USING FULL-FRAME FISHEYE IMAGES WITH STITCHER™
A Tutorial by Charles Evans
by Charles Evans
| Using Full-frame Fisheye Images with Stitcher™ |
This page describes how to use full-frame fisheye images with REALViZ
Stitcher. Stitcher was designed to stitch images captured with ordinary
(rectilinear) camera lenses. There are other types of lenses, however,
that may be used in panoramic photography. One such example is the fisheye
lens. Fisheye lenses are different from ordinary lenses in that a fisheye
lens makes straight lines appear to bend. Compare:
Fisheye Image 
A fisheye lens makes straight lines look bent.
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Normal Image 
A normal lens preserves straight lines.
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Why would you want to use a fisheye lens if it causes such distortion?
There are two practical reasons why you might want to use a fisheye
lens for panoramic photography:
- Fisheye lenses are designed to capture a very wide field of view.
A wide field of view reduces the total number of images you must
take to complete the panorma. This means you can take a panorama
faster and easier.
- Fisheye lenses, such as the full-frame fisheye lens, are, in general,
much less expensive than a normal lens having an equivalent field
of view.
To use full-frame fisheye images with REALViZ Stitcher you must first
convert the images to make the curved lines straight like a normal image.
Once converted, you can stitch the images just as you would stitch any
other image. There are a variety of software programs available that
convert fisheye images. Some of these can be obtained freely on the
Internet while others are commercial products.
Panorama
Tools by Helmut Dersch
This tutorial describes how to convert fisheye images using a PhotoShop
Plugin called Panorama Tools created by Helmut Dersch. Panorama Tools
is available for both the Mac and PC. In case the Panorama tools web
site is down I have provided alternative links here:
1 - Filter Menu
Open a full-frame image in PhotoShop. Make sure you have a backup of
your original images. If you need to, rotate the image so it is upright
(portrait orientation). Go to the PhotoShop "Filter" menu,
pull down to Panorama Tools, and select Remap:
 PhotoShop Filter Menu
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2 - The Remap Options Box
Selecting "Remap" will bring up the dialog box shown bellow.
Select the button that says "Fisheye Hor" on the left and
also the button that says "Normal" on the right. In the
field labeled "Hfov" enter the horizontal field of view
of your camera lens in degrees. (Ignore the "Vfov" field)
 Panorama Tools "Remap" Dialog box The value "92" was used as an example only!
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3 - Set the Preferences
Now click on the "Pref" button in the upper right corner of
the Remap Options box to open the Preferences dialog shown bellow. Select
(a) only and no others and click "OK" when done.
Step 4 - Convert the Image
Now you will be back at the Remap Options box. With your settings entered
click the OK button and Panorama tools will "remap" your fisheye
images into a normal image!
Press OK to remap the image
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Step 5 - Confirm the Results
Look at the converted image carefully to see that the lines appear straight.
If they still seem to bend as before then select the Undo command in
PhotoShop to restore the original image. Go to the Panorama Tools Remap
Options box again and increase the "Hfov" value by one degree
and click OK to apply the new conversion. Repeat this process until
the lines in the image look straight. Once you find the right "Hfov"
value you can use it to convert any images taken with the same lens.
Tip! If you plan to convert many images you can simply record the
procedure once to create a Photoshop Action and perform a Batch command
to convert (and rotate if necessary) all your images automatically.
The first time you run a Panorama Tools batch job the Remap Options
window will pop-up giving you a chance to confirm that the settings
are correct. From that point on the rest of the images will be converted
without any further user input.
6 - Stitching the images
Now you are ready to load your converted images into Stitcher and
begin stitching your panorama. To start, drag your first image into
the workspace. Now open the Stitcher Properties window (under the
Edit menu). In the "degrees" field enter in the the same
number that you used to convert the images in Panorama Tools:
Stitcher Properties - Enter lens field of view in degrees. The value
"92" is used as an example only! The correct value for your
images may be different. Close the Properties window and begin stitching
as normal. |
Visit Charles Evans’ website www.digitalpanos.com for more tutorials.Email: charles@digitalpanos.com
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