Chapter 6: Modifying Pixels by Position

There are four conditional statements in this program for turning the red flowers in the arch into moon-colored flowers.

One of the generated this image. Which one?

Pixels are in a matrixMatrices have two dimensions: A height and

a widthWe can reference any element in the matrix

with (x,y) or (horizontal, vertical)We refer to those coordinates as index

numbers or indicesWe sometimes want to know where a pixel is,

and getPixels doesn't let us know that.

Pixels in a Matrix

>>> h = makePicture("horse.jpg")>>> print getHeight(h)640>>> print getWidth(h)480>>> print getPixel(h,0,0)Pixel red=62 green=78 blue=49>>> print getPixel(h,479,639)Pixel red=113 green=89 blue=77>>> print getPixel(h,480,640)getPixel(picture,x,y): x (= 480) is less than 0 or bigger than the width (= 479)The error was:Inappropriate argument value (of correct type).An error occurred attempting to pass an argument to a function.

Indices from the function rangeRange returns a sequence between its first

two inputs, possibly using a third input as the increment

>>> print range(1,4)[1, 2, 3]>>> print range(-1,3)[-1, 0, 1, 2]>>> print range(1,10,2)[1, 3, 5, 7, 9]>>> print range(3)[0,1,2]

Notice:• End value is never included.• range(0,10) ends at 9.

• If you leave out a start value, it's assumed to be zero.

Side Note:That thing in [] is a sequence>>> a=[1,2,3]>>> print a[1, 2, 3]>>> a = a + 4An attempt was made to call a function with a parameter of an invalid type>>> a = a + [4]>>> print a[1, 2, 3, 4]>>> a[0]1

We can assign names to sequences, print them, add items to sequences, and access individual pieces of them.

We can also use for loops to process each element of a sequence.

We can use range to generate index numbersWe'll do this by working the range from 0 to the height-1, and 0 to the width-1.Using the range function will make it easy to

start from 0 and stop before the end value.But we'll need more than one loop.

Each for loop can only change one variable,and we need two for indexing a matrix

Working the pixels by numberTo use range, we'll have to use nested loops

One to walk the width, the other to walk the height Be sure to watch your blocks (i.e., indentation) carefully!

def increaseRed2(picture): for x in range(0,getWidth(picture)): for y in range(0,getHeight(picture)): px = getPixel(picture,x,y) value = getRed(px) setRed(px,value*1.1)

The first time through the first loop, x is the name for 0.

We'll be processing the first column of pixels in the picture.

Next, we set y to 0. We're now going to process each of the pixels in the first column.

With x = 0 and y = 0, we get the leftmost pixel and increase its red by 10%

Next we set y to 1 (next value in the sequence range(0,getHeight(picture))

x is still 0, and now y is 1, so increase the red for pixel (0,1)

We continue along this way, with y taking on every value from 0 to the height of the picture (minus 1).

Now that we're done with the loop for y, we get back to the FOR loop for x.x takes on the value 1, and we go back to the y loop to process all the pixels in the column x=1.

Lightening a Picture with Nested Loopsdef lighten2(picture): for x in range(0,getWidth(picture)): for y in range(0,getHeight(picture)): px = getPixel(picture,x,y) color = getColor(px) color = makeLighter(color) setColor(px,color)

Which function did A?

Reducing Red Eye with Nested Loopsdef removeRedEye2(pic,sX,sY,eX,eY,endColor): for x in range(sX,eX): for y in range(sY,eY): px = getPixel(pic,x,y) if (distance(red,getColor(px)) < 165): setColor(px,endColor)

This version is far faster than the previous version

Timingfrom time import clock

def yellowbox1(pict): start = clock() for px in getPixels(pict): x = getX(px) y = getY(px) if 10 <= x < 20 and 10 <= y < 20: setColor(px,yellow) print "Time:",clock()-start

def yellowbox2(pict): start = clock() for x in range(10,20): for y in range(10,20): setColor(getPixel(pict,x,y),yellow) print "Time:",clock()-start

>>> b = makePicture("bridge.jpg")>>> bPicture, filename /Users/guzdial/Desktop/mediasources-4ed/bridge.jpg height 640 width 480>>> yellowbox1(b)Time: 1.317775>>> yellowbox2(b)Time: 0.00316000000001

What can you do if you know where the pixels are? One answer: MirroringImagine a mirror horizontally across the

picture,or vertically

What would we see?How do generate that digitally?

We simply copy the colors of pixels from one place to another

Work it out with matricesmirrorPoint is halfway across: getWidth(picture)/2

If left pixel is at (x,y), right pixel is at (width-x-1,y)

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)

def mirrorHorizontal(source): mirrorPoint = getHeight(source) / 2 height = getHeight(source) for x in range(0,getWidth(source)): for y in range(0,mirrorPoint): topPixel = getPixel(source,x,y) bottomPixel = getPixel(source,x,height - y - 1) color = getColor(topPixel) setColor(bottomPixel,color)

Of course!

What if we wanted to copy bottom to top?Very simple: Swap the order of pixels in the

bottom linesdef mirrorBotTop(source): mirrorPoint = getHeight(source) / 2 height = getHeight(source) for x in range(0,getWidth(source)): for y in range(0,mirrorPoint): topPixel = getPixel(source,x,y) bottomPixel = getPixel(source,x,height - y - 1) color = getColor(bottomPixel) setColor(topPixel,color)

Mirroring bottom to top

Doing something useful with mirroringMirroring can be used

to create interesting effects, but it can also be used to create realistic effects.

Consider this image from a trip to Athens, Greece.Can we “repair” the temple

by mirroring the complete part onto the broken part?

Figuring out where to mirrorUse MediaTools to find the mirror point and

the range that we want to copy

Writing functions for specific files…generallyThe function to mirror the temple needs

to work for one and only one file.But we still don't want to write out the

whole path.setMediaPath() allows us to pick a directory where our

media will be stored.getMediaPath(filename) will generate the entire path for

us to the filename in the media directoryTHIS ONLY WORKS WHEN WE'RE ACCESSING FILES

IN THE MEDIA DIRECTORY AND WHERE WE HAVE SET THE PATH FIRST!

Some Utility FunctionsIf you know the name of the file, searching

for it with pickAFile() feels tediousYou 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 foldergetMediaPath(basefilename) lets you

generate a complete filename out of only the last part

Example>>> setMediaPath()New media folder: C:\Documents and Settings\Mark Guzdial\My Documents\mediasources\>>> getMediaPath("barbara.jpg")'C:\\Documents and Settings\\Mark Guzdial\\My Documents\\mediasources\\barbara.jpg'>>> barb=makePicture(getMediaPath("barbara.jpg"))

Program to mirror the templedef mirrorTemple(): source = makePicture(getMediaPath("temple.jpg")) mirrorPoint = 276 for x in range(13,mirrorPoint): for y in range(27,97): pleft = getPixel(source,x,y) pright = getPixel(source,mirrorPoint + mirrorPoint - 1 -

x,y) setColor(pright,getColor(pleft)) show(source) return source

Did it really work?It clearly did the

mirroring, but that doesn't create a 100% realistic image.

Check out the shadows: Which direction is the sun coming from?

Understanding the Temple FixWhat is the very first transfer of pixels from

and to? Which (x,y) pixel from? Which (x,y) pixel to?

What is second?How many pixels get copied?

Adding print statements to see what's happeningdef mirrorTemple(): source = makePicture(getMediaPath("temple.jpg")) mirrorPoint = 276 for x in range(13,mirrorPoint): for y in range(27,97): 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

First pixels are either side of the mirrorpoint, then moving down>>>

p2=mirrorTemple()Copying color from

13 27 to 538 27Copying color from

13 28 to 538 28Copying color from

13 29 to 538 29

Counting pixelsdef mirrorTemple(): source = makePicture(getMediaPath("temple.jpg")) mirrorPoint = 276 count = 0 for x in range(13,mirrorPoint): for y in range(27,97): pleft = getPixel(source,x,y) pright = getPixel(source,mirrorPoint + mirrorPoint - 1 - x,y) setColor(pright,getColor(pleft)) count = count + 1 show(source) print "We copied",count,"pixels" return source

Counting pixels

Where did that come from?How many rows? Y goes from 27 to 97

= 70 rows of pixelsHow many columns? X goes from 13 to 276

= 263 columns of pixels70 * 263 = 18410

>>> p2=mirrorTemple()We copied 18410 pixels

Which function did A?

The same function below did the two pictures, but with one line difference. Which one did which picture?

Replacing colorsin a range

def turnRedInRange(): brown = makeColor(57,16,8) file=“/Users/guzdial/mediasources/barbara.jpg" picture=makePicture(file) for x in range(70,168): for y in range(56,190): px=getPixel(picture,x,y) color = getColor(px) if distance(color,brown)<50.0: redness=getRed(px)*1.5 setRed(px,redness) show(picture) return(picture)

Get the range using MediaTools

Walking this codeLike last time: Don't need input, same color

we want to change, same file, make a picture

def turnRedInRange(): brown = makeColor(57,16,8) file=“/Users/guzdial/mediasources/barbara.jpg" picture=makePicture(file) for x in range(70,168): for y in range(56,190): px=getPixel(picture,x,y) color = getColor(px) if distance(color,brown)<50.0: redness=getRed(px)*1.5 setRed(px,redness) show(picture) return(picture)

The nested loopI used MediaTools to find the rectangle where

most of the hair is that I want to change

def turnRedInRange(): brown = makeColor(57,16,8) file=“/Users/guzdial/mediasources/barbara.jpg“ picture=makePicture(file)

for x in range(70,168): for y in range(56,190): px=getPixel(picture,x,y) color = getColor(px) if distance(color,brown)<50.0: redness=getRed(px)*1.5 setRed(px,redness) show(picture) return(picture)

Same thing as last time (could raise threshold now)Then we're looking for a close-match on

hair color, and increasing the redness

def turnRedInRange(): brown = makeColor(57,16,8) file=“/Users/guzdial/mediasources/barbara.jpg“ picture=makePicture(file) for x in range(70,168): for y in range(56,190):

px=getPixel(picture,x,y) color = getColor(px) if distance(color,brown)<50.0: redness=getRed(px)*1.5 setRed(px,redness) show(picture) return(picture)

Could we do this without nested loops?Yes, but

complicated IF

def turnRedInRange2(): brown = makeColor(57,16,8) file=“/Users/guzdial/mediasources/barbara.jpg“ picture=makePicture(file) for p in getPixels(picture): x = getX(p) y = getY(p) if x >= 70 and x < 168: if y >=56 and y < 190: color = getColor(p) if distance(color,brown)<100.0: redness=getRed(p)*2.0 setRed(p,redness) show(picture) return picture

Moving pixels across picturesWe've seen using index variables to track the

pixel position we're working with in a picture.We can copy between pictures, if we keep

track of: The source index variables

Where we're getting the pixels from The target index variables

Where we're putting the pixels at(Not really copying the pixels: Replicating

their color.)

What can you do then?What can you do when copying from one

picture to another?Collages: Copy several pictures onto

oneCropping: You don't have to take the

whole pictureScaling: Make a picture smaller, or

larger when copying it

Copying pixelsIn 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

Copying Barb to a canvasdef 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

CommentsPython ignores from “# ” through the rest of

the lineIf you start a line with “# ”, the whole line is

ignoredWhy do we want lines to be ignored?

To be able to leave notes to ourselves or someone else about how the program works

Walking through the copying functionFirst, get the source (barb) and target

(canvas) files and pictures as names we can use later.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

We get the color of the pixel at sourceX and sourceY

We set (copy) the color to the pixel in the target picture at targetX and targetY

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

Setting up the copy looptargetX gets set to 0

at the beginningsourceX will range

across the width of the source picture

INSIDE the loop, we set targetY to 0 Inside because we want

it to start at 0 each time we do a new X

sourceY will range from 0 to one less height of source

Just before we end the sourceY loop, we increment targetY It's now set up for the

next time through the loop

It's set correctly for the next value of sourceY

Just before we end the sourceX loop, we increment the targetX Note carefully the

indentation to figure out which goes with which loop

What's this naming something as itself?targetX = targetX + 1This isn't really naming something as itself

targetX + 1 is evaluated It will result in the number after targetX

targetX = then sets the value of targetXThe result is that targetX gets incremented

At the very end, we show the source and target

And return the modified target.

Works either waydef copyBarb2(): # 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 sourceX = 0 for targetX in range(0,getWidth(barb)): sourceY = 0 for targetY in range(0,getHeight(barb)): color =

getColor(getPixel(barb,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY),

color) sourceY = sourceY + 1 sourceX = sourceX + 1 show(barb) show(canvas) return canvas

As long as we increment sourceX and targetX together, and sourceY and targetY together, it doesn't matter which is in the for loop and which is incremented via expression

Copying into the middle of the canvasdef copyBarbMidway(): # 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 = 100 for sourceX in range(0,getWidth(barb)): targetY = 100 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

Copying a Horse to a Canvasdef copyHorse(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying targetX = 0 for sourceX in range(0,getWidth(src)): targetY = 0 for sourceY in range(0,getHeight(src)): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 show(src) show(canvas) return canvas

Copying another waydef copyHorse2(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying sourceX = 0 for targetX in range(0,getWidth(src)): sourceY = 0 for targetY in range(0,getHeight(src)): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 1 sourceX = sourceX + 1 show(src) show(canvas) return canvas

Copying to a new Locationdef copyHorseMidway(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying targetX = 100 for sourceX in range(0,getWidth(src)): targetY = 200 for sourceY in range(0,getHeight(src)): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 show(src) show(canvas) return canvas

Cropping just the Facedef copyHorseFace(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying targetX = 100 for sourceX in range(104,267): targetY = 200 for sourceY in range(114,422): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 #show(src) show(canvas) return canvas

Same cropping, different loopsdef copyHorseFace2(): # Set up the source and target pictures src=makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying sourceX = 104 for targetX in range(100,100+163): sourceY = 114 for targetY in range(200,200+308): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 1 sourceX = sourceX + 1 show(canvas) return canvas

Copying: How it worksHere's the initial

setup:

Copying: How it works 2After incrementing

the sourceY and targetY once (whether in the for or via expression):

Copying: How it works 3After yet another

increment of sourceY and targetY:

When we finish that column, we increment sourceX and targetX, and start on the next column.

Copying: How it looks at the endEventually, we copy

every pixel

Making a collageCould 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!

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=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 #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

#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 #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 #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,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 show(canvas) return(canvas)

171 (4ed edition)

Can we make that easier?The collage code is

long, yet simple.It's the same thing

over-and-over.We can generalize

that copying loop, and with parameters, use it in many places.

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

Exact same collage!def createCollage2():

flower1=makePicture(getMediaPath("flower1.jpg"))

print flower1

print flower2

canvas=makePicture(getMediaPath("640x480.jpg"))

print canvas #First picture, at left edge

copy(flower1,canvas,0,getHeight(canvas)-getHeight(flower1)-5)

#Second picture, 100 pixels over

#Third picture, flower1 negated negative(flower1)

#Fourth picture, flower2 with no blue clearBlue(flower2)

#Fifth picture, flower1, negated with decreased red

decreaseRed(flower1)

return canvas

Bigger or Smaller?

Does this function make the src bigger or smaller on the canvas?

1.Increases size by 50%

2.Decreases size by 50%

3.Decreases size by 50% and skips some pixels in target

4.Increases size by 50% and skips some pixels in target

>>> c = makePicture("caterpillar.jpg")>>> copyPicDifferent(c,c1,10,10)>>> explore(c1)>>> copyAnyPic(c,c1,10,10)>>> explore(c1)

Transformation = Small changes in copyingMaking relatively small changes in this basic

copying program can make a variety of transformations.Change the targetX and targetY, and you copy

wherever you wantCropping: Change the sourceX and sourceY

range, and you copy only part of the program.Rotating: Swap targetX and targetY, and you

end up copying sidewaysScaling: Change the increment on sourceX and

sourceY, and you either grow or shrink the image.

Copying face to small canvasdef copyHorseFaceSmall(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(163,308) # Now, do the actual copying targetX = 0 for sourceX in range(104,267): targetY = 0 for sourceY in range(114,422): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 show(canvas) return canvas

Changing while copyingdef copyHorseFaceSmallBlack(): hcol = makeColor(216,169,143) # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(163,308) # Now, do the actual copying targetX = 0 for sourceX in range(104,267): targetY = 0 for sourceY in range(114,422): color = getColor(getPixel(src,sourceX,sourceY)) if distance(color,hcol) < 40: setColor(getPixel(canvas,targetX,targetY), black) else: setColor(getPixel(canvas,targetX,targetY), color) targetY = targetY + 1 targetX = targetX + 1 show(canvas) return canvas

Copying vs. Referencing>>> a = 100>>> b = a>>> print a,b100 100>>> b = 200>>> print a,b100 200>>> a = 300>>> print a,b300 200

Referencing works differently>>> pictureBarb = makePicture("barbara.jpg")>>> pixel1 = getPixelAt(pictureBarb,0,0)>>> print pixel1Pixel red=168 green=131 blue=105>>> anotherpixel = pixel1>>> print anotherpixelPixel red=168 green=131 blue=105>>> setColor(pixel1,black)>>> print pixel1Pixel red=0 green=0 blue=0>>> print anotherpixelPixel red=0 green=0 blue=0

Making a collageCould 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!

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=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 #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

#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 #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 #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,sourceY) cx=getPixel(canvas,targetX,targetY) setColor(cx,getColor(px)) targetY=targetY + 1 targetX=targetX + 1 show(canvas) return(canvas)

92 (2ed edition)

Can we make that easier?The collage code is

long, yet simple.It's the same thing

over-and-over.We can generalize

that copying loop, and with parameters, use it in many places.

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

Exact same collage!def createCollage2():

print flower1

print flower2

print canvas #First picture, at left edge

#Second picture, 100 pixels over

#Third picture, flower1 negated negative(flower1)

#Fourth picture, flower2 with no blue clearBlue(flower2)

#Fifth picture, flower1, negated with decreased red

decreaseRed(flower1)

return canvas

Rotating the copydef flipHorseSideways(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying targetX = 0 for sourceX in range(0,getWidth(src)): targetY = 0 for sourceY in range(0,getHeight(src)): color = getColor(getPixel(src,sourceX,sourceY)) # Change is here setColor(getPixel(canvas,targetY,targetX), color) targetY = targetY + 1 targetX = targetX + 1 show(canvas) return canvas

Rotating: How it worksWe increment the

same, but we use targetX for the Y coordinate and targetY for the X coordinate

Rotate: How it endsSame amount of

increment, even same values in the variables, but a different result.

Doing a real rotation

def rotateHorseSideways(): # Set up the source and target pictures src = makePicture("horse.jpg") canvas = makeEmptyPicture(1000,1000) # Now, do the actual copying targetX = 0 width = getWidth(src) for sourceX in range(0,getWidth(src)): targetY = 0 for sourceY in range(0,getHeight(src)): color =

getColor(getPixel(src,sourceX,sourceY)) # Change is here setColor(getPixel(canvas,targetY,width -

targetX - 1), color) targetY = targetY + 1 targetX = targetX + 1 show(canvas) return canvas

ScalingScaling a picture (smaller or larger) has to do

with sampling the source picture differentlyWhen we just copy, we sample every pixelIf we want a smaller copy, we skip some pixels

We sample fewer pixelsIf we want a larger copy, we duplicate some

pixels We over-sample some pixels

Scaling the horse face downdef copyHorseFaceSmaller(): # Set up the source and target pictures src=makePicture("horse.jpg") canvas = makeEmptyPicture(82,155) # Now, do the actual copying sourceX = 104 for targetX in range(0,int(163/2)): sourceY = 114 for targetY in range(0,int(308/2)): color = getColor(getPixel(src,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 2 sourceX = sourceX + 2 show(canvas) return canvas

Scaling the picture downdef copyBarbsFaceSmaller(): # 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 sourceX = 45 for targetX in range(100,100+((200-45)/2)): sourceY = 25 for targetY in range(100,100+((200-25)/2)): color = getColor(getPixel(barb,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 2 sourceX = sourceX + 2 show(barb) show(canvas) return canvas

Scaling Up: Growing the pictureTo grow a picture, we

simply duplicate some pixels

We do this by incrementing by 0.5, but only use the integer part.

>>> print int(1)1>>> print int(1.5)1>>> print int(2)2>>> print int(2.5)2

Scaling up

def copyHorseLarger(): # Set up the source and target pictures src = makePicture("horse.jpg") w = getWidth(src) h = getHeight(src) canvas = makeEmptyPicture(w*2,h*2) srcPixels = getPixels(src) trgPixels = getPixels(canvas) trgIndex = 0 # Now, do the actual copying for pixel in srcPixels: color = getColor(pixel) # Once trgPixel = trgPixels[trgIndex] setColor(trgPixel,color) trgIndex = trgIndex + 1 # Twice trgPixel = trgPixels[trgIndex] setColor(trgPixel,color) trgIndex = trgIndex + 1 show(canvas) return canvas

Scaling up just the Facedef copyHorseFaceLarger(): # Set up the source and target pictures src=makePicture("horse.jpg") canvas = makeEmptyPicture(163*2,308*2) # Now, do the actual copying sourceX = 104 for targetX in range(0,163*2): sourceY = 114 for targetY in range(0,308*2): srcpx = getPixel(src,int(sourceX),int(sourceY)) color = getColor(srcpx) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 0.5 sourceX = sourceX + 0.5 show(canvas) return canvas

Scaling the picture updef copyBarbsFaceLarger(): # 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 sourceX = 45 for targetX in range(100,100+((200-45)*2)): sourceY = 25 for targetY in range(100,100+((200-25)*2)): color = getColor(getPixel(barb,int(sourceX),int(sourceY))) setColor(getPixel(canvas,targetX,targetY), color) sourceY = sourceY + 0.5 sourceX = sourceX + 0.5 show(barb) show(canvas) return canvas

Scaling up: How it worksSame basic setup as

copying and rotating:

Scaling up: How it works 2But as we increment

by only 0.5, and we use the int() function, we end up taking every pixel twice.

Here, the blank pixel at (0,0) in the source gets copied twice onto the canvas.

Scaling up: How it works 3Black pixels gets

copied once…

Scaling up: How it works 4And twice…

Scaling up: How it ends upWe end up in the

same place in the source, but twice as much in the target.

Notice the degradation: Gaps that weren't there

previously Curves would get “choppy”:

Pixelated

What to do?How do we clear up the degradation of

scaling up?Variety of techniques, but mostly following

the same basic idea:Use the pixels around to figure out what color

a new pixel should be, then somehow (e.g., by averaging) compute the right color.

Different techniques look at different pixels and compute different averages in different ways.

A simple Blurdef blur(source): target=duplicatePicture(source) for x in range(1, getWidth(source)-1): for y in range(1, getHeight(source)-1): top = getPixel(source,x,y-1) left = getPixel(source,x-1,y) bottom = getPixel(source,x,y+1) right = getPixel(source,x+1,y) center = getPixel(target,x,y) newRed=(getRed(top)+ getRed(left) + getRed(bottom) + getRed(right) + getRed(center))/5 newGreen=(getGreen(top) + getGreen(left) + getGreen(bottom)+getGreen(right)+getGreen(center))/5 newBlue=(getBlue(top) + getBlue(left) + getBlue(bottom) + getBlue(right)+ getBlue(center))/5 setColor(center, makeColor(newRed, newGreen, newBlue))

A different blurdef blur(pic,size): for pixel in getPixels(pic): currentX = getX(pixel) currentY = getY(pixel) r = 0 g = 0 b = 0 count = 0 for x in range(currentX - size,currentX + size): for y in range(currentY - size, currentY + size): if(x<0) or (y<0) or (x >= getWidth(pic)) or (y

>=getHeight(pic)): pass # Skip if we go off the edge else: r = r + getRed(getPixel(pic,x,y)) g = g + getGreen(getPixel(pic,x,y)) b = b + getBlue(getPixel(pic,x,y)) count = count + 1 newColor = makeColor(r/count,g/count,b/count) setColor(pixel,newColor)

We'll see pass and else later, but you can probably get a sense here of what's going on.

Blurring out the pixelation

Average from four sides, to compute new color

Things to try:Can you come up with general copy, rotate,

copy, and scale functions?Take input pictures and parametersReturn the canvas the correct transformation

appliedAlso think about generalizing the

transformations:Scaling up and down by non-integer amountsRotating by something other than 90 degree

increments

Blending picturesHow do we get part of one picture and part of

another to blur together, so that we see some of each?It's about making one a bit “transparent.”Video cards sometimes support this transparency

in hardware, called an alpha level to each pixel.We do it as a weighted sum

If it's 50-50, we take 50% of red of picture1's pixels + 50% of red of picture2's pixels, and so on for green and blue, across all overlapping pixels.

Example blended picture

Blended here

Blending code (1 of 3)def blendPictures(): barb = makePicture(getMediaPath("barbara.jpg")) katie = makePicture(getMediaPath("Katie-smaller.jpg")) canvas = makePicture(getMediaPath("640x480.jpg")) #Copy first 150 columns of Barb sourceX=0 for targetX in range(0,150): sourceY=0 for targetY in range(0,getHeight(barb)): color = getColor(getPixel(barb,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY),color) sourceY = sourceY + 1 sourceX = sourceX + 1

Straightforward copy of 150 column's of Barb's picture

Blending code (2 of 3) #Now, grab the rest of Barb and part of Katie # at 50% Barb and 50% Katie overlap = getWidth(barb)-150 sourceX=0 for targetX in range(150,getWidth(barb)): sourceY=0 for targetY in range(0,getHeight(katie)): bPixel = getPixel(barb,sourceX+150,sourceY) kPixel = getPixel(katie,sourceX,sourceY) newRed= 0.50*getRed(bPixel)

+0.50*getRed(kPixel) newGreen=0.50*getGreen(bPixel)

+0.50*getGreen(kPixel) newBlue = 0.50*getBlue(bPixel)

+0.50*getBlue(kPixel) color = makeColor(newRed,newGreen,newBlue) setColor(getPixel(canvas,targetX,targetY),color) sourceY = sourceY + 1 sourceX = sourceX + 1

Here's the trick. For each pixel, grab 50% of each red, green and blue

Blending code (3 of 3) # Last columns of Katie sourceX=overlap for targetX in

range(150+overlap,150+getWidth(katie)): sourceY=0 for targetY in range(0,getHeight(katie)): color = getColor(getPixel(katie,sourceX,sourceY)) setColor(getPixel(canvas,targetX,targetY),color) sourceY = sourceY + 1 sourceX = sourceX + 1 show(canvas) return canvas

Drawing lines on Carolina

def lineExample(): img = makePicture(pickAFile()) verticalLines(img) horizontalLines(img) show(img) return img def horizontalLines(src): for x in range(0,getHeight(src),5): for y in range(0,getWidth(src)):

setColor(getPixel(src,y,x),black) def verticalLines(src): for x in range(0,getWidth(src),5): for y in range(0,getHeight(src)):

setColor(getPixel(src,x,y),black) We can use the color name “black” – it's pre-defined for us.

Yes, some colors are already definedColors defined for you already: black, white,

blue, red, green, gray, lightGray, darkGray, yellow, orange, pink, magenta, and cyan

That's tediousThat's slow and tedious to set every pixel you

want to make lines and text, etc.What you really want to do is to think in

terms of your desired effect (think about “requirements” and “design”)

New functionsaddText(pict,x,y,string) puts the string

starting at position (x,y) in the pictureaddLine(picture,x1,y1,x2,y2) draws a line

from position (x1,y1) to (x2,y2)addRect(pict,x1,y1,w,h) draws a black

rectangle (unfilled) with the upper left hand corner of (x1,y1) and a width of w and height of h

addRectFilled(pict,x1,y1,w,h,color) draws a rectangle filled with the color of your choice with the upper left hand corner of (x1,y1) and a width of w and height of h

The mysterious red box on the beachdef addABox(): beach = makePicture(getMediaPath("beach-

smaller.jpg")) addRectFilled(beach,150,150,50,50,red) show(beach) return beach

Example picturedef littlepicture(): canvas=makePicture(getMediaPath("640x480.jpg")) addText(canvas,10,50,"This is not a picture") addLine(canvas,10,20,300,50) addRectFilled(canvas,0,200,300,500,yellow) addRect(canvas,10,210,290,490) return canvas

A thought experimentLook at that previous page: Which has a

fewer number of bytes?The program that drew the pictureThe pixels in the picture itself.

It's a no-brainerThe program is less than 100 characters (100

bytes)The picture is stored on disk at about 15,000

Vector-based vs. Bitmap Graphical representationsVector-based graphical representations are

basically executable programs that generate the picture on demand.Postscript, Flash, and AutoCAD use vector-

based representationsBitmap graphical representations (like JPEG,

BMP, GIF) store individual pixels or representations of those pixels.JPEG and GIF are actually compressed

representations

Vector-based representations can be smallerVector-based representations can be much

smaller than bit-mapped representationsSmaller means faster transmission (Flash and

Postscript)If you want all the detail of a complex picture,

no, it's not.

But vector-based has more value than that

Imagine that you're editing a picture with lines on it. If you edit a bitmap image and extend a line, it's just more bits.

There's no way to really realize that you've extended or shrunk the line.

If you edit a vector-based image, it's possible to just change the specification Change the numbers saying where the line is Then it really is the same line

That's important when the picture drives the creation of the product, like in automatic cutting machines

How are images compressed?Sometimes lossless using techniques like run

length encoding (RLE)Instead of this:

B B Y Y Y Y Y Y Y Y Y B BWe could say “9 Y's” like this:

B B 9 Y B BLossy compression (like JPEG and GIF) loses detail, some

of which is invisible to the eye.

When changing the picture means changing a program…In a vector-based drawing package, changing

the drawing is changing a program.How could we reach in and change the actual

program?We can using string manipulation

The program is just a string of charactersWe want to manipulate those characters, in

order to manipulate the program

Example programmed graphicIf I did this right, we

perceive the left half as lighter than the right half

In reality, the end quarters are actually the same colors.

Building a programmed graphicdef greyEffect(): file = getMediaPath("640x480.jpg") pic = makePicture(file) # First, 100 columns of 100-grey grey = makeColor(100,100,100) for x in range(1,100): for y in range(1,100): setColor(getPixel(pic,x,y),grey) # Second, 100 columns of increasing greyness greyLevel = 100 for x in range(100,200): grey = makeColor(greyLevel, greyLevel, greyLevel) for y in range(1,100): setColor(getPixel(pic,x,y),grey) greyLevel = greyLevel + 1

# Third, 100 colums of increasing greyness, from 0 greyLevel = 0 for x in range(200,300): grey = makeColor(greyLevel, greyLevel, greyLevel) for y in range(1,100): setColor(getPixel(pic,x,y),grey) greyLevel = greyLevel + 1 # Finally, 100 columns of 100-grey grey = makeColor(100,100,100) for x in range(300,400): for y in range(1,100): setColor(getPixel(pic,x,y),grey) return pic

Another Programmed Graphicdef coolpic():

for index in range(25,1,-1): color = makeColor(index*10,index*5,index) addRectFilled(canvas,0,0,index*10,index*10,color) show(canvas) return canvas

And anotherdef coolpic2(): canvas=makePicture(getMediaPath("640x480.jpg")) for index in range(25,1,-1): addRect(canvas,index,index,index*3,index*4)

addRect(canvas,100+index*4,100+index*3,index*8,index*10) show(canvas) return canvas

Why do we write programs?Could we do this in Photoshop? Maybe

I'm sure that you can, but you need to know how.

Could I teach you to do this in Photoshop? MaybeMight take a lot of demonstration

But this program is an exact definition of the process of generating this pictureIt works for anyone who can run the program,

without knowing Photoshop

We write programs to encapsulate and communicate processIf you can do it by hand, do it.If you need to teach someone else to do it,

consider a program.If you need to explain to lots of people how to

do it, definitely use a program.If you want lots of people to do it without

having to teach them something first, definitely use a program.

Chapter 6: Modifying Pixels by Position

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