Image preparation
Camera calibration & lens distortion measurement
This is an extremely important factor when using consumer-grade digital cameras. Every camera distorts the real world when capturing it on a image. Cheap digital cameras suffer more from these problems than professional cameras but even these nead a proper calibration. The most important type of distortion is radial lens distortion, this makes straight lines curved on the image.
There are several comercially available programs which can calibrate cameras (e.g. Photomodeller). This is generally done by taking a dozen or so pictures of a printed grid and importing these into the program. The program then calibrates a formula which describes the distortion. But this calibration can also be done without sofisticated and expensive software (see my manual).
Correcting the images for lens-distortion
When the function of the distortion is known, the images can be corrected for this distortion. In general all software used for the extraction of the 3d-models claim that this step is not nescessiary. But we and others do get a lot better results when we correct images beforehand.
I've written a script for Matlab which removes all lens-distortion. Matlab is software written for mathematical computing for scientists. The images which are corrected using this script have a better geometrical-quality than raw images of a professional camera.
Before correction(left) and after correction of distortion(right).
The script i've written for this correction can be found on the download page.