Portra uses iOS6's support for file inputs to let you take a photo, apply a filter with Canvas and share it to Twitter. Just a little proof of concept to show what's possible. Code is at https://github.com/interstateone/portra

Notes: It can be slow, there's probably some optimization to be done in the filter. There's also a squished image bug that pops up every once in a while when using a photo directly from the camera, let me know if you have any ideas what may be causing this.