Perspective control

Under equalization is understood in photography correction ( rectification) of geometric aberrations. This may include problems of the objective and issues of preparation and orientation of the camera ( Converging lines).

Correction of geometric aberrations of the lens

Many lenses exhibit pincushion or barrel distortion. Straight lines are there when they do not pass through the center of the image, not shown as straight lines. For complex optics with many lenses also " wavy " distortion may occur.

The correction of the distortions can be obtained by

• Optical methods (for example, rear-projection through the lens ), or by
• Calculations of the electronic image processing

Carried out. When correcting means of electronic image processing to make use of the fact that the degree of distortion mostly depends on the distance from the image center. For such a case, the image can be described by polar coordinates. The position of the pixels is in this case represented by the distance from the center of the image and an angle from the horizontal, for example. The correction to be applied depends on the distance from the center of the image and can be described as a mathematical function. To calculate a polynomial is used, for example:

( = Corrected distance from the image center, = uncorrected distance from the image center, = constants)

Odd powers ( phenomenological modeling )

About the phenomenological modeling of the effects to be compensated in the image by selecting the best mathematical model. For example, through the introduction of the camera constant as the virtual size:

Even powers ( physical modeling )

From a physical perspective, the radially symmetric distortion errors usually correspond to even functions.

Color channels

If this correction is applied only to individual colors of a digital image, and color fringing ( chromatic aberration) can be partially corrected.

Correction of distortions caused by camera position or design

A photograph produced according to the laws of central perspective. Therefore, parallel lines are only also extend parallel in the area in the scene when they are in the motif in a plane that is parallel to the film plane. So when the camera is rotated, for example in front of a house up, arise Converging lines, the house seems to tilt backwards. For large format cameras and the tilt and shift lens by small-and medium-format cameras, this is avoided by not swung the camera to select the image details but the picture detail.