Crafting Artisanal Memes with RMagick

Joking aside, ImageMagick and RMagick give us some pretty powerful tools for adding formatted text to images. Here's a quick example of how to write text with custom per-line formatting.

Formatted Text

Writing text is done via RMagick's Magick::Draw. Let's define a simple format that we can pass around that defines our line format in a way that's easy to serialize and deserialize.

For talking purposes, something like this:

{
  text: 'Lorem Ipsum',      # The text to write
  width: 480,               # The width of our text box
  height: 640,              # The height of our text box
  alignment: 'north'        # Which side of the text box should the text float toward?
  x: 0,                     # Horizontal offset
  y: 0,                     # Vertical offset
  size: 40,                 # Text size
  color: 'white',           # Text color
  outline_color: 'black',   # Text outline color
  font_weight: 'bold',      # Font weight
  font_family: 'Helvetica', # Font
  font_style:  'Normal',    # Font style
  line_spacing: 0           # Spacing adjustment between text lines
}
      

For text box sizing it's often convenient to use the full image dimensions and let alignment handle the rest if you're adding header or footer text.

Obviously that's a lot of formatting options and it would be a pain if we had to specify all of them all the time, so let's make sure we have happy defaults.

Format Wrangler

I've put together a little helper to wrangle the text formatting and add the text to our image. Typically I prefer to wrap RMagick in a helper class with chainable methods, but we'll keep this simple and just make a little helper.

require 'rmagick'

class TextWriter
  class << self
    def write(image, text_lines)
      text_lines.each { |line| write_line(image, line) }
    end

    private

    def write_line(image, line)
      draw = Magick::Draw.new

      text_format(line).each { |key, value| draw.send("#{key}=", value) }

      draw.annotate(image, line.fetch(:width, 0), line.fetch(:height, 0), line[:x], line[:y], text(line))
    end

    def text_format(line)
      {
        interline_spacing: line.fetch(:line_spacing, 0),
        font_family:       line.fetch(:font, 'Helvetica'),
        font_weight:       magick_const(line.fetch(:font_weight, 'normal'), 'Weight'),
        font_style:        magick_const(line.fetch(:font_style, 'normal'), 'Style'),
        pointsize:         line.fetch(:size, 20),
        gravity:           magick_const(line.fetch(:alignment, 'north_west'), 'Gravity'),
        stroke:            line[:outline_color],
        fill:              line[:color]
      }.compact
    end

    def text(line)
      # escape magick characters (https://rmagick.github.io/draw.html#annotate)
      line[:text].gsub('%', '\%')
    end

    def magick_const(weight, category)
      # Use .constantize here if you have ActiveSupport included.
      # Sanitize this if you're taking input from your users!
      Object.const_get("Magick::#{weight.capitalize}#{category}")
    end
  end
end
      

A Simple Example

Let's try doing something basic with that to generate some simple text on an image. This is leaning heavily on our formatting defaults.

require './text_writer'

format = { width: 480, height: 640, x: 0, y: 20 }

img = Magick::Image.read('wizard:').first
TextWriter.write(img, [
  { text: 'I CAN HAZ',   alignment: 'north' }.merge(format),
  { text: 'CHEEZBURGER', alignment: 'south' }.merge(format)
])
img.write('cheezburger_wizard.jpg')
      

Meme Text

Finally, let's lean more heavily on our customizable formatting to appeal to the youths.

require './text_writer'

format = {
  width: 480,
  height: 640,
  x: 0,
  y: 20,
  size: 40,
  color: 'white',
  outline_color: 'black',
  font_weight: 'bold'
}

img = Magick::Image.read('wizard:').first
TextWriter.write(img, [
  { text: 'I CAN HAZ',   alignment: 'north' }.merge(format),
  { text: 'CHEEZBURGER', alignment: 'south' }.merge(format)
])
img.write('cheezburger_wizard.jpg')