1. Some Utility Functions If you know the name of the file, searching for it with pickAFile() feels tedious You can set and get a media folder (path) for remembering a place where your media will be coming from (or going to)  setMediaPath() lets you pick a file in your media folder  getMediaPath(basefilename) lets you generate a complete filename out of only the last part

2. Example >>> setMediaPath() New media folder: C:\mediasources\ >>> getMediaPath("barbara.jpg") 'C:\\mediasources\\barbara.jpg' >>> barb=makePicture(getMediaPath("barbara.jpg"))

3. Blank files in mediasources file = makeEmptyPicture(100,100) will create a blank picture of size 101x101 (why not 100x100?) DO writePictureTo(file,”100x100.jpg”) to save the blank picture canvas = makePicture(getMediaPath(“100x100.jpg”)) gives you a JPEG canvas of 101x101 pixels

4. Edge detection Pixel is different from its neighbors => an edge Measure (criterion) of pixel differences ?  One possibility – compare B/W value of a pixel with those at the left and below  If differences are above threshold, then an edge (black), otherwise (white) For each pixel in picture1: get B/W values of the pixel, its left and below (how?) if differences of (pixel, left) and (pixel, below) > Threshold paint the pixel black otherwise, paint the pixel white

5. Edge detection code def edgeDetect(pic, tHold): wid = getWidht(pic) hgt = getHeight(pic) edge = makeEmptyPicture(wid, hgt) for x in range(1, wid): for y in range(1, hgt): t = getPixel(pic, x, y) l = getPixel(pic, x-1, y) b = getPixel(pic, x, y+1) thisBW = (getRed(t) +getGreen(t)+getBlue(t))/3 leftBW = (getRed(l) +getGreen(l)+getBlue(l))/3 belBW = (getRed(b) +getGreen(b)+getBlue(b))/3 if abs(thisBW-leftBW) > tHold and abs(thisBW-belBW) > tHold: setColor(getPixel(edge, x, y), black) else: setColor(getPixel(edge, x,y), white) show(edge)

6. Making a collage Could we do something to the pictures we copy in?  Sure! Could either apply one of those functions before copying, or do something to the pixels during the copy. Could we copy more than one picture!  Of course! Make a collage!

7. Making a collage Given a blank canvas  Copy flower1 at lower left corner of canvas  Copy flower2 next  Copy negated flower1  Copy flower2 with blue removed  Copy flower1, negated and red reduced How do I copy to lower left corner?  Upper left corner is easy  Need to utilize getHeight(canvas) and getHeight(flower1) How do I copy flower2 adjacent to flower1 ?

8. Copy to lower left corner targetX = sourceX targetY = sourceY + ?  ? : getHeight(canvas) – getHeight(flower1) sourceX sourceY flower1

9. Copy flower2 targetX = sourceX + getWidth(flower1) targetY = sourceY + ?  ? : getHeight(canvas) – getHeight(flower2) sourceX sourceY flower1flower2

10. Put them together #First picture, at left edge targetX=1 for sourceX in range(1, getWidth(flower1)): targetY=getHeight(canvas)-getHeight(flower1)-5 for sourceY in range(1,getHeight(flower1)): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 #Second picture, 100 pixels over targetX= getWidth(flower1)# 100 for sourceX in range(1,getWidth(flower2)): targetY=getHeight(canvas)-getHeight(flower2)-5 for sourceY in range(1,getHeight(flower2)): px=getPixel(flower2,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

11. def createCollage(): flower1=makePicture(getMediaPath("flower1.jpg")) print flower1 flower2=makePicture(getMediaPath("flower2.jpg")) print flower2 canvas=makePicture(getMediaPath("640x480.jpg")) print canvas #First picture, at left edge targetX=1 for sourceX in range(1,getWidth(flower1)): targetY=getHeight(canvas)-getHeight(flower1)-5 for sourceY in range(1,getHeight(flower1)): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 #Second picture, 100 pixels over targetX=100 for sourceX in range(1,getWidth(flower2)): targetY=getHeight(canvas)-getHeight(flower2)-5 for sourceY in range(1,getHeight(flower2)): px=getPixel(flower2,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 #Third picture, flower1 negated negative(flower1) targetX=200 for sourceX in range(1,getWidth(flower1)): targetY=getHeight(canvas)-getHeight(flower1)-5 for sourceY in range(1,getHeight(flower1)): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 #Fourth picture, flower2 with no blue clearBlue(flower2) targetX=300 for sourceX in range(1,getWidth(flower2)): targetY=getHeight(canvas)-getHeight(flower2)-5 for sourceY in range(1,getHeight(flower2)): px=getPixel(flower2,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 #Fifth picture, flower1, negated with decreased red decreaseRed(flower1) targetX=400 for sourceX in range(1,getWidth(flower1)): targetY=getHeight(canvas)-getHeight(flower1)-5 for sourceY in range(1,getHeight(flower1)): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 show(canvas) return(canvas)

12. Making a collage createCollage() too messy Any good way to simplify it ? Go back to what processes were involved => find any pattern to exploit ?  Copy flower1 at lower left corner of canvas  Copy flower2 next  Copy negated flower1  Copy flower2 with blue removed  Copy flower1, negated and red reduced  Sure! Repetition of ‘Copy’ Let us make a general picCopy() function What info do we need for picCopy() ?

13. LAB: Write picCopy() Write picCopy(fPic,tPic,x,y) function in Program Area, which copies fPic to tPic starting from (x,y) of tPic In Command Area, call picCopy() five times to create a collage on the right You need negate(), clearBlue(), decreaseRed()