22. Idea
Let's make up our own "picture" from scratch!

23. Where?
(xpos, ypos)

24. Scaling
Can we make pictures bigger or smaller?
Can we stretch them?