1. A Media Computation Cookbook
Manipulating Images and Sounds for Use in Alice
Part 1: Image Manipulations
Part 2: Changing colors in an area
Part 3: Chromakey for digital video effects
Part 4: Manipulated images in Alice
Part 5: Sound manipulations
Part 6: Manipulated sounds in Alice

2. “Can’t I do everything in Alice?”
Why do programming outside of Alice?
Sometimes you want special images or sounds in your Alice story.
You can make them by programming those images and sounds, then bringing them into Alice.
Sometimes you want to add in special movie effects to your Alice movie.
Overall, programming outside of Alice is the special effects studio for Alice.

3. Sound Frequency Project
Create an Alice world with 3 frogs
Resize one to be bigger and one to be smaller
Using croak.wav
Create a higher sound
Take every other sample
Create a lower sound
Take every sample twice
Import the sound files and have the frogs play their sounds and tap their foot
Alice and Media Computation Intro

4. Using Chromakey Create objects in Alice and position them as desired
Delete the ground
Set the color of the background to green
in the world properties
Use a conditional to replace the green color
You may also need to scale one of the pictures
Alice and Media Computation Intro

5. Drawing Projects Draw something on an Alice picture
Like a hat, glasses, or a scarf
Fireworks
Create images in Media Computation that you use as textures in Alice
like a gradient for the ground
Clip an Alice picture
To look like a porthole
Create a poster advertisement for your Alice movie.
With your name on it
Create a comic panel with Alice pictures
Alice and Media Computation Intro

6. Comic Strip Project
Create several scenes in Alice and take pictures of the scenes
Use Media Computation to create a Comic Panel and/or Comic Strips
Draw different types of text balloons
Speech balloon, thought balloon, scream balloon
Alice and Media Computation Intro

7. Add Yourself to an Alice Movie
Alice and Media Computation Intro

8. Add Alice Characters to a Real Movie
Split out frames from a movie of people
Capture frames from an Alice movie using MovieCapturePanel
Use chromakey to copy the Alice items to the real movie
Alice and Media Computation Intro

9. Start JES
Double-click the JES.exe (Python with glasses) icon

10. Using JES to access images
Type commands in the bottom part of JES to get filenames, print filenames, make pictures, and view pictures.
.JPG/.JPEG files are images
.WAV files are sounds. (JES can read some MP3’s)

11. An example interaction with JES
>>> filename = pickAFile() >>> print filename C:\mediasources\barbara.jpg >>> picture = makePicture(filename) >>> explore(picture)

12. Key commands to use in JES
(UPPERCASE/lowercase matters!)
print - prints out the value of whatever
variable=Something – sets variable equal to the value of Something.
pickAFile() – lets you pick a file, and has a value of the filename you pick.
makePicture(filename) – takes a filename as input, and has a value of a Picture object.
explore(picture) – shows you the picture.

13. Making a new function in JES
def decreaseRed(picture): for p in getPixels(picture): value=getRed(p) setRed(p,value*0.5)

14. Save the function in a file to use it later
First, save it
Then hit the Load button.
Then use it.

15. 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=pickAFile()
>>> picture=makePicture(file)
>>> explore(picture)
>>> decreaseRed(picture)

16. Saving the picture to use in Alice: writePictureTo(picture,file)

17. Yup, that worked

18. How writing functions works
To make a function, use the command def
Then, the name of the function, and the names of the input values between parentheses (“(input1)”)
End the line with a colon (“:”)
The body of the recipe is indented (Hint: Use three spaces)
That’s called a block

19. How does that function work?
What are pixels?
How does color work on a computer?
How does that function reduce red in all the pixels of a picture?

20. Digitizing pictures as bunches of little dots
We digitize pictures into lots of little dots
Enough dots and it looks like a continuous whole to our eye
Our eye has limited resolution
Our background/depth acuity is particularly low
Each picture element is referred to as a pixel
Pixels are picture elements
Each pixel object knows its color
It also knows where it is in its picture

21. Encoding color
Each pixel encodes color at that position in the picture
Lots of encodings for color
Printers use CMYK: Cyan, Magenta, Yellow, and blacK.
Others use HSB for Hue, Saturation, and Brightness (also called HSV for Hue, Saturation, and Value).
We’ll use the most common for computers
RGB: Red, Green, Blue
CMYK is Cyan, Yellow, Magenta, blacK
HSV is Hue, Saturation, Value. HSB is Hue, Saturation, Brightness

22. Encoding Color: RGB In RGB, each color has three component colors:
Amount of redness
Amount of greenness
Amount of blueness
Each does appear as a separate dot on most devices, but our eye blends them.
In most computer-based models of RGB, a single byte (8 bits) is used for each
So a complete RGB color is 24 bits, 8 bits of each

23. Encoding RGB
Each component color (red, green, and blue) is encoded as a single byte
Colors go from (0,0,0) to (255,255,255)
If all three components are the same, the color is in greyscale
(50,50,50) at (2,2)
(0,0,0) (at position (1,2) in example) is black
(255,255,255) is white

24. How does that work? Used like this:
def decreaseRed(picture):
for p in getPixels(picture):
value=getRed(p)
setRed(p,value*0.5)
Used like this:
>>> file="/Users/guzdial/mediasources/katie.jpg"
>>> picture=makePicture(file)
>>> explore(picture)
>>> decreaseRed(picture)

25. Let’s walk that through slowly…
Here we take a picture object in as a parameter to the function and call it picture
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
picture

26. Now, get the pixels
We get all the pixels from the picture, then make p be the name of each one one at a time
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
picture
getPixels()
Pixel, color r=135 g=131 b=105
Pixel, color r=133g=114 b=46
Pixel, color r=134 g=114b=45 … p

27. Get the red value from pixel
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
We get the red value of pixel p and name it originalRed
picture
getPixels()
Pixel, color r=135 g=131 b=105
Pixel, color r=133g=114 b=46
Pixel, color r=134 g=114b=45 … …
value = 135 p

28. Now change the pixel
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
Set the red value of pixel p to 0.5 (50%) of originalRed
picture
getPixels()
Pixel, color r=67 g=131 b=105
Pixel, color r=133g=114 b=46
Pixel, color r=134 g=114b=45 …
value = 135 p

29. Then move on to the next pixel
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
Move on to the next pixel and name it p
picture
getPixels()
Pixel, color r=67 g=131 b=105
Pixel, color r=133g=114 b=46
Pixel, color r=134 g=114b=45 …
value = 135 p

30. Get its red value Get its red value
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
Set originalRed to the red value at the new p, then change the red at that new pixel.
picture
getPixels()
Pixel, color r=67 g=131 b=105
Pixel, color r=133g=114 b=46
Pixel, color r=134 g=114b=45 …
value = 133 p p p

31. And change this red value
def decreaseRed(picture):
for p in getPixels(picture):
originalRed = getRed(p)
setRed(p, originalRed * 0.5)
Change the red value at pixel p to 50% of value
picture
getPixels()
Pixel, color r=67 g=131 b=105
Pixel, color r=66 g=114 b=46
Pixel, color r=134 g=114b=45 …
value = 133 p p p

32. And eventually, we do all pixels
We go from this… to this!

33. How do we change anything else?
Each component of the pixel is change- able.
getRed/setRed
getBlue/setBlue
getGreen/setGreen
We can multiply each by anything we want, or even just set it to a single value.

34. Some more functions to add to your file (feel free to make more!)
def decreaseRed(picture): for p in getPixels(picture): value=getRed(p) setRed(p,value*0.5) def decreaseBlue(picture): value=getBlue(p) setBlue(p,value*0.7) def maxBlue(picture): setBlue(p,0)
def decreaseGreen(picture): for p in getPixels(picture): value=getGreen(p) setGreen(p,value*0.7) def clearRed(picture): setRed(p,0)