How to make spherical (360) panoramic image with 2:1 aspect ratio?

Question

The objective is to make a spherical-typed (360 degrees) panoramic photo, With 2:1 aspect ratio, and its dimensions are 1024x512 or 2048x1024.

Tried searching in Google but still don't know where to start. Please describe a step by step guide.

Possible questions :
What are the needed tools for taking the photos ?
How many photos needed to be taken ?
What is the best software for stitching those photos ?
And how to use it ?

If there are anything I missed, please mention it. Thank you very much !

Update :
I want to make an Android application that displays virtual tours with spherical panoramas.
In one scene, there is something like a ball / sphere, with the camera inside, on its center, and the user can look freely in 3-dimensional 360 degrees.

I'm using PanoramaGL for Android (https://code.google.com/p/panoramagl-android/), by Javier Baez.
The sample panoramic photo looks like this : (Photos by Geovanny Raura)
https://i.sstatic.net/7FDls.jpg (There are 3 images)

Answer 1

Spherical panoramas have a 2:1 aspect ratio because the field-of-view is 360° x 180°. You obviously need enough photos to cover the whole surrounding. If you use stitching software, then you need to have some overlap between images and will take slightly more images than enough to cover exactly the 360°.

As a minimal setup, a single camera with a lens on each side, mounted on a tripod, can do this. If you use such camera, a remote-trigger device, like a cell-phone is needed to trigger it.

Otherwise, most camera will do. If the camera has manual controls, including manual focus, then it will be easier because you can ensure consistency between shots. With a smaller the field-of-view, more shots will be necessary. Considering your resolution requirements are low though, I would opt for something very wide. With a fisheye lens covering 185°, you only need two shots. A compatible camera is obviously required.

Ideally you take the shots while rotating around the nodal-point of the lens. Doing so precisely by hand is nearly impossible, so most people use a panoramic head. If your lens is fixed focal-length, there are some models which are made precisely for a combination of camera and lens and need no adjustments. Otherwise, you need to calibrate the head to your particular combination of camera and lens at the focal-length you intend to use. This is not hard, just tedious and you have to be careful not to accidentally change things. The closer things are to your camera, the more important this is. For an indoor spherical panorama, consider a panoramic head essential.

Most stitching software can stitch such images and the success-rate depends mostly on the subject matter. You can even try free software first and if those do not work, move on to a paid solution. A good number of software now attempt to automatically stitch images which works surprisingly well. One such is MS ICE which I reviewed here. It's hit or miss. When it works, it does and when it does not, well, you have to trying another.

Answer 2

I have been using Hugin as a panorama stitching tool. Its help file states that the equirectangular mode that it supports is a spherical mode. The last tab is the stitcher page and it has dimensions that you can enter for cropping. It also shows how many pixels the panorama has before cropping. I am thinking that with this info you should be able to output a 2:1 ratio equirectangular mode panorama. I hope that this helps you.

You would first need to shoot enough frames to cover 360 degrees. Remember that you may have to shoot in portrait mode and have two or more rows of exposures to get enough height to allow a 2:1 ratio when going 360 degrees. I would normally sweep 8 exposures overlapped about 30-40 percent (10mm crop sensor lens) to get 360 degrees. Don't forget to measure the nodal point of the lens and buy ($1200) or make ($10) a panoramic head so the camera always rotates about the lens nodal point to avoid parallax which will make it difficult to stitch the frames together if there are objects close to the lens.

Depending on your camera you could end up with a 15,000 x 7500 pixel photo (112 megapixels). I would then downsize it in something like Adobe Lightroom to the exact pixels you need.

Sincerely, Steve Pituch http://hugin.sourceforge.net/

Answer 3

The tools you need are a camera with a lens, and panostitching software that can create a 360x180 panorama in equirectangular (2x1) format (Hugin is a good open source application).

Tools you'll probably also want are a tripod and panohead to rotate the lens around its no-parallax point to reduce possible stitching errors. The smaller the space you're shooting in, the easier it is to get parallax that will interfere with a clean stitch, because objects will have moved relative to each other between member shots.

The number of photos you need to take depends upon the camera and lens you're using. Each image can only cover a specific amount of the scene, and to make an equirectangular, you need to cover the entire sphere, so even with an ultrawide zoom, you're liable to be shooting multiple rows of images, as well as a zenith (straight up) and nadir (straight down) shot. Most people who shoot these kinds of panos prefer fisheye lenses, because of the larger coverage. A lens with a 180-degree HFoV can cover the scene in four shots (theoretically two, but there would be no overlap for stitching). A fisheye lens with a 135 degree HFoV (like the micro four-thirds Samyang 7.5 fisheye or Sigma/Nikon 10mm-ish fisheyes) would require six shots around and a zenith and nadir. An ultrawide like a 10-20 rectilinear lens would typically require two to three rows of 5-8 images, and a zenith and nadir.

The best free package for stitching these types of panos is, as I mentioned above, Hugin. Commercially, there are quite a few other packages, but PTGui tends to get mentioned the most. Using these packages, well, each has its own tutorials on the website, but the basic steps are typically loading the files, aligning them (where the package software determines control points on the member images that correspond to the same places in the scene), optimization/alignment using the control points, and then output of the final stitch.

This is a rather involved task and it has a steep learning curve. Don't expect to learn it all in a day.

See also: "How are virtual tour photos taken?"