Equirectangular Panorama with AutoPano Giga
Equirectangular Panorama is, in simple terms, a panorama that represents a 360˚ horizontal and 180˚ vertical field of view. In other words, it’s a panorama that reflects the entire field of view around you. Obviously, there aren’t any camera lenses capable of capturing such an enormous field of view yet in one capture, so these panoramas have to be stitched from multiple images. Due to a rather technical stitching process, this kind of images are not very popular in mainstream photography but are slowly gaining followers, especially in architectural photography as well as interactive panoramic photography.
This post will explain the basics behind this kind of photography as well as describe the process of taking and stitching the images into a complete equirectangular panorama.
There are basically two ways of capturing images necessary to stitch an equirectangular image. You can either shoot it handheld or use an expensive panoramic head, designed especially for this kind of images. My experience with panoramic tripod heads is limited to a brand called Nodal Ninja, which produces a range of reliable and well-build panoramic heads, as well as provides a great deal of support and tutorials on how to set up and use them. However, there are other, equally good, brands out there and, if you decide to buy one, just define your budget and do some Internet research. Personally, there are some advantages and disadvantages of using panoramic heads you need to be aware. First of all, these heads are quite expensive comparing to other tripod heads and serve only one purpose. Secondly, even though most of them come with a hard case, they are quite heavy and take up space, which is something you have to consider as an outdoor landscape photographer. Lastly, they usually consist of several elements that take some time to assemble and can easily get left behind or lost. The panorama capturing process, including setting up the head, also takes a considerable amount of time. The pros of using a panoramic head, on the other hand, is that you can use virtually any lens to shoot your panoramas and the stitching process, provided the head is set up properly, produces a high quality image which is free of any stitching errors. However, the tripod remains an integral part of the final image.
Unfortunately, in most cases the light conditions are far too challenging and panoramic heads are the only option, especially if you want to overcome the limitations of available light and capture a HDR panorama. I have written more about the pros and cons of using a panoramic head in my recent post about HDR panoramic photography where you can also find out how to remove the tripod from the final image.
Anyway, in this post I will describe the handheld process of capturing equirectangular images, as shooting panoramas using the panoramic head is quite easy and straightforward.
You will need: a DSLR camera, a 8mm Fisheye lens (absolutely essential), an inexpensive hot shoe bubble level (you can get one on Amazon or E-Bay), a long piece of string, a small calibration weight, Hugin (free open source panorama stitching software available for Mac, Linux and Windows) or Autopano Giga (a paid alternative) and a steady hand.
First of all, you will need to make a ‘virtual tripod’. It is simply a piece of string attached to your lens on one end (as close to the rim as possible) and a weight on the other end. Please read the Shooting Panoramas with a virtual tripod post for pictures and a detail description. Instead of a pendulum, I personally prefer using a weight and rest it on the ground but I have also used a small suction cup attaching it to any smooth and even ground such as floor tiles. The main reason for using this technique is to rotate your camera around its Nodal Point (the point where the light enters the lens) instead of rotating it around yourself, as most inexperienced photographers do.
The pictures below demonstrate the correct camera rotation in panoramic photography
Additionally, when rotating your camera, the pitch and roll angles have to remain the same. Therefore, when using the ‘virtual tripod’ technique, the string will lock the position of your camera and the bubble level will lock the pitch and roll angles. This is absolutely essential to avoid stitching errors after the stitching process is complete. Finally, while shooting your panorama, put your camera in portrait orientation. The reason for shooting in portrait orientation is simple. An 8mm Fisheye lens has approximately a 180˚ horizontal field of view. This means that if put in portrait mode, it will be capable of capturing the Nadir (the spot you are standing) and Zenith (the point directly above you) of your panorama without the need to take their separate pictures, which can be quite troublesome.
In panoramic photography, shutter speed and aperture usually depend on the available light. Remember that you will be capturing the whole 360˚ field of view so the light will change with every shot and you should not expect every picture to be perfectly exposed. Simply look through your camera’s viewfinder and set the correct shutter speed. Then, take a look around, observing the light meter of your camera, to determine the least and most exposed readings. If you are facing the sun directly, this will be the most exposed reading, Alternatively, standing back to the sun will be the least exposed reading. The correct exposure lies right in the middle of these readings. For example, if you are facing the sun and your picture is 2EV overexposed, when you face away from it the picture should be 2EV underexposed. Don’t worry about the exposure too much as most panorama stitching software is capable of correcting and blending exposure. The most important thing, however, is to lock shutter speed, aperture and White Balance. Therefore you should switch to Manual mode, set the aperture, shutter speed and White Balance and use the same settings for every picture you take. Finally, shoot in RAW, export your images in TIFF and then stitch your panorama.
So, put your weight on the ground, attach the bubble level to your camera, stretch out the string and, remembering your position, take the first picture. Then, rotate the camera while observing your bubble level in order to preserve the pitch and roll angles and take another picture. Repeat the whole process until you have made a full 360˚ turn and end up in the initial position. While shooting your panorama, also preserve the position and tension of the string attached to your lens. I usually take 8 pictures and always end up with a decent 30%-40% overlap. Before shooting your panorama you can make a small test to calculate how many pictures you can take to achieve a good overlap. Even though, as mentioned before, an 8mm Fisheye lens in portrait orientation will capture both the Zenith and Nadir, most photographers still prefer to capture them separately in case some parts of the image are missing. The whole process may sound complicated but is actually very simple. It also takes some practice to make it perfect. Some people, after shooting their panoramas with the virtual tripod for a while, are able to capture an equirectangular panorama handheld, without using the string at all. It’s all a matter of a stable hand and correct camera rotation. Remember, practice makes perfect!
The stitching process requires panorama stitching software. There is a number of equally good panorama stitching tools on the Internet and my personal favourites are: Hugin 2011 (free open-source, cross-platform panorama stitcher) and AutopanoGiga. This post explains how to stitch a panorama with AutopanoGiga.
Whether you shoot your panorama handheld or with a panoramic head, you should have 8-10 images (if you choose to capture the Zenith and Nadir separately). Below I used images captures with a panoramic head so you can see how the tripod remains an integral part of the picture.
Open AutopanoGiga and load the images.
Next, click on the green icon to create control points. You can also set the number of control points you want the software to find and define the detection type under the ‘group settings’ icon next to the green ‘detection’ icon. When the software finds control points, it will automatically align and display the panorama on the right.
Now, you can either render the panorama straight away or you can edit it. AutopanoGiga offers many editing possibilities so don’t hesitate to play around with your panorama. Just click on ‘edit’ and your panorama will appear in a separate window.
Here, you can shift the centre of your image or straighten your panorama. Click on the ‘vanishing point’ icon and then click along the horizontal line to change the centre of your panorama. Alternatively, if your panorama is distorted you can click on the ‘automatic horizon’ and the software will attempt to straighten your image. If you are still not happy with the result, use the ‘vertical tool’ icon, indicate a few vertical lines in the panorama and the software will try to make them straight. If the ‘stitching quality’ is low you may try to remove the bad control points manually and optimise the panorama again. Finally, close the window and click ‘render’. A separate window will appear where you can select the size of your image and access more advanced option relating to the blending type.
The output image will be an equirectangular panorama which has a 2:1 ratio. The top and bottom of the image will always be slightly distorted, that’s why I always crop my panoramas to give them a more natural look. The final panorama should look like this:
Note that the tripod remains an integral part of the image. If you shoot your panoramas handheld, then you won’t have this problem but you may end up with minor stitching errors. This image shot with a panoramic head, on the other hand, has a perfect stitch with no errors. If you want to find out how to remove the tripod from your panorama, read my other post: How to capture a perfect Nadir
This is it. I hope you have enjoyed this post and will try to shoot your own panorama soon.
For inspiration visit the following Flickr groups:
Read about the largest indoor panorama in the world, taken by Jeffrey Martin in the Strahov Monastery in Prague and stitched from 2947 images.
If you want to learn more on this subject visit Rosauro Photography for sound advice on equipment, capturing techniques and the stitching process.
This article was also published in Cultor – an Italian arts and photography collective
Thanks for reading and good luck!
Please see the ‘About‘ section for copyright information.