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


Our attempt: Introduction to Media Computation


And what the solution might look like
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


At many departments, CS retention rates are lower than the
rest of campus



CS1 is one of the most despised courses for non-majors
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


120 students this semester,
planning 400-600 in the Fall


International Affairs, Literature, Public Policy,
Architecture, Management, Biology, etc.
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



Minimal syntax
Looks like other programming languages


Industrial Light & Magic, Google, Nextel, etc.
Potential for knowledge transfer
Actually using Jython (http://www.jython.org) for
Java class libraries
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 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 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)
original
Used like this:
>>> file="/Users/guzdial/mediasources/barbara.jpg"
>>> picture=makePicture(file)
>>> show(picture)
>>> decreaseRed(picture)
>>> repaint(picture)
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 Function
def makeSunset(picture):
for p in getPixels(picture):
value=getBlue(p)
setBlue(p,value*0.7)
value=getGreen(p)
setGreen(p,value*0.7)
SlowSunset
Just one canvas
repeatedly being
manipulated
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)
Not showing you
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)
writeFrame()
because you
know how that
works.
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 down
def 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 up
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
Recipe for halving the
frequency of a sound
def half(filename):
source = makeSound(filename)
target = makeSound(filename)
This is how a
sampling synthesizer
works!
sourceIndex = 1
for targetIndex in range(1, getLength( target)+1):
setSampleValueAt( target, targetIndex,
getSampleValueAt( source, int(sourceIndex)))
sourceIndex = sourceIndex + 0.5
Here’s the
play(target)
return target
piece that
does it
Compare these two
def copyBarbsFaceLarger():
# Set up the source and target pictures
barbf=getMediaPath("barbara.jpg")
barb = makePicture(barbf)
def half(filename):
canvasf = getMediaPath("7inX95in.jpg")
source = makeSound(filename)
canvas = makePicture(canvasf)
target = makeSound(filename)
# Now, do the actual copying
sourceX = 45
for targetX in range(100,100+((200-45)*2)):
sourceIndex = 1
for targetIndex in range(1, getLength( target)+1): sourceY = 25
for targetY in range(100,100+((200-25)*2)):
setSampleValueAt( target, targetIndex,
color = getColor(
getSampleValueAt( source,
getPixel(barb,int(sourceX),int(sourceY)))
int(sourceIndex)))
setColor(getPixel(canvas,targetX,targetY), color)
sourceIndex = sourceIndex + 0.5
sourceY = sourceY + 0.5
sourceX = sourceX + 0.5
play(target)
show(barb)
show(canvas)
return target
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 Motion
def 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




50-(50-50) = 50
addRectFilled(canvas,500,250,50,50,
red)
When frame = 51,



addRectFilled(canvas,490,285,50,50,
red)
When frame = 50,


addRectFilled(canvas,20,10,50,50,re
d)
When frame = 49,


addRectFilled(canvas,10,5,50,50,red)
When frame = 2,


addRectFilled(canvas,frame*10,fr
ame*5, 50,50,red)
if frame >= 50: #Greater than 50,
move up
addRectFilled(canvas,(50-(frame50))*10,(50-(frame-50))*5,
50,50,red)
When frame = 1,
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


Sounds



Psychophysics, data structures, defining functions,
for loops, if conditionals
Text


Psychophysics, data structures, defining functions,
for loops, if conditionals
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?”



“Movie-manipulating programs take a long time
to execute. Why?”


Object-oriented programming
Functional programming and recursion
Algorithmic complexity
“Why is PhotoShop so much faster?”


Compiling vs. interpreting
Machine language and how the computer works
Tools to support media
computation
MediaTools for exploring media
JES: Jython environment for students
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 #2
Given 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
guzdial@cc.gatech.edu
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