I appriciate the helpfullness, but unfortunately I cannot share the
images since the originals are not mine.
However, I worked this evening with this on a few images and tested
several methods and have great help of your input. I get good results
now (often subpixel fits), and consistent enough.
The interesting fact is that setting a 1 - 2 degrees FOV is required
for the best results. I've tried to let Hugin optimize it by itself
but it rarely goes down to those low values, even when starting with
the calculated 5.42 degrees. The fit often gets kind of ok with that
5.42 starting point, but not as good as it can get. I suspect that
this is a special case occuring for this type of repro setup when
there are just minor but still some yaw/pitch errors. Almost perfect
perpendicular, but not 100% as a flatbed scanner, and not as large as
hand held mosaics of walls. Seems to fall outside normal optimization
space.
I've also tested auto control points, and it works kind of ok, but
there's always some outliers so I think I continue do them manually,
having relatively few points and well-defined places gives me a better
overview of stitching result I think, but I guess it is a matter of
taste.
I normally don't pre-correct lens distortion, since Hugin indeed does
better fitting result if it can correct barrel etc itself, but in this
special case the optimizer easily goes haywire so having close to
perfect rectilinear input seems to work better. I've also tried to pre-
correct roll, but it is not really worth it, that correction works
well.
This is the hugin workflow that gives me consistent results so far for
this application:
* Create new project
* Open the 16 bit tiff images (usually four)
* Don't use the field of view from EXIF, instead pre-set to 1 degree.
* Make control points to connect all images
* Make horizontal (and possibly also vertical) guides on all images
* You should have included film edge on all your frames and that is
what you use as guide
* Now the exciting part - the optimizer tab
* First correct X and Y for all but one
* Then add roll to all and optimize again
* Theoretically this would yield perfect result already here,
but as
said the repro setup is rarely that perfect
* Then add Z for all but one and yaw and pitch for all, and
optimize
again
* Then open up GL preview, goto move/drag and select drag
mode "mosaic", and then drag the image into the center of the
view,
close and optimize again
* Typically the optimizer has put the image far from center,
and
moving it back into the middle again and reoptimizing can
give
better result.
* You can try to add lens view as a final parameter but that
usually
does not improve things.
* Open up GL preview
* Choose rectilinear projection
* Mosaic-drag so the center is in the center of the image
* Fit/autocrop the view
* Stitch to 16 bit tiff output, for further processing in your
favourite raw converter or photo editor
On Jan 30, 7:08 pm, "Carlos Eduardo G. Carvalho (Cartola)"
<[email protected]> wrote:
> Well, I did mosaic maybe only a couple of times, but I didn't remember
> having difficulties. I wouldn't do lens correction before hugin and I
> wouldn't think of doing so much precise controls. Maybe with macro they are
> more important, but I really don't know. Manual CP are surely not a
> problem, just make sure you use at least 3 between each pair. Many times I
> use only 3 (but to do spheric panoramas). Can't you give us an example
> image set? Could be reduced size jpg preferably without any previous
> processing, like that lens correction you mentioned.
>
> Is FoV so much important? Many times I just put a reasonable value and let
> the optimizer correct this. More important is to guarantee that it won't
> think it is a 360º panorama, so I would think any kick to guarantee that
> the total FoV is not going to get to 360 would be a good start, but again,
> "guessing" here looks to me like a little loose of time if compared to see
> your images to address the real problem.
>
> Cheers,
>
> Carlos E G Carvalho (Cartola)http://cartola.org/360
>
> 2012/1/30 torger <[email protected]>
>
>
>
>
>
>
>
> > Sorry for spamming... just came to think about FoV. Macro lenses are a
> > bit special, fov doesn't match focal length at near limit. My 150mm
> > macro lens from the focal length says "13.69 degrees fov". But at 1:1
> > distance is 380mm so the fov would then be 2 * arctan(36/2 / 380) =
> > 5.42 degrees, that is about the same as a 380mm lens. Anyway, I'll do
> > some more experiments and report about the results.
>
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