Autoexposure Hugin Example Files

Ripon Cathedral Library. The contrast within the scene was quite large, varying from 0.63s exposure at ISO100 F8 looking down into the dark interior of the Cathedral, to 1/40th when pointed at the sunlit windows of the Library. But since these appeared on two different frames, I could simply expose separately. The traditional approach would have used a 1/5th base exposure together with a +/-3EV bracket to capture the darkest and brightest parts of the scene.

Traditionally, panoramas would be taken using a fixed manual exposure, bracketed if needed. But panoramic software has advanced to the point that they can handle the assembly and blending of source images taken with wildly different exposures. I am making available a set of files taken in Ripon Cathedral that shows the ease at which high contrast scenes can be tackled without having to take large amounts of bracketed photos.

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

In this example, the base exposure throughout the scene varied by 6 stops (1/40th to 0.63s) hence there was a large amount of inter-frame contrast. But the contrast in any one frame (intra-frame) was just within the capabilities of my camera, hence I was able to take a 5+1+1 shooting pattern, without bracketing, and capture the scene without excessively blown highlights. This is variation of the usual 4+1+1 shooting pattern but with an extra shot that was taken aimed at the bright highlights of the sunlit windows.

Hugin Fast Preview Window. The position of the control points are marked by green crosses. The frames have been exposure matched and photometrically optimised for better blending. Normally, I use a 4 shots taken at -10 deg pitch and at 90 degree yaw intervals, together with zenith and nadir shots (4+1+1 shoot pattern). Here, there is an extra shot taken in between the 3rd and 4th shot at approximately 225 deg yaw that has captured the highlights of the sunlilt windows.

This extra shot was masked into the rest of the pano and invoked for an “underexposed” export of the stitch in addition to the normally exposed export. Hugin has no problems in handling the differently exposed frames and after photometric optimisation, the frames blend seamlessly. The normal and underexposed versions were combined using Enfuse and minor edits performed.

Top: Assembled panorama before photometric optimisation. Bottom: Optimised and exposure blended result (before final adjustments).

Hopefully this example demonstrates that panoramic software tools have come a long way since the traditional advice of locking off exposure was formulated. With some practice, the use of autoexposure when taking panoramas can be quite effective in speeding up workflow and creating a more efficient workflow. Of course, judgement is still required to use where necessary bracketing in order to tame intra-frame (as opposed to inter-frame) contrast.

Example Files for Hugin

I am making available image files and the Hugin PTO file for the purposes of education and training. I presuppose some familiarity with Hugin. Tutorials on the basic functionality can be found here.

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This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.

Panorama Preview

Suggested steps:

  • Download Example Files (from above) and extract to folder
  • Open Hugin and import source files
  • Set the lens parameters (Focal Length 8.7mm, Crop 1.5), Full Frame Fisheye for images taken around at 90 degree yaw intervals, Circular Fisheye for the Zenith and Nadir images. Assign lenses so that the the first 4 images are Lens 0, Zenith is Lens 1, Nadir is Lens 2.
  • Mask each image. For the first 4 images, mask off the tripod/panohead and any other extraneous objects, also the corners. Set crop circles for the Zenith and Nadir.
  • Now add control points to each overlapping pair of images. Concentrate on placing a good spread of points along the centre of the overlapping regions. There is no need for placing points away from the likely seam lines.
  • Add vertical control points/lines so that the pano will be level
  • Start optimising the position, gradually including field of view, barrel, then everything except translation. Periodically check for control points with large errors, correct if necessary. Use the Custom Optimisation options to fine tune the process.
  • Check that the geometry of the assembly is satisfactory using the Preview Window.
  • Start on optimising exposure. Choose Low Dynamic Range, then Custom. Deselect optimisation of Vignetting and Camera Response. Optimise just the exposure values, the the Red and Blue Multipliers.
  • Finally, stitch and export the panorama in your preferred format.
Final Stitched Panorama – Projection: Equirectangular (2) FOV: 360 x 180 Ev: -0.42

You try stitching the image using the automatic mode in Hugin, or in any other panoramic programme of your choice.