Automatic Crop?

[thomash2]

Is there such a thing as automatic cropping of circular fisheye
images? I thought I noticed them before while trying out other
stitching software. Is it possible with PTGui, or could it be
something to look forward to in the future?

Sometimes my camera or lens shifts a little bit and each shot doesn't
have the circle exactly at the same place. Using a template, I
sometimes have to manually adjust the circle and it's time consuming.

Thanks
Thomas

[John Houghton]

On Feb 22, 10:20 am, thomash2 <thomashua...@gmail.com> wrote:
> Sometimes my camera or lens shifts a little bit and each shot doesn't
> have the circle exactly at the same place. Using a template, I
> sometimes have to manually adjust the circle and it's time consuming.

For small lens shift variations, just optimizing with individual shift
parameters should be good enough. It might be useful to provide a
facility to adjust the individual crop parameters by adding the shift
values in order to centre the crop circle on the optical centre of
each image.

John

[PTGui Support]

Yes that might be useful.

But for alignment, optimizing for shift is sufficient; the resulting
image transformation is exactly the same as when shifting the crop, only
the masked circle is not moved.

I assume the lens doesn't move between shots, so a global optimization
for shift should be sufficient. PTGui now does this by default.

Joost

[Bjørn K Nilssen]

Pￜ Wed, 22 Feb 2012 14:46:03 +0100, skrev PTGui Support <sup...@ptgui.com>:

> Yes that might be useful.
>
> But for alignment, optimizing for shift is sufficient; the resulting
> image transformation is exactly the same as when shifting the crop, only
> the masked circle is not moved.
>
> I assume the lens doesn't move between shots, so a global optimization
> for shift should be sufficient. PTGui now does this by default.

My lens actually moves, or rather bends/sags, because it is so long and heavy (Raynox).
I typically shoot 4 + zenith(60 degree) in HDR, and the zenith shot(s) have a slightly shifted circle.
I usually start with the same crop circle for all.
Then I go to the zenith shot and just move the crop circle (individual + HDR-linked) slightly to make it fit better.
Works very well, and isn't much work :)
It does work pretty well without that special crop/shift treatment as well, but the optimal is to use a different shift.

--
Bjï¿œrn K Nilssen - b...@bknilssen.no - 3D and panoramas

[thomash2]

> I assume the lens doesn't move between shots, so a global optimization
> for shift should be sufficient. PTGui now does this by default.

My lens shifts a little bit between shots. Sometimes a little to the
left, sometimes a little to the right, etc.

I just wonder if there was a way to automatically crop all of them
without having to go in and adjust each time.

[PTGui Support]

Hi Thomas,

Recognizing the crop circle is easier for a human than for a computer.
An automatic cropping algorithm would not be very accurate: it would be
disturbed by black areas near the edge, or by lens flare reflecting
inside the lens. So the automatic adjustment of the crop circle would
probably cause greater errors than the actual movement of your lens.

Joost

[John Houghton]

On Feb 23, 4:37 pm, PTGui Support <supp...@ptgui.com> wrote:
>
> Recognizing the crop circle is easier for a human than for a computer.

This is true, but what is happening here is that the image circle is
physically shifting from shot-to-shot, but remaining a constant size.
If the individual lens shift parameters are optimized and the
respective image circle crops are adjusted to be centered on the
optical centre of each image, the shift parameters then take up values
close to 0 and the circular mask is nicely positioned on the image
circle. I have done this manually and it works quite well. Hugin
already provides this option, though there the crop circle is simply a
mask with no cropping action, so the individual lens shift parameters
aren't affected by the changes in mask positions.

John