Topics

Assignment structures

Lablets go out on Wednesday, are due on Friday (with some extensions to Monday)

When there are outstanding labs, optional recitations are held on Thursday nights
Lablets are collaborative: Students can work together, but one turn-in per person.
Some lablets interact with homework or projects, e.g., do something with the output like post it on the CoWeb
Goals are for these to be 1-2 hour projects

Pre-quizzes go out on Mondays, are due on Wednesday

Where there are outstanding pre-quizzes, optional recitations are held on Tuesday nights
Pre-quizzes are collaborative
Pre-quizzes should take about 1 hour

Quizzes are on Wednesdays
Exams are on Mondays
Homework goes out on Monday and is due on following Monday

Where there is outstanding homework, optional recitations are held on Tuesdays and Thursdays
Homework can be collaborative
Homework will vary in size and complexity, but the goal is for it to take 1-4 hours

Projects also go out on Monday and are due on following Monday

Projects are not collaborative
Projects are meant to be slightly smaller than Homework, but not take less than 1 hour

Week 1

MONDAY: Introduction: Computer Science and Media Computation

Computer Science is about specifying process (recipes)
Why should you care about process?

The Media Argument: If you ever want to say something that Adobe and Microsoft won't let you, you need to know something about programming

All media are going digital
Digital media are manipulated via software
Programming (the creation of software) is a communications skill

Many fields are about exact specification of process

Business, science
Specification of process involves lots of aspects

What do you name things?
What are your units? How do you describe the things your process is working with?
How do you specify what to do and when?
How do you do this without driving yourself crazy writing down tedious detail over and over again?
How can you do this efficiently?

KEY IDEA: Encoding

Basically, computers only understand numbers

Sequences of numbers from 0 to 255, to be exact

But we can create standard definitions and agreements on how to interpret those numbers

When you save an "A" in a file, your word processor actually stores the number 65. It agrees to INTERPRET that 65 as an A. (DEMO)
Look at an A on the screen. It's actually a series of lit and unlit dots on the screen. We can represent a "graphical" A as a series of binary numbers that correspond to the dots on the screen.

We can encode more complicated things by relying upon increasingly sophisticated encodings

Complicated things like sounds, pictures, and movies (DEMO)

WEDNESDAY: Functions and Naming

KEY IDEA: Naming

Anything the computer knows about, we can associate with a name
Its our own encoding -- we use it to establish our own conventions for how we want to think of things
We can associate an encoding, like a sound, with a name, then manipulate the name like it's the original thing. (DEMO)

We've already been asking the computer to do things for us

Print
Making and playing sounds

We can think of all of these doing things as functions

Like the math idea: There's some input, something happens, and there's an output
With computers, we don't always care about the output.

Sometimes we care about what happens IN the box, like with Print or playing a sound

One of the things that a function can do for us in re-encode something or unencode it

There are functions that move between different representations of basic data like letters and numbers (DEMO)
But more interestingly, there are functions that allow us to take apart sounds and pictures into their component encodings

What does that mean? To get there, we need to know a little about the standards and encodings for sounds and pictures.
Some examples: Playing with the samples in sounds, playing with the pixels in pictures (DEMO)

Lab: Introduction to Email and Web
FRIDAY: Arrays and loops

We talked about encodings and layers of encodings.
The simplest layer of an encoding is going from one number, to a series of numbers.

KEY CS IDEA: We'll call that an array

We can create such series easily, [1 2 3], range(), etc. (DEMO)
More importantly, sounds and pictures can be understood as an array of encodings (numbers), and we can manipulate these.
How do we manipulate arrays? Typically with a loop

We can do something to each element of an array with FOR X in ARRAY

Example: Let's do something to each "sample" of a sound (DEMO)

Multiply it by 2
Multiply it by 0.5

Week 2

Monday: Sound

Let's talk a bit about sound, using the MediaTools for examples, so that we can figure out what we're doing with it.
Sound is a wave

Physically, it's molecules moving around in the air -- hitting one another, and then getting bounced away. That creates pressure and less-pressure.
We can see in an oscilloscope the increasing and decreasing pressure (DEMO)

Increasing pressure is positive
Decreasing pressure is negative
Zero pressure is, well, zero

We can associate numbers with the amount of pressure (actually, it's the voltage coming from the microphone) (DEMO)

We can see that LOUDER sounds create a greater variation in the pressure: Difference from top to bottom gets large
softer sounds stay closer to zero

Each of those numbers is called a sample

Wednesday: Changing Sounds

Recording sound well takes LOTS of samples

We can hear (most of us -- less so for us older folk) between 7 Khz and 22 Khz

That's 7000 ups-and-downs (one cycle) per second, and 22,000 cycles per second

There's a mathematical result that says that if you want to capture everything that occurs in a sound, you have to capture at TWICE the frequency of the highest sound you want to capture

2 * 22 Khz = 44 Khz
This means that we have to capture 44,000 samples (numbers) PER SECOND to get everything in a recording that we might hear.
That's the rate at which a CD is recorded. 44,000 numbers per second. In an array (a sequence)

What were we doing when we multiplied or divided the samples? Increased or decreased the range => Increased or decreased the volume (DEMO)

Lab: Running a program in JES
Friday: Developing a mental model of the program: Debugging

Computers only do what you tell them to do

Computers only do what you tell them to do

Computers only do what you tell them to do

The tricky part is figuring out exactly what you told them to do

There are two things that we're concerned with

The "Flow of execution" -- what happens first, then second, then whatever
The "Flow of data" -- what variables got what when

Both parts can be studied by adding Print statements

Print statements can be signposts telling you where the code is at and when (DEMO)

Is your code running slowly? Where IS your execution? What's the computer doing NOW? A well-placed Print statement can show you that

Print statements can also show you what the (invisible) variables values are

So far, we've only been dealing with linear flows of execution and iterative flows of execution (looping). Conditional is still to come, and then it gets trickier to track the flow

Using show_vars for debugging trickier situations (DEMO)

Week 3

Monday: Manipulation Sound Playback

We can use loops for more than just walking all the values of an array: We can also use them for generating values

Think about what happens when a sound is played

The samples are sent to the speaker, one at a time, at the same rate as they were recorded

Consider what would happen if we skipped every other sample when we played it back.

We'd double the frequency and half the time (DEMO)

What about if we skipped 0.5 samples each time (i.e., sent a sample twice)

We'd half the frequency and double the time (DEMO)

Pre-Quiz on tracing programs
Quiz on tracing programs
Wednesday: Sounds with multiple loops

Can we play with the frequency by changing the playback rate? Can we try this for a range of numbers?

Sure, but isn't it tedious to type in all these examples?
For x in [0.1 0.2 0.5 1.0 1.5 2.0], play sound at freq x (DEMO)

What happens if we add samples? We can create REVERB! (DEMO)

We'll need two sounds, and we'll add from one to the other
Now we'll need TWO loops

One will track where we are in the source sample
The other one will handle the fading out of the sound over time

Lab: Modifying some sound programs
FRIDAY: Building a sound out of smaller sounds

We can combine sounds linearly (DEMO)
We can combine sounds in parallel, but doesn't work out well (DEMO)
We can combine sine waves

How to build a sine wave
How to add together sine waves
Making different sounds

Week 4

Monday: Images/Pictures

KEY CS IDEA: A linear sequence of values is ONE way to think about data. Another common way is with a table

Examples of tables: From newspapers, from textbooks, from lots of places
Some recipes need more than a series

A picture is actually a table of pixels

Remember a sound was an array of samples, where each sample was just a number
A picture is a table (not just a sequence) of a more sophisticated encoding.

Not one number, but three.
A value for the amount of redness (0 to 255)
A value for the amount of greenness, of blueness, and of "transparency" (called alpha), all 0 to 255

KEY CS IDEA: We can use representations and encodings within one another
This is how it really works. Go put a magnifying class on a TV, or a monitor, or even an LCD. The screen is made up of "dots" (picture elements => pixels), and each dot has smaller dots corresponding to different colors.

We can load pictures, see their pixel values, set their pixel values (DEMO)

Homework: Sound Manipulation Program
Wednesday: Manipulating images: Changing ARGB values, Filtering, functions

Pictures are made of pixels that we can change
We can walk through an image and change all the reds to less red, or more red (DEMO)
Same for green, blue, or alpha (DEMO)

Lab: Using the MediaTools to help in understanding sound
Friday: Filtering Part 2: Using more sophisticated functions. Conditionals

KEY CS IDEA We can make a function and apply it to a BUNCH of data

Make up a function to do some kind of filtering (changing of pixel values) and use a loop to apply the function to each pixel in a picture

By just increasing/decreasing pixel values, we're doing simple PhotoShop-style filtering, but that's pretty simplistic.

It's called a linear function

Often, you want to make choices about pixels and treat them differently

For example: Everything that's mostly red (say, over 200), decrease the red. If the redness is less than 200, leave it alone
This is a form of thresholding: There's a threshold value that determines what you do.

KEY CS IDEA Computers don't have to do just one thing after another, nor just loop. They can also make choices

But real limited choices: They only understand number, they only understand numbers, and they only understand numbers

We can use an If-Then which is a Test.

IF this is true, Then the computer must, Must, MUST do the Then
No choices about it. "Test this, computer. And if it's true, DO IT!"

Change the redness, if needed (DEMO)
Creating more kinds of threshold functions (DEMO)

Week 5

Monday: MIDTERM EXAM
Wednesday: Working with a portion of an image: Masks and looping

Oftentimes you don't want to do something to an entire image. Instead, you want to apply some filter to just part of an image

For example, turn the lady's hat red; blur only the one character; blur everything BUT the one character; make the box eerily-transparent

How do we do that? Easiest way: change the limits on your loops

Don't go from 1 to the width and 1 to the height.
Instead, just go from 10 to 250 and 5 to 100 (for example) DEMO

But that approach can only handle a rectangle. Most areas you want to manipulate are more complicated

The answer: Compute a mask
This is an unusual thing. It's a "picture" (of a sort) with data in it that does NOT correspond to pixels. Instead we just store 0's and 1's in it.

KEY CS IDEA: Creating some data just to make the "recipe" easier
1's mean "This is part of the picture that we want to process"
0's mean "This is part of the picture that we do NOT want to process"

You end up going through all the pixels TWICE

First time, with a conditional, to decide whether you want to process that part of the picture. If so, put a 1 in the corresponding parts of the mask, and a 0 in all the others
Now, go through all the pixels, and where ever there's a 1, apply the filter/function. Otherwise, don't.

Lab: Manipulating image programs
Friday: Drawing on an image: Adding lines, circles, text, and other elements

Week 6

Monday: Developing a mental model of the program: Debugging conditionals

How do you figure out what happened where? Especially with sequential, iterative, and conditional computation?
KEY CS IDEA: Play computer! Trace the program and do as it would do

Print statements to find out where it went and what the data values are is KEY
Important to look at the input: What's really going on?

In real software development, you work at figuring out the input that breaks a program
One way of finding these is to try the boundary conditions: What happens at 0? At 255?
Then you make it work for that input too

Homework: Manipulating a program that does image manipulation
Wednesday: Files

Media are mostly stored in files today. If you want to manipulate lots of media, you need to manipulate files.
There are more ways of encoding data than just arrays and tables

KEY CS IDEA Frequently, you want a hierarchy, which is represented as a tree
Think about outlines, about the structure of dictionaries and encylopediae
You've seen this already in file structures. Directories are nodes in a tree. Files in the directory (a sequence within the node) are peers or children of the directory
We can use the directory tree to find things, move things around

Remember how pixels are inside pictures -- a sophisticated encoding inside of another encoding? Files are similar

Files have contents, creation dates, names -- all inside of a linear list inside a directory, which is part of a tree
It's data representations and encodings all the way up and down!

Lab: Using the CoWeb, uploading your image homework for display
Friday: Walking the Files, Manipulating Trees

We can write programs to manipulate all the sounds or images in a directory (DEMO)

We use loops to walk the sequence in a directory

Week 7

Monday: Writing Utility Functions: Moving/manipulating your files

We can use the other ideas we've introduced, like conditionals

For example, process only the sounds whose names end in ".wav" (DEMO)

We'll have to do a little string manipulation here
A string is a linear encoding of characters

Or, process only the sounds whose modification date is today (DEMO)

Dates are another encoding on numbers

We can also copy files from one place to another

But how we do it depends on the encoding in the file

You can always read and write the numbers. This is called a binary copying (for reasons we'll see later)
We could also read and write the letters, the strings. This is assuming the data is text
We can use a loop to get all data across
KEY CS IDEA: But a loop that doesn't count. Instead, it tests if we're at the end of the file. A WHILE

Project: Image or Sound Manipulations
Wednesday: Drawing in bunches

Combining different graphic techniques
Writing programs that do bunch of drawing on bunches of image files

Putting your copyright on every image (DEMO)

Lab: Microsoft Word
Friday: File Formats

Why are some files bigger than others?
How are JPEGs and MP3s and such so small?
Why are Flash files so small?
Bitmaps vs. Vectors

Scaling vs. detail

Techniques for compression

Run-length encoding

Week 8

Monday: Seek and you shall draw!

Looking for something, then drawing on it
Computer vision is WAY hard! Lots of stray pixels

Pre-quiz on tracing image programs
Wednesday: Video: A series of pictures/frames

A Video is a series of images called frames
We can process them JUST like we did images, but we have to do it for every frame
Easiest way: Convert your video to frames, manipulate the frames, reassemble them into a movie

Demonstration with MediaTools (DEMO)

Now, apply some processing to those frames, by combining what we know about processing files with what we know about manipulating images (DEMO)

Quiz on tracing image programs
Lab: Powerpoint and images and drawing
Friday: Filtering a range of pictures

What if we want to do something to just SOME of the frames? Same techniques as processing just SOME of the pixels

Insert a blue balloon in SOME of the frames of a picture (DEMO)

We can also do masking

How the weatherman works! Background subtraction and "bluescreening" (DEMO)

Week 9

Monday: MIDTERM EXAM #2
Wednesday: "WHY IS THIS TAKING SO LONG?!?"

Why is video processing taking so long? Is it just the speed of my processor?
KEY CS IDEA: The "order" (Big Oh) of an algorithm

The more loops you have, the more basic operations you do
Array processing is order n, O(n)
Table/matrix processing is O(n*m)
If you have f frames in a video, that's O(n*m*f)
What if you compute a mask for each frame THEN process it? O(2*n*m*f)

KEY CS IDEA: Moore's Law: Every 18 months, the processor speed doubles for the same cost

But that only cuts the time cost in HALF
That's great, but it doesn't make processing a movie like processing an array

How do we make things faster? Fixing how we specify the recipe/process

An example: Finding things in an array

Just searching one-after-the-other: O(n)
What if they're in a particular order? We can use a binary search O(log n)

Example: How to search a dictionary or phone book efficiently (DEMO)

How do we get things in order? Sorting.

Worst we can do O(n*n)

Compare everything to everything

Best we can do is probably O(n log n) (Not planning to give more than an intuitive sense here)

Lab: Excel, especially, how to Graph
Friday: And Somethings Take TOO Long!

Guess what: Some things CAN'T be made faster!

Imagine an optimal arrangement of sounds in a composition/synthesis. You have to check EVERY combination.
Let's say that you have 60 sounds you want to arrange and any order is possible, but you want to figure out the best one

Basically, if you have to try every combination of n things, there are 2 ^ n combinations (can demo this pretty easily)
O(2 ^ 60) = 11,52,921,504,606,846,976
Imagine that you have a 1 Ghz computer (1 billion basic operations per second) -- a top of the line processor today
It'll take you 1152921504.606847 seconds to optimize that data

That's 19,215,358.41011412 minutes
That's 800,639.933754755 days
That's 2,193 years
With Moore's law, in two years, you can do that in only 1,000 years!
And 60 sounds is a SMALL amount -- most songs have many more notes than that

Can we do better? Maybe -- can you be satisfied with less than perfect? Can we be smarter than checking EVERY combination? THAT'S PART OF WHAT COMPUTER SCIENTISTS DO!

Week 10:

Monday: Text as a Media Type

KEY CS IDEA: Text itself is a media type that computers are good at manipulating
We've already been doing some string manipulation.
Imagine that you've got a file with RGB values specified as TEXT. Can we turn that into a picture? DEMO
Can we go from a picture and generate those RGB values? DEMO
KEY CS IDEA: This is interpretation -- we're moving between encodings, and using an encoding to tell the computer what to do.
If text is language, we can process it, still, but it's less well-formed so harder to process

A demo or two goes here

Homework: Modify a program to do media manipulation
Wednesday: Creating HTML

HTML is text
Writing programs that generate HTML is VERY common
Basics of HTML
Basics of String manipulation

Lab: Creating a homepage
Friday: From text to text

Find some information in a file, and put it into HTML
Find some information on the Web, and put it into HTML

Week 11:

Monday: Making other programs do the work

Writing fast, smart algorithms is a lot of work.

Let other people do it!
We can use what they produce!

CS CONCEPT: We can write programs to control other programs

Sometimes called scripting

Not all programs are scriptable! Photoshop is not. GIMP, a free, open-source, cross-platform version of PhotoShop is
Multiple ways of scripting

Sometimes, can just call functions within your own language, and inter-application communication handles it
Sometimes, you write a program that creates files that the other program understands

Command files
Data files

Homework: Create a program to create a web page with sound and images
Wednesday: Making image processing fast(er)

Demonstrate both techniques for controlling GIMP

Lab: Installing and using the GIMP
Friday: Why is the GIMP faster? How a computer works...

The GIMP is written in machine language. What's that?

Introducing the CPU, Memory, Disk, and Network

Memory is faster than Disk is faster than Network
What a compiler does.
What an interpreter does.

Week 12

Monday: Graphing data

What data/information visualizers do: Take some data, turn it into a picture
We can do that ourselves, using what we know about graphics, reading files, and interpreting text

Building a simple scatterplot, say with stock quotes or other data from the Web DEMO

But building graphs is hard -- let's make somebody else do it!

We can get data ready for Excel

Demo creating a tab-delimited file of data

Or we can use a sophisticated plotting package

Project: Do some text and image manipulation on own
Wednesday: Graphing data with GNUPlot

Use what we know about using other programs and make GNUPlot do it!
Get data ready for GNUPlot

Lab: Installing and using GNUPlot
Friday: Moving the data around

How do we put data on disk? Two ways: Files and databases

A little review of files

Why databases?

Fast access
Well structured

Simple database stuff in Jython

Putting data into the database
Getting it out

Plotting what's in the database (DEMO)
Getting stuff from Web into database (DEMO)

Week 13

Monday: "Can't we do this any easier?": Functional Decomposition

Writing lines and lines and lines of code is tedious and error prone. How do we make it easier?
Wherever possible, create a function to do it!

Remember how we created a function with our filter to apply to our images?
We can use this idea more generally

Pre-quiz on writing programs to manipulate text/HTML
Wednesday: "Can't we do this any easier?": Recursion

Some problems are more easily solved by doing something other than straight sequential, iterative, and conditional computation
KEY CS IDEA: Recursion is functional programming to the max! A function calling itself!

Use all the Brian Harvey ways of thinking about recursion here

Quiz on writing programs to manipulate text/HTML
Lab on Writing Recursion
Friday: More models of recursion

Think about it as elves
Think about it as copies
Think about it as a "leap of faith"

Week 14

Monday: "Can't we do this any easier?": Functional programming

We can take functions further
Remember when we said in Week 1 that ANYTHING can have a name? So can functions!
Remember how functions took inputs? Functions can also be inputs to other functions!
We can apply function to data, rather than pass data to functions

Reduce, Map, Apply, Filter/Select

Homework: Functions and recursion program writing
Wednesday: "Can't we do this any easier?": Objects

Pixels and files, and pictures and directories, are more than just sequences of numbers
How do we represent these kinds of related encodings?
Functions that manipulate these complex encodings probably differ depending on the data we're manipulating

Sometimes we may want to re-use the same names
Sometimes we don't even want to use functions -- instead, we want to touch the numbers (like red value) directly!

KEY CS IDEA: An Object encapsulates (combines) data and behavior into one encoding that we can manipulate more easily

Pixels as objects
Files as objects

How we make objects (DEMO)

Lab on functional programming in Jython
Friday: Re-visiting media manipulation as functional and object-oriented programming

Re-do some of the earlier examples, but in terms of functions
Re-do some of the earlier examples, but in terms of objects

Week 15

Monday: Languages and Representations for Recipes: It's much of what computer scientists do

Jython isn't the only language that computer scientists use.
Other languages allow us to represent data or process (recipes) better for some kinds of problems
Examples: No more than 2-3 screens each, just to give a flavor, the "sound" of the language

Lists and functions and functional programming in Lisp
Manipulating pixels and sounds in Smalltalk
Manipulating arrays and matrices in MATLAB

Much of the world uses Java these days: Let's talk about what Java looks like

Homework: Write an object-oriented Jython program
Wednesday: Introduction to Java

Using Java; Code goes in files, we "compile" the files, we execute the "object" code
All of Java is objects

How classes are defined in Java

All data in Java is "typed"

Tell it the encoding!

Walking a Java file -- what it looks like

Lab: Modifying a Java program
Friday: Introduction to Java Media Manipulation

We can call functions (called methods) in Java to do all that we did before
Picture and Image manipulation in Java EXAMPLES