Expanding pixels in an image

Question

Custom class Image takes a 2-D array of 0's and 1's upon initialization. Method transform returns a modified array by modifying 0's adjacent to a 1, such that

[[0,0,0],
 [0,1,0],
 [0,0,0]]

returns

[[0,1,0],
 [1,1,1],
 [0,1,0]]

I've been working on method blur(n), which outputs an array that has been transformed n times, such that n=3 changes

[[0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,1,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0],
 [0,0,0,0,0,0,0,0,0]]

into

[[0, 0, 0, 0, 0, 0, 0, 0, 0]
 [0, 0, 0, 0, 1, 0, 0, 0, 0]
 [0, 0, 0, 1, 1, 1, 0, 0, 0]
 [0, 0, 1, 1, 1, 1, 1, 0, 0]
 [0, 1, 1, 1, 1, 1, 1, 1, 0]
 [0, 0, 1, 1, 1, 1, 1, 0, 0]
 [0, 0, 0, 1, 1, 1, 0, 0, 0]
 [0, 0, 0, 0, 1, 0, 0, 0, 0]
 [0, 0, 0, 0, 0, 0, 0, 0, 0]
 [0, 0, 0, 0, 0, 0, 0, 0, 0]
 [0, 0, 0, 0, 0, 0, 0, 0, 0]
 [0, 0, 0, 0, 0, 0, 0, 0, 0]]

Right now my solution to blur(n) works, by first creating a new Image object, transforming and then transforming additional instances of Image an additional (n-1) times. I've been getting errors if I try to apply blur without instantiating a new Image and transforming it — the transform method is not available to class Array. How could I go about applying transform iteratively without having to instantiate Image inside the class?

class Image
  attr_accessor :arr

  def initialize(arr)
    @arr = arr
  end

  def transform 
    cloned = self.arr.map(&:clone)

    #scan original array for 1; map crosses into clone if found
    self.arr.each.with_index do |row, row_index|
      row.each.with_index do |cell, col|
        if cell == 1
          cloned[row_index][col+1] = 1 unless col+1 >= row.length #copy right
          cloned[row_index+1][col] = 1 unless row_index+1 >= cloned.length # copy down
          cloned[row_index][col-1] = 1 unless col.zero? # copy left
          cloned[row_index-1][col] = 1 unless row_index.zero? #copy up
        end
      end
    end
    cloned
  end

  def blur(n) 
    blurred = Image.new(self).arr.transform
    (n-1).times do 
      blurred = Image.new(blurred).transform
    end
    blurred
  end

end

image = Image.new([[0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,1,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0]])

image.blur(3)

#returns...
# [[0, 0, 0, 0, 0, 0, 0, 0, 0], 
#  [0, 0, 0, 0, 1, 0, 0, 0, 0], 
#  [0, 0, 0, 1, 1, 1, 0, 0, 0], 
#  [0, 0, 1, 1, 1, 1, 1, 0, 0], 
#  [0, 1, 1, 1, 1, 1, 1, 1, 0], 
#  [0, 0, 1, 1, 1, 1, 1, 0, 0], 
#  [0, 0, 0, 1, 1, 1, 0, 0, 0], 
#  [0, 0, 0, 0, 1, 0, 0, 0, 0], 
#  [0, 0, 0, 0, 0, 0, 0, 0, 0], 
#  [0, 0, 0, 0, 0, 0, 0, 0, 0], 
#  [0, 0, 0, 0, 0, 0, 0, 0, 0], 
#  [0, 0, 0, 0, 0, 0, 0, 0, 0]]

Answer 1

I assume you are trying to do something like:

def blur(n) 
  blurred = Image.new(self).arr.transform
  (n-1).times do 
    blurred = blurred.transform
  end
  blurred
end

And getting an error like:

`block in blur': undefined method `transform' for #<Array:0x00000002d51ba8>

The reason is that transform is a instance method of Image, which is why you need to convert back into an image before calling it.

There are a couple of way this can be handled. I've chosen to make transform a static method that only works on arrays. The instance methods transform and blur call the static method as needed

class Image
  attr_accessor :arr

  def initialize(arr)
    @arr = arr
  end

  def transform
    result = Image.arr_transform(@arr)
    Image.new(result)
  end

  def self.arr_transform(array) 
    cloned = array.map(&:clone)

    #scan original array for 1; map crosses into clone if found
    array.each.with_index do |row, row_index|
      row.each.with_index do |cell, col|
        if cell == 1
          cloned[row_index][col+1] = 1 unless col+1 >= row.length #copy right
          cloned[row_index+1][col] = 1 unless row_index+1 >= cloned.length # copy down
          cloned[row_index][col-1] = 1 unless col.zero? # copy left
          cloned[row_index-1][col] = 1 unless row_index.zero? #copy up
        end
      end
    end
    cloned
  end

  def blur(n)
    blurred = @arr
    (n).times do 
      blurred = Image.arr_transform(blurred)
    end
    Image.new(blurred)
  end

end

Testing:

image = Image.new([[0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,1,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0],
                   [0,0,0,0,0,0,0,0,0]])

require 'pp'
pp image.blur(3)

Returns:

#<Image:0x00000002e9fb40
 @arr=
  [[0, 0, 0, 0, 0, 0, 0, 0, 0],
   [0, 0, 0, 0, 1, 0, 0, 0, 0],
   [0, 0, 0, 1, 1, 1, 0, 0, 0],
   [0, 0, 1, 1, 1, 1, 1, 0, 0],
   [0, 1, 1, 1, 1, 1, 1, 1, 0],
   [0, 0, 1, 1, 1, 1, 1, 0, 0],
   [0, 0, 0, 1, 1, 1, 0, 0, 0],
   [0, 0, 0, 0, 1, 0, 0, 0, 0],
   [0, 0, 0, 0, 0, 0, 0, 0, 0],
   [0, 0, 0, 0, 0, 0, 0, 0, 0],
   [0, 0, 0, 0, 0, 0, 0, 0, 0],
   [0, 0, 0, 0, 0, 0, 0, 0, 0]]>