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lab42
mixing images

TASK SETUP: Find two images that are both 640x480. (You can include "640x480" in the google-images search, or you can crop an larger photo using, say, Windows Photo Manager or OS X's Preview.) Download them to your H: drive, and start a JES program which puts each in a variable.
Use variable-names that describe each picture. Example: kittenz = makePicture( 'H:\\itec109\\frolicking-tiger-cubs.jpg' )

Last time we demo'd mix1, which mixed two pictures together (presuming they are the same size). Here is the code (which happens to use the nested loop we discussed):

# mix1 : Picture, Picture -> Picture
# Return a mixture of p1 and p2 (every other pixel)
# Both pixtures *must* by 640x480.
#      (Challenge: rewrite to allow any-two-same-sizes;
#       add'l challenge: re-write to allow different sizes, clamping the result to the smaller size.)
# 
def mix1( p1, p2 ):
    mixPict = makeEmptyPicture( 640, 480 )
    show(mixPict)
    for rowNum in range( getHeight(p1) ):
        for colNum in range( getWidth(p1) ):
            if atEvenGridPosition(rowNum,colNum):
                sourcePx = getPixelAt(p1,colNum,rowNum)
            else:
                sourcePx = getPixelAt(p2,colNum,rowNum)
            newPx = getPixelAt(mixPict,colNum,rowNum)
            setRed(   newPx, getRed(  sourcePx) )
            setGreen( newPx, getGreen(sourcePx) )
            setBlue(  newPx, getBlue( sourcePx) )
        repaint(mixPict)
    return mixPict


# atEvenGridPosition : int, int -> boolean
# Is location (x,y) at an 'even' grid location 
#  (e.g., a *red* check-square, where the checker-tiles are 1x1 pixel)
#
def atEvenGridPosition(x,y):
  if ((x+y)%2==0):
    return True
  else:
    return False
  # Note: a simpler one-line version: `return (n%2==0)`.

Note the use of the helper function “atEvenGridPosition” — we can design our top-level code, and come back to that.

We'll work together: Make a similar function mix, which is like mix1 except that it makes a checkerboard pattern (bigger than a single-pixel square):
- if our x,y position is exactly on a grid-outline, use black;
- else if we're in an even grid-location (for grid of n x n pixels), use the pixel from the first picture picture
- else use the pixel from the second picture.
Use top-down design to write the above function, inventing helper-functions (“the method of wishful thinking”); then we can go back and complete those helper-functions later; each helper-function will be a smaller/easier problem than the overall task.

Although BMI isn't a great measure of overall health, current standards classify people as "underweight", "normal", "overweight", or "obese" based on various BMI levels.

Write a function which computes somebody's weightStatus, given their weight (in Lbs) and height (in whole-feet, with extra-inches):

# weightStatus : float, float, float -> string
#
def weightStatus( weightLbs, wholeFt, extraIn ):
  return "TODO"
  
  
def test():
  print( "status of a skinny beanpole:"
  print( "actual: " + str(weightStatus(150,6,3)) )
  print( "expect: " + "underweight" )

  print( "status of a normal person:" )
  print( "actual: " + str(weightStatus(150,5,4)) )
  print( "expect: " + "underweight" )

  print( "status of a stout person:" )
  print( "actual: " + str(weightStatus(220,6,6)) )
  print( "expect: " + "underweight" )

  print( "status of the penguin:" )
  print( "actual: " + str(weightStatus(220,3,3)) )
  print( "expect: " + "obese" )

Don't repeat code; we've already written bmi in lab14:

# bmi : float, float, float -> float
#
def bmi( weightLbs, wholeFt, extraIn ):
  kgs = weightLbs / 2.2
  totalInches = 12*wholeFt + extraIn
  heightCm = totalInches * 2.54
  heightM = heightCm / 100
  return kgs / pow(heightM,2)

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©2014, Ian Barland, Radford University
Last modified 2014.Apr.23 (Wed) Please mail any suggestions
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lab42 mixing images

lab42
mixing images