Adding text to pictures with Rmagick and Rails.

Recently I needed to add some dynamically generated text to an image with Ruby on Rails. For some reason there do not seem to be many tutorials on how to work with RMagick so I thought I would share what little I now about it. Originally I looked at Image Science but it turns out that its very focused on simply resizing images. So for this I turned to RMagick. I was a little worried that the installation would be nightmarish but it turned out to be quite painless (at least on Ubuntu. I can’t imagine what it would be like on Windows. Probably bad.):

mike@sleepycat:~$ sudo aptitude install imagemagick librmagick-ruby libmagickwand-dev

Then install the gem:

mike@sleepycat:~$ sudo gem install rmagick

RMagick is a complex library that has tonnes of graphics functions and can transform images in many different ways.
It seems that RMagick works conceptually the same for both Vector graphics and bitmap images: create an image and add text objects to it or create a canvas and add vector objects to it (using Ruby Vector Graphics aka:RVG). So lets do that. So here is an image to start with:

To start playing with RMagick, you can stick this in one of your controllers:

require ‘RMagick’
include Magick

def lolcat

img = ImageList.new(‘public/computer-cat.jpg’)
txt = Draw.new

img.annotate(txt, 0,0,0,0, “In ur Railz, annotatin ur picz.”){
txt.gravity = Magick::SouthGravity
txt.pointsize = 25
txt.stroke = ‘#000000’
txt.fill = ‘#ffffff’
txt.font_weight = Magick::BoldWeight
}

img.format = ‘jpeg’
send_data img.to_blob, :stream => ‘false’, :filename => ‘test.jpg’, :type => ‘image/jpeg’, :disposition => ‘inline’

end

And here is the output of that script:

Although sticking that in a controller is a quick way to see the results of some tinkering and experimentation, this is the kind of stuff that should really be in a model. You would likely want to return img.to_blob from one of your model methods and then use send_data from there.

It’s pretty basic but it was all I needed to get my project working. RMagick does seem to be a little arcane. A lot of the things I tried along the way failed in pretty confusing ways and with pretty cryptic errors. While simple stuff like this is fine its going to take a lot more reading and fiddling to make me truly comfortable with RMagick. At least I have this written down for next time…