FlattenVideoCylinder

My mum had a favourite mug, said mug broke and we couldn't find the design anywhere. It was too involved to just draw from scratch so... I wrote some code for fun.

This code takes in a recording of a spinning object, divides the video per frame, and crops a thin, vertical segment at the centre of the frame. It then appends all of these segments horizontally to output a single image.

Its intention is to create a flattened image of the surface of a cylindircal shape.

Video Requirements

There are a lot of assumptions made about the video here and no kind of error correction or aligning done. The video requires:

• A stable, imobile video (i.e. prop up your camera and make sure it doesn't budge)

• An object centrally aligned in the middle of the camera (vertically and horizontally)

• An object rotating about its central vertical axis, with no precession

• Object rotating at a constant rate

• The video must start and stop when the rotation starts and stops (so crop in time if necessary)

• The best results come from a high frame rate video, high resolution video, and slow (but not snail-paced) rotation speed.

  • Yes there is probably some optimal combination of these factors, no I haven't worked it out. I spun the mug a few times and picked the best output, it was Christmas...

In layman's terms, place the object in the middle, on a flat surface, make sure it doesn't move in any direction other than spinning like a (slow) Beyblade.

Obviously, many of these aspects are difficult to control in a home environment. I recommend:

• Most microwave ovens have a rotating plate and wheel set. This works a charm, just place your object in the middle and turn
• Controlling the rotation speed is near impossible. Try and do it as consistently as you can (from experience, a very fast rotation will give the most uniform result but also lowest quality...unless you have a very fast camera, slow-motion on some phones perhaps could work, I didn't try)
  • Maybe you have a remote control car or a rotating power tool you can keep pressed very lightly with a rubber wheel attached to the end, to spin the microwave oven plate slowly and uniformly. Or maybe you have a lab-based set up, who knows, the world is your oyster.
• Set up your phone as stabley as possible, maybe slightly raised if necessary to make sure it is as close to central as possible to both vertical and horizontal axes

Python requirements:

• Python3 (written in 3.12)
• Packages: cv2, numpy, sys

Usage:

• python Cylinder2Flat.py <input_video_path> <output_image_path> <clockwise (bool)>
  • Arguments:
    • input_video_path: The path/name of an .mp4 file
    • output_image_path: The path/name of the output .png file
    • clockwise (bool): "true/false", is entirely dependent on whether your video has an object turning clockwise (to the left) (true) or anticlockwise (to the right) (false)
• Example: python Cylinder2Flat.py my_perfect_video.mp4 flattened_surface.png true

Disclaimer:

I made this as a fun mini-project just to recreate the surface of my mum's mug after it broke. The result wasn't perfect, but good enough to apply some post-processing colour correction, edge detection and a little bit of editing magic for blemish removal; then uploaded the result to a custom mug website et voila, could barely tell the difference. Well, I definitely could, but she liked it anyway. In theory, it should produce a perfect result, if the video conditions are also perfect, which they will never be... But you can get close in a controlled setting

Feel free to fork and modify this for fun, I hope it can help some people out (or inspire to do better), but I'm unlikely to make any modifications beyond this initial push.