A few months ago I purchased a Canon PowerShot G3 X. It’s a relatively new model, and consequently, no DarkTable noise profile exists for it. That means the "denoise (profiled)" plugin (or filter) didn’t work. That’s a problem.
Darktable does lots of things extremely well, but the characteristics of the sensor are different for each camera model. The DarkTable developers can’t build noise profiles for every imaginable camera because, well, you have to buy the camera in order to have something to profile. Open source projects can’t do that. There’s no budget. Consequently, the DarkTable team needs us (the user community) to use our own cameras and create the profile if it doesn’t already exist. We can then load the profile in our local copy of DarkTable, and we can also send the profile to the DarkTable project team, so it will be available to everyone else that has a camera like ours.
"How can I build a DarkTable noise profile?", you ask. Well, there’s a DarkTable document that tells you all about it. Now don’t freak out! I’m going to explain the process for you, but to give you an idea of how "simple" it is (not), see http://www.darktable.org/2012/12/profiling-sensor-and-photon-noise/.
If you’re a total techie dweeb, that probably made perfect sense. For the rest of us, there’s a lot of unintelligible gibberish in there. Here’s what I did to build the profile for my PowerShot G3 X. You’ll need to make some minor adjustments for the capabilities of your camera, but hopefully those differences will be minor enough to be obvious to you.
First, if, like me, you run your desktop on Ubuntu, and you have installed DarkTable from the Ubuntu package manger, you’ll need to uninstall it, and build your own version from the project source. Ubuntu doesn’t include the "tools" directory that you’ll need to use, and the "noise" utilities in "tools" are DarkTable release dependent. (i.e. They won’t work with the older release that you already have installed. At least, they didn’t for me.)
Just for total disclosure, I’m not completely reckless. My Ubuntu desktop is a VM, so if I toast it, I can restore and be back in operation in just a few minutes. I wouldn’t be playing "let’s experiment" on a bare metal system. The advantage for you is that I’ve actually successfully done this, so chances are pretty good that you can too. That said, you should have a backup before you try this, and if it reduces your desktop to steaming slag, it’s on you. I guarantee nothing.
So, open the Ubuntu package manager, search for DarkTable and uninstall it. Don’t try to leave the Ubuntu package on the system. You’ll have issues with running the wrong versions of things if you try to do that. I know. I did. You can always re-install it later if you want to.