BackProjectionVerfahren

Backprojection is a fundamental concept in image processing and computer vision, referring to the process of projecting data from an image domain back onto another domain, typically a model or a space of possible solutions. In essence, it's the inverse of a forward projection, where information is cast from a source onto a target. A common application is in computed tomography (CT) scanning, where X-ray projections taken from multiple angles are backprojected onto a 2D or 3D grid to reconstruct a cross-sectional image of the object.

The core idea of backprojection is to distribute the intensity values from the projection data across the target space. For instance, in CT, a point in the reconstructed image accumulates intensity based on how much of the X-ray beam passing through that point contributed to the measured projection values at different angles. This distribution is typically done by smearing or spreading the projection values along the path of the X-ray beam.

While conceptually simple, direct backprojection can lead to significant blurring in the reconstructed image. To mitigate this, a technique called filtered backprojection is widely used. This involves applying a filter to the projection data before backprojection. The filter, often a ramp filter, sharpens the data and compensates for the inherent blurring, resulting in a much clearer reconstruction. Backprojection is a versatile tool, finding applications beyond medical imaging in areas such as seismic imaging, radar, and even in the training of certain neural network architectures.