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More than Just a Pretty Picture: New Methods for Camera Calibration

diffraction grating consists of many tiny structures © DLR

diffraction grating consists of many tiny structures © DLR

If we want to use a camera to measure something, we need images with a known relation to reality. Data from the camera must be able to reproduce with exact precision the proportions and distances of buildings and surfaces.  "To do this, we need more than just a pretty picture", notes Anko Börner, head of the Optical Information Systems department at the German Aerospace Center (DLR). Together with the Berlin-based company HOLOEYE Photonics AG, Börner and his team are currently developing new approaches to ensure the accuracy of cameras using light diffraction. 

 

Test Photographs from an Airplane

 

There are different ways to calibrate a camera.  One method is to take test photographs from an airplane; another is test boards. Both procedures assume a certain number of easily identifiable points with known positions from whose image points we can determine the camera’s image characteristics. Both methods are laborious and quite costly.

 

Researchers making the most of high-precision laser light distribution

In contrast to previous methods, scientists at the DLR – together with the team at HOLOEYE Photonics AG – are currently making use of high-precision laser light distribution behind an optical diffraction grating. The diffraction grating consists of many tiny structures that are applied on a glass surface or etched into it. When a laser beam hits the grating, the light is diverted. The beams overlay themselves into a regular light pattern. This pattern can be measured precisely and allows for a comparison with the image that the camera records from the pattern. The differences between the desired image and the actual image are then used to determine a mapping relation between the object and the image space. The procedure is fast, compact, precise and, in comparison to other methods, economical.

 

Strategic Location near Adlershof Tech Park

 

The idea of calibrating cameras using diffraction arose many years ago at the DLR. The fact that HOLOEYE Photonics – a company specializing in diffractive optics including optical diffraction gratings – was operating in the direct vicinity of the Adlershof Tech Park, was a happy coincidence. After cooperating on the joint development of the new method, the two partners are now attempting to position it next to more established methods on the market. This is no easy task.

 

Already a Success Story

Beispiel für ein bearbeitetes Foto

Example of a picture editing: on the left you can see the uncorrected picture, on the right side the edited version © DLR

These days, the teams at the DLR and HOLOEYE Photonics AG are working hard to convince everyone that their technology is as precise as previous, well-known methods. To start with, the partners are specializing in satellite cameras. On a long term basis, however, Anko Börner and Sven Krüger, technical director of HOLOEYE Photonics AG, are convinced that their technology can be applied in a wide variety of spheres, for example in industrial and architectural cameras. It would also be conceivable to calibrate infrared cameras for use in distance measurement for cars. There is a lot of work for the cooperation partners to do until then. “And yet”, argues Börner, “for us, the whole thing is already a major success story.”

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German Aerospace Center

Logo of the German Aerospace Center

The German Aerospace Center (DLR) is a research center operated by Germany’s federal government. The DLR develops and performs research in the fields of aeronautics, space, security, energy and transportation. It is also the body responsible for the planning and implementation of Germany’s space program.

 

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HOLOEYE Photonics AG

Logo of the HOLOEYE Photonics AG

Diffractive optics (DOE) and active spatial light modulation (SLM) are two of the fields covered by the Berlin-based company HOLOEYE Photonics AG.

 

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