For the Instagram Challenge - Unshredder

unshredder.rb

require 'rmagick'
include Magick

shredded = ImageList.new "TokyoPanoramaShredded.png" # the original source
ROWS = shredded.rows # number of lines of pixes
working = [] # a working array of images

def strip_width
  32
end

# pixel distance is calculated using the Euclidean distance of the 2 pixels
# assuming the RGB is xyz
def dist(p1,p2)
  red, green, blue = p1.red - p2.red, p1.green - p2.green, p1.blue - p2.blue  
  Math.sqrt((red*red) + (green*green) + (blue*blue))
end

# compare pixel distances between the right-most pixel column of shred1 with
# the left-most pixel column  of shred2
def compare_shreds(shred1, shred2)
  distances = []
  ROWS.times do |n| # for every pixel in a narrow strip
    pixel1 = shred1.pixel_color(strip_width-1,n) 
    pixel2 = shred2.pixel_color(0,n)
    distances << dist(pixel1, pixel2)
  end
  distances.inject{|sum,x| sum + x }/ROWS # find the mean
end

# crop individual shreds into a temporary working image list
(shredded.columns/strip_width).times do |n|
  working << shredded.excerpt(n*strip_width,0,strip_width,shredded.rows)
end

sequence = [0] # working sequence, starting at 0 but can start at any number
pic_break = 0 # to store the place where the sequence breaks

# iterate through every shred to find correct sequence
working.size.times do 
  averages = []
  working.size.times do |n| # compare this shred with every other shred
    averages << compare_shreds(working[sequence.last], working[n])
  end
  # the next shred should be the one with the left-most pixel column the 
  # closest pixel distance from the right-most pixel column of the current shred
  next_number = averages.index(averages.min) 
  if next_number == sequence.last # if the next shred is the same as this shred
    pic_break = sequence.count # this is where the image break is
    sequence << averages.find_index(averages.sort[1]) # use the next closest
  else
    sequence << next_number
  end
end
final_sequence = sequence[pic_break..sequence.count] + sequence[1..pic_break-1]
final_imagelist = ImageList.new
final_sequence.each do |seq|
  final_imagelist << working[seq]
end

final_imagelist.append(false).display # display the image