"The problem is these decisions should be made by film-makers, they shouldn't be made by studios, because if it was up to studios they're going to sacrifice quality for lower cost," Cameron said.
Since the success of Tim Burton's 3D Alice In Wonderland, which was made into 3D after it was filmed, studios are looking to convert more movies.
Speaking last month at the launch of Alice, Burton said it is more about technique, rather than the process.
"With all these tools, you can see good 3D, bad 3D, good conversion and bad conversions," he said.
Transformers director Michael Bay has also joined the debate, telling movie industry website Deadline.com that he is "not sold right now on the conversion process".
Yikes, studios taking over is always a blah in my book. Not to mention, I'm still not entirely thrilled with 3D. For me, it still blares "Hello! I'm 3D!" for me, the subtlety of losing yourself to the story is totally dashed by the "look at me reach out of the screen now" effect of 3D.
The idea of 3D badly done makes me shudder.
My 2 pence.