Quality loss importing AVCHD to iMovie 11

Hi - I'm importing AVCHD from a Canon Vixia M50 to iMovie 11 on a new 27" iMac purchased in Jan 2013. There is a significant loss of video quality after imported. Specifically the image is very grainy. I am comparing playback of DVDs I've burned from iMovie 11 to the playback of original video (camera connected directly to the TV). The picture from the camera is so much sharper with much better color, etc.

I've downloaded trial versions of Adobe Premier Elements, Premier Pro, and Final Cut Pro and all have the same issue. I've read so many posts on how to get the AVCHD video into iMovie but none have mentioned quality loss. Is anyone else seeing this loss in quality? If not, maybe there is something wrong with the camera.

Thanks

You are burning standard definition dvds. Their resolution is only 720 x 576/480.
DVD-Video - Wikipedia, the free encyclopedia

If you want HD dvds, you'll need something like Roxio's Toast and an external BluRay/HD dvd writer.
Roxio Toast 11 Titanium - CD, DVD, Blu-Ray Burning Software Program for Mac

Thanks MightyGem. I should have also stated that the video quality is equally as poor when viewing it on the mac. It was the same with all programs. None of them showed good quality. I also tried it on another mac and had the same results.

I used Wondershare DVD Creator software to burn DVD and the drive is a Samsung Blu-ray drive.
Amazon.com: Samsung SE-506BB/TSBD 6X USB2.0 External Slim Blu-ray Writer Drive (Black): Electronics

Knowing all this, could it still be the DVD software and drive issue?