teaching programming to everyone through media computation mark guzdial college of computing/gvu...
TRANSCRIPT
Teaching Programming to Everyone through Media Computation
Mark Guzdial
College of Computing/GVU
Georgia Institute of Technology
Story
Perlis’ challenge: Computer science is more important than calculus
Evidence that we’re not there yet And what the solution might look like
Our attempt: Introduction to Media Computation Potential tie to mathematics classes
Results so-far
Computer science is more important than Calculus In 1961, Alan Perlis argued
that computer science is more important in a liberal education than calculus Explicitly, he argued that all
students should learn to program.
Calculus is about rates, and that’s important to many.
Computer science is about process, which is important to everyone
How close are we to being able to teach everyone CS?
Not very CS1 is one of the most despised courses for non-majors
At many departments, CS retention rates are lower than the rest of campus At Georgia Tech: 65% for 1995 cohort, vs. 73% for
Engineeering
Drop-out rates near 50% at many institutions Female enrollment in CS has been dropping nationally
Why?
Several recent studies and books claim that CS instruction tends to dissuade anyone but white males “Tedious,”
“taught without application relevance,”“boring,” “lacking creativity,” “asocial”
The best uses for computing technologies will come from others
Thomas Edison vs. D.W. Griffith Suggestion: D.W. Griffith knew things that Edison didn’t. Consider George Lucas today
If we want computing technologies to become useful, they have to get out of our hands.
It can’t be just through applications. Computer science will never have the potential that it
might, if future practitioners hate our introductory course!
The Challenges
We need to motivate CS, potential CS, and non-CS students to care about computing
We need to make it social, creative, relevant,exciting, and not tedious
Which is how many of us already see Computing, but that’s not getting communicated
Our Attempt: Introduction to Media Computation A course for non-CS and non-Engineering majors
International Affairs, Literature, Public Policy, Architecture, Management, Biology, etc.
120 students this semester,planning 400-600 in the Fall 2/3 female in this semester’s CS1315
Focus: Learning programming within the context of media manipulation and creation
Motivating the Computing
As professionals, these students will often the use the computer as a communications medium.
All media are going digital,and digital media are manipulated with software.
Knowing how to program, then, is a communications skill.
Programming as a Communications Skill Knowing how to program means to
understand one’s tools. Maybe means can transfer tool skills more
easily Students tell us that they’re excited to learn
how PhotoShop works.
And it means that, if you have to, you may be able to grow your own
Python as the programming language Huge and contentious issue Use in commercial contexts legitimizes the choice
Industrial Light & Magic, Google, Nextel, etc.
Minimal syntax Looks like other programming languages
Potential for knowledge transfer
Actually using Jython (http://www.jython.org) for Java class libraries
def negative(picture): for px in getPixels(picture): red=getRed(px) green=getGreen(px) blue=getBlue(px) negColor=makeColor(255-red,255-green,255-blue) setColor(px,negColor)
def clearRed(picture): for pixel in getPixels(picture): setRed(pixel,0)
def greyscale(picture): for p in getPixels(picture): redness=getRed(p) greenness=getGreen(p) blueness=getBlue(p) luminance=(redness+blueness+greenness)/3 setColor(p, makeColor(luminance,luminance,luminance))
def chromakey(source,bg): for x in range(1,getWidth(source)): for y in range(1,getHeight(source)): p = getPixel(source,x,y) # My definition of blue: If the redness + greenness < blueness if (getRed(p) + getGreen(p) < getBlue(p)): #Then, grab the color at the same spot from the new background setColor(p,getColor(getPixel(bg,x,y))) return source
Use a loop!Our first picture recipe
def decreaseRed(picture): for p in getPixels(picture): value=getRed(p) setRed(p,value*0.5)
Used like this:>>> file="/Users/guzdial/mediasources/barbara.jpg">>> picture=makePicture(file)>>> show(picture)>>> decreaseRed(picture)>>> repaint(picture)
original
Recipe to Increase the Volume
def increaseVolume(sound): for sample in getSamples(sound): value = getSample(sample) setSample(sample,value * 2)
Using it:>>> f="/Users/guzdial/mediasources/gettysburg10.wav">>> s=makeSound(f)>>> increaseVolume(s)>>> play(s)>>> writeSoundTo(s,"/Users/guzdial/mediasources/louder-g10.wav")
A Sunset-generating function
How do we turn this beach scene into a sunset?
What happens at sunset? Tried increasing the red,
but that failed.
New Theory: As the sun sets, less blue and green is visible, which makes things look more red.
A Sunset-generation Functiondef makeSunset(picture): for p in getPixels(picture): value=getBlue(p) setBlue(p,value*0.7) value=getGreen(p) setGreen(p,value*0.7)
SlowSunset
def slowsunset(directory): canvas = makePicture(getMediaPath("beach-smaller.jpg")) #outside the loop! for frame in range(0,100): #99 frames printNow("Frame number: "+str(frame)) makeSunset(canvas) # Now, write out the frame writeFrame(frame,directory,canvas)
def makeSunset(picture): for p in getPixels(picture): value=getBlue(p) setBlue(p,value*0.99) #Just 1% decrease! value=getGreen(p) setGreen(p,value*0.99)
Not showing you writeFrame() because you know how that works.
Just one canvas repeatedly being manipulated
SlowSunset frames
Introducing IF:Making Barb a redhead
def turnRed(): brown = makeColor(57,16,8) file = r"C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\barbara.jpg" picture=makePicture(file) for px in getPixels(picture): color = getColor(px) if distance(color,brown)<50.0: redness=getRed(px)*1.5 setRed(px,redness) show(picture) return(picture) Original:
Generalizing Algorithms
We talk about algorithm complexity later in the course, after the media is done.
We talk about different approaches to the same problem, where the criteria might be aesthetics or correctness, instead of speed or size For example, generating greyscale
During the media, we point out similar themes in different functions. We refer to them as “sub-recipes”
Scaling the picture downdef copyBarbsFaceSmaller(): # Set up the source and target pictures barbf=getMediaPath("barbara.jpg") barb = makePicture(barbf) canvasf = getMediaPath("7inX95in.jpg") canvas = makePicture(canvasf) # Now, do the actual copying sourceX = 45 for targetX in range(100,100+((200-45)/2)): sourceY = 25 for targetY in range(100,100+((200-25)/2)): color = getColor(getPixel(barb,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 2 sourceX = sourceX + 2 show(barb) show(canvas) return canvas
Scaling the picture updef copyBarbsFaceLarger(): # Set up the source and target pictures barbf=getMediaPath("barbara.jpg") barb = makePicture(barbf) canvasf = getMediaPath("7inX95in.jpg") canvas = makePicture(canvasf) # Now, do the actual copying sourceX = 45 for targetX in range(100,100+((200-45)*2)): sourceY = 25 for targetY in range(100,100+((200-25)*2)): color = getColor(getPixel(barb,int(sourceX),int(sourceY))) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 0.5 sourceX = sourceX + 0.5 show(barb) show(canvas) return canvas
Recipe for halving the frequency of a sound
def half(filename): source = makeSound(filename) target = makeSound(filename)
sourceIndex = 1 for targetIndex in range(1, getLength( target)+1): setSampleValueAt( target, targetIndex,
getSampleValueAt( source, int(sourceIndex))) sourceIndex = sourceIndex + 0.5
play(target) return target
This is how a sampling synthesizer works!
Here’s the piece that does it
Compare these two
def half(filename): source = makeSound(filename) target = makeSound(filename)
sourceIndex = 1 for targetIndex in range(1, getLength( target)+1): setSampleValueAt( target, targetIndex,
getSampleValueAt( source, int(sourceIndex)))
sourceIndex = sourceIndex + 0.5
play(target) return target
def copyBarbsFaceLarger(): # Set up the source and target pictures barbf=getMediaPath("barbara.jpg") barb = makePicture(barbf) canvasf = getMediaPath("7inX95in.jpg") canvas = makePicture(canvasf) # Now, do the actual copying sourceX = 45 for targetX in range(100,100+((200-45)*2)): sourceY = 25 for targetY in range(100,100+((200-25)*2)): color = getColor(
getPixel(barb,int(sourceX),int(sourceY))) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 0.5 sourceX = sourceX + 0.5 show(barb) show(canvas) return canvas
Both of them are sampling
Both of them have three parts: A start where objects are set up A loop where samples or pixels are copied from one
place to another To decrease the frequency or the size, we take each
sample/pixel twice In both cases, we do that by incrementing the index by
0.5 and taking the integer of the index Finishing up and returning the result
Ties to Mathematics
I don’t know how to exploit them yet, but significant mathematics issues do arise here. Integration, in understanding how to digitize sound (and
pictures, to an extent) Discrete representations of motion and curves.
Digitizing Sound: How do we get that into numbers? Remember in calculus,
estimating the curve by creating rectangles?
We can do the same to estimate the sound curve Analog-to-digital conversion
(ADC) will give us the amplitude at an instant as a number: a sample
How many samples do we need?
Nyquist Theorem
We need twice as many samples as the maximum frequency in order to represent (and recreate, later) the original sound.
The number of samples recorded per second is the sampling rate If we capture 8000 samples per second, the highest frequency
we can capture is 4000 Hz That’s how phones work
If we capture more than 44,000 samples per second, we capture everything that we can hear (max 22,000 Hz)
CD quality is 44,100 samples per second
Simple Motiondef movingRectangle(directory): for frame in range(0,100): #99 frames canvas = makePicture(getMediaPath("640x480.jpg")) if frame < 50: #Less than 50, move down # Generate new positions each frame number addRectFilled(canvas,frame*10,frame*5, 50,50,red) if frame >= 50: #Greater than 50, move up addRectFilled(canvas,(50-(frame-50))*10,(50-(frame-50))*5, 50,50,red) # Now, write out the frame # Have to deal with single digit vs. double digit frame numbers differently framenum=str(frame) if frame < 10: writePictureTo(canvas,directory+"//frame0"+framenum+".jpg") if frame >= 10: writePictureTo(canvas,directory+"//frame"+framenum+".jpg")
A Few Frames
frame00.jpg frame02.jpg frame50.jpg
The trick here is all mathematics
if frame < 50: #Less than 50, move down
# Generate new positions each frame number
addRectFilled(canvas,frame*10,frame*5, 50,50,red)
if frame >= 50: #Greater than 50, move up
addRectFilled(canvas,(50-(frame-50))*10,(50-(frame-50))*5, 50,50,red)
When frame = 1, addRectFilled(canvas,10,5,50,50,red)
When frame = 2, addRectFilled(canvas,20,10,50,50,red)
When frame = 49, addRectFilled(canvas,490,285,50,50,red
) When frame = 50,
50-(50-50) = 50 addRectFilled(canvas,500,250,50,50,red
) When frame = 51,
50-(51-50)=50-1=49 addRectFilled(canvas,490,285,50,50,red
) When frame = 99,
50-(99-50)=50-49=1 addRectFilled(canvas,10,5,50,50,red)
Can we move more than one thing at once? Sure!
def movingRectangle2(directory): for frame in range(0,100): #99 frames canvas = makePicture(getMediaPath("640x480.jpg")) if frame < 50: #Less than 50, move down # Generate new positions each frame number addRectFilled(canvas,frame*10,frame*5, 50,50,red) if frame >= 50: #Greater than 50, move up addRectFilled(canvas,(50-(frame-50))*10,(50-(frame-50))*5, 50,50,red) # Let's have one just moving around addRectFilled(canvas,100+ int(10 * sin(frame)),4*frame+int(10* cos(frame)),50,50,blue) # Now, write out the frame # Have to deal with single digit vs. double digit frame numbers differently framenum=str(frame) if frame < 10: writePictureTo(canvas,directory+"//frame0"+framenum+".jpg") if frame >= 10: writePictureTo(canvas,directory+"//frame"+framenum+".jpg")
addRectFilled(canvas,100+ int(10 * sin(frame)), 4*frame+int(10* cos(frame)),50,50,blue)
What’s going on here? Remember that both sine and cosine vary between +1
and -1. Int(10*sin(frame)) will vary between -10 and +10 With cosine controlling y and sine controlling x, should
create circular motion frame=1
x is 108, y is 9 frame=2
x is 109, y is 4
Frames from two motions at once
Using your personal pictures
And messin’ with them
Data-first Computing
Real users come to a user with data that they care about, then they (unwillingly) learn the computer to manipulate their data as they need.
CS1315 works the same. We use pictures of students in class demonstrations. Students do use their own pictures as starting points for
manipulations. They started doing this in the second week
How often do students use their second week of CS1 on their own data?
How does that change the students’ relationship to the material?
Rough overview of Syllabus Defining and executing functions Pictures
Psychophysics, data structures, defining functions, for loops, if conditionals
Sounds Psychophysics, data structures, defining functions, for
loops, if conditionals Text
Converting between media, generating HTML, “flattening” media and saving to a database
Movies Then, Computer Science
Computer science as a solution to their problems “Writing programs is hard! Are there ways to
make it easier? Or at least shorter?” Object-oriented programming Functional programming and recursion
“Movie-manipulating programs take a long time to execute. Why?” Algorithmic complexity
“Why is PhotoShop so much faster?” Compiling vs. interpreting Machine language and how the computer works
Tools to support media computation
JES: Jython environment for students
MediaTools for exploring media
Assignments encourage collaboration Homework are all collaborative Quizzes are preceded by nearly-identical,
collaborative pre-quizzes Two “take-home exams” (programming
assignments) are non-collaborative “Lablets” on application software are
collaborative
Assignments encourage creativity
For several homeworks, the task is to manipulate media in some way, but we don’t care what media For example, creating a collage or building an animation
Encouraging homework results to be posted to CoWeb (collaborative website) in galleries
First Homework assignment
Homework 1:
Write a program named hw1 to accept a picture as input, and change its pixels as follows:
• Set the green component to 125% of its current value • Decrease the blue by 25% • Decrease the red by 75%
Solutions shared in the CoWeb
Grade distribution
Much better than anticipated.
Homework #3: Make a collage with images that you modify by code only—any images you want
Grades on Homework #3
Take-Home Exam #2Given a folder with images and sounds in it, create an index HTML page with links to each image and sound.
You will write a function called indexPage that takes a string which is the path to a directory. You will create a page in that directory named index.html. Index.html should be an HTML page containing a link to every JPEG file and every WAV in the directory. At the top of the page, put a heading (level 1) with the phrase "Directory listing of sounds and images in " and then the directory, e.g., "Directory listing of sounds and images in C:\Documents and Settings\Mark Guzdial\mediasources"
The links should be each an item in an unordered (<ul>) list. The anchor text in each link should be the filename of the image or sound. The destination (href) should be the same filename.
For each image, on the same line as the filename, list the horizontal and vertical size (in pixels) of the image. For each sound, list the length of the sound in seconds.
This is a NON-COLLABORATIVE ACTIVITY! You may not talk to anyone about their code, nor look at anyone else's code, nor allow anyone to see your code. This is a TAKE HOME EXAM. It is an "open book" exam. You may use your book, any slides, any material in the CoWeb, and any programs you've written (even with others) that you already have direct access to.
When you turn in your exam, you are to enter into the Comment area the statement: "I did not provide nor receive any aid on this exam." IF YOU CANNOT MAKE THAT STATEMENT TRUTHFULLY, DO NOT SUBMIT YOUR EXAM! ANY EXAM WITHOUT THAT STATEMENT WILL NOT BE GRADED.
Take-Home Exam Results
Assessment results so-far
Of the 120 students who started, only two dropped the course.
97% of the students on a midterm survey answered Yes to “Are you learning to program?” Compared with 88% in our traditional CS1
What do you like about the class?
“I like the feeling when I finally get something to work.” “Very applicable to everyday life.” ‘I dreaded CS, but ALL of the topics thus far have been
applicable to my future career (& personal) plans- there isn't anything I don't like about this class!!!”
“When I finally get a program to work like I want it to.” “The professor answers questions in class and online and is
concerned about our success in the class. He also seems to understand that most of us are not engineers and most likely won't do straight programming in the future- just the way of thinking is important.”
What have you learned that you found interesting or surprising? “The most useful things I have learned are the
basics about computers and pictures/sound. I think when we learn HTML- that will be interesting and useful to real life applications.”
“Just general concepts about programming. It's pretty logical, sort of like in math, so it's understandable.”
“Programming is fun and ANYONE can do it!”
Summary
Perlis’ challenge suggests that CS is more important than Calculus But need to update our pedagogy to make it happen
Media Computation may be a useful context to motivate student performance
Our class is aimed at addressing the challenges we’ve identified, and we’re trying it this semester
The approach right now is aimed at non-majors, but certainly could be used with majors, too.
Acknowledgements
Course materials development: Jason Ergle, Claire Bailey, David Raines, Joshua Sklare, Adam Wilson, Andrea Forte, Mark Richman, Matt Wallace, Alisa Bandlow.
Assessment: Andrea Forte, Rachel Fithian, Lauren Rich Thanks to Vice-Provost Bob McMath and the Al West
Fund, to GVU and CoC, and the National Science Foundation
For further information
Course CoWeb: http://coweb.cc.gatech.edu/cs1315
Where we planned the course:http://coweb.cc.gatech.edu/mediaComp-plan
Course Objectives
Students will be able to read, understand, and modify programs that achieve useful communication tasks Not programming from a blank piece of paper
Students will learn what computer science is about, especially data representations, algorithms, encodings, forms of programming.
Students will learn useful computing skills, including graphing and database concepts
Data structures
Some data structure discussions come naturally Sounds are in arrays Pictures are matrices of pixels, each of which has red,
green, and blue components Files are stored in trees
Much of our discussion of data structures comes in the form of encodings comparisons RGB vs. CMYK for encoding color 22.1 Khz vs. 44.2 Khz for audio sampling rates