Using PTGUI for 2D scanning

[Bellevue Fine Art Repro]

Hi Group, 

I'd like to go back to this as a general question now that I've had some time to go through the last comments and issues we've had using PTGUI for stitching 2D artwork, because we're having a lot of problems getting it to work. 

I've looked at ALL of the tutorials online, and from what I see, there isn't a tutorial that discusses how to use PTGUI to stitch images that have been scanned, for example, using a scanner. As I said in my first post, we are using a medium format camera, and the camera is parallel to the wall where the artwork his hung, and the artwork is moved, but the camera is not. This means that the camera angle never changes, and each shot is parallel to the artwork. But PTGUI by its very nature is looking for curvature and, and when it doesn't find it, it creates it. 

We've noticed that when we run "optimize", PTGUI changes the angles and pitch (yaw) and the lens setting to what it thinks it should be. We've also noticed that when an image doesn't stitch, we're better off moving images around in the preview window and letting them snap into place, but as soon as we run optimizer after that, PTGUI messes it up again. 

We have also noticed that PTGUI seems to do better with landscapes than with Illustrations, as if it's looking for landscapes in an AI sort of way, and recognizing the horizon line. 

The only information we've gleaned from the tutorials is to turn off lens correction but leave chromatic aberation checked when exporting from Light Room... 

So my general question is, Is there a set of best practices to setup PTGUI for putting together artwork? What should we. be doing with these settings to flatten out the image again when there are issues?

It would be very helpful to have some understanding of what each of these things does, and this: 

For example, I am adding a dropbox link to a project I created. It is a painting with three rows of five images. PTGUI seems to recognize that there are three rows of images, as we can see them in three sets of five in the source images panel. But PTGUI wants to put them all on the same row, despite there being enough information in the image to differentiate between the rows.... 

NB: We are not using the pro version. It looked like the pro didn't give us anything we needed, but we can upgrade to pro if it will help. 

NB 2: I just deleted all of the images in this post because I was getting an error that the message was too long. 

Project: 

https://www.dropbox.com/scl/fo/9w8x2c4djl6no7306qh6z/h?rlkey=fkysxc7n86dqy7y7s678oqg76&dl=0

Thanks for all your help. 

Scott

[Bellevue Fine Art Repro]

This image has only two pieces, and was taken with a Betterlight 4x5 scanback. PTGUI asked for the sensor size, and then gave me this: 

This is an example of what we're seeing with PTGUI with flat 2D art that should be very easy to stitch... 

[PTGui Support]

Hi Scott,


Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

On 06-02-2024 00:14, Bellevue Fine Art Repro wrote:
> I've looked at ALL of the tutorials online, and from what I see, there
> isn't a tutorial that discusses how to use PTGUI to stitch images that
> have been scanned, for example, using a scanner.

This should work, see 6.5:
https://ptgui.com/support.html#6_5

If the camera was pointing perpendicular, the first method described
here should work. For all other cases (non constant distance from the
artwork, non perpendicular) you would need to use viewpoint correction.

> We've noticed that when we run "optimize", PTGUI changes the angles and
> pitch (yaw) and the lens setting to what it thinks it should be. We've
> also noticed that when an image doesn't stitch, we're better off moving
> images around in the preview window and letting them snap into place,
> but as soon as we run optimizer after that, PTGUI messes it up again.

The only explanation I could give is there is a faulty control point
somewhere. Perhaps there's a duplicate or repeating structure in the
image. One way to find out is by dragging the image into place as good
as possible. Then take a look at the Control Points table, sort it by
distance and check if there's an outlier with a very large distance.

> We have also noticed that PTGUI seems to do better with landscapes than
> with Illustrations, as if it's looking for landscapes in an AI sort of
> way, and recognizing the horizon line.

The control point generator works best for landscapes and photographs in
general. It struggles with other kinds of images, like line drawings or
night skies.

> > For example, I am adding a dropbox link to a project I created. It is a
> painting with three rows of five images. PTGUI seems to recognize that
> there are three rows of images, as we can see them in three sets of five
> in the source images panel. But PTGUI wants to put them all on the same
> row, despite there being enough information in the image to
> differentiate between the rows....

The tiff files in your dropbox are broken, they are all zero size. So I
can't see the images but I can open the project file.

If I go to Control Points and select image 1 and 6, I'm seeing two
control points which are both in the left bottom corner of the two
images. If the images are on two different rows, I would expect them to
be at left bottom in one image, and left top in the other. With the
images loaded perhaps you can see what's going on there.

Secondly, the project is not set up as explained in 6.5 above. You can
fix that as follows:

Go to Lens Settings, and set Focal Length to 1000mm.
Click Reset to set all lens correction parameters to zero.
Go to Optimizer and uncheck 'Optimize lens focal length'
and set 'Minimize Lens Distortion: Heavy'.
Then re-run the optimizer.

If you are able to share the original images I'd be happy to take
another look.

Joost

[PTGui Support]

The red warning message in the main window tells me there are no control
points at all. This should be fixed first.

But please start from scratch and follow 6.5:
https://ptgui.com/support.html#6_5

You certainly will not see any bulging if you follow this.

Kind regards,

Joost Nieuwenhuijse
www.ptgui.com

On 06-02-2024 00:51, Bellevue Fine Art Repro wrote:
> This image has only two pieces, and was taken with a Betterlight 4x5
> scanback. PTGUI asked for the sensor size, and then gave me this:

> *Project: *
>
> https://www.dropbox.com/scl/fo/9w8x2c4djl6no7306qh6z/h?rlkey=fkysxc7n86dqy7y7s678oqg76&dl=0 <https://www.dropbox.com/scl/fo/9w8x2c4djl6no7306qh6z/h?rlkey=fkysxc7n86dqy7y7s678oqg76&dl=0>

>
> Thanks for all your help.
>
> Scott
>

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[Bellevue Fine Art Repro]

Thanks so much for your help Joost. We're learning how to use PTGUI for flat scanning, even if that's not what it was intended for, and with your help we're starting to get some good results, even with illustrations. The FAQ section 6.5 was very helpful. 

We too discovered in some cases we didn't have enough overlap, but in most cases using your recommended settings as a starting point has been very helpful. Also upgrading to pro so that we can use the masking tool has been helpful as well. 

thanks for your help. 

Scott