open-source or free AVCHD conversion to image sequence
Wonderful ffmpeg command line utility is the solution. Just check their documentation, but something like the following will probably work for your case:

ffmpeg -i video.mts video%05d.png


This will take your video, and create video00001.png, video00002.png... files in the same folder.

You can find a lot of guides for ffmpeg, or ask here for a specific soltion. We can try to figure out.