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Add Text Over an Image with Ruby

11 April 2020

If you want to programatically add a text to an image with Ruby, using RMagick is a simple and quick way to get it done. There is nothing new here, and there are a few articles explaining how to do it already. However when I had to get it to work it for a side project, I ran into some minor issues with the code already published, so I figured I’d share what I did myself!

Installing RMagick and ImageMagick

RMagick uses ImageMagick behind the scene, so you’ll need to install it. When I did it I had some issues with the installation steps provided, especially when it came to generating jpg on MacOS. Using this command instead fixed the problems:

brew install imagemagick --build-from-source

Then you can install bundler and setup your Gemfile:

source 'https://rubygems.org'
gem 'rmagick'

One the file is created, you can run:

gem install bundler
bundle install

…and you should be all set.

Coding

In the same folder, add your source image background.jpg and a new Ruby file image_generation.rb. Now to write the actual code:

require "RMagick"

img = Magick::ImageList.new("background.jpg")

text = Magick::Draw.new
message = "Hello World"

img.annotate(txt, 0,0,0,0, message) do
  text.gravity = Magick::CenterGravity # Text positioning
  text.pointsize = 100 # Font size
  text.fill = "#1c1c1c" # Font color
  text.font = "/absolutepath/Font.ttf" # Font file; needs to be absolute
  img.format = "jpeg"
end

img.write("generated.jpg") # Destination image

To run the script, simply go ruby image_generation.rb  and that should generate a new image, generated.jpg!

Going Further

You can change position by adjusting the gravity and the positioning passed to the annotate method. All the documentation is here.

Gravity with ImageMagick

I tried to keep the example really simple and copy/pastable. If you want to change the text formatting, there are a lot of options available. Just know that in a lot of cases, if you make a mistake, the changes won’t be applied but you will not get any error message. This is especially confusing when you are trying to do some really minor alterations.

You can find the different possibilities in the documentation and play around to get something that looks the way you want.

Read the comments or contribute with your own