A HDR (High Dynamic Range) image is a compilation of multiple shots of the same subject taken at different exposure levels to capture a wider dynamic range of light that is then blended together into a single image.
This gives the final resulting image the possibility of showing much more detail and a more realistic representation of what we would see with our own eyes, given that as you look around a space your pupils dilate and constrict according to your focus and attention.
A camera normally takes a single shot with a fixed exposure that can be adjusted for the intended subject but may miss details in darker areas or clip brighter areas of the image. The HDR techniques that we use combine multiple exposures to replicate the tonal ranges available in real life.
Some cameras have an inbuilt HDR mode that combines multiple exposures within the camera. We actually take 3 or more bracketed images for each of at least 4 aspects of our 360 degree capture. That’s at least 12 DSLR full-sized hi-res images that are processed from RAW images, blended and stitched to create a single 360 degree image.
We often take multiple sets of these for any given spin-point to ensure we can deliver the best possible output. In the time required to complete the capture of 12 or more frames to cover the full 360 x 180 degrees there may be movement or lighting changes that may affect the final outcome. This can be especially tricky with outside shots, under skylights or close to windows due to cloud movement affecting stitching & lighting or with object/people movement in and between the frames.