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Q. Photostitching
Asked by Michael Kanemoto
(K=22103) on 1/25/2005
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Someone out there wanted me to document my photostitching techniques, and I can't be the expert at this, so I'm hoping others will join in.
I do have some examples on Usefilm.
http://www.usefilm.com/photographer/64104.html
I've used three different programs for stitching multiple images together to create large format panoramics. In most cases I start with around 8 6 megapixel images and wind up with an 18 megapixel final image.
I've found that stitching is a good solution to producing large prints around 20" x 30" at 150 dpi, or in one case 1 foot high by 6 feet wide at 150 dpi. I don't have a superwide lens, so in some cases I can get that nice 120 degree view.
I have tried three programs.
The first I used was Photoshop Elements 2.0, Photomerge. It works by flattening the perspective to a 50 mm lens and then you overlay the images togehter. It blends the seams to make the final. If you use a 50mm equivalent and a tripod it sometimes comes out. This program was moderately successful.
The second was Canon's PhotoStich. You put in the mm lens and it flattens the perspective and then does an automatic join by twisting and turning the photographs. It then does a blend over the seams. This product was more flexible in allowing for differnt mm lenses, but ultimately had problems joining up scenes with indistinct landmarks or visual cues.
I lastly used and am using Arcsoft's Panoramic maker. It analyzes the pictures and triangulates visual features to warp and bend the images into a whole. The blending is also more localized. This has worked really well and has some manual intervention which I use a lot on tricky merges where I did not use a tripod.
TECHINQUE:
In my viewfinder (a Nikon) I have a nice grid in the middle and one quarter frames horizonal and vertical. Basically, if you shoot a shot, mark with your eye the feature that the horizon and quarter mark rest on and move the quarter mark and horizon over the same location for the next shot. If you are using a wide angle lens (less than 50 mm), I move the quarter mark to the half mark because the perspective shifts incredibly for close objects. The more telephoto, the flatter the image and the better the merge will be.
Ignore the rule of thirds. Putting your level right on the horizon is the best bet. When I have shot above, the vertical perspecive causes a bending upwards, and below the horizon causes a bending downwards.
Using a tripod that is level is the best way to go - especially if the mounting is right on the plane of the CCD or negative. The tripod will stop you from panning which is a no-no in most cases.
Also - meter the whole scene and manually set the meter to be the same through all the shots - changes in F-stop and shutter speed will produce different shades so the merge will look a little uneven. Also remove a polarizer and other filters that will cause shading - the objective is to be uniform.
AFTER THE FACT
I often don't use the tripod as I don't have the setup time, so in the end I have a choppy merge and have to crop. I do wind up with shading problems and funky seams, and I have to tell you I am really good at using the clone and healing brush in PS, as well as quick mask and using Cntl+B and Cntl+L as often as possible to smooth things out. I try to stay as accurate to the scene as possible.
Since I have to remove filters when shooting, I do go back and apply a gradient mask and then create a gradient after the fact.
Lastly, there are times, and the Grand Teton photo is a great example, where I have had to go through pixel by pixel and clean up the image to make it PERFECT. This one has taken me probably two months of work, but the end result was stunning.
In the case of where I have bending upwards or downwards I have applied a curving matte look by importing the image into Illustrator, drawing the curved frame, and the exporting the illustrator paths back into Photoshop as a layer. This is probably way beyond what most people will do, so you can always inquire how I do it at gmail under mkanemoto.
Have fun - seeing the details in some of these photos is really rewarding, and the general public really loves the immersive quality of seeing a location in a full 120 degree view down to individual branches and trees on the horizon.
Uh, other than that I've actually hit the 30,000 pixel limit in Photoshop 7, but Photoshop CS has a greater limit...
Photoshop CS has a merge capability now, but I can't afford it (quiet crying in background)... but I will always take donations! If anyone has used it I'd like to know how it functions - flatten and stitch approach, or the triangulate and warp approach.
Also - buy some RAM or boost up that hard drive cache for these larger images.
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Kevin H
(K=22502) - Comment Date 1/25/2005
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Thanks you for the information. I've always wonder how people did this and now I know.
Keep up the good work.
Kevin
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Judi Liosatos
(K=34029) - Comment Date 1/27/2005
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Michael Kanemoto
(K=22103) - Comment Date 10/12/2006
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Updated text:
_____________________
Stitching
If you want to start trying some for yourself:
Google on "Autostitch", it is a free program and is small. It just needs some RAM to go and runs on a PC. You open the preferences, set to 100% scale, 100 JPEG quality, and then open the files. It uses pattern recognition to match the shots, stretch, and blend. I've tried some other programs as well.
Arcsoft Panorama Maker is the next best in my experience. You are constrained by choosing one shot side to side, vertical, or matrix (4x4). You have to manually adjust the matching points. Does a great job.
Canon's Photostitch is neat - you enter in the mm of the lens (for digital users you have to convert to 35mm equivalent) and it merges and blends. Moderate results because if you do not line up the image plane you are in trouble.
Adobe Elements has Photomerge. Close to the Canon technology, but I just can't get this sucker to work for me. Probably user error.
To take a great stitch:
- Shoot digital. It's about matching pixels, and digital will get you the most consistent results (sharpness, tones, etc.)
- Use a tripod if you can. You want to match up on the nodal point (where the light flip flops internally in the lens) to get a perfect perspective match as you rotate. However, I find it easier just to use a normal tripod head and move across the image plane (your sensor in your camera or film) along the same fulcrum. This means if you have a mounting point in line with that senor or film the tripod will force you to swivel right down the middle if you shoot in landscape mode. The "flatter" your photo from perspective the less this will matter.
- Remember that wider is not better. No tripod? It's OK. Perspective is a problem with shooting stitches, the more shifting of near ground elements due to a wide angle means you will have to overlap more. The "flatter" your images, the more two dimensional they are, the less "stretching" the software will have to do, or you will have to do using something like PT lens later on, to flatten the image for merging. When I shoot, I at most go to 28 mm at the widest, and in those cases I will do at least 50% overlap. At 70 mm and beyond, 1/4 overlap is the way to go.
- Use a grid system. My viewfinder projects a grid with lines on the quarter and one half as vertical lines and horizontal lines. I look at the cross-hatches where the lines intersect. For example, if I see that there is a tree at the intersection in the middle of my viewfinder, I remember that tree and then put it at the 1/4 intersection when I move the camera over. This makes sure that the perspective is forced to consistency as you turn the camera and everything will join smoothly. If you do not have grid lines you can use your autofoucs "dots" or eyeball it.
- Force everything manual. I look like an idiot by moving my camera around the whole scene, metering F-Stop and Exposure across the scene, and then choose the average and force the same: F-Stop, Exposure, White Balance, sharpening, etc across all the photos. This also means you have a lot less latitude to getting a really nice shot - in bright days the deep shadows and bright sky vary across the landscape. Sorry. Like most photos, the first and last hours of daylight are best. I do allow the autofocus to work, but with landscapes remember to use hyperfocal distance. Google "hyperfocal" if that just whizzed on by you. It just means using F-stop with where you focus to make sure everything winds up in focus. High depth of field (DOF).
- Lose the filters. Grad filters and polarizers will change the image as you move. IR, UV, ND, and other filters that are consistent are OK.
- Lastly, when you shoot leave room for cropping. Stitching programs love to stretch images, and you may find little blank spaces and gaps. The only way is to give a little buffer to your subjects and crop down later on. This is counter to the normal mode of cropping to the image you want in camera.
Have fun. You never know what will pop out until you are done stitching. I've noticed stitches of 20 images and discover that one of them was out of focus messing up the whole thing. Others that I thought would be boring wind up being absolutely great.
Another benefit is that if the image does not look a panorama, the end result is that you can get 18 - 24 megapixel images from a 6 megapixel camera. This means that you can get away with a wonderful 20" x 30" 150 dpi print for your wall.
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Doyle D. Chastain
(K=99842) - Comment Date 10/12/2006
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One other pointer that can help save a LOT of trouble later is to have the same exposure and focal length for each shot . . . and wide-angle shots are VERY difficult.
Regards,
Doyle I <~~~~~
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Salvatore Rossignolo
(K=13547) - Comment Date 10/24/2006
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