Blank space

[Fugue]

Hi,

I'm trying to refine my process of creating panoramas which I then use to create photomontages using 3D software.

I have to follow a set of guidelines in creating these images and when taking the photographs I'm careful to set the camera up as close to perfectly level as possible. Often, when aligning the images in PT, I get a line of blank space, sometimes at the top, sometimes at the bottom. Whilst it's easy to crop out this space it does lead to some slight issues when I'm working on the 3D side of things (which is convoluted to explain).

Does this blank space mean that the panorama wasn't as level as I thought? It's strange because even though there is this blank space, the photographs line up perfectly level and evenly when using a cylindrical projection.

[Erik Krause]

Am 29.11.21 um 10:37 schrieb Fugue:

> Does this blank space mean that the panorama wasn't as level as I thought?
> It's strange because even though there is this blank space, the photographs
> line up perfectly level and evenly when using a cylindrical projection.

Please show us an example, otherwise it's only guessing we can do.

However, most of the time you simply didn't shoot an image where the
black space is. So you need to check your shooting pattern.

BTW.: It is not strictly necessary to shoot exactly level, especially if
you have vertical lines in the panorama that can be used to level later
in PTGui. See f.e. http://www.johnhpanos.com/levtut.htm

If your zenith shows a black area it might be advisable to shoot one
additional image upwards. Similar applies to the nadir.


--
Erik Krause

[Fugue]

Hi Erik, thanks for your quick response. Attached is an example of what I'm seeing happen although this isn't quite as pronounced as it sometimes is. There's often a bit more space at the top showing.

If I crop it using either method the horizon isn't in the centre of the image which I can see because of the 3D work I have to do. I can only assume that the panorama wasn't shot perfectly level but then why does it not exhibit some sort of curve in the panorama if the camera was pointing down (or up) slightly? All photos are taken with a tripod, levelling plate and uses a sliding plate to avoid the parallax error, just to be clear.

[John Houghton]

On Monday, November 29, 2021 at 9:37:28 AM UTC Fugue wrote:

I'm careful to set the camera up as close to perfectly level as possible. Often, when aligning the images in PT, I get a line of blank space, sometimes at the top, sometimes at the bottom. Whilst it's easy to crop out this space it does lead to some slight issues when I'm working on the 3D side of things (which is convoluted to explain).

Normally, it is the panorama head that needs to be levelled rather than the camera.  This is to ensure that the vertical axis of rotation is exactly vertical.  When the panorama is then levelled to get the vertical features properly vertical, you will get a panorama image with nice straight top and bottom edges.  If the camera was angled very slightly up or down, the Panorama Editor window may show a narrow black line at the bottom or top owing to a symmetrical crop, assuming your panorama vertical fov is less than 180 degrees.

John

[Fugue]

Thanks John. It is the panorama head that I'm levelling as it sits on the levelling plate, then (as I don't trust the bubble in the panorama head) I place a bullseye spirit level on top of this to get it levelled as precisely as possible.

I think I better do a few more test shots to work out what's going on.

[Erik Krause]

Am 29.11.21 um 12:55 schrieb Fugue:

> Attached is an example of what I'm
> seeing happen although this isn't quite as pronounced as it sometimes is.
> There's often a bit more space at the top showing.

Ok, this is far from spherical, so no zenith coverage problem. But since
the black stripe is almost identical in width it shows that your tripod
head is perfectly level. It might be the camera which points slightly down.

> I can only assume that the panorama wasn't shot perfectly level but
> then why does it not exhibit some sort of curve in the panorama if
> the camera was pointing down (or up) slightly?

The curve only occurs if the rotation axis is not vertical. If the
camera points slightly down, which it seems to do here, all images are
tilted down the same, which shifts the whole panorama down a bit. So if
you want to shoot with symmetrical space below and above the horizon
you'd need to level the camera in an extra step. What kind of panoramic
head do you use? Does it allow to tilt the camera up or down?

--
Erik Krause

[Fugue]

It's a nodal ninja 6 so no, it doesn't allow me to tilt the camera unfortunately. I mainly shoot in landscape using a bracket and sliding plate attached to the camera but also use it for portrait panoramas in which i get the same problem. I've tried to use the levelling system inside the camera too (Canon 5d mkIV) out of interest but still get this same issue - you can't fine tune the levelling with the in-built levelling system so not surprised here.

I've just tried it - levelled the camera using the spirit level, then checked the in-built one and it is showing as perfectly level. Taken 8 shots at 15˚ intervals and aligned them in PT. Same thing, line of black space at the top. Then tried adjusting the level to point the camera up a little and I got the same output.

I wonder if it is the process I'm doing within PT... I did set up a lens profile a while ago as this 50mm lens (Canon EF f/1.2 L) seems to always show up in PT as near 51mm when using 'Optimise lens focal length'. My process then would be to have that option unchecked by default (since I have the lens profile selected) and click align images. One thing that I'm confused about is that no matter which option I select on 'minimise lens distortion' the optimizer switches to 'Heavy + lens shift' and introduces about -0.5%.

[Erik Krause]

Am 29.11.21 um 15:19 schrieb Fugue:

> It's a nodal ninja 6 so no, it doesn't allow me to tilt the camera
> unfortunately.

The NN6 has an upper horizontal arm. that can be tilted, such that the
camera points above or below the horizon. Don't you use it?

If you do, simply point the camera slightly up.

--
Erik Krause

[Fugue]

When I'm doing portrait panoramas I could do but they're in notches, I think every 7.5˚.

When doing landscape panoramas I can only adjust it with the levelling plate and I'm still getting the black space no matter what I do.

[Erik Krause]

Am 29.11.21 um 15:47 schrieb Fugue:

> When I'm doing portrait panoramas I could do but they're in notches, I
> think every 7.5˚.
>
> When doing landscape panoramas I can only adjust it with the levelling
> plate and I'm still getting the black space no matter what I do.

Try the following:
Set up your panoramic head as usual in a place with flat floor (your
living room might do, use the longest possible distance to the opposite
wall). Measure the exact height from the floor to the lens center (or
simply shoot it as near to the lens as possible). Now place your rule on
the opposite wall and shoot an image, such that the rule runs across the
center. Zoom in and read the rule in the image center. It should be the
same height as previously measured. If not, correct the NN6 camera plate
accordingly, it has two sliders that can be adjusted:
->
https://cdn.shopify.com/s/files/1/0220/4654/products/NN6_SP_14_625x625.jpg

In your example image the image center is clearly below the horizon.
However, if it's only the black stripe that bothers you: You can drag in
yellow cropping lines from the edges of the panorama editor to crop them
away.

--
Erik Krause

[John Houghton]

On Monday, November 29, 2021 at 2:19:13 PM UTC Fugue wrote:

One thing that I'm confused about is that no matter which option I select on 'minimise lens distortion' the optimizer switches to 'Heavy + lens shift' and introduces about -0.5%.

If you select the Advanced panel of the optimizer tab, you have complete control over which parameters can be changed by the optimizer and which parameters will remain fixed.  Check and uncheck boxes accordingly.

John

[PTGui Support]

Leveling is not the issue: if you shoot unleveled, the result is a wavy
panorama (or a straight panorama with a wavy horizon).

The vertical asymmetry is caused by shooting tilted. The camera may be
sagging a little bit under the lens weight.

Or it could be caused by parallax: you'll have control points on the
floor but none in the sky. The optimizer may shift the panorama up or
down in an attempt to fix parallax. But parallax would be evident from
high control point errors (say, above 5).

Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

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[Fugue]

Thanks both.

Erik - I'll give that a try tomorrow. I think it makes sense to take it back to complete basics and work out why these aren't coming out level no matter what I try.

I would love to just be able to crop out the black stripe and, to a degree, I can. The problem is that when I match the camera in the 3D program I have to use a camera type that can simulate a cylindrical panorama and if I have to angle the camera up or down too far it bends the edges and so I can line the 3D model neatly in the middle but then towards the edge of the panorama it doesn't look right.

John - I had literally just spotted that when you sent the message. Should have seen that before so will make good use of that in future.

I was reading some other threads and there was talk of not using 'Align images', just generating the control points and then using the optimizer. But I guess all that is doing is cutting out a few of the processes that PT does automatically which you can control in the project settings...

Thanks for your help so far, it's much appreciated.

[Fugue]

I will double check my parallax setup but think it should be ok. I don't get very many errors and looking at the example I gave there isn't one higher than 2.

[PTGui Support]

> degree, I can. The problem is that when I match the camera in the 3D
> program I have to use a camera type that can simulate a cylindrical
> panorama and if I have to angle the camera up or down too far it bends
> the edges and so I can line the 3D model neatly in the middle but then
> towards the edge of the panorama it doesn't look right.

If you shot leveled (and parallax is ruled out), the horizon of the
scene will be dead center in the middle of your panorama. The tilt
doesn't matter. Even if you shot at a significant tilt angle, the
horizon will be exactly in the middle.

So I think (if I understand you correctly) your virtual 3d camera
shouldn't be tilted.

Joost