Image distortion

The pincushion distortion is a distortion of the image geometry of the picture tube of a computer monitor or TV set, is shown by the fact that a rectangle has an earing at the corners, like a ( eponymous ) looks pillows.

Formation

Because the beam path due to the curved screen of the flat edges is longer than at the center, caused so-called pincushion distortion.

Rectification

In black / white tubes, these distortions can be compensated by correcting magnets which are mounted on the deflector.

In color display tubes, this is no longer possible. Therefore you need there, the East-West correction ( horizontal correction ) to compensate for the lateral distortion and the north - south correction ( vertical correction ) for the distortion up and down.