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]]

• Rotem: Very relevant: blog.ostermiller.org/dilate-and-erode
• Murtuza Ali Khan Mohammed: The best way is to use SVG when dealing with image blur or zooming issues.

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]]>