Spherical panography

PTGui 5.8 and Stitcher Unlimited 5.5

Automatic stitching comparison

Part 1:

Object of the tests:

I shot some photographs with two Canon cameras (EOS 20D and EOS 5D). The first one was fitted successively with the 18-55 mm Canon "kit" lens, the Sigma 8 mm fisheye and the EOS adapted and "shaved" Nikkor 10,5 mm. The second was fitted with the same Nikkor fisheye lens.

This limited number of lenses and DLSR Cameras represents the majority of the situations that face the vast majority of serious panographers: from standard (rectilinear) kit lens to short focal fisheye lenses (not forgetting fullframe fisheye) and from small APS-c sensor (r=1,6) to full sized 24 x 36 mm sensor (r=1)

For some reasons, I have used three different panorama heads on top of my old Manfrotto tripod to get four sets of photographs. All H/W have been home made and most have been described elsewhere (1, 2) in this Web site. I have attempted to avoid parallax errors as much as I could and also simultaneously let as less as possible intrusive parts to obstruct the Nadir area.

No specific "polar" (i.e. Nadir or Zenit) shot was done where this is not required to totally cover the whole sphere.

While these different Camera/Lens associations would yield panoramas with very much different resolution (from 17500 x 8750 to 6000 x 3000, I have produce 6200 x 3100 pixels JPG images in each case and then converted these files into about 1500 x 1500 pixels cubic faces QTVR movies.

No sharpening has been done in all the cases after PS CS2 Raw conversion. No curve or level correction of the spherical (equirectangular) panorama;-)

In short: no attempt was made to produce esthetically rewarding panoramas. I just wanted to compare technical documents in order to spot possible stitching ability differences or any flaw coming from the software application .

Stitch and blend process:

Stitching:

I had four sets of images to be processed by Stitcher Unlimited and by PTGui.

I tried to simulate as close as possible what a casual user of the sofware would routinely do and used Automatic processing wherever possible.

Exception: Automatic alignement (offered by Stitcher Unlimited as an optional process step) happens to be not 100% reliable. PTGui automatic alignement can not be set or tuned a priori by the user AFAIK. I decided to make manual -or assisted i.e. semi automatic- alignement for every case under both program (BTW for that purpose, Stitcher has always been a jewel).

Similar steps are required by both programs and notably possible manual rectification of the circle that limit the usefull field of view for the fisheyes. The technical purpose is not exactly the same in each application but I was amazed by the similarity of the required user implication and step imposed by the two software.

Most (all but one) QTVR were converted by Stitcher Unlimited whatever the program that originated the equirectangular image file was.

Blending:

PTGui internal blender and Smart blend option in Stitcher Unlimited rendering were selected.

Only one panography was done using a Nadir image insertion: EOS 20D + Nikkor 10,5 mm (It's a FulFrame fisheye in this configuration. In fact two face-to-face Nadir images have been shot. For the Stitching by PTGui, two blenders have been successively used at this occasion:

As the internal blender for Stitcher Unlimited is the so-called "Smart"Blend option, I wanted to eventually show the same effect with PTGui (i.e. the panorama head is not erased from the Nadir when more than two images are overlapped). That is a specific drawback of Smartblend amongst other blenders which on the contrary effectively get rid of most of the Nadir intrusion by using two face-to-face Nadir images.

RESULTS

The following table presents the whole comparison test results:

Please click on the link to see the related full screen movie.

Camera
EOS 20D
EOS 20D
EOS 20D
EOS 20D
EOS 5D
Lens (all set at ~f11)
18-55 mm @ 18 mm
Sigma 8 mm
Nikkor 10,5 mm
Nikkor 10,5 mm
Nikkor 10,5 mm
Number of rows
3
1
3
3
1
Inclination angle from horizontal
-60Deg

0 Deg

+60 Deg

0 Deg
Nadir (-90 Deg)

0 Deg

Zenit (+90 Deg)

Nadir (-90 Deg)

0 Deg

Zenit (+90 Deg)

0 Deg
Number of images per row
10, 10, 10
4
2, 6, 1
2, 6, 1
4
PTGui 5.8.4

Blending Module

Stitcher Unlimited 5.5 (OS)

Blending "Option"

(Windows)

Smart

(Mac OS X)

Smart

(Windows)

Smart

-
(Windows)

Smart

Converter from JPEG equirectangular to QTVR Movie

(OS)

Stitcher

(Windows)

Stitcher

(Windows)

Stitcher

(Windows)

CubicConverter

(Mac OS X)

Stitcher

(Windows)

Conclusion:

Both software are equal very excellent performer when it comes to easy fully automatic stitching process with the three different lenses.

During a ten days test sequence, I used resources available on my Windows machine as well as on my Mac. I also used images shot with quite a few other lenses (such as Canon 10-22 mm, Canon 15 mm fisheye) and/or other cameras. I have made about eighty runs on each program by using source images from entirely different panoramas.

I have encountered only two or three failures to automatically stitch at least a pair of images. When this happened, it did on both programs.

Note: the programs have tuning possibility for the sensibility of detection of matching points in adjacent images. This is a very tricky thing to compare as to make sure both are set to the optimum point in their scale.

Michel Thoby

Post Scriptum:

This article shall be soon completed, as another side of the coin has not been shown that concerns the apparent sharpness that can be really obtained and observed from rendered panoramas in the different configurations of combinations above.

In fact as the 18-55 mm lens (it only fits APS-C EOS DLSR) allows to get 17700 x 8850 pixels equirectangular images whereas only about 6200 x 3100 is obtained with a 10,5 mm on a 5D and this is the main reason of course.

I shall then show that the cheaper lens gives sharper panoramas amongst all other combos, but of course with a much longer time for shooting and processing. I cannot imagine also how to use such a lens for news reporting with action and moving people. That is where this Nikkor 10,5 mm / EOS 5D combo is the King today and it however provides very good, crisp and clear images.

Update (2 August 2006)

While it concerns most of the ways that panographers normally use, the above article doesn't deal with advanced -and sometimes rather touchy- ways to shot 360 panoramas that some adventurous panographers may do.

I have then written a second part to cover some of these exotic solutions that represent certainly a small fraction of the panography at least today. Who knows for tomorrow?

Second part: the Challenges