The word 'stereo' comes from a Greek word meaning solid. It was first used to refer to our ability to see 'solid' objects in 3D when viewing a pair of images from slightly different angles. It was only much later that the word was used to refer to sound reproduction (using our two ears rather than eyes).

In normal vision, each of your eyes views objects from a slightly different angle. The lines of sight from an object to each eye forms a small angle and the further away the object the smaller the angle. In the picture opposite, the angle between the lines of site from Object A to the eyes of the Observer (O) (the red angle) is greater than the angle for the object at B (the blue angle). Your brain uses this angle to estimate how far away the points are relative to each other. This results in you being able to see an object as having depth, rather than simply as a flat picture. This is called Stereo Vision.

Stereo photography is the process of taking two photographs from slightly different angles. When the two images are presented so that one eye sees one image and the other eye sees the other image, we see the scene as having 'depth' and objects as being three dimensional. The original stereo photographs were viewed with a special viewer though some people can see in 3D if they view the two images cross-eyed. Indeed some people can see the model skull, opposite, in 3D in that way.

Thus Stereo Photography is simply a way of presenting images so that the brain has an impression of 3D. In the same way, the Scanetica 3D Scanner can process the images and, using the same principles as our own vision, work out the distance to each part of a model and so construct a 3D model of the subject.

However not just any two images are useful. They must be matched images taken from very slightly different directions. The instructions provided on this website will allow you to take suitable photographs using one or two cameras.

After taking the pair (or pairs) of stereo photographs, the Scanetica scanner can use them for processing.

The Scanetica 3D Scanner needs to know specific information about how the photographs were taken. The required information is often provided in the 'exif' header contained in each image file. That, combined with data from our own camera database, is usually sufficient to calculate the shape of the subject. This can give rise to two problems.

• Removing the 'exif'.

  Most image editors, such as Photoshop, removes this information if the image is edited or if saved as a different file. (Many programs will retain this information if the file is simply opened and 'Saved' again.) Do not edit the image files before processing them.

• Incomplete information.

  Unfortunately some camera makers do not add all the correct information to the 'exif' header. We have sufficient knowledge about most common cameras and that, coupled with the information provided in the 'exif' header, is sufficient. The Scanetica 3D Scanner consults this database of information, where necessary, for each photograph.

  If your camera is not in our database you have the opportunity of providing suitable information directly to the program.

Note on the 'exif' header.

The 'exif' header is contained in all digital photographs. You can find this information yourself (in Windows). Use Windows Explorer to find the file on your computer, and right click on the file name. Select 'Properties' from the drop down list. In the dialog box which pops up, choose the 'Summary' option from the top selection and then click on the 'Advanced' button if necessary. Other operating systems have similar ways of accessing this information.

In the same way as stereo vision uses your brain to interpret the angles between the lines to each object, The Scanetica 3D Scanner uses the two photographs to do the same.

The Scanetica 3D Scanner loads the photographs and matches each feature, both large and small, and works out the angle to each. The Scanner uses these angles to determine the distance from each feature to the camera and then plots each point in space to give a model of joined points as shown.

Once the positions of all the features has been determined, the Scanetica 3D Scanner then joins the points into triangles and forms a surface giving a blank shape.

The surface is then smoothed to give the final shape.

Once the basic shape has been formed, the Scanetica 3D Scanner projects one of the photographs on to the surface to give the surface colour, or 'texture'. This gives the completed 3D model of the subject.

After completing the 3D Model of the subject, you can save the model on to your computer. You can view this model at a future time, as well as having the model packaged into a Flash Viewer. This flash viewer can be placed on the Scanetica server or transferred to another server so that you can add it to your own personal webpage. In this case Scanetica will provide the code to be placed in your webpage.