October 30, 2008

Hugin panoramic photo editor extends its reach

Author: Nathan Willis

The developers of the free panoramic photo editor Hugin released version 0.7 this month, culminating a two-year development cycle. The new release incorporates key new technical abilities and usability improvements to help demystify the panorama creation process for the average shooter.

The 0.7 release is available from the Hugin project's Web site in the form of a universal binary for Mac OS X and a source tarball for Linux and Windows. Binaries for Windows are expected to arrive "soon." Hugin is also provided through the package management systems of most major Linux distributions, several of which have been supplying beta releases of 0.7 during the long run-up to the final release.

If you just can't wait for the final version 0.7 code to make it into your distribution's package management repository, the Panotools.org wiki maintains detailed instructions for compiling from source, tailored for Fedora, Ubuntu, and Gentoo. Compiling Hugin is not tricky, but the application depends on a lot of supporting packages to cope with the wide variety of image formats and calculations involved in aligning, warping, stitching, and blending photographs.

I followed the Ubuntu compilation instructions and ran into only one hiccup: the latest CVS version of the support tool enblend crashed on a few of my tests. Following the advice of the hugin-ptx mailing list, I backed up to an earlier release and had no further trouble.

The compilation instructions specify 10 steps, but several of these are optional, covering add-ons such as alternative "control point"-generating packages that are still in testing. This peculiarity is the result of Hugin's history; it was born from a suite of panorama tools that each performed one step of the process -- either alignment, stitching, blending, or control point matching. As the project matured, many of the original components were replaced. On the whole, that is a strength: the blender enblend can do more than the component it replaced, as can the stitcher nona. It's just that the replacement control point generator isn't here yet.

New, new, new as far as the eye can see

The changes in 0.7 are substantial. New users will appreciate the addition of an "assistant" mode that greatly simplifies the process of creating a panorama. The assistant allows you to select images, align them, and create a panorama with one click per step. The assistant does its best to guess the appropriate values for details like image blending and panorama projection, but it works entirely within Hugin's existing tool set, so if the automatically generated image is not to your liking, you do not have to start over from scratch to fix it, but can simply tweak the individual settings. So far, the assistant only assists you in stitching panoramas and not Hugin's other functions, such as perspective correction, but it is good and effective at its task.

The software's online help system has been thoroughly updated, which is far more important for a technically tricky application like Hugin than for a casual-use program like a media player. By and large, Hugin does an excellent job of automatically setting the large number of options and parameters involved in stitching and blending images, but when the end result doesn't quite work, the detailed help makes making adjustments easy. It includes both feature-by-feature documentation and clear, well-written tutorials with common use cases as examples.

Several of the tool screens include usability improvements. From the preview tool you can now make adjustments and see updated results instantly. In the all-important control points screen, matching pairs of control points are now numbered -- a big improvement over the color-coded system of past releases -- and pop-up magnifying glasses make it easier to precisely align control points. Projects can be saved as templates, and there are several new panoramic projections to choose from, including several from cartography.

On the technical level, 0.7's powerful new "photometric model" opens the door to new kinds of image adjustments. In addition to the geometric alignment and matching used to seamlessly fit individual pictures together, Hugin can now perform similar corrections for exposure, color balance, chromatic aberrations, and even vignetting. This means that component images can be blended together with far greater accuracy, but it also means Hugin can do new tricks, like fuse multiple exposures together into wider dynamic range images, and even output the results in high dynamic range (HDR) formats like OpenEXR and 16-bit TIFF.

Hugin 0.7 also introduces a new image alignment tool, straight-line control points. Historically, control points were used to match scene features that appeared in two adjacent images, with the shift between the points' locations determining the transformation needed to align the two images. Previous versions of Hugin introduced vertical line and horizontal line control points, which were used to mark scene features that should retain perfect vertical and horizontal alignment. Straight-line control points take this idea further, allowing you to mark any edge in the scene and prevent it from being bowed or warped by the transformation. This is especially useful when a straight object cuts directly across the seam between two images; a broken line in the finished panorama would be very distracting.

Several automatic control point generating utilities are available for use with Hugin 0.7, primarily because the dominant control point generator, Autopano-SIFT, is patented. It is freely available for most users, but the Hugin development community still needs to find a patent-free replacement that can be shipped in any jurisdiction and with strict adherence to free software licensing issues. You can test out several alternatives in various stages of development: autopano (no relation), panomatic, or matchpoint. Changing control point generators is a simple setting in the Hugin preference panel.

Finally, Hugin 0.7 now handles stitching and blending in external processes, which you can run in the background while you edit a different project, put in a batch queue to run unattended, or even send to a different machine.

Just over the horizon

Developers say they hope to accelerate the release cycle for Hugin 0.8, incorporating new work done in the 2008 Google Summer of Code. Teased features including masking out objects, automatic removal of moving objects such as clouds, and a more complete batch processing tool.

There are still a few quirks in Hugin 0.7, such as the necessity of using the mouse to make fine adjustments to control points and to re-center and re-align the panorama in the preview image. Since users have such precise control over other aspects of the panorama generating process, it sticks out that these few tasks remain eyeball-accurate only. I also could not uncover any way to disable automatic exposure adjustment altogether, something I wanted to employ for a peculiarly lit scene that never looked right with Hugin's adjustments.

Although I appreciate the new preview tool, it is still difficult to use for anything precise. Right-clicking is supposed to reset the horizon line, but exactly what it changed was never exposed in the interface, either numerically or visually. The preview window shows individual toggle buttons for every input image in the panorama, but only the buttons and not the images are labeled. The tutorials make good use of labeled overlap diagrams to explain panorama stitching; the same technique might help in the actual user interface.

Finally, I was a little disappointed to learn that Hugin supports reading lens parameters only from EXIF tags in JPEG files. Working with TIFF is the cowboy way, after all, particularly when it comes to HDR formats like 16-bit TIFF, which is now supported by version 0.7.

Still, none of that detracts from the excellence of Hugin 0.7. The app has come a long way since the 0.6 series, and it is always nice when a new release features gifts for both the casual and power user. If you stitch a lot of oversized images, the photometric adjustments and the straight-line control points make this release worth an immediate upgrade. If you think that all of this talk about stitching and control points sounds like technobabble not worth your time, try out the assistant mode. It's easier than you think to piece together a prize-worthy photograph these days.

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