In many films we see a character “magically” changing connotations, transforming himself into another person. The most famous example is the polyjuice potion in the Harry Potter series: using Kdenlive we can replicate the effect at no cost.
Among the main films that are produced in an amateur way we find categories such as horror and science fiction, and more recently also fantasy. Horror films have obviously always been the most popular among independent producers because they require very little effort: a good horror movie can also be shot with just one camera and with effects created in the room, without having to worry too much about editing and computer graphics. In the last decade, thanks to the appearance of free, open source, and free tools for the digital post production of movies, science fiction and the fantasy genre have also taken hold. Among the various effects that it has become possible to achieve very easily there is the transformation of one actor into another: in science fiction futuristic devices are often imagined capable of changing the characteristics of a person by pressing a button, while in the fantasy world it is rather frequent think of a magic potion capable of transforming people. The most frequent example in mass culture is the polyjuice potion of the Harry Potter saga, which allows you to transform yourself into other people. Realizing a similar effect with Kdenlive is quite simple: we suggest a generic method, which you can then adapt to your needs. We will begin with two shots of the actors: the first will obviously be the actor who drinks the potion and who turns into the second actor. These two shots must be made with the actors in front of a green sheet, in order to then perform the chroma key effect ( Chromatic key ) so you can easily remove the background and then move the actors where needed in the scene. Obviously then you need a photograph or a shot of the background: on this background you can position the actors. The effect itself is a simple fade between the two clips: only the film with the first actor must be seen first and, at a certain point, the second actor’s clip must appear. We will not, however, use the classic opacity fade transition. Instead, we will use a custom fade, which Kdenlive calls Wipe . They are fades built on the basis of specific grayscale images: they can be created specifically, but there are already many included in the program. In particular, the one that interests us makes the second clip appear above the first with a series of spots that gradually become larger, until the complete transition from one clip to another is obtained. By exploiting the transitions and the effects of Kdenlive we will be able to align the two actors and the background, to create a plausible image. It is essential to make the two faces coincide very well, in particular the eyes of the two actors must be superimposed perfectly. The attention of the spectators will in fact probably be directed precisely towards the eyes and the rest of the face, during the transformation, so it is important that this part is well overlapped. For the rest of the body, however, there are no particular problems, precisely because the attention of the public is always turned towards the face of the actors. As always, you can see the example video at the following address: https://www.youtube.com/watch?v=N8e2fASxxy0
Even without the green background
Of course, the effect can also be achieved without the chroma key, directly filming the two actors in the same place in the room. The problem is that, as we said, the face of the two actors must be in the same place: therefore one must be careful not only not to move the camera between the two shots, but also to make the position of the actors coincide perfectly (you can help making a sign on the floor to indicate where exactly they should go). The advantage of not using the green sheet is that the brightness certainly always remains the same and the actors are very well integrated into the scene (because they really are). The problem can arise when the background we want to have contains moving objects.
Clips in place
We need three clips on three different tracks: the background, the first actor, and the second actor
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Clear the green sheet
The two clips of the actors must have a transparent background: we will use the chromatic key
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The transition we want
For our effect we need a particular transition in the shape of “clouds”
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Finish the transition
By adjusting some details we can make the effect more credible
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