The WP of the German Aerospace Center is one of the world leaders in the development of high performance digital cameras. There is a great depth of expertise in hardware and software design for image acquisition and image processing.
These experiences are based on a large number of sensors for airborne and spaceborne applications. The combination of the know-how of sensor technology, signal theory, calibration, and image processing was the base for the success of all of digital cameras projects at the DLR-WP.
As an outstanding example the project “ADS” may be mentioned. It contained the development of the world’s first commercial digital airborne camera for photogrammetry and remote sensing, ADS was realized by an co-operation between DLRWP and LH-Systems, Switzerland.
The ADS camera includes features like high geometrical and radiometric resolution, high-speed on-board processing, and mass memory concepts being able to handle huge amounts of data.
The introduced digital FilmReader concept for film digitisation is a result of the combination of recent camera technology based on the experiences of the WP-team and the knowledge about film properties and imaging system provided by Optronik.
Figure 1: Principal assembly of the film scanner
Figure 1 shows the principal assembly of the film scanner. The film will be scanned by different CCD line sensors including RGB and near infrared sensor (NIR) mounted perpendicular to themoving direction. Firstly, a pre-scan of the film will determine the radiometrical and geometricalsetups of the sensor lines. For that purpose a real-time Fast Fourier Transform (FFT) is implemented. Another feature of the FilmReader system is the possibility to detect and removegeometrical artefacts on the film surface (e.g. scratches). This is possible due to the near infrared filter, which is attached in front of a CCD-line. In this wavelength range the film material is transparent, but stray light caused by scratches is visible.
Figure 2: Transmission of different film materials in dependence on the wavelength
Figure 2 shows the transmission curve of different film materials. Geometrical artefacts can be removed by some intelligent and optimised filters either automatically in real-time or in an off-line processing step depending on the scanning mode. The same arrangement can control theradiometric properties of the scanned film. At first, all CCD lines are calibrated without the film. The influences of the optics, the lamp and the electronics are known afterwards. Only the CCD amplification and the lamp current depending on the film material, exposure, and development have to be defined in the next step.