class ChunkyPNG::Canvas

def replace_canvas!(new_width, new_height, new_pixels)

Replaces the image, given a new width, new height, and a new pixel array. 
def replace_canvas!(new_width, new_height, new_pixels)
  unless new_pixels.length == new_width * new_height
    raise ArgumentError, "The provided pixel array should have #{new_width * new_height} items"
  end
  @width, @height, @pixels = new_width, new_height, new_pixels
  self
end