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Google Street View Photography Virtual Tour Visual Storytelling

What is a photosphere?

A photosphere is a panoramic image that covers 360 degrees horizontal and 180 degrees vertical. In other words, it covers an entire sphere, which is where it got its name.

But the real question is how is it created? Images are shot with a camera on a special mount made specifically for the task. The details of how the mount works are very technical. If you’re interested in exploring them, here is a good article: Entrance Pupil Alignment. Using the special mount, four or more overlapping images are captured. The number of images varies depending on the lens used and the resolution required for the final image.

Images required to assemble photosphere

Capturing the images

These eight images where shot in two rows of four. Each image overlaps four other images. I also use a technique called HDR for capturing the dynamic range of the scene as explained in my previous blog. I take eight positions with five images each for a total of 40 images. The 40 images are fed into PTGui, which is a panoramic stitching program used to assemble the images. The resulting image is called an equirectangular projection and it has an aspect ratio of 2:1 or 360:180 degrees.

Resulting image from the 40 images

Stitching the images together

The bottom of the image includes an area that was obscured by the camera head and tripod. I bring the image into the program Pano 2 VR where a patch for the area lost to the tripod is cut out. A replacement image is created in Photoshop and used to replace the patch. There is also an option for creating a mirror ball that reflects the image onto a sphere.

Equirectangular image with nadar patch

You can see in this image that the brickwork has been cloned in. The image is ready for publishing.


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Creating the tour

This isn’t the end of creating a virtual tour. Once all the images have been uploaded to the server, they need to be connected and placed in their proper position on Earth. The moderation process is a science in itself. Each image is moved and rotated until it lines up. This ensures that the perspective doesn’t change as viewers move from one photosphere to another. For quality control, Google inspects each tour. If all the requirements are not met, the tour is removed from public viewing until the errors are fixed. This is one of the reasons why you need to be a hire a Google Trusted Photographer. Google wants the photographers who create virtual tours to be trained and capable of creating tours that the public and business owners will enjoy without any intervention required on the part of Google. Yes, you can get photospheres shot and hosted on other sites. But why not put your business in front of Google Maps users by working with a Google Trusted Photographer like Story In Focus?

Categories
Google Street View Photography Video Production Virtual Tour

What is HDR

When shooting virtual tours, we take three to nine images, each at a different exposure. Then we combine these images into one image. Yes, we use the M setting on our camera. And no, it doesn’t stand for missed another one. The reason we take multiple exposures is so that we can achieve what is called High Dynamic Range (HDR). HDR gives us expanded capabilities which enable us to capture the entire brightness range of the scene and adjust the final image to look just right.

HDR Exposures

In this image, the five exposures are each one stop apart. On the far left, you can see detail in the sky. On the far right, you can see detail in the shadows. When combined these images can have various outputs, depending on the editor.

High Dynamic Range HDR output

We prefer the photographic look of the center image. Although the image on the left is useable, it doesn’t look realistic because the shadows are boosted too much. The image on the right is an art project, which is fine if that is the intent.

Where a single exposure gives a reasonable image most of the time, an HDR makes a good exposure possible in places where there is a high dynamic range. Imagine having to get the same exposure when shooting photos all the way around in a circle. Facing one direction, the photos would be directly into the sun. Facing the other, the sun would be lighting the scene. This is why HDR is important. It prevents the images from being a complete disaster. When we combine the HDR images into a panorama by careful adjustment, the entire scene becomes viewable. Special software also helps blend the exposure from one direction to the next. No one likes skies that are so blown out it looks like a blizzard is coming, or shadows that obscure large portions of an image.