fix quality

[Maxime-J]

For the console version:

• Default maxNumPixels was set to 512*1024 whereas it should have been set to the same value than quality 3.
• quality is a string argument and was compared to an integer, so maxNumPixels was always set to the (as we just see) wrong value of 512*1024
• Values weren't the same as in the GUI version

For the GUI version:

• Default case for quality isn't necessary

By the way, it could be a good thing to match quality levels to what being said in the GUI: (1, 2, 3, 4) instead of (0, 1, 2, 3). What's your opinion on that ? I can do it before you merge this pull request.

[pfautrero]

thanks for your contribution. Sorry for this merge very very late !