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Introduction


What is panoramic photography?

The history of panoramic photography has its origins perhaps in the 19th century, when a popular amusement with high society was viewing large panoramic paintings in art galleries. These paintings were painted on the walls of round rooms. In 1843 the first panoramic camera was patented. Since then panoramic photography has been further developed. Examples of today's panoramic cameras are the Noblex swing lens camera or Seitz Roundshot cameras. Thanks to computers now it is not necessary to spend lots of money for such equipment to make a panorama - special programs allow to put conventional pictures together and create digital panoramic images. Panoramic photography is now a part of multimedia and virtual reality technologies. Since a complete 360 degree panorama often looks somewhat strange, digital panoramas are usually experienced with special panorama viewers which only show one sector of the panorama at a time. The viewer can 'look around' by moving the mouse.

How can I create panoramic pictures?

What can Helmut Dersch's Panorama Tools do?

Helmut Dersch's great Panorama Tools (PTools) can do all these working processes and much more. With Panorama Tools there are different possible stitching methods and you can even correct barrel/pincushion distortion. Unlike other stitching programs PTools offers full control of all the possible lens/camera parameters but it is more complicated to handle than more automatic stitchers. As a matter of fact you need to read carefully this guide and the documentation before you can do anything useful with PTools.

PTools is available for Macintosh, Windows and Linux and - it is free! Currently the PTools consist of two packages:

PTools provides more than just stitching software. I have found PTools useful for creating textures of a different kind for VRML scenes. See an
example (VRML viewer required).

What is parallax error?

Try the following. Hold your hand out in front of your face. Turn your head right and left without moving your hand. See how the background and your hand are shifted relative to each other. This is called parallax error. Now imagine what you see is recorded by your camera. First turn your head to the left, imagine you take a picture, turn your head to the right and imagine to take one more picture. Your hand is in the overlapping area. As anyone will see, the overlapping area has a different content and there is no way to stitch these images together.

How can I correct/avoid paralax error?

Not even Panorama Tools can correct parallax error. The only way to avoid this error to rotate the camera exactly around the so called 'nodal point' of the lens. I rigged up a holding device for finding out where this magic point is. In most cases there is no way to get this information from the manufacturer of your camera so you need to find it yourself. As you can see in the picture, it is possible to adjust the camera postition relative to the turning axis. The only way to find the nodal point is to try out at which position objects are not shifted relative to each other while turning the camera.
Don't worry if this is too complicated, if most of the objects you are picturing are distant from your lens little parallax error will occur anyway (again try out with your hand). If you are just planning to take panoramic pitures of a landsdcape with no close objects a cheap tripod will be perfectly all right. Even freehand picturing is possible. If you are palnning to make a pano of the inside of your camping bus, you should use about a special tripod setup.

What is barrel/pincushion distortion?

Imagine you are standing in front of a tiled wall and take a picture of it (picture 1). The result might not be what you expect. The single tiles are distorted as shown in the picture. This is due low quality of your lens (but dont't worry, even high quality lenses for professionals might have this problem). Picture 2 shows barrel distortion. Picture 3 shows pincushion distortion.
If you leave these errors uncorrected your images might not get stitched correctly as shown in the left picture. PTools can correct the barrel/pincussion distortions by radial shifting each pixel of the component images.

How can I correct barrel/pincushion distortion?

PTools can for you - using a polynomial function, which will transform each pixel of your image in such a way that it is 'corrected' and barrel/pincushion distortion disappears. But the polynomial function needs to know four parameters a,b,c and d which are specific to your particular lens. You need to find them out in a calibration process, which PTools supports. But since you are not yet familiar with the scripting syntax it would be too complicated to explain now. I reccomend that you take a picture of a tiled wall and decide if you have barrel- or pincushion distortion. When photographing the camera should be positioned exactly horizontal and exactly parallel to the wall. Open the image in your image manipulation program and select Filter - Panorama Tools - Correct and find the parameters (they are the same for all three colors in most cases) of the Radial Shift dialog with trial and error. Note that negative parameters act against barrel- and positive against pincussion distortion. First try out with the b-parameter and leave a and c zero. d should be chosen so that the sum of a, b, c and d is 1 (a+b+c+d=1). Your picture is sufficently corrected, if all lines appear straight.

If you are more familiar with the scripting syntax you can calibrate your lens as described by Peter Murphy in one of his articles.

What is pitch/roll/yaw?

For creating panoramic pictures you need to tell Panorama Tools some information about your lens and its orientation while taking the individual images. Panorama Tools will then rotate and warp and tilt the images so that they fit together. Therefore you need to know what the following terms mean:

What is the HFOV?

HFOV: means "horizontal field of view". In this context we should distinguish between the HFOV of your lens and the HFOV of the final panoramic picture.

What about image quality?

Keep in mind that always when an image is scaled or distorted, pixels need to be interpolated. This means that given pixel's properties are approximated to some extent by the software when the image is interpolated. Since PTools author Helmut Dersch is a mathematicican, the interpolator is the highlight of this software, exceeding most commercial products. PTools lets you select between four interpolation options providing good to excellent image quality. (Better options mean the interpolation process is somewhat slower).

Image quality can be lost further due to some compression algorithms. For example each time you save your image as JPEG file quality becomes poorer and poorer. Hence you should never work with JPEG files when you are saving your intermediate working steps. Use the PSD or TIFF file format instead.


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