I usually don't quote an entire article, but I don't think I can do any better. Softpedia covered RawTherapee very well here.
"RawTherapee is a cross-platform raw image processing program released under the GNU General Public License Version 3. It is written in C++, using a GTK+ frontend and a patched version of dcraw for reading raw files.
96-bit (floating point) processing engine
Advanced color handling
Much, much more
RawTherapee is an application that specializes in the development of RAW images and it's probably one the best you will find on the Linux platform. It comes with so many features that it might even put Adobe's Photoshop Lightroom to shame.
Editing RAW images usually requires some very expensive applications. If you are running anything else besides Linux, you will have to spend a ridiculous amount of money to get some decent features. The latest version of Photoshop Lightroom is the perfect proof.
Nobody is disputing the fact that Photoshop Lightroom is a great asset, but Linux users would expect to get the same kind of functionality for free from an open source product. Like many other software categories, you will find a variety of applications competing for the prize of being the best at what they do.
RawTherapee is among the better solutions available for RAW processing, and the software is so complex that it will take a professional to completely enjoy and experiment with the application. I am more of a novice, so I will only talk about some of the features that I use on a regular basis. Keep in mind that RawTherapee is capable of much, much more.
If you check the official website, you will find that it's a little behind what can be found in the repositories. We installed RawTherapee from Ubuntu Software Center and it features a higher version number, 18.104.22.168.
You will need to be root in order to install the application, but it should work without any problems. If you choose to download it from the official website, you must select the appropriate version for your system.
RawTherapee works like any other application of its kind. You import a folder with the RAW files (it works with regular images as well) and you start by editing each of them. You won't have to worry about modifying the originals because the software doesn't touch them, so it's perfectly safe.
If you are like me, you probably just want to make sure that the images look as close to natural as possible. All the major features of the application can be found on the right side, in a series of five tabs: Exposure, Details, Color, Transform, and RAW.
For beginners like myself, the first tab is usually enough. Users can change the exposure of the image, influence the shadows and contrast, and they can even apply a little vignetting if they feel like it.
The Details tab, on the other hand, has options like Sharpening, Edges, Microcontrast, Noise Reduction, Defringe, and Contrast by Details levels. You can see that the more you go into the application, the more you find complex functions that are usually not accessible to beginners.
Users can also perform a number of simple actions, like Crop and Resize, although those functions do support a number of options that can't be found in some professional editing applications.
Other functions that you will discover in RawTherapee are Advanced color handling, denoising methods, Batch processing, a good CIE Color Appearance Model 2002 module, a 96-bit (floating point) processing engine, and much more.
It's also possible to apply one of the many presets that are available if you don't want to do all the work that is usually required. Those presets might be enough for what you are trying to achieve with the images.
This is such a complete application that it's hard to find any faults with it. Maybe it's missing some extravagant options that only a handful of users will notice, but it's difficult to determine which ones. I only had one problem with it because I couldn't figure out how to do some basic editing and how to start the process itself. This is mostly because the interface is flooded with buttons and you have to find out by process of elimination what everything does.
This is one of the most complex applications for RAW editing that I have tested so far, and I have to say that I was impressed with the sheer number of features. It's unlikely that you won't find something that you need, and this is probably that greatest strength of the software." -Softpedia
If you use Adobe photo software such as Photoshop or Lightroom, then you are already very familiar with the raw photo processing power they have.
What you may not know is that Linux is keeping in stride with Adobe's best, with programs like GIMP and RawTherapee.
I don't do much with photos, so for me GIMP and RawTherapee are over kill, but for those of you who work with photos all the time and are forver adding new layers, lighting effects and the like, I suggest giving RawTherapee a try. (And also GIMP.)