Few notes on RawTherapee 3.0
Few days ago RawTherapee 3.0, a free digital photography application, was finally released to the masses. We thought we'd do a short review of it.
It's the first stable free version of this digital photography application that focuses on processing Raw images. And when I say "free", I refer to both money and freedom aspects: v3.0 is a result of 1.5 years of work by a new team since release of RT's source code back in January 2010.
Even though I'm decidedly a darktablehead, one thing I can say for sure is that RawTherapee is a well-known source of ideas and algorithms for other free Raw converters. The AMaZE interpolation alone has been adopted by tools like digiKam, Photivo and, of course, darktable. We owe that to Gábor Horváth and the new team behind RawTherapee.
Some features of the new version I find rather interesting, and not all of them are covered in the official press-release, which is more than a good reason to say a few words about them.
Adjustments in LAB color space
Since v3.0 there is now a new tool called Lab Adjustments in the Exposure tab. What it provides is various means to edit luminance and chromatic characteristics of a photo in CIE LAB color space. In fact it's the old Color Boost tool, rewritten for more features and more generic approach to work in LAB.
While the old tool focused on doing the good old saturation bump trick, the new one is more universal and allows correcting brightness, contrast and saturation, as well as edit L*, a* and b* curves. Each of the curves can be edited in four modes: Linear, Custom, Parametric and Control cage. Of them I find the last two most interesting.
The parametric mode is very much like curves in both Lightroom and darktable, but closer to Lightroom's approach, since you can input values numerically for all four zones (Highlights, Lights, Darks, Shadows). As for Control cage mode, RawTherapee uses classic quadratic splines to define the curve:
The Tone Curve in the Exposure tool uses same UI and same approach which is rather handy.
By the way, if you used to have a soft spot for saturation limit control, it hasn't gone: you can still do it from the new Lab Adjustments tool.
This is where the inheritance pattern has clearly reversed: if you ever used darktable (or Blender, where the idea came from), you will find HSV Equalizer very familiar: it provides same means to edit pixels in Hue, Saturation and Value channels. Basically, you get a linear representation of hues circle (in HSV hues are measured in angles), and for an interesting part of the hue range you can adjust brightness and saturation. That is, you can e.g. control brightness and saturation for skintones.
Both principle and implementation are very similar to darktable's, including adjustment of of hue zones borders. The only functional difference apropos darktable is that the implementation in RawTehrapee is missing a color picker.
Contrast by detail levels
Frequency filters and wavelets are increasingly popular as photography tools. It's a huge world to explore. RawTherapee team couldn't stand aside, so now the application has this new tool called Contrast by detail levels.
The tool does exactly what is says on the label: all features in an image are separated into detail levels, and for every level you can tweak contrast. While it's not a local contrast tool per se, it's still a very nice way to add a punch to details and increase sharpness.
The three buttons on top uniformly and proportionally apply changes to all detail levels. Again, it's somewhat similar to darktable's equalizer, except here you get numeric input instead of a curve.
You will definitely find a good use for some of the other new features in RawTherapee 3.0. Let me list just a few:
- a new tool for fixing purple fringes;
- hot pixels removal filter;
- dark frame filter;
- automatic mode for finding and fixing chromatic aberrations;
- pictures can be saved to 16bit TIFF for ICC profiles generation;
- some changes in UI, including support for dualhead configurations;
- performance boost in many processing tools.
The most visible UI change, however, is ability to open multiple images for editing, for which tabs based UI is employed. The caveat is that RawTherapee is still somwhat resource-hungry.
RawTherapee's developers recommend keeping no more than 10-200 images per folder, and not switching from an image tab to the browser tab while some processing is going on. For comfortable work they recommend 4GB of RAM, even though you might get reasonable performance with even 2GB (which I confirm).
In general, I have mixed feelings about new version of RawTherapee. On one hand, there's clearly a lot of work put into the major new release. I have not a single doubt that the team worked hard and deserves a lot of respect (again, if you use AMaZE and green channel equilibration in darktable or Photivo, this is where it comes from).
On the other hand, as much as I adore color adjustment tools in RawTherapee, the user interface clearly needs lots and lots of work. Even though it's somewhat configurable now (including an option to use a tighter placement of widgets), the approach to using screen space by UI elements is far less than optimal.
On top of that very little work seems to have been done on transformation tools. The cropping tool is still, subjectively, difficult to use, and there are still no tools to fix various distortions. This is where I hope RawTherapee will advance in the next development cycle.