If a projector is parallel to the screen, the image is a right-angled plane.
If the projector is shifted horizontally or vertically the right-angled projection gets trapezoid.
This effect is called keystoning.
Original image
Distorted projection
(tilt upward)
This effect can be minimized by using the keystone correction.
Keystone correction recalculates the image that it is shown right-angled independent of the position of the projector. Therefore the pixels must be compressed and the image is made smaller.
Important:
The keystone correction always causes a compression of the projected image. This causes a loss of quality of your projection.
This correction is done in the camera fixture:
For every edge of the image 1…4 there exists two attributes (Keystone 1A-1B…Keystone 4A-4B). With these attributes the edges can be moved in horizontal and vertical direction: Attributes keystone: X and Y are for the distribution of the picture content in X and Y direction.
The resulting output image for this distorted layer looks like the image beside.
Hint:
On the desk you can use the special dialog to edit the values for the keystone values.
Selecting the keystone feature of a camera fixture will enable the special dialog button:
All values can be entered in a graphical way with a preview in this special dialog:
Attributes keystone: X and Y are for the distribution of the picture content in X and Y direction.
