Panorama and Image Stitching Tips
Panorama and Image Stitching Tips
I stitch images largely for image quality, having worked with 4×5 and 8×10 view cameras a great deal. I tend to treat my pano setup the same way I shot large format. If you want exceptional results, the following will, hopefully, help you to get there.
You can get acceptable results shooting hand-held, pivoting any which way as long as the images overlap. How well these images stitch will be somewhat dependent on the software you use. Don’t expect perfect stitches that can be printed huge, when shooting this way!
A great resource for panorama photography is Max Lyons Digital Image Gallery and Forum http://www.tawbaware.com/maxlyons/ The forum link is at the bottom of the page, a site I visit daily for information and inspiration. I post under earth-sea.
Presently, I use the following to do my panoramic photographs:
Camera: Canon 40d, 10 megapixel DSLR
Lenses: Canon 17-40 L, and Canon 60mm Macro
Tripod: Giottos MT 9180 with 3 way head
Panoramic Head: Panosaurus spherical pano head Panosaurus
Image Software: PhotoShop CS4/Adobe Camera RAW
Stitching Software: PTGui (Panorama Tools Graphic User Interface) PTGui
First some basics! For shooting stitched images, whether panorama or mosaic images, you will get the better results using the following guidelines.
1. Shoot in manual mode, or if with an automatic camera, use exposure lock. Otherwise, you’ll get differing exposures as you move the camera, and the stitches are very likely to vary considerably in brightness. We’ll talk more about exposure in a bit.
2. If possible, shoot in RAW mode, otherwise, try locking the white balance, so tonal ranges don’t change as you pan the camera around and auto white balance compensates.
3. Ideally, the camera should be level, and rotated around the optical center of the lens, rather than the tripod socket. This is especially important if the subject you are shooting has objects close to the camera, as well as at a distance. This is where a pano head really helps! With a telephoto lens and only distant objects, pivoting on the camer tripod socket or lens tripod mount works fine, it’s much less critical.
4. Don’t use a polarizing filter when shooting panoramas! This filter darkens blue skies, but….it has by far, the most effect 90 degrees from the sun, and falls off at 0 and 180, so you end up with deep blue, fading to light and back to dark across the image.
5. Overlap your photos around 20% – 30%, and if doing more than 1 row, do the same, top to bottom of the next row, as well as side to side.
6. Shoot in portrait orientation (camera held vertically) to get more resolution for printing larger, especially in 1 row panos.
7. Process the images, white balance, levels, etc., exactly the same, so when you stitch them, they blend smoothly. If using a RAW converter, process all images in one batch with the same settings.
8. I find it very worthwhile to shoot both small JPG files and Large RAW files. That way I can do a quick and dirty stitch with the JPG’s right away. It’s amazing how easy it is to miss an overlap or leave out a corner image, ruining the entire image. No point doing all the RAW conversions on that bunch!
9. If using a panoramic head, remember that most zoom lenses change their optical center as the focal length changes, so you need to calibrate for several focal lengths. Often it is easier to use a fixed lens, like the Canon 60mm Macro I use. A very few zooms, like the Canon 17-40 L , stay constant through the zoom range, making them ideal pano lenses.
Most of the time, I find that picking a representative area of the pano, in an outdoor scene, part sky, part foreground, and taking a sample shot, at the indicated exposure helps. I then look at the histogram and see if I need to adjust to keep the highlights from overexposing. Once I have a reasonable looking histogram, I then shoot (in manual mode) all the images for the pano.
If shooting a single row group, a graduated neutral density filter can help to keep the sky from blowing out, while still holding shadow detail. In a 2 row stitch, I sometimes will shoot the sky and about 20% ground in the upper row with about 2 stops less exposure than the ground and 20% sky row. Always make this kind of change with the shutter speed, not the F stop, or the depth of field will be different!
In post processing (I use Adobe Camera RAW) I can then somewhat equalize things, while holding both highlights and shadows. I’ll adjust the whole batch to the same settings, for the upper group, then modify eposure, brightness, fill light and sometimes a bit of contrast differently for the lower row. Don’t modify the color balance though!
Most stitching software will have some blending capability, PTGui is very good at equalizing differing exposures. Things are always better with less processing, but you do have some leeway here.
Often, it is best to shoot in manual focus mode. Otherwise, as you do the pan, almost always, there will be a shot where the camera either focuses completely differently, or a spot where it hunts and can’t focus. I shoot with a fairly wide angle lens (I just see that way and always have), so for me, focus is less critical than with a moderate telephoto, like my Canon 60mm macro (really a great pano lens).
Know your lens and it’s depth of field characteristics. Often, when shooting (17mm – 40mm wide angle lens @20mm)a wide ranging image, say, a mountain meadow with wildflowers, and distant mountains, I’ll focus fairly close on the lower row, maybe 10 feet away, knowing my lens will then give me a sharp image from 5 feet to 20 feet or so, then shoot the upper row set around 30 feet, which will give me a sharp image from 15 feet to infinity. The stitching software will warp and blend these very seamlessly.
How many images?
That depends on many factors! If you are shooting a very broad, single row panorama it may take 4 shots with a wide angle lens, but possibly 10 or more with a moderate telephoto. If you are doing a mosaic, to get a larger file and sharper image, it mostly depends on how large you might want to be able to print it.
With my 10 megapixel camera, typically:
1 row x3 images ends up about 6900 x 3800 pixels tall, and prints 30”x16”@240ppi
2 rows x 4 images (my most common size) 8750x6170pixels, 37”x26”@240ppi
They will vary depending on how much overlap, and how messed up the edges are. So these are slightly cropped sizes.
Some photographers shoot much larger groups, sometimes making Gigapixel stitches, I’ve never gone over 24 images yet, as I’ve never had the need to print billboard size images, or wait for many hours for my computer to churn it out!