360 Media What the Heck Is It?

An Introduction into 360 Media.

March 16, 2020

Have you ever searched for a restaurant on google maps when you’re in a new city? If so, you’ve probably encountered 360 photography. Maybe you’ve also seen a 360 photo on your facebook feed by a friend who’s experimenting with 360 photography as well. The introduction of 360 photography, 360 video, Virtual Tours and Virtual Reality into Google’s and Facebook’s product offering is changing how we interact with small business and international brands, but largely this new type of media still lives in the world of science fiction to many people in the world. People who’ve been exposed to the media know it exists, but understanding its possibilities can be difficult, but in this article I’ll distill what is 360 photography and how is a 360 photo made.

A 2D photograph is a window or frame into another time & place created by a photographer. A skilled photographer can give you a glimpse into a styled environment sending you a specific visual message while also suspending your disbelief that this environment is fabricated. Maybe the photographer forgoes the suspension of disbelief and shows you a ideal fantasy for you to strive towards. Constructing an image within 2D constraints takes vision and forethought that sometimes can include a photographer, a stylist, a creative director and possibly more! Now imagine all the work put in by this team to create a specific frame and add a third spatial dimension to the process. You lose the ability to high production behind the frame. The camera now sees everything within its 360 visual line of direction. You no longer have the ability to think linearly when the cartesian constraints are thrown out. You now need to think spherically.

Thinking spherically… where to begin. First, let’s start out with some thought experiments. The origin of photography begins at the 2D frame. Imagine this frame is a rectangle laying flat on the ground; now, draw a line from the top to the bottom of the rectangle in the middle. With your imaginary hand grab the top of the line and lift it so that the top of the line is now directly above the bottom and your rectangle is standing upright. Let’s rotate the rectangle around the line like a spinning top. At each infinitesimal change of the rectangles position as it turns around this line captures a new image unique from the previous or next image. What you’re doing is precisely what your camera will need to do in order capture a 360 image if you’re working with a standard DSLR. This thought experiment is actually more of a cylindrical approximation of a sphere. What takes us from a cylinder to a sphere will be discussed later!

This though experiment is a useful tool because everything within the view of this imaginary rectangle will need to be considered because it will be within the 360 composition. You can’t leave your photography equipment laying around, you can’t hide any flaw in the environment. So you must consider the room as whole. This can be problematic for real estate agents or real estate marketers. If there’s a dent / scratch / mark / on a wall, it will be seen. My recommendation before even picking up your camera is to go into the space you’ll be capturing and pick your shooting location(s) carefully.

What takes us from the cylindrical mode above depends on your equipment and technique. From an equipment standpoint, there’s two ways you could go. One is to buy a 360 photo specific camera. Here are some examples.

These will create all content you need to make your 360 photo or create 360 photo for you in the camera. If the option you selected doesn’t output a 360 photo for you but instead provides only 2D frames that need to be stitched. I’ll explain how to stitch these later. If this is what you’re planning on doing, you can really stop here because going forward is practical and theoretical. It pertains only to shooting a 360 photo with a DSLR. You won’t be faced with these complications if you use a 360 camera.

The second method uses a DSLR, panoramic tripod head and a camera lens plus post production magic. Ideally, you’ll be using a circular fisheye lens and a full frame camera, but this technique is possible with a crop sensor DSLR and any lens focal length; the larger the focal length though the more painful and time consuming your prost production will be. The most important piece of equipment in this technique is the panorama gimbal head. It will make or break your 360 image as well play a big part in your post production. If you have a stable and accurate “pano-head”, you can really use any camera lens system. Before we discuss using this equipment we need to talk about a few theoretical aspects. Namely, field of view (FoV) and parallax.

Field of View is measured in degrees and is part of the technical specification of your lens. Field of view is basically what your camera sees from the camera sensor out. High focal length have small field of view, low focal length a large field of view. Now make note of what dimension they mean when they list the field of view of your lens. It’s not always simply the horizontal or vertical FoV, many times it’s the diagonal FoV. For example the samyang 14mm f2.8 fisheye has a diagonal 180 field of view. A circular fisheye by definition has a 180 degree field of view horizontally and vertically.

Back to our original experiment of the spinning rectangle. If we had a FoV 0 degrees, we would see nothing at all because literally nothing is in the FoV. If we had a FoV of 180 degrees we would see everything in front of the frame from ceiling to floor and wall to wall. As I said the only lens that has a FoV of 180 degrees is the circular fisheye lens. Now to capture everything that would be seen in the condition of FoV of 180, you would only need theoretically 2 pictures, a front and back. Circuluar fisheye lenses come really close to 180 degrees but are not perfect so in a realistic situation you could do it with 3. Now as we move down from the 180 degree FoV scenario, we need to do a little bit of math. Let’s think about a FoV of 114 degrees (diagonal) which is an approximate FoV of your typical wide angle lens. For a 24x36 format, the vertical FoV is going to be 81 degrees and horizontal 104. To capture 360 degrees vertically and horizontally we’ll need 4 photos horizontally and 3 photos at every horizontal position. 12 photos total.

How did I do that calculation?

First I calculate the horizonal panorama. 360/104 = ~3.46. You’ll always need to round up on any non integer value.

If I took only these images level with the horizon though I’d only have a field of view of 81 degrees from the ceiling to the floor. To fill in the missing floor and ceiling, I need two more images.

But wait… that covers 243 degrees and not 360 vertically! We didn’t capture everything! But yes we did at the same time.

We stitch the horizontal panorama to create a 360 degree panorama and then fill in the floor and ceiling on each image creating a panorama that 360 degrees horizontally and 180 degrees vertically (2x1) capturing all of the image data for a sphere. This is the equirectangular format and is the standard for mono 360 photography.

I took that FoV discussion to basically its end but we learned some important topics.

  • Calculating the number of images of stitch
  • Equirectangular Format (Mono)

Let’s do one more example at 70mm. The diagonal Field of View 34 degrees at 24x34mm format. The horizontal FoV is 29 degrees and vertical FoV is 19 degrees.

360/29 = 13

180/19 = 10

13 * 10 = 130 images!

That is a lot of images and as the number of images increases so does processing time and the risk of image errors. For this reason I generally shoot with a circular fisheye to speed up my live shooting time and post processing time. If I want a higher resolution image, I might increase to 15mm, but I never go farther than that focal length because it would just be too time consuming.

We need to discuss parallax, and it’s going to take a while to understand if you’re unfamiliar with the word and the concept. Parallax is an amazing phenomena that astronmers use to calculate the distance of galaxies and our brain uses to create depth perception. I think parallax is best described visually.

parallax 1.png

In the first image, I show 2 objects with an overlapping field of view. This is how astronomers calculate the distance of objects in deep space from earth. Imagine that the blue circles are the earth and in between them is the sun. At different times during our revolution around the sun, objects in the sky appear to be in slightly different places. If you measure the distance they move in our field of view and with the know the distance we move in our own solar system, we can calculate the distance of the object. Clearly I’m not a flat earther over here!

parallax 2.png

This is the first application of parallax but what about 360 photography. Let’s look at the second image. Imagine we take a photograph. Then we move forward a meter and take the photo again. The image red object went from being completely in our field of view to being cut off just because we moved forward a little bit. No brainer! It seems completely logical when you look at it. But really think about how it moved. It’s not only closer but if we think spherically, the objects angular position to us has also changed. From the center of the field of view, the angle has increased.

parallax 3.png

In the third image we see the tripod in the center and let’s say the camera is the blue circle in this image. If you rotate the tripod 180 degrees the camera then revolves around the tripod’s center point 180 degrees. Makes sense right? Now Think about what’s behind the camera. FoV A is photographing what’s behind the FoV in B and FoV B is photographing what’s behind FoV A.... but at a different linear position exactly like the second image. What does this mean… This means that the angular distance of objects in this environment from the center of the field of view of these circular blue cameras has changed.

Why is this bad… This is bad because you’re trying to build a sphere. But you can’t build a sphere if you keep moving the center of the sphere around. Practically this means you’ll have stitching errors and maybe even a failed 360 image.

parallax 4.png

Let’s continue with this look at image 4. Now we’re looking at the floor above the tripod. This time I rotate the tripod just a little bit. Now when we measure the distance of the red object from the blue circular cameras as it rotates, the distance is changing. Not only the cartesian distance but the angular distance from the center of the field of view.

parallax 5.png

Now in Image 5, I take the two camera positions, and I place them directly over the center of the camera. FoV A and FoV B overlap, the red object is in FoV B and not in FoV A, but that’s okay because we’re making a 360 panorama and the red object will be in the final 360 photo and all of the objects in the environment will be at the appropriate angular position, and we’ll have a clean 360 photo.

stereo.png

The last image is something I wanted to touch which is stereo 360 images. Stereo is not only a thing that plays music. Stereo describes a dual channel system. Right and Left audio signals vs a mono audio signal is the most basic example. Go listen to Queen right now if you’re confused; they loved to change audio signals between right and left to play with the audience's perception. 360 images, 360 videos Real 3D, VR etc also can use stereo. Visual content creators do this to create a depth perception.

For example you have two eyes, while reading this can you see your nose? Well if you try it will get uncomfortable quickly, but your nose lies in between the FoV of your eyes making it invisible when you’re generally looking around at the world around you. Each eye sees something a little differently because they are physically in different locations like in image 1. This creates depth perception because your brain knows that they’re in different locations and can estimate the distance of things in your composite field of view through years of training your neural networks. Young children and people with only one working eye have worse hand eye coordination because their depth perception is undertrained or they only have one working eye.

Stereo in 360 photography literally means that two 360 photos are taken in different positions and then combined together digitally to give depth perception. That’s why in VR systems there’s a screen for each eye. It is to provide the effect of depth perception. Stereo 360 photos in an equirectangular formar are two equirectangular photos stacked on each other. Equirectangular is 2x1. 2x1 + 2x1 stacked vertically is 2x2 or 1x1. Make sense?

Okay we now know parallax and it’s consequences and usefulness. How can we correct for in mono 360 photography. In the real world, a camera and lens work as a system. This system has a point in it called the “No parallax point” where when the pano-head is turned and the parallax effect does not occur. I’ll discuss the method of finding the no parallax point in a later article, but for now we’ll take it as found.

Now what do we know

  • We know what a 360 photo is
  • We know how many 2D images we need to take in order to create a 360 image.
  • We know how the equirectangular format is created.
  • We know how the parallax effects our 360 photography.

After we have taken our images we go into stitching. I use PTGui as my stitching software. It has other uses outside of 360 Photography which I will also discuss later. I will also talk about using PTGui as well.

In closing of this article, I want to say for 360 photos I prefer the DSLR method. You get 100% control over your images dynamic range, exposure time, depth of field, etc. You can also take 360 photos at night. Using a prebaked 360 camera system takes the risk out of shooting 360 photography, but you sacrifice some elements of control where photography can get really creative. Shooting at night can also be problematic for 360 cameras. In the end though function determines form, and each tool has its proper application.

Thanks For Reading,

Wes


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