Photometric alignment and vignetting correction

Upcoming version of Hugin will contain an advanced photometric alignment, which can correct the panorama for exposure, vignetting, white balance and response curve. The combination of geometric and photometric alginment will also enable the creation of HDR panoramas directly in Hugin.

The algorithm can be used in fully automatic mode. It took 7 seconds to estimate vignetting and camera response of the 61 image Venice panorama shown below.

The method is described in this paper. The presentation slides are also available.

Some preliminary results

These results can be compared with previous work by Dan Goldman and Jing-Hung Chen. Compared to their algorithm, the method in Hugin can properly handle white balance differences and is a lot faster, because it does not need to solve for the scene irradiance directly. The implementation in Hugin will also allow the creation of extended and high dynamic range mosaics

Green lake panorama

Goldman and Chen have used this image sequence in their paper. Their results can be directly compared against the images shown here. The images were captured in aperture priority mode. By examining the source images, small white balance differences between adjacent images can be detected, especially at the right border of the panorama.

Venice panorama

This panorama consists of 61 image, captured by Jeffrey Martin, using a Canon 5D with a manual focus Yashica 300mm lens. The images have been captured in manual mode to ensure constant exposure and white balance.

As seen in (a), this lens suffers from very strong vignetting. When blending the images with enblend (using 20 blending levels, to ensure a blended area), large, unpleasant residuals of the vignetting remain, especially in the sky. After correcting the vignetting (b), a very good result is obtained by just just stacking the images without any seaming. The remaining small defects can the easily be removed by enblend.

Metapanorama by gadl

This equirectangular panorama consisting of 60 images has been shot by gadl with a Sony DSC-T5 camera which only provides an automatic exposure mode. Thus the images have been captured with varying exposure and aperture settings (f3.5 and f5.6). The visible seams in the sky are due to moving clouds, and not caused by photometric misregistration. This scene also shows that the proposed method can robustly handle images with some moving objects (clouds) and works on large, equirectangular mosaics.

Gadl has managed to do a very good job with assembling and post-processing the panorama, using only enblend and PTblender. However the new method is much simpler to use.

When comparing the images, please keep in mind that the images below have not been processed for tone curve and color in GIMP or Photoshop, they are the raw results, straight after stitching with Hugin. This example also shows that enblend is quite good in compressing the large dynamic range, since each picture predominatly contains one useful exposure setting. By close inspection of the panorama produced by enblend, one can see that some areas, such as the two other photographers and the tree with the bicycle suffer from strong blending artefacts due to large exposure differences. Enblend 3.0 has been used without the new seam-optimisation (it crashed when it was enabled), and the images have been blended in exactly the same order

(a) Aligned Originals
No blending

(b) No correction
Only blending

(c) Vignetting, exposure and white balance correction
No blending

(d) Vignetting, exposure, white balance correction
Blending

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