Thanks for the tutorial! Finally got around to shooting some handheld panoramas and practicing them. In addition to the original post, I found a couple of gotchas:
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When adding 16-bit TIFFs to the project, Hugin (as of version 2021.0.0) doesn’t consider them linear files but sets out to fit a “response curve” to the data during the photometric calibration. Given the lack of multiple exposures per view, this is going to fail (as far as I understand). I wondered why the output TIFFs from Hugin looked like the contrast had been boosted and response to edits was really different from the original images. For 32-bit TIFFs, hugin flags them as “linear response” and doesn’t do the curve fitting. You can set the 16-bit TIFFs to linear as well by selecting them all, right click → Edit image variables → Camera response → Type → Linear. Afterwards, perform photometric calibration.
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Hugin seems to take white balance coefficients from the EXIF data and tries to utilize them to unify the white balance between the images. However I found that causing strange color casts in some parts of the panorama, and Hugin shouldn’t be applying any white balance adjustments to the scene-referred data anyway. After loading the images, select all images, right click → Reset → Reset user defined → check only Color and select *to one (no color correction). Click ok.
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After considering the above, I began wondering if any of the photometric corrections are meaningful. After setting the image response to Linear and disabling all the color corrections, vignetting correction is all that is left. However if lens correction is applied in darktable, vignetting should be already taken care of. After resetting the values as described above, one can probably actually skip pressing the photometric calibration button altogether and leave vignetting parameters to zero.
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Speaking of lens corrections, distortions are also already handled in darktable lens corrections module if data is present. Therefore you can skip optimizing the distortion parameters in Hugin. Select e.g. Positions (y, p, r) in the Geometric optimizations combobox instead of Everything. Note that the case may be different if you can’t undistort the image in darktable. For my handheld panorama this turned out to be sufficient.
Pretty satisfied with the outcome. Could have bracketed several exposures for each view to improve SNR in the dark areas, but I’ll leave it for the next time.
