Photographing skies for sky domes
polycounter lvl 19
So I just got a Nikon D80 for taking pictures and I was wondering if anyone knew of some tutorials or themselves knew how to take pictures of skies to create skydome or skybox textures.
The only two methods I know of now are:
get a 180deg fisheye lens, put camera on the tripod facing up and take a photo. The only problem with this is the D80 does not have a full frame sensor so I dont think I'll get the full 180degrees. If anyone knows a way to get that or if there are fisheye's out there that will provide the full circle for a medium fame sense let me know!
second method would be the old take a picture of a chrome ball technique but I'm afraid I'd lose to much detail on the poles facing upward (Where I need the -most-) detail.
If anyone knows a way of taking multiple pics and stitching them together or something i'd love to know! Thanks!
The only two methods I know of now are:
get a 180deg fisheye lens, put camera on the tripod facing up and take a photo. The only problem with this is the D80 does not have a full frame sensor so I dont think I'll get the full 180degrees. If anyone knows a way to get that or if there are fisheye's out there that will provide the full circle for a medium fame sense let me know!
second method would be the old take a picture of a chrome ball technique but I'm afraid I'd lose to much detail on the poles facing upward (Where I need the -most-) detail.
If anyone knows a way of taking multiple pics and stitching them together or something i'd love to know! Thanks!
Replies
Then turn the camera x degrees and take multiple shots. You'll usually need one row for the ground level, a second for the close sky level, and a third for the zenith.
You can also do this manually by just picking landmarks to keep on the edge of each frame, though a tripod is still needed. Also make sure that your camera is on full manual, and set your fstops, shutter speed, and iso ahead of time and don't change them while shooting!
here's what happens if you do this without a tripod and with a not fully manual camera. It still works but creates pretty bad seams
(click to enlarge)
http://www.cs.ubc.ca/~mbrown/panorama/panorama.html
http://windowshelp.microsoft.com/Windows/en-us/help/c7eed0fd-033d-4c9d-a304-656e8908430c1033.mspx
Hey that's the same camera I have.
Sorry I can't really help you with the skydome creation help. Just thought I would point out that I have the same camera. :P
File->automate->photomerge in cs3 I think its the same path in CS2 and cs and I know it even existed in prior versions as well.
Don't even spend time on the mirror ball technique, it's a lot of work and the results are not very good. You are very limited by the resolution of your camera, so at best you'll get a 4000px wide panorama full of distortions. Good enough for HDR lightingt but worthless as a background image.
The best way to photograph the sky is using a panorama head and a tripod. It's a lengthy process, but I'll do my best to describe it in detail.
A panorama head lets you precisely rotate your camera at fixed angles, for example, it locks at 45, 90, 135, 180 degrees. It also makes sure the lens is rotated around it's 'nodal point' so the individual shots line up. If you just rotate the camera around a random point then you will have problems as the fore and background have moved differently.
Rotating around the nodal point is not really needed when you only want to photograph the sky, so you could use a normal tripod as a low cost solution.
I photograph my skies with a fullframe camera and a 20mm lens. This gives me enough overlap to take 8 images (45 degrees) and a single image for the top of the sky (zenith):
The D80 is has cropped sensor, so you probably need something like a 14mm lens to get the same angle of view. Another option would be to shoot 2 rows of images, but this will more work and be harder to stitch.
There are 180 fisheye lenses for cropped sensor cameras, but they usually cost more than your camera and you won't have much image quality left after defishing.
HDR - High Dynamic Range
As you can see in the preview the clouds and the sun tends to overexpose into nasty white blobs. That's why I photograph my skies in HDR (High Dynamic Range). For every angle I take 3 shots, for the part which has the sun I usually take 6 to 9 photos.
A very useful camera feature is Auto Exposure Bracketing (AEB). When this is enabled the camera will take 3 shots, each with a different exposure. For example: when a correctly lit photo has a shutterspeed of 1/80 sec, it will take the following exposures:
1/20 (-2 stops underexposed)
1/80 (correctly exposed)
1/320 (2 stops overexposed)
By using the exposure bracketing you'll never have the problem of the sky being overexposed.
One thing I noticed after photographing a lot of skies is that while they are easy to overexpose (the clouds being too white), they are almost never underexposed. The average sky is pretty even in color, with the occasional bright part (clouds or sun) This means the brightest shot in your bracketed series is almost always so overexposed it's useless:
The shot that is overexposed 2 stops (+2EV) is almost completely white. This shot will not add any valuable information to your HDR image.
Most cameras also allow you to shift the exposure (Exposure Correction). By shifting the exposure by -2 stops AND using the bracking at the same time I get a much more useful set of exposures for the sky:
As you can see nothing is dramatically under or over exposed, which is just as we need it.
Photographing
With the Auto Exposure Bracketing and Exposure Compensation set I can finally photograph my sky. These are the other camera settings I use:
- Camera set to Aperture priority mode
- ISO as low as possible
- Aperture at F8 to F10 (sharpest image)
- Manual focus (AF focus on the horizon first, don't set it to infinity!)
- White balace on Daylight
- Image quality: JPG at highest quality
- Drive mode: continuous drive (hold shutter to take 3 pictures)
The reason I set my camera to Aperture Priority (A) and not manual (M) is that it is much faster. On manual mode I would either set a fixed exposure for all photos, or need to dail in the correct exposure for each angle by hand.
On Aperture Priority mode the camera will take the correct exposure for each set of 3 bracketed images. Because we convert to HDR we can easily change the exposure afterwards, so the fact that the bracketed sets are all at a different exposures doesn't matter.
The panorama head locks at the correct angles, so photographing the panorama is very quick, I can photograph a full sky in under 30 seconds.
If your camera has a very big buffer then you could photograph in RAW, but mine fills up after 10 photos so I need to photograph in JPG.
To prevent camera shake a remote release cord can be very useful. Even when you are very careful when pressing the shutter button you'll always nudge the camera a bit.
The end result is a series images which looks like this:
If the sun is very strong you could take more pictures for that part of the sky. You'd need to set your camera to Manual mode, set the shutter speed to 1/2000 sec and take another bracketed set (1/500, 1/2000 and 1/4000 sec)
Post Processing
Back home I sort all the panoramas in seperate folders, and merge the 27 photos to 9 HDR files. You can use Photoshop's 'File->Automate->Merge to HDR', or use a program like Photomatix to do this in batch mode. Use the same program for all shots, or you'll get color differences.
If it is windy and the clouds move fast you might see some misalignment in your resulting HDR. Most of the time this happens in the part with the sun when you've take more than 3 photos. While you are fiddling with the camera to set the correct exposure the clouds have already moved. The only way to fix this is to open all shots in Photoshop and move around the clouds until everything aligns. Aligning the images is annoying to do, but not rocket science.
Stitching
To get from 9 HDR shots to a single HDR panorama you need a stitching program. There are a lot of open source panorama stitchers, but most of them can't do HDR.
I use PTGui Pro (www.ptgui.com) to stitch my panoramas. It's a wonderful program and it's creator is continuously improving it.
In PTGui I load all images, set the correct angles numerically, correct the exposures so all images are the same brightness and press 'process'.
After 45 minutes of harddisk abuse it spits out a 300MB HDR file of a fully spherical panorama.
Tonemapping
Photoshop can convert from HDR to 8bit, but it hardly has any parameters you can use to fine tune the conversion. Luckily there exists a wonderful open source tool called PictureNaut which can do a much better conversion:
http://www.hdrlabs.com/picturenaut/
The idea is to get the sky well exposed without the sun turning into a huge white blob.
Here is an example of a tonemapped sky:
Converting to a cubemap
Most games need the sky in a cubemap format. It also is a much more effecient way to use your texture memory because every pixel is used 1:1 (the 'equirectanglar' layout has a massive amount of stretching at the top of the sky, which wastes a lot of pixels). There are a couple of programs to convert between different panorama formats. I use Pano2VR because it is a piece of software I already own to create the Flash previews of panoramas.
A cheaper option is Bixorama (http://www.outerspace-software.com/bixorama.html). I haven't tried it myself so I can't say if it works correctly.
Don't forget to double the canvas height, most programs expect a 360x180 degree panorama.
The cubemap in NVidia DDS exporter format:
As you can see creating a high quality skydome is a lot of work, but it is a lot of fun to do. Everytime I'm out there the sky is different. I've photographed and stitched more than 250 skies, and I still enoy it :poly142:
If you have any questions just let me know.
http://i36.photobucket.com/albums/e28/vailias/Pano_Adjust.jpg
I use it to make panoramas. Like this one of Quincy Market in Boston.
Marcel: Excellent post. Thank you for the information. Once I have a decent camera again I may have to give this a go again. The skys are really great here, and can often get a cloudless one in late spring.
As far as software goes I think i'm going to be using Autodesk's stitcher, i tried the demo out and it was pretty nice, it reads EXIF data to help stitch the pics, supports HDRI filetypes and will convert to different layouts, cube,cyl, sphere etc....i think it's like $350 but I'm going to be doing this for work so price isnt really a problem when it comes to software so It'll be nice to just use one program for the whole workflow aside from color touchups and junk in PS.
http://usa.autodesk.com/adsk/servlet/index?id=11390049&siteID=123112
One thing that I didn't see in Stitcher was the option to align the images numerically. When you are using a panorama head it can be very nice to just punch in the numbers instead of having to drag the images to their location by hand. The angles are the same everytime, so in PTGui I can use a template file to skip a lot of steps.