1. 02-RangesInPictures1 Barb Ericson Georgia Institute of Technology Oct 2010 Working with ranges in pictures

2. 02-RangesInPictures2 Learning Goals How do you create a range of values? What is a two-dimensional array? How do you loop through a two-dimensional array? –Nested loops How do you simplify a hard problem? How do you copy one picture to another? How do you make a general function?

3. Try the following in JES >>> print range (0, 3) >>> print range (5, 7) >>> print range (0,10) >>> print range (3,1) What do you think the range function does?

4. Creating ranges of values You can create a range of values in python >>> print range (0,3) [0, 1, 2] >>> print range (0,10) [0, 1, 2, 3, 4, 5, 6, 7, 8, 9] >>> print range (3,1) [] [0,1,2] is an array of values [] is an array with no values

5. Pictures are really two dimensional Pictures have a width and a height –getWidth(picture) –getHeight(picture) You can access a pixel of a picture by using the x and y values for the pixel –pixel = getPixel(picture, x, y)

6. Working with part of a picture What if you want to only modify part of a picture? –Not every pixel in the picture You need to be able to say where you want to start and stop –Using ranges for x in range(0, getWidth(picture)): for y in range(0, getHeight(picture) / 2): pixel=getPixel(picture, x, y)

7. Challenge Create a version of decrease red that only changes the red in the top half of the picture

8. Mirroring a Picture If you put a vertical mirror in the middle of a picture and looked in the mirror you would see something strange

9. Mirroring from left to right

10. What is the Vertical Mirror for this? Try the solve the problem for small samples If you can’t solve it on a small sample –You can’t write a program to solve it 123 456 789 012 0 1 2 012 0 1 2

11. Mirror Vertical Algorithm Loop through all the rows (y starts at 0 and is less than the picture height) –Loop with x starting at 0 and x less than the midpoint (mirror point) value Get the left pixel at x and y Get the right pixel at width – 1 - x Set the color for the right pixel to be the color of the left pixel 12345 54321 12345 12321 54345 12321

12. Algorithm to Code def mirrorVertical(source ): mirrorPoint = getWidth(source) / 2 width = getWidth(source) for y in range(0, getHeight(source )): for x in range(0, mirrorPoint ): leftPixel = getPixel(source, x, y) rightPixel = getPixel(source, width - x - 1,y) color = getColor(leftPixel) setColor(rightPixel,color)

13. Challenge – right to left? Copy mirrorVertical and modify it to mirror from right to left instead –What part of the function needs to change? 12345 54321 12345 54345 12321 45345

14. Mirror Horizontal What about mirroring around a mirror held horizontally in the vertical center of the picture? –Like a reflection in a lake?

15. Thinking Through Mirror Horizontal Again think of a number at each x and y location –Instead of a color –And try it with a small sample How can we write a nested for loop to do this? 123 456 789 123 456 123 012 0 1 2 012 0 1 2

16. What is the horizontal mirror of this? Try to solve the problem for several small samples problems See if you can come up with the algorithm to solve it –Test it more small samples 12345 678910 1112131415 01234 0 1 2

17. Mirror Horizontal Algorithm Get the height midpoint –Picture height / 2 Loop through all the x values –Loop from y=0 to y < vertical midpoint Get the top pixel –At x and y Get the bottom pixel –Height - 1 - y Set the bottom pixel’s color to the top pixel color 123 456 789 123 456 123

18. Challenge Write the function to mirror top to bottom Write the function to mirror from bottom to top How about diagonal mirroring? –In just a square section

19. Mirror part of a picture Can we mirror just part of a picture?

20. Mirror part of the temple def mirrorTemple (): source = makePicture(getMediaPath("temple.jpg")) mirrorPoint = 277 for x in range (14, mirrorPoint ): for y in range (28,98): print "Copying color from",x,y,"to",mirrorPoint+mirrorPoint -1-x,y pleft = getPixel(source,x,y) pright = getPixel(source,mirrorPoint+mirrorPoint -1-x,y) setColor(pright,getColor(pleft )) show(source) return source fixedTemple = mirrorTemple()

21. Copying Pixels to a New Picture Need to track the source picture x and y –And the target picture x and y We can use a blank picture –As the target picture Several blank pictures are available –640x480.jpg –7inX95in.jpg 12 34 12 34

22. Copy Picture Algorithm Copy a picture to the 7 by 9.5 inch blank picture –Create the target picture object –Invoke the method on the target picture Create the source picture object Loop through the source picture pixels –Get the source and target pixels –Set the color of the target pixel to the color of the source pixel

23. Copying pixels In general, what we want to do is to keep track of a sourceX and sourceY, and a targetX and targetY. –We increment (add to them) in pairs sourceX and targetX get incremented together sourceY and targetY get incremented together –The tricky parts are: Setting values inside the body of loops Incrementing at the bottom of loops

24. Copy picture code def copyBarb (): # Set up the source and target pictures barbf=getMediaPath("barbara.jpg") barb = makePicture(barbf) canvasf = getMediaPath("7inX95in.jpg") canvas = makePicture(canvasf) # Now, do the actual copying targetX = 0 for sourceX in range(0, getWidth(barb )): targetY = 0 for sourceY in range(0, getHeight(barb )): color = getColor(getPixel(barb,sourceX,sourceY )) setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 show(barb) show(canvas) return canvas

25. Challenge How do we change where we copy the picture to? –Can we start the copy somewhere other than 0,0?

26. Create a Collage

27. Collage Code def createCollage (): flower1=makePicture(getMediaPath("flower1.jpg")) flower2=makePicture(getMediaPath("flower2.jpg")) canvas=makePicture(getMediaPath("640 x480.jpg")) #First picture, at left edge targetX =0 for sourceX in range(0, getWidth(flower1 )): targetY=getHeight(canvas)-getHeight(flower1 )-5 for sourceY in range(0, getHeight(flower1 )): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

28. Collage Code - continued #Second picture, 100 pixels over targetX =100 for sourceX in range(0, getWidth(flower2 )): targetY=getHeight(canvas)-getHeight(flower2 )-5 for sourceY in range(0, getHeight(flower2 )): px=getPixel(flower2,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

29. Collage Code - continued #Third picture, flower1 negated negative(flower1) targetX =200 for sourceX in range(0, getWidth(flower1 )): targetY=getHeight(canvas)-getHeight(flower1 )-5 for sourceY in range(0, getHeight(flower1 )): px=getPixel(flower1,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

30. Collage Code - continued #Fourth picture, flower2 with no blue clearBlue(flower2) targetX =300 for sourceX in range(0, getWidth(flower2 )): targetY=getHeight(canvas)-getHeight(flower2 )-5 for sourceY in range(0, getHeight(flower2 )): px=getPixel(flower2,sourceX,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

31. Collage code - continued #Fifth picture, flower1, negated with decreased red decreaseRed(flower1) targetX =400 for sourceX in range(0, getWidth(flower1 )): targetY=getHeight(canvas)-getHeight(flower1 )-5 for sourceY in range(0, getHeight(flower1 )): px=getPixel(flower1,sourceX,source cx=getPixel(canvas,targetX,target) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 show(canvas) return(canvas)

32. General Copy Function def copy(source, target, targX, targY ): targetX = targX for sourceX in range(0, getWidth(source )): targetY = targY for sourceY in range(0, getHeight(source )): px=getPixel(source,sourceX,sourceY) tx=getPixel(target,targetX,targetY) setColor(tx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1

33. Better Collage Function def createCollage2 (): flower1=makePicture(getMediaPath("flower1.jpg")) flower2=makePicture(getMediaPath("flower2.jpg")) canvas=makePicture(getMediaPath("640 x480.jpg")) h1 = getHeight(flower1) h2 = getHeight(flower2) hc = getHeight(canvas) #First picture, at left edge copy(flower1,canvas,0, hc - h1 – 5) #Second picture, 100 pixels over copy(flower2,canvas,100, hc – h2 – 5)

34. Better Collage - continued #Third picture, flower1 negated negative(flower1) copy(flower1,canvas,200, hc – h1 – 5) #Fourth picture, flower2 with no blue clearBlue(flower2) copy(flower2,canvas,300, hc – h2 – 5) #Fifth picture, flower1, negated with decreased red decreaseRed(flower1) copy(flower1,canvas,400, hc – h1 – 5) return canvas

35. Challenge Create your own collage –Use at least 1 picture –Use at least 3 image filters –Mirror the results

36. Summary You can create ranges of values –range(10) = 0 – 9 –range(0,10) You can loop through a picture –Using x and y ranges You can loop through part of a picture –By starting and ending at different values than normal You can break long methods into shorter parts –Pull out common code and put it in a method