Hugin

Stereo image alignment

Asked by Michael Perryman

I am using Hugin 2014.0.0 (Mac) to generate aligned stereo image pairs from two photos taken with two (nominally identical) cameras (although the zoom setting might differ slightly).

I have followed the tutorial at http://hugin.sourceforge.net/docs/manual/Align_image_stack.html. It works well.

After Hugin finds a solution, I can open the .pto with Hugin, work with the left and right images, and then iterate (e.g. by suppressing outliers, adding new control points, and changing the normal point) then running the Geometric Optimiser. Again, all seems to work. My questions are (Q5 is the most important for me to proceed!):

(1) can I use the GUI for the stereo alignment option, or is only the command line option available for this first stereo alignment step?

(2) what geometric transformation terms are solved for? Is it just yaw/pitch/roll, or some general 3rd order polynomial, or something else?

(3) when inspecting the resulting .pto file in the "control points" dialogue window of the Hugin GUI, I assume that the (quite wide) horizontal lines associated with each control point are the (large) x-axis error bars resulting from the fact only horizontal alignment is optimised for the stereo pairing?

(4) [the reason I ask 2] why are these horizontal lines not strictly (but only approximately) parallel to the horizontal axis of the dialogue window?

(5) after iterating the alignment points and running the Geometric Optimizer, how can I output the two optimized (left and right) .jpg images? I understand that the .pto file contains the parameters of the optimisation, and for panorama users the next step of stitching does not require access to the separate optimised images. But I need access to the resulting left and right .jpg since I want to use them to create/control the anaglyph image.

(6) since my two images are generally not perfectly matched in intensity, I go to the Exposure tab for the photometric optimisation, and see Ev=0, Er=1, Eb=1 for both images. I have not been able to perform any photometric adjustments to the two images following the instructions in that window. Should this be possible?

(7) is there likely to be a 2015 release as a Mac .dmg image any time soon?

With many thanks to the Hugin collaboration for this very fine tool!

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Best tmodes (tmodes) said : 		#1

For the stereo feature of align_image_stack see http://vndlinuxphoto.blogspot.de/2011/01/stereo-image-alignment-in-hugin.html for more details.

To (1): This can also be done in the GUI. Add a new cp detector setting in the preferences with your options
To (2): Normally only yaw, pitch and roll. Maybe also the translation parameters. But not sure.
To (3): No these are no error bars. The indicate how the horizontal line is spanned between the 2 points. This feature may be not so helpful for stereo alignment.
To (5): Go the stitcher tab, select projection "rectilinear", "calculate field of view" and "calculate optimal size". Then under "remapped images" select only "exposure corrected, low dynamic range" (deselect all other) and then "stitch now". Now you will get the corrected images
To (6): Recently there were 2 bug found and fixed in the photometric optimizer. (but not yet released). Maybe you are affected by these bugs. It may help to set the output projection and the output size correctly (as described in the answer to question (5)) before the photometric optimizer.

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Michael Perryman (mac-perryman) said : 		#2

Very many thanks for this quick and complete answer. For (2), further reading suggests that this also solves for a differential magnification (which it should, and which I need).