March 13th, 2007
I’ve been having an interesting discussion with my friend Kevin Caskey about HDR (High Dynamic Range) processing of spherical panoramas. Kevin is a photographic savvy Realtor in Bellevue, WA that shoots his own spherical panoramas. Kevin discovered and pointed out Photomatix software to me. He showed me his QuickTime VR panorama of his living room that he processed created with Photomatrix.
The typical problem encountered when shooting panoramas is that since you have to shoot all shots being stitched together at the same exposure settings so that you can stitch them together so you have a hard time dealing with scenes that have an extreme dynamic range.
Here’s some background on HDR and Photomatix. The way HDR works is that in addition to the normal exposure you take one or more exposures with less exposure and one or more exposures with more exposure than the normally exposed image. You then combine the multiple images together in a way that takes the “best” parts of each image and results in an image that has a dynamic range of all the combined images. This combining process is what Photomatix does.
Why would you want to go to the work of taking multiple images and combining them? For interiors, it’s an alternative to artificial lighting. For outdoor shots it’s the only way to get the shot if you are faced with a wide range of brightness.
So Kevin used HDR processing with Photomatrix on this QuickTime VR shot of his living room. To appreciate this use of HDR, compare it with this panorama which is some of the same files from Kevin’s panorama only without HDR processing. This second shot is just one shot in each of 3 directions stitched together. Whereas Kevin’s shot is 3 shots in each of 3 directions and all 3 images in each direction combined with Photomatix and the final 3 HDR image stitched toghether. In comparing the two panoramas you will quickly see that Kevin’s HDR panorama has more even lighting around the whole 360 view much like you would get if you’d used a flash unit. In the non-HDR version of the panorama the lighting is more uneven around the 360 degrees of view. The windows are well exposed but the opposite direction is quite underexposed.
When working inside I’d rather use a external flash unit and take one shot in each direction since it’s a lot less processing work than using Photomatix and shooting 3 times more images. However, when you are shooting outside where you can’t can’t control the lighting there is no other way of capturing the total brightness range of a scene with a bright sky and not so bright foreground.
Last April I did a post on some ways to do image blending for interiors as an alternative to using lighting equipment. Photomatix is another piece of software that goes works in a similar way to the techniques I described in that post. However, with Photomatix you have much more control over the combining of images with a process that’s called “tone-mapping”. For a complete tutorial on HDR and using Photomatrix see www.naturescapes.net.