You can download Raw Therapee built for either libc6 or libc5 Linux systems. If you are not sure which you need, try the libc6 version first. The package is a gzipped tar archive containing compiled binaries and support files. That's right -- no source as of right now. Horváth told me he is still debating what approach to take regarding licensing.
For image demosaicing, Raw Therapee uses EAHD, Horváth's variation on the Adaptive Homogeneity-Directed (AHD) algorithm first popularized by Keigo Hirakawa. Demosaicing is a core process in RAW conversion, and is perhaps the more widely debated topic among RAW aficionados. Horváth provides a comparison set showcasing results from Raw Therapee, Adobe Camera RAW, Nikon Capture, RawShooters Essential, Bibble Pro, Capture One Pro, Silkypix, and UFRaw side by side.
Tools and basic usage
|Shadow recovery. Click to enlarge.|
Raw Therapee gives you the requisite developing controls -- adjustable white balance, exposure, sharpening, and highlight/shadow compression. On these basic tasks it performs on the same level as its peers -- but I particularly like the fact that Raw Therapee exposes the correct, technical names for its functions and settings.
Take shadow compression, for example. This function boosts the luminance of the darkest pixels in an image (below a particular threshold) without altering the luminance of brighter pixels. The result is that it brightens the shadow areas without washing out the highlights. Raw Therapee calls this what it is -- shadow compression -- and lets you choose the dark-pixel threshold. Bibble Pro, on the other hand, employs the same feature, but calls it "fill light" -- an analogy to how you would fix the lighting ratio if you were still at the shoot. That name might be helpful the first time you see the associated slider in the toolbar, perhaps, but it's non-descriptive and a little condescending toward the user. And Bibble Pro does not allow you to adjust the dark pixel threshold.
In general, Raw Therapee gives you more detail and control over all of its image adjustment parameters -- from sharpening to color correction -- than many other RAW converters. The color shift and luminance-channel tools are excellent, and transformations are done in the CIELab color space.
On the down side, it does not yet offer hand-adjustable curves and levels, which a lot of users may be expecting. Horváth has labeled these features to-dos, and the level histograms are already in place, so it may come in the next release.
In spite of the fact that many people think they need hand-adjustable curves, all the possible operations are exposed by the existing exposure, shadow, and highlight controls. We are used to seeing the curves in raster image editors, but even Adobe has opted out of including them in its RAW converter Lightroom. Better to adjust the exposure while looking at the image itself than at a curve or histogram graph.
|Color correction. Click to enlarge.|
There are more substantial problems with this first release of Raw Therapee, however. It is prone to crashing and can be slow to load thumbnails from a large directory of images, two problems Horváth is aware of and that betray the youth of the application on Linux. It also failed to correctly read EXIF rotation information from my photos, which is annoying but not dangerous.
Furthermore, although Raw Therapee offers some features other proprietary RAW converters do not, there are still holes in the feature set that prevent it from being a full-fledged workflow tool. It does not offer image collection management, metadata, or batch processing, none of which are image-processing features but all of which are still get-down-to-business necessities.
Lastly, although it is probably a matter of taste, I did have some problems with the user interface. Not with the grouping of the image adjustment functions -- all RAW converters seem to just dump their adjustment tools into long, scrolling sidebars full of sliders. But in Raw Therapee the sliders always seem to grab cursor focus when the mouse is above them. Thus, in order to use your mouse's scroll wheel to move up or down the sidebar, you have to carefully hover over the sidebar's scrollbar, or else you risk accidentally throwing one of the sliders up or down, causing yourself at least a moment's panic.
All those shortcomings are peripheral, though. Performance and UI improvements will no doubt come as the app matures. It would be nice to have integrated workflow tools, but if Horváth chooses not to provide them, the value of the app as a RAW converter will not be affected. The core of Raw Therapee is solid; it is easy to use and offers an excellent, flexible set of adjustment tools.