Example of complex blur using Image Magick + mini_magick

probabalistic-patterened-blur.rb

# Copyright Ognjen Regoje, 2021
# https://ognjen.io/generating-more-interesting-image-previews-using-imagemagick/
#
####
require 'mini_magick'

INPUT_FILE = "input-1-lg.jpg"

image = MiniMagick::Image.open(INPUT_FILE)
size = image.dimensions.map{|x| x}
height = size[0]
width = size[1]

density = 10

sh = height / density
sw = width / density

fragments = []

hh = height / 2
hw = width / 2

density.times do |w|
  density.times do |h|
    c = rand
    prob = 1 - ((((hw.to_f - (w*sw).to_f).abs / hw.to_f) + (hh.to_f - (h*sh).to_f).abs / hh.to_f) / 2)
    if c < prob
      fragments.push({w: w*sw, h: h*sh})

      convert = MiniMagick::Tool::Convert.new
      convert << INPUT_FILE
      convert.crop("#{sh}x#{sw}+#{h*sh}+#{w*sw}")
      convert.blur("0x200")


      convert.fill("black")
      convert.draw("polygon #{sh/2},#{sw} #{sh},#{sw} #{sh},0") # Use sh/2 instead of just sh so that the "triangle" starts in the middle rather then in the corner to cover more of the image
      convert.fuzz("15%")
      convert.define('png:color-type=6')
      convert.transparent("black")

      convert << "output-crop-with-triangle-#{w*sw}-#{h*sh}.png"
      convert.call

    end
  end
end

image = MiniMagick::Image.open(INPUT_FILE)
fragments.each do |x|
  cropped = MiniMagick::Image.new("output-crop-with-triangle-#{x[:w]}-#{x[:h]}.png")
  result = image.composite(cropped) do |c|
    c.compose "Over"
    c.geometry "+#{x[:h]}+#{x[:w]}"
  end
  result.write "image-previews-output-with-probability-transparent-triangles.jpg"
  File.delete("output-crop-with-triangle-#{x[:w]}-#{x[:h]}.png")
  if fragments.last != x
    image = MiniMagick::Image.open("image-previews-output-with-probability-transparent-triangles.jpg")
  end
end