How to capture a perfect Nadir
Capturing the Nadir (the area of the ground directly below the Nodal point of your lens) is probably the most challenging and time-consuming aspect of panoramic photography. It is also important to compose the Nadir properly if you want to turn your image into an interactive panorama. This post will explain some techniques you can work on in order to improve or even design the Nadir of your panoramas. If you are completely new to panoramic photography please read my previous posts: Equirectangular Panorama and HDR Panorama.
As I mentioned before, there are several ways of capturing a perfect Nadir. The most obvious and straightforward technique is to shot your panorama handheld with an 8mm fisheye lens and a so-called ‘virtual tripod’ (a technique I have described in my previous post on Equirectangular Panorama). These lenses have a 180° horizontal field of view so, when placed in portrait orientation, are capable of capturing the entire field of view from top (Zenith) to bottom (Nadir). This also eliminates the need to capture the Zenith and Nadir separately. Unfortunately, handheld panoramic photography is rather challenging, requires a lot of practise and has some serious limitations. Firstly, even with the ‘virtual tripod’, it is still difficult to rotate the camera exactly around the Nodal point. If you distance yourself from the objects you want to capture, in bright daylight, this technique still brings really good results. However, if you get really close, you may experience some stitching mistakes in the final output image. Secondly, this technique is almost impossible to use in low-light conditions and to capture HDR images.
Capturing your panorama with a panoramic head makes the whole process much easier and allows you to capture HDR as well as night panoramas. However, there is a significant price to pay as the tripod remains an integral part of your image. Nevertheless, there are ways of compensating for this.
One of them is to capture the Nadir by extending your tripod’s centre column as demonstrated here. As the author of this excellent post admits himself, this technique may damage your equipment, if you are careless, and may not always be possible as it requires a lot of space.
Another less dangerous and more convenient technique is also described here. This simply requires capturing your panorama with a panoramic head and then detaching your camera from the head for the final Nadir shot. You will probably need an assistant to move the tripod away, while you stay in the same position, holding the camera. Again, while it’s possible to do this in bright daylight, this technique is impractical in HDR and night panoramic photography.
Finally, the last technique is the one I prefer the most and you can read about it here. The only difference is that instead Photoshop, I use Pano2VR to extract the Nadir from my image and then work on it in Photoshop.
What you need is an equirectangular panorama, Pano2VR, Photoshop CS4/5 and some basic Photoshop skills. Below is the panorama I will be working on and, as you can see, the tripod covers the bottom part of the image. Before we start, remember that there’s a lot you can do before shooting your panorama in order to improve the Nadir. First of all, choose the smallest tripod head you have to support your panoramic head. Secondly, tuck your tripod legs in slightly to reduce the area of the image they cover. However, remember that your tripod has to be stable so don’t tuck them in too much as you may damage your camera if the tripod falls over.
The first step is to compose your Nadir from two separate shots as seen in the pictures below. Here I captured the nadir twice, each from a different side, and then combined the two pictures into one image in Photoshop.
Open both images in Photoshop, rotate one of them, and then stack both layers together.
Next, highlight both layers and go to ‘edit’ and then select ‘auto align layers’. Photoshop will then align both images.
Finally, select the ‘eraser tool’ and paint over the part of the image covered by the panoramic head arm. Then, flatten the layers and save the image.
Next, use this image as Nadir to stitch your panorama. Don’t worry if Photoshop slightly rotated the image and there are white spaces near the edges.
Now let’s get down to patching the panorama with Pano2VR. Open your image in Pano2VR and then select ‘Patch Input’. Next, a separate window will appear where you have to adjust the tilt so the preview shows the Nadir. Then, select ‘ok’ and the software will create a patch file in the same folder as your panorama. You can then work on this file in Photoshop.
Open the patch file in Photoshop and now, depending on the version of your Photoshop and your skills, you can either remove the tripod using the clone brush, content-aware fill (CS5) or vanishing point tool. Just select the area you want to remove as seen below. I personally prefer to let the software do the hard work, use the content aware fill and then correct imperfections with the clone-brush tool. The content-aware fill will work in most cases but if your nadir has complicated patterns, you may want to use the clone brush.
As you can see, the final result looks great.
Finally, update the patch and export the equirectangular image in the ‘Convert Input’ menu. You can also use this technique to cover the tripod with your own logo or the company you are shooting the panorama for.
Once you have a panorama with a perfect Nadir, you can experiment with it and place a stereographic projection in the centre of your image. Open your panorama in Photoshop. Then right-click on the layer tab and select ‘duplicate layers’. You should now have two layers stacked on top of each other. Just select one of the layers with the ‘marquee tool’.
Now, right-click on the layer and select ‘free transform’. Scale the top layer down so that the width remains the same and the height now covers approximately 10% of the original image. Next, rotate it by 180 degrees and place it at the bottom of the image. You can also add a shadow to the edge of the layer. The final image should look like this:
Now, if you load this image to any interactive panorama viewer, a small reversed stereographic projection will appear in the centre of the Nadir. See for yourself here.
Thanks for reading and good luck with your panoramic photography.
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