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A place to politely discuss the tools, technique and culture of photography.

This is not a good place to simply share cool photos/videos or promote your own work and projects, but rather a place to discuss photography as an art and post things that would be of interest to other photographers.

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Stitching, How to completely remove perspective distortion? (alien.top)

submitted 10 months ago by Haunting-Crab-1771@alien.top to c/photography@viewfinder.pro

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Hi, I use a Canon 600D with standard 18-55mm, mainly for taking pictures of vehicles that I use as references for drawing and 3D modeling.

My camera is a little old so I have problems to capture enough details for example in dark parts.

Here are some example of photos with the 600D: https://mega.nz/folder/ggcGkC5Z#BtIibPxs4RDETtMRTrqoFw

They have different exposure because some people suggested me to try using bracketing (before buying any new hardware) to have better HDR and details in light and dark but it's not enough so I have to go close to the subject and take photos of the details with smartphone (Oppo find x5 pro): https://mega.nz/folder/cs8mnK4I#iBi2IK9XBikryj4XdNWIRw

Then they suggested me to try stitching which should help even for long subjects like this: https://mega.nz/folder/YwVh3Ryb#znPi53HWDR16HvtEWyd8hQ

with which it is difficult to get closer and photograph the details with the same perspective of the camera.

So I tried stitching with these groups of photos (taken in bracketing just to see the difference of details in dark and light): part 1: mega.nz/folder/El8R0KIJ#IsafbJ2cEpC11aBEpTMR9w

part 2: mega.nz/folder/x1dCWZwS#fNGVUQ5nVu0H8tKTDwtcug

part 3: mega.nz/folder/8kFjUYAK#7PSOl1_oubWSIDsjlnXoWQ

For the stitching I used the 4th photo of each group and this is the result with a bit of post production to try to correct the perspective distortion and enhance the details: https://mega.nz/folder/h4slBaDb#t3ktdm8VuLb-NDfBBc0Lkg

An this is the same vehicle with normal bracketing to compare the perspective: mega.nz/folder/g91XlCbA#9uRM6nnoG7lWPXy5HeqBvQ

I tried the stitching again with this: mega.nz/folder/FwlCiZaC#_2KGhc2nkQNTMAcV3Vya4Q (inside there is both the composite photo and the photo taken normally, for bracketing, to be used for comparison)

And this is one photo of those used for the stitching above which had the zoom right on the point where there were the most hidden details. I tried a little post production but It wasn't able to capture very precise details, they are still too blurred.

So in some cases the stitching helped me to have better details despite the olf 600D with kit lens but there's still the problem of perspective distortion. Is there a way to completely fix the stitching perspective distortion?

(some people also suggested me to mount the camera on a similar slider to fix the distortion: https://www.amazon.it/Neewer-Fotocamera-Cuscinetti-Compatibile-Smartphone/dp/B09WYPRLGM/ref=psdc_412610031_t4_B09QRSVSP3/?&tag=juzaphoto-21 )

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[–] ApatheticAbsurdist@alien.top 1 points 10 months ago

As you move farther away (approaching infinitely far away) the perspective approaches one of being perfectly flat. But for that to work you need to have a VERY long telephoto lens and shoot from a very long distance away.

If you try to stitch a panorama, you need to be parallel to a flat surface. if the object is not flat or not perfectly parallel to you (it's closer on one side and recedes in the other) you're going to have issues with perspective. Closer things will be magnified more, farther things will be magnified less.

There are two solutions. The first you cannot do... and that is a telecentric lens. A telecentric only looks at parallel rays so the magnification in the image is the same regardless of how far the subject is and will create images with no perspective. The problem is for this to work the front element of the lens has to be larger than whatever you're photographing. So it's useful on machine vision cameras checking screws coming off an assembly line but not a giant truck.

The other thing you should look at is photogrammetry where you take many photos and build a 3D model. Once you make that model, you can create an orthomosasic or orthorectified view that corrects eliminates any perspective, but you need 3D data first to be able to do that.

Try to make sure you're shooting straight on to the side of the object and not at a slight angle if you're going to stitch a panorama, that will help. If that isn't good enough, look at photogrammetry.

[–] Omnitographer@alien.top 1 points 10 months ago (2 children)

Can you repost all this images as sanely sized jpg? I'm not scrounging through a bunch of folders on mega measuring in the 10's of megabytes and I don't know who would. All of this could be replaced with a single imgur gallery with labeled images.

Beyond that, photoshop has an Align Layers function which can do various geometry corrections to align images with pretty solid results, have you tried that? I don't know if it applies to your need though because again, your choice of upload format and host is not great.

[–] Haunting-Crab-1771@alien.top 1 points 10 months ago

I used mega because I uploaded the original images in raw format.

With imgur I'd have to reconvert every single image in .jpg

I don't understand what's the problem with mega.

[–] Haunting-Crab-1771@alien.top 1 points 10 months ago

Beyond that, photoshop has an Align Layers function which can do various geometry corrections to align images with pretty solid results, have you tried that?

Yes, I've tried that tool but it didn't completely fix the distortion problem.