What is, however, the difference between the planetarium fulldome format and the standard film format, for example Full HD? Firstly, it’s the shape. The Full HD format is a horizontal rectangle, as opposed to the fulldome format, which has the shape of a circle. To be exact, it should be a circle but this is not entirely possible because the popular graphic formats do not support such round-shaped files. For this reason, the Fulldome format is a square frame with a circle inscribed in it. Anything outside of this circle is not displayed, while the contents inside it will, in turn, appear on the screen. The perimeter of the circle outlines the edge of the screen – the lower part of the circle is the front of the screen, while the upper part is at the back. You can imagine such a frame as a hat that you grab on both sides and “pull over” your head. The inside of this imaginary hat reflects the way in which a fulldome image is transferred to the screen of a planetarium. This brings us to a more significant difference, which is the difference in the content of these two formats. And this difference is huge.
Let’s imagine we are showing a regular movie in a planetarium. Of course, a significant part of the planetarium screen will remain unlit. The film will be visible only at the front. The part of the screen which remains dark marks the difference between the content of fulldome material and regular cinematic footage. A filmmaker, when creating individual rectangular shots, consciously adjusts the frame – the line between what they want the viewer to see and what is not visible in the shot. In case the same film was to be shown on the dome of a planetarium as fulldome, it would be necessary to abandon the concept of a frame and expand the camera view in order to show everything that, in a classic movie, is left outside of the frame, and to cover the entire dome with such an extended, but not stretched image. Therefore, there is no way of converting a regular film into a fulldome film. During every production for a planetarium, each image, animation or film has to be designed as a fulldome film right from the start.