Amateur films often have a defect: the sky appears white due to the excessive brightness of the Sun. But with Kdenlive we can replace the sky, inserting a photograph with realistic colors in its place.
In all films, especially those of action but not only, it happens that you have to show the subject of the shot against the light, with the sky in the background. The situation occurs when the camera is positioned at the bottom, and therefore takes the actor from the bottom to the top, with the result that often the Sun is behind him. The problem with this situation is that in order to see the actor’s face we have to increase the exposure of the shot: the image therefore becomes brighter and allows us to see the details of the actor or objects in the foreground. But it ends up overexposing the sky: the cameras, in fact, have a fairly limited contrast range (even the most expensive ones do not reach the capacity of the human eye). This means that they are unable to correctly expose both relatively dark objects in the foreground and the sky excessively lit by the Sun. The result is a shot in which the sky appears completely white: the effect is unpleasant, because it makes the idea of a decidedly amateur movie, without attention to detail. And above all not very realistic, since usually with our eyes we can see at least a little blue in the sky (even if we still can’t see the Sun directly). Even with large sums of money, the problem cannot be solved “in the room”: it is a defect of all cameras, even professional ones. So how can we solve the problem? Simple: with post production editing. The solution is to replace the sky with another image. What we need is the original film, in which the actor is seen in front of a white sky, and a photograph of the blue sky, correctly illuminated. We can take the photo ourselves, or search for one on Google Images, or even draw one with Blender or Gimp to obtain clouds with a shape of our liking. And then we need Kdenlive, our video editor. With Kdelive we can replace everything that appears white with the image of the sky, leaving instead the other colors of the film remain original. In this way we are able to obtain a movie that resembles an HDR photo, or a photo made with a wide dynamic contrast range. In fact, we will be able to correctly illuminate both the sky and the objects in the foreground at the same time, keeping lights and shadows faithful to the original shot. Of course, some precautions are needed to prevent colors from fading. Furthermore, we have to make some differences between the half-length or close-up shots, and those shot in the long shot instead: for example, the close-up shots will have the sky slightly blurred due to the shallow depth of field, while those shot with a wide angle lens will have almost the entire image in focus, and we can also avoid that the majority of the image undergoes the bright blue reflection of the sky (a problem that usually does not arise in close-up shooting). As always, you can see the example video at the following address: https://www.youtube.com/watch?v=f12n_zm26iY
Speed and movement
In the example movie we use two other tricks that are often useful in action movies, such as those that represent a race or a fight: slow motion and reverse. Today, most cameras can shoot movies at 50 or 60 frames per second. The fact is that the standard display frequency is always 24 frames per second (for YouTube and also for digital cinema films). This means that by shooting the footage at 60fps, we can use the Kdenlive effect Speed up to the value of 40%. And up to 20% if the movies are shot at 120fps. If instead we want to show a jump backwards, it is easier to resume the jump forward, and then play the movie backwards: for this just click on the clip with the right button and choose Clip Jobs / Reverse . We will get a new dummy clip that represents the movie in reverse.
The clips and tracks
We put the movie on the storyboard and add a new video track
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See how the sky changes you
We take advantage of the darken transition to replace the sky
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It takes the right light
We correct the brightness of the movie to make it look realistic
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Long shot scenes
In wide-angle shots, the sky is only for a portion of the image
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