Barbara Ericson is a research scientist and the director of Computing Outreach for the College of Computing at Georgia Tech. She has been working on improving introductory computing education since 2004. She has served as the teacher education representative on the Computer Science Teachers Association board, the co-chair of the K-12 Alliance for the National Center for Women in Information Technology, and as a reader for the Advanced Placement Computer Science exams. She enjoys the diversity of the types of problems she has worked on over the years in computing including computer graphics, artificial intelligence, medicine, and object-oriented programming. Mark and Barbara received the 2010 ACM Karl V. Karlstrom Award for Outstanding Computer Educator for their work on Media Computation including this book. They led a project called “Georgia Computes!” for six years, which had a significant impact in improving computing education in the US state of Georgia [3]. Together, they Mark and Barbara are leaders in the Expanding Computing Education.

1 Introduction to Computer Science and Media Computation 3

1.1 What Is Computer Science About? 3

1.2 Programming Languages 6

1.3 What Computers Understand 9

1.4 Media Computation: Why Digitize Media? 11

1.5 Computer Science for Everyone 13

1.5.1 It’s About Communication 13

1.5.2 It’s About Process 13

1.5.3 You Will Probably Need It 14

2 Introduction to Programming 18

2.1 Programming Is About Naming 18

2.2 Programming in Python 21

2.3 Programming in JES 22

2.4 Media Computation in JES 23

2.1.1 Files and Their Names 20

2.5 Making a Program 33

2.4.1 Showing a Picture 27

2.4.2 Playing a Sound 30

2.4.3 Naming Values 30

2.5.1 Variable Recipes: Real Math-Like Functions That Take Input 37

3 Creating and Modifying Text 44

3.1 Strings: Making Strings 44

3.2 Taking Strings Apart with For 49

3.1.1 Making Strings from Strings: Telling Stories 46

3.2.1 Testing the Pieces 51

3.2.2 Taking String Apart, and Putting Strings Together 54

3.2.3 Taking Strings Apart with Indices 57

3.2.4 Mirroring, Reversing, and Separating Strings with Index 59

3.2.5 Encoding and Decoding Strings Using a Keyword Cipher 61

3.3 Taking Strings Apart by Words 63

3.4 What’s Inside a String 66

3.5 What a Computer Can Do 67

4 Modifying Pictures Using Loops 74

4.1 How Pictures Are Encoded 75

4.2 Manipulating Pictures 80

4.3 Changing Color Values 86

4.2.1 Exploring Pictures 84

4.3.1 Using Loops in Pictures 86

4.3.2 Increasing/Decreasing Red (Green, Blue) 88

4.3.3 Testing the Program: Did That Really Work? 93

4.3.4 Changing One Color at a Time 94

4.4.1 Making Sense of Functions 95

4.4 Creating a Sunset 95

4.5 Lightening and Darkening 100

4.6 Creating a Negative 101

4.7 Converting to Grayscale 102

4.8 Specifying Pixels by Index 104

5 Picture Techniques with Selection 114

5.1 Replacing Colors: Red-Eye, Sepia Tones, and Posterizing 114

5.1.1 Reducing Red-Eye 118

5.1.2 Sepia-Toned and Posterized Pictures: Using Conditionals to Choose the Color 120

5.2 Comparing Pixels: Edge Detection 126

5.3 Background Subtraction 129

5.4 Chromakey 132

5.5 Coloring in ranges 137

5.5.1 Adding a Border 137

5.5.2 Lightening the Right Half of a Picture 138

5.6 Selecting without Retesting 139

6 Modifying Pixels by Position 145

6.1 Processing Pixels Faster 145

6.1.1 Looping across the Pixels with Range 147

6.1.2 Writing Faster Pixel Loops 149

6.2 Mirroring a Picture 151

6.3 Copying and Transforming Pictures 158

6.3.1 Copying 159

6.3.2 Copying Smaller and Modifying 165

6.3.3 Copying and Referencing 167

6.3.4 Creating a Collage 169

6.3.5 General Copying 172

6.3.6 Rotation 173

6.3.7 Scaling 176

6.4 Combining Pixels: Blurring 181

6.5 Blending Pictures 184

6.6 Drawing on Images 186

6.7 Programs as Specifying Drawing Process 191

6.6.1 Drawing with Drawing Commands 188

6.6.2 Vector and Bitmap Representations 189

6.7.1 Why Do We Write Programs? 192

Sounds 201

7 Modifying Sounds Using Loops 203

7.1 How Sound Is Encoded 203

7.2 Manipulating Sounds 215

7.3 Changing the Volume of Sounds 220

7.1.1 The Physics of Sound 203

7.1.2 Investigating Different Sounds 206

7.1.3 Encoding the Sound 211

7.1.4 Binary Numbers and Two’s Complement 212

7.1.5 Storing Digitized Sounds 213

7.2.1 Open Sounds and Manipulating Samples 215

7.2.2 Using the JES MediaTools 218

7.2.3 Looping 219

7.3.1 Increasing Volume 220

7.3.2 Did That Really Work? 221

7.3.3 Decreasing Volume 225

7.3.4 Using Array Index Notation 226

7.3.5 Making Sense of Functions in Sounds 227

7.4.1 Generating Clipping 229

7.4 Normalizing Sounds 227

8 Modifying Samples in a Range 235

8.1 Manipulating Different Sections of the Sound Differently 235

8.2 Splicing Sounds 238

8.3 General Clip and Copy 245

8.4 Reversing Sounds 247

8.5 Mirroring 249

8.6 On Functions and Scope 249

9 Making Sounds by Combining Pieces 255

9.1 Composing Sounds Through Addition 255

9.2 Blending Sounds 256

9.3 Creating an Echo 258

8.1.1 Revisiting Index Array Notation 236

9.4 How Sampling Keyboards Work 261

9.5 Additive Synthesis 265

9.6 Modern Music Synthesis 273

9.3.1 Creating Multiple Echoes 259

9.3.2 Creating Chords 260

9.4.1 Sampling as an Algorithm 265

9.5.1 Making Sine Waves 265

9.5.2 Adding Sine Waves Together 267

9.5.3 Checking Our Result 268

9.5.4 Square Waves 269

9.5.5 Triangular Waves 272

9.6.1 MP3 274

9.6.2 MIDI 274

10 Building Bigger Programs 279

10.1 Designing Programs Top-Down 280

10.1.1 A Top-Down Design Example 281

10.1.2 Designing the Top-Level Function 282

10.2 Designing Programs Bottom-Up 288

10.3 Testing Your Program 290

10.4 Tips on Debugging 292

10.1.3 Writing the Subfunctions 285

10.2.1 An Example Bottom-Up Process 289

10.3.1 Testing the Edge Conditions 291

10.4.1 Finding Which Statement to Worry About 293

10.4.2 Seeing the Variables 293

10.4.3 Debugging the Adventure Game 296

10.5 Algorithms and Design 299

10.6 Connecting to Data outside a Function 299

10.7 Running Programs Outside of JES 303

11 Manipulating Text with Methods and Files 310

11.1 Text as Unimedia 310

11.2 Manipulating Parts of Strings 311

11.3 Files: Places to Put Your Strings and Other Stuff 317

11.4 The Python Standard Library 327

11.2.1 String Methods: Introducing Objects and Dot Notation 312

11.2.2 Lists: Powerful, Structured Text 314

11.2.3 Strings Have No Font 316

11.3.1 Opening and Manipulating Files 318

11.3.2 Generating Form Letters 320

11.3.3 Reading and Manipulating Data from the Internet 321

11.3.4 Scraping Information from a Web Page 323

11.3.5 Reading CSV Data 324

11.3.6 Writing Out Programs 326

11.4.1 More on Import and Your Own Modules 328

11.4.2 Adding Unpredictably toYour Program with Random 329

11.4.3 Reading CSV Files with a Library 331

11.4.4 A Sampling of Python Standard Libraries 331

12 Advanced Text Techniques: Web and Information 337

12.1 Networks: Getting Our Text from the Web 337

12.1.1 Automating Access to CSV Data 341

12.1.2 Accessing FTP 343

12.2 Using Text to Shift Between Media 344

12.3 Moving Information Between Media 347

12.4 Using Lists as Structured Text for Media Representations 349

12.5 Hiding Information in a Picture 351

12.5.1 Hiding a Sound Inside a Picture 353

13 Making Text for the Web 359

13.1 HTML: The Notation of the Web 359

13.2 Writing Programs to Generate HTML 364

13.3 Databases: A Place to Store Our Text 369

13.2.1 Making Home Pages 366

13.3.1 Relational Databases 371

13.3.2 An Example Relational Database Using HashTables 372

13.3.3 Working with SQL 375

13.3.4 Using a Database to Build Web Pages 377

14 Creating and Modifying Movies 382

14.1 Generating Animations 383

14.2 Working with Video Source 392

14.3 Building a Video Effect Bottom-Up 396

15 Speed 403

15.1 Focusing on Computer Science 403

15.2 What Makes Programs Fast? 403

14.2.1 Video Manipulating Examples 392

15.3 What Makes a Computer Fast? 417

15.2.1 What Computers Really Understand 404

15.2.2 Compilers and Interpreters 405

15.2.3 What Limits Computer Speed? 409

15.2.4 Does It Really Make a Difference? 411

15.2.5 Making Searching Faster 413

15.2.6 AlgorithmsThat Never Finish or Can’t BeWritten 415

15.2.7 Why Is Photoshop Faster than JES? 417

15.3.1 Clock Rates and Actual Computation 417

15.3.2 Storage: What Makes a Computer Slow? 419

15.3.3 Display 420

16 Functional Programming 423

16.1 Using Functions to Make Programming Easier 423

16.2 Functional Programming with Map and Reduce 427

16.3 Functional Programming for Media 430

16.4 Recursion: A Powerful Idea 432

16.3.1 Media Manipulation Without Changing State 431

16.4.1 Recursive Directory Traversals 438

16.4.2 Recursive Media Functions 440

17 Object Oriented Programming 444

17.1 History of Objects 444

17.2 Working with Turtles 446

17.3 Teaching Turtles New Tricks 451

17.2.1 Classes and Objects 446

17.2.2 Sending Messages to Objects 447

17.2.3 Objects Control Their State 449

17.3.1 Overriding an Existing Turtle Method 453

17.3.2 Working with Multiple Turtles at Once 454

17.3.3 Turtles with Pictures 456

17.3.4 Dancing Turtles 458

17.3.5 Recursion and Turtles 460

17.4.1 Making the Slide Class More Object-Oriented 465

17.4 An Object-Oriented Slide Show 461

17.5 Object-Oriented Media 466

17.6 Joe the Box 471

17.7 Why Objects? 473

Bibliography 480

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