Low-cost stereo camera

Introduction

It's possible to find action cams for few dozens of euros. Building such a low-cost stereo camera could be a big interest for 3Denlive development, because of cumulative problems that need to be fixed.

I bought 2 full-options cameras for 70€ each (with an Amazon 30% promo):

• 20Mpx photos
• 4K videos
• back preview tactile screen
• remote control
• a lot of small equipment provided
• a lot of filtering capabilities: HDR, Stabilization, Lens Distortion Correction, etc

I also bought a small equipment to build a stereo slider:

• 2 base plates
• a set of rods

Together with 2 SD memory cards the total cost is around 270€.

First contact

Assembling the stereo slider is just a play for a kid.

Good news: the remote control is firing both cameras at the same time!

It's not enough synchronized to take a shot of a fast moving object, but comfortable to take multiple shots of a scene with only one click at each.

Video mode is a bit more capricious: both cameras are often properly starting together, but sometimes only one is stopping while the second one still records. It's thus necessary to end it with its own button to avoid restarting the first one.

Tiny technical problem: the plastic USB socket cover is not opening enough to plug it comfortably. It's a risk for the USB plug to be altered in time. Fortunately, the link of this plastic cover is a bit elastic. It may be lengthened by pulling on it without breaking.

Horizontal alignment

Using one of the rods properly put on the back screens of the cameras, it's possible to get a first honorable alignment of the cameras, leading only a very small convergence problem. It's possible to adjust the convergence doing several test shots. But, it's hard to be perfect. This means little perspective problems to deal with afterward.

The slider then offer the possibility to change comfortably the stereo base without damage on the convergence adjustment.

Vertical alignment

On my cameras I get a vertical misalignment. I first thought is was because of the plastic cages. But, when exchanging the cameras, the vertical alignment is also reversed. It's thus certainly a problem like a lens-shift due to a not homogeneous built of the cameras. At this time, I didn't find a comfortable way to fix this problem. Using one of the provided holder with vertical rotation capabilities will certainly be even more complex to adjust. Without a solution, the stereo needs to be vertically aligned in a software post-processing.

Distortions

I obtained quite comfortable stereo views, but the fish-eye distortions makes the surrounding very hard to align, thus a bit uncomfortable to view.

I think this problem on surrounding parts is aggravated by the above building lens-shift. Doing a lens-correction to avoid curvature of straight lines is then very tricky! It's often better to keep the fish eye distortions than trying to rectify the images.

Using the built-in rectification parameter doesn't bring a good solution: there are still complex distortions between views.

Image quality

Zooming to the pixel level there is a lot of grain. But, the 4K global image is quite good.

Images seems to be a bit under-exposed and with quite a low contrast. Colors are also a bit dull. This could be fixed either by cameras exposition parameters or by a software post-processing.

(TO BE CONTINUED)