Londinium was established as a town by the Romans almost 2000 years ago. It was common practice for Romans to adopt and romanize native names for new settlements. Not so the Brits: when they settled North America, they brought their names with them. So there are a dozen Londons in North America, one of them in Canada.
We’ve been to the original London many time, and we visted London, Ontario for the first time last summer. We were lucky to find the most welcoming bed and breakfast in London, Just For You. Owned and operated by Ron and Gerard two Dutch expatriates, this bed and breakfast combines the coziness and warmth of a B&B with a level of service that competes with the best five stars hotels of the world. It was an inspiring place to recharge our energy before and after our busy days in the city. Gerard served us healthy and creative breakfasts. One day he treated us to Poffertjes, a sweet complement to the varied and well presented fruit salad and accompanied with original Dutch Hagelslag and real cumin Gouda.
The room was so welcoming, I felt inspired to shoot an HDR panorama and to test if recent developments have made it easier on artists to create HDR panoramas. The bottom line is: things will soon become easier. For this panorama I had to work through some issues of the tool chain.
A New Approach to High Dynamic Range (HDR) Panoramas
Disclaimer: the author has been contracting with Photomatix.
Stacking and stitching or stitching and stacking exposure stacks has been discussed in the past, as a manually controlled workflow. It has been automated in Hugin 2009.2.0. As a reminder: stacking and stitching is generally more efficient but had a draw back for full spherical panoramas. Last time I tried it suffered from vortex-like artifacts at nadir and zenith. The upcoming enblend-enfuse 4.0 introduced new algorithms that may linder the problem. Time to try again.
The process in a nutshell:
- Shoot the brackets for a full spherical panorama using a tripod (i.e. perfectly aligned stacks).
- Merge the stacks to individual HDR pictures.
- Stitch the pictures as if they were LDR pictures (the current Stitcher tab in Hugin really need some explanation – details below).
This is how I did it, in detail.
1. Shot bracketed RAWs. Fed them to Photomatix Pro and batch processed into HDR. Optional: In the same batch Photomatix Pro can also generate an initial tonemapped version (needed to set up the stitching project).
There are many software to merge RAWs into HDR, some of them Open Source. The reason why I use Photomatix is the automated batch processing that includes fixing chromatic aberration and noise. This automates those deterministic aspects of the process and let me focus on those aspects where human creativity makes a difference.
Photomatix’ Manual recommends using a third-party RAW converter and gives detailed instructions for white balance, basic settings, and curves. I did not find any drawback in using Photomatix’ integrated RAW converter.
2. Identified control points between the images.
None of the control points detectors known to me support HDR files (out of Photomatix) as input at this time. Hence the need for the initially tonemapped images. For this specific panorama, taken with an 8mm fisheye, there were not that many images to link, so I opened the HDR images in Hugin’s Control Points tab and clicked myself through them. A passage through that tab is anyway mandatory to establish vertical control lines.
3. Stitch in “Normal” output mode.
This is the confusing part. Currently Hugin’s Stitcher tab has three main output modes, each with their variations: Normal; Exposure Fusion; and HDR merging. Intuitively, this is HDR, right? but it’s not merging. We (the Hugin team) need to do our homework and improve the interface.
Another confusing point is the output format selection for the “Normal Output”. The only options available are TIFF, JPEG, PNG. Don’t worry, choose TIFF and the result can be loaded and tonemapped in most HDR software, including Qtpfsgui (soon to be renamed Luminance) and Photomatix (correction: with Photomatix Pro 3.2.6 I had to open it with Photoshop first and save as EXR). It would be nice if we had also EXR there, like for the merging process. And Radiance HDR too. Or at least an indication that the TIFF output will be 32bit.
Hickups And Fixes
The resulting HDR equirectangular had an artefact at the Zenith. Enblend 4.0 pre-release, with default settings, produced a dark speckle instead of a vortex. Smaller, but still disturbing.
To study this, I pitched the panorama down 90°, bringing the Zenith to the middle of the equirectangular, on the equator (and consequently the Nadir on the 360° at the equator). And to make it visible, I used plain color images. The four images on the right are: a simple, unblended output of the six layers on top of each other; the blend with Enblend 3.2; the blend with Enblend 4.0; and last the working workaround: the blend with the –no-optimize option suggested by Christoph Spiel, release manager for Enblend 4.0. The not optimized version enabled me to produce a usable HDR equirectangular and continue the process. On Christoph’s request, I dug deeper in the code to isolate when the artefact is introduced. With his patient guidance and a few experiments it seems narrowed down to the seam-line vectorization or de-vectorization code.
The resulting HDR equirectangular is technically correct. Enblend 4.0 (pre-release) is an improvement, though not yet perfect. As an added bonus, on multi-core CPUs it is also significantly faster than previous versions.
The other obstacle left is tonemapping: many tonemappers, notably Qtpfsgui (soon to be renamed Luminance) don’t deal properly with zenith and nadir, limiting the user’s choices. The latest Photomatix is tested to deal with the 360° seam and the zenith. In the meantime this is just a post-processing inconvenience that can be solved with a brush in Photoshop or GIMP.
That was a much longer than expected processing for a panorama, but it was worth it. I hope it helps advance Enblend 4.0 toward release.