Finishing up enlarging pictures

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Session 14

• Finishing up enlarging pictures
• Removing Red-Eye

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Review Scaling Up
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• Copy each pixel in the source multiple times to
  the target
• Source (0,0) Target (0,0)
• Source (0,0) Target(1,0)
• Source (1,0) Target(2,0)
• Source (1,0) Target(3,0)
• Source (2,0) Target(4,0)
• Source (2,0) Target(5,0)
• Source (0,0) Target(0,1)
• Source (0,0) Target(1,1)

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Another way to Scale Up
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• Copy each pixel in the source only once.

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Another way to Scale Up
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• Copy each pixel in the source only once.
• For the remaining empty pixels, insert the
  average of the two neighbor pixels.

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Remove Red Eye

• Red eye is when the flash from the camera is
  reflected from the subjects eyes
• We want to change the red color in the eyes to
  another color

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Red Eye Algorithm

• Use the explorer to find the RGB values of the
  red eyes
• For every pixel in the Picture find the distance
  between the current color and our definition of
  red
• And change the color of the current pixel only if
  the current color is within some distance to the
  desired color
• Wait, we need to know TWO new things in order to
  do this!

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New thing 1 Conditional Execution

• Sometimes we want a statement or block of
  statements executed only if some expression is
  true
• We can use the if statement in Python
• if (colorDistance lt value)
• Statement 1
• Statement 2, etc
• next statement

false
if (expression)
true
Statement or block
statement
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New thing 2 Color Distance

• The distance between two points is computed as
• Square root of (( x1 x2)2 (y1 y2)2)
• The distance between two colors can be computed
• Square root of ((red1 red2)2 (green1-green2)2
  (blue1 blue2)2)
• There is a method in the Pixel class to do this
• dist distance(color1,color2)

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removeRedEye() method

• def removeRedEye(picture)
• redEye makeColor(155,25,35)
• for pix in getPixels(picture)
• if (distance(redEye,getColor(pix)) lt 50)
• setColor(pix,black)

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Oops, MOSTLY got rid of the red eye but also
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Detailed Red Eye Algorithm

• Loop over a subset of the pixels
• Requires we give it starting and ending points
  for both x and y
• This allows us to leave the shirt alone while
  also using a wider distance for redEye

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Remove Red Eye Method

• def specificRemoveRedEye(pic,startX,startY,endX,en
  dY)
• redEye makeColor(155,25,35)
• for x in range(startX,endX1)
• for y in range(startY,endY1)
• pixel getPixel(pict,x,y)
• if (distance(redEye,getColor(pixel)) lt
  75)
• setColor(pixel,black)

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If we still have time

• What would we do to take a picture to true Black
  and White??