PlaidMaker is an online tool for making plaid patterns.
You can create patterns for free and either download them to your computer or save them to the site. If you'd like to save private patterns you can sign up for PlaidMaker Plus.
After studying the thread pattern of my favorite plaid shirt, I theorized that its pattern could easily be represented, pixel by pixel, with a gif image.
I took a close look at my shirt and noted the number of threads, their colors and their directions. With MS paint and the pencil tool, I drew each pixel of the pattern and copied and pasted it repeatedly. This, however, was a tedious process and I found a much more efficient way to make plaids with Photoshop using layers, masks and patterns.
The Photoshop method was still not good enough for me; I had always wanted to write a program to do it. The algorithm, I knew, was extremely simple but I didn't know how to create images. Finally I learned PHP and the GD library which gave me the tools to make my program.
PlaidMaker exists thanks to *a lot* of open source technology. The application on the server side uses Python and the Django web framework. Plaid images are rendered with PIL, the Python Imaging Library. The client side uses Bootstrap for layout, jQuery for interaction and Backbone for the interactive plaid making interface. The color picker was developed by eyecon.ro.