Recently I had to convert some functionality from an old MS Access system to a Ruby on Rails application. The Access system generated a report that included a barcode; they were using a barcode font installed on the machine running access. I figured generating the barcode server side in the web app was going to be much nicer than installing barcode fonts on the client browsers. And since this is Ruby, I figured...
There must be a gem for that
Sure enough, the barby gem. It allows you to output your barcode as png, gif, svg, pdf, etc...
In my case I generated png barcodes and included image references to those in my view files.
Sample code
There is no pixel setting, it uses some other type of unit to determine size; using the xdim, margin and height options you can tweak the size, but I found that it was not very precise - for my use case it was good enough.
The generated barcode does not include the value, it is just the image which can be scanned using a barcode scanner, but it would be nice if there was an option to include the value below that. This is somewhat trivial to add in your view using html.