RawTherapee: the newest open source raw photo editor

Gábor Horváth has been developing the raw photo converter RawTherapee single-handedly, on Linux and Windows, since 2006. The application has been freeware the entire time, with Horváth accepting Paypal donations through the project's web site. Consequently, although there are significant changes in the 3.0 alpha release announced on January 4th, it was arguably bigger news that the project was switching to the GPLv3.

RawTherapee is a raw image conversion and editing utility that (like most raw converters) supports the native file formats of virtually all digital cameras courtesy of the dcraw project. It offers exposure control, highlight and shadow recovery, color and tint balancing and adjustments, sharpening and noise reduction, and basic crop/rotation tools. On the workflow side, it supports color management, Exif and IPTC tagging, quality ratings, batch processing, saved snapshots, and sending images to an external editor for detailed work.

Getting started

Builds for 3.0 alpha 1 are available for Linux and Windows, and for the first time, source tarballs as well. The Linux builds are provided as 32-bit and 64-bit standalone binaries; simply extract the package and run ./rtstart from a shell prompt to get started. There is no dependency checking, but RawTherapee is compiled against standard GTK+ and GNOME libraries. A more complete list of dependencies is found in a forum thread about compiling the source on Linux; the only special-purpose libraries are libtiff and libiptcdata, which should already be pulled in by other modern image editing packages.

In use, RawTherapee behaves like most comparable raw converters, sporting a three-pane window with a file browser in the left-hand column, an image viewer in the center, and a tabbed image-adjustment toolbox on the right. The vast majority of raw converters take this approach, exposing the image adjustment controls as a vertical stack of sliders and checkboxes. Novices may need to familiarize themselves with the terminology before feeling comfortable tweaking the myriad of settings, but on the positive side, RawTherapee is non-destructive — it saves adjustments not by changing the original image, but by storing an auxiliary "sidecar" file in the same directory.

As raw converters go, RawTherapee offers a full palette of controls, with multiple user-selectable sharpening algorithms, separate luminance- and color-noise reduction sliders, an RGB channel mixer, and multiple demosaicing algorithms. Nevertheless, the tool layout is organized, providing a sensible division of the potentially overwhelming controls into four main tabs (Exposure, Detail, Color, and Transform), and sub-dividing each tab into groups. Batch operations are easy to queue, offering the choice of a specified output folder or a user-defined template, with which you can rename and store output files based on their original name and directory.

RawTherapee does diverge from other converters in a few areas, such as its use of tabbed windows. Starting with 3.0, opening an image to edit opens it in a separate tab. This allows the user to keep multiple editing sessions open at once without exporting, and is definitely a nice feature. There is also no "filmstrip" window pane displaying other image thumbnails in the current directory; the only way to open an new image for editing is through the file browser — a difference that some users might find less convenient. It also provides floating "magnify" windows to zoom in on particular parts of the current image without zooming the entire image view, something not every editor supports.

Linux users will find several oddities in the user interface, though, such as the lack of any menus (standard or otherwise) — the closest thing are the "Preferences" and "Exit" text-buttons on the bottom right-hand corner. And those users with a scroll mouse must take care when scrolling the vertical toolbox; it is easy to accidentally throw off an adjustment slider if the cursor happens to land hovering over one of the controls. This release also lacks tooltips for many of the settings, which would be a boon to new users.

For real-world work, it is also critical to take the "alpha" status of this release seriously. 3.0 alpha 1 is crash-prone, and the adjustment sidecar files it creates automatically are not compatible with the 2.x-series. Those who use the current, stable release of RawTherapee (2.4.1) must be sure to back up their work before testing 3.0.

Open source and further development

Horváth cited three factors behind his decision to change the licensing of RawTherapee: personal lack of time, the difficulty of reproducing and fixing reported bugs, and interest in focusing his own time on the core image-processing features of the program rather than the GUI and other components. He set up a RawTherapee project on Google Code, including Subversion access to the source, build instructions, and an issue tracker. He has also opened developer discussion forums on the main RawTherapee site.

The RawTherapee code breaks into three parts: the image processing library, an Exif support library, and the GUI application itself. Bug reports and enhancement requests have already begun to appear at the Google Code site; Horváth has stated that his top priority for the moment is working out the kinks in the CMake build system.

Moving forward, Horváth's intent to focus on the image processing core is a key component of the 3.x roadmap. Part of the rewrite that led up to 3.0 alpha 1 — although not yet visible to end users — is a separation of the editor component to make it easier to add more algorithms, such as additional demosaicing and noise-reduction choices and new tools to correct fringing and perspective distortion.

Looking at the state of RawTherapee and its user base, the decision to move the code to an open source license is undoubtedly a good one. The application already has an active community, including many Linux users and language translators. But as Horváth discovered maintaining the project in closed source state, supporting that user community's bug reports and support requests became more and more time consuming as the project grew in popularity — a fact many solo software developers may not consider when starting a new project.

Furthermore, Horváth wants to focus on the part of the code he finds most interesting, the image adjustment algorithms. By adopting a free software license, RawTherapee might be able to slim down by swapping out some other components for existing open libraries (such as libexiv, rather than its own separate Exif library).

There is clearly room for what Horváth wants to do with RawTherapee in the open source graphics space. Arguably the most similar raw converter, Rawstudio, takes a different approach, aiming to make raw image editing accessible for the average non-technical photographer. RawTherapee's decision to make multiple user-selectable algorithms available for so many controls will make it appealing to a different crowd, those that like to experiment or who have very specific opinions about their image editing. There are other raw-capable editors and applications, such as Digikam, that emphasize more image collection management, raster editing, or other functions.

All in all, RawTherapee has been a consistently good performer on Linux and Windows for years. As one of the few free choices in a space dominated by high-priced applications, it was a standout. Considering that most of the underpinnings of raw image editing — dcraw, Exif and IPTC, and the various mathematical algorithms — are not proprietary, it only makes sense that good, open source solutions would emerge. With the upcoming 3.0 release, it is excellent to see that RawTherapee will be among them.