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

Questions being answered here today How do we make it easier to build new things? How do we make it easy to write a program to access specific pictures? How do we change the size of a picture? How do grab part of a picture? How do you combine parts of pictures? How do we use programming to replace re- typing code? How do we replace the background of a picture with something else?

How do we make it easier to build new things? Don’t start from scratch! Use the old file and add more to it. When you start JES, open up the file that you used last time. ◦ If you end your file name with “.py” you can figure out which are Python files. Type more code into that file. If you want, you can download my myfunctions.py from

How do we make it easy to write a program to access certain pictures? setMediaPath() ◦ Type this in the Command Area (black area at bottom of JES) and find the folder where you store your pictures. ◦ (Could be the Desktop, probably better to use a particular folder. I call mine “mediasources”.) makePicture(getMediaPath(“IMG_0810.JPG”)) ◦ Will make a picture from that file in the “media path” folder.

How do we change the size of a picture? To copy a picture, get the color values from pixels in one picture, and set those color values in the pixels in the other picture. def copyPicture(picture): returnPicture = makeEmptyPicture(getWidth(picture),getHeight(picture)) for pixel in getPixels(picture): color = getColor(pixel) setColor(getPixel(returnPicture,getX(pixel),getY(pixel)),returnPicture) return returnPicture

To scale the picture smaller = scale(picture,0.5) How does it work? ◦ To get it to be only ½ the size (in both horizontal and vertical) directions, we need to lose some pixels. ◦ Easiest way: Skip a few. Every other pixel gets copied. ◦ Can generalize this for any size scaling.

Code to scale def scale(picture,factor): newHeight = int(factor*getHeight(picture))+1 newWidth = int(factor*getWidth(picture))+1 returnPic = makeEmptyPicture(int(newWidth),int(newHeight)) sx = 0 for tx in range(0,newWidth): sy = 0 for ty in range(0,newHeight): if (int(sx) < getWidth(picture)) and (int(sy) < getHeight(picture)): sp = getPixel(picture,int(sx),int(sy)) tp = getPixel(returnPic,tx,ty) setColor(tp,getColor(sp)) sy = sy + (1/factor) sx = sx + (1/factor) return returnPic

How do we grab part of a picture? guys = makePicture(getMediaPath("IMG_0805.JPG")) james = copyPartPicture(guys,352,217,618,475) copyPartPicture(picture,startX,startY,endX,endY) ◦ Gives you a new picture inside the box defined by upper-left corner and lower-right corner.

Code to grab part of a picture def copyPartPicture(picture,x1,y1,x2,y2): returnPicture = makeEmptyPicture(x2-x1,y2-y1) targetx = 0 for srcx in range(x1,x2): targety = 0 for srcy in range(y1,y2): srcpixel = getPixel(picture,srcx,srcy) targetPixel = getPixel(returnPicture,targetx,targety) setColor(targetPixel,getColor(srcpixel)) targety = targety + 1 targetx = targetx + 1 return returnPicture

How do we combine parts of a picture? grayscale(betsy) clearRed(james) pastePicture(betsy,scale(james,0.35),0,0) pastePicture(canvas,partial,startX,startY) ◦ Pasting “partial” picture onto the “canvas” starting from (startX,startY)

Code to paste a picture def pastePicture(canvas,source,startx,starty): targetx = startx for x in range(0,getWidth(source)): targety = starty for y in range(0,getHeight(source)): srcpixel = getPixel(source,x,y) if (targetx < getWidth(canvas)) and (targety < getHeight(canvas)): targetPixel = getPixel(canvas,targetx,targety) setColor(targetPixel,getColor(srcpixel)) targety = targety + 1 targetx = targetx + 1

How do use programming to replace re-typing code? Building a collage of pictures: def makeACollage(): betsy = makePicture(getMediaPath("IMG_0802.JPG")) hunter = makePicture(getMediaPath("IMG_0808.JPG")) guys = makePicture(getMediaPath("IMG_0805.JPG")) james = copyPartPicture(guys,352,217,618,475) grayscale(betsy) clearRed(james) pastePicture(betsy,scale(james,0.35),0,0) maxBlue(guys) pastePicture(betsy,scale(guys,0.35),450,340) negative(hunter) pastePicture(betsy,scale(hunter,0.35),0,340) writePictureTo(betsy,"C:/collage.jpg")

Result:

How do we replace the background of a picture with something else? Take a picture with a background that is easy to test and isn’t in the foreground. Two examples. Which one do you think will work?

Code to chromakey for any background color def chromakey(picture,background,color,threshold=100.0): for pixel in getPixels(picture): pixelColor = getColor(pixel) if distance(color,pixelColor) < threshold: newColor = getColor(getPixel(background,getX(pixel),getY(pixel))) setColor(pixel,newColor)

Trying to make the yellow background work >>> chromakey(yellowBarb, moon, makeColor(167,159,110)) >>> writePictureTo(yellowBarb, "C:/yellowBarb-th100.jpg") >>> chromakey( yellowBarb, moon, makeColor(167,159,110),50) >>> writePictureTo( yellowBarb, "C:/yellowBarb-th50.jpg") Yellow is too close to Barb’s skin tone to work.

Using the general chromakey form for a blue background >>> chromakey(blueJenny,moon,makeColor(36,62,95))

Doing a specific version of Chromakey Coming up with a test for being “truly blue” def chromakeyBlue(picture,background): for pixel in getPixels(picture): pixelColor = getColor(pixel) if getRed(pixel)<getBlue(pixel) and getGreen(pixel)<getBlue(pixel): newColor = getColor(getPixel(background,getX(pixel),getY(pixel))) setColor(pixel,newColor)

Nicely chromakeyed

Try it! Take your own picture and put it on a new background. Create a collage with various pieces of the pictures we have.