Scale an image

#scale down a picture by half in each dimension. Error is at bottom of page

def scaleDown(src, dest) :
  skipRow = "false"
  skipCol = "false"
  destX = 1
  for srcX in range(1, getWidth(src)) :
    if skipRow == "true" :
      skipRow = "false"
    else :
      skipRow = "true"
      destY = 1 #checking coordinate (1, 1) at the start, then scanning all y in x, then checking next column
      for srcY in range(1, getHeight(src)) :
        if skipCol == "true" :
          skipCol = "false"
        else :
          skipCol = "true"
          srcPixel = getPixel(src, srcX, srcY)
          destPixel = getPixel(dest, destX, destY)
          setColor(destPixel, getColor(srcPixel))
          destY = destY + 1
      destX = destX + 1

def scaleDownExercise() :
  srcPic = makePicture(pickAFile())
  destWidth = getWidth(srcPic)/2
  destHeight = getHeight(srcPic) /2 #this is where the error is
  destPic = makeEmptyPicture(destWidth, destHeight)

  show(srcPic)
  show(destPic)
  scaleDown(srcPic, destPic)
  repaint(destPic)

#error:
#getPixel(picture,x,y): y (= 450) is less than 0 or bigger than the height (= 449)
#The error was:
#Inappropriate argument value (of correct type).
#An error occurred attempting to pass an argument to a function.
#Please check line 19 of C:\Users\Matt\Desktop\Test Python\test3.py