Thanks to the digital color correction it is possible to obtain surprising results: it is even possible to simulate a night shot with images shot during the day. It is the so-called “day to night effect”, and we can achieve it with Kdenlive.
Shooting scenes at night can be a problem, especially for a filmmaker who doesn’t have a lot of money. In fact, good lighting is necessary to take good shots (which do not go jerky) during the night. It seems strange, because our eyes immediately get used to the moonlight. Unfortunately, cameras are not as sensitive. And sometimes, to illuminate a few meters of ground, you need a very powerful lamp. Of course, Stanley Kubrick shot “Barry Lyndon” without the aid of illuminators, only with natural light sources and candles. But it had a 400 ISO sensitive film which, like all films, could be pulled to an even higher sensitivity without too much noise in the image (something that cannot be done with digital, because the sensors are much more rigid). In addition, he had adapted a Zeiss lens with a relative aperture of 0.7 for his camera. And it is likely that we will not be able to get something like this. In fact, the Sony A7S camera has the ability to resume even night scenes in natural light without too much noise. But the camera body alone costs more than 2000 euros. So do we have to give up shooting those night scenes we had imagined? No, if we are willing to accept a result that perhaps will not be perfect, but that will still convince the spectators. Thanks to digital color correction, in fact, we can transform an image taken during the day into a sequence with classic dark blue tones of the night in an automatic way. So let’s try to understand what a night shot looks like: first of all, the highlights are blue: this is an optical effect, because our eyes are generally very sensitive to blue (technically, the sky during the day is purple, but we we see blue because we perceive blue more than purple). The other colors, red in particular, are quite desaturated: they are barely recognizable. Another important fact is the brightness: both the shadows and the midtones must be quite dark, and only the high lights appear with a fair brightness. But there is one detail: the objects closest to the camera are slightly brighter than the others. This is because the light emitted by each object dispersed in space, and therefore decreases as a function of distance. In our tutorial, we will try to take into account all these details. In addition, we also want to add an unrealistic detail: the starry sky. This is unreal because, and if you have ever tried to take real night shots you will have realized it, the stars are too weak to appear in the movie. In order to be able to shoot the stars, a very high exposure time is necessary, even a few seconds. In Full HD movies, however, the maximum exposure time is a fiftieth of a second: too little for the stars. Adding them digitally to the movie, however, will give greater credibility to the video: after all, viewers automatically associate the presence of the stars at night, and will therefore more easily accept the effect, without asking too much if it is really possible to shoot the starry sky with a simple amateur camera. As always, you can see the example video at the following address: https://www.youtube.com/watch?v=Qru3PH0IWBM
The shooting conditions
The effect we present is not perfect: in professional productions, we proceed with the manual retouching of each frame (for example with CinePaint, the cinema version of GIMP). We, however, wanted to automate the whole procedure as much as possible. The rendering of the effect is better if the original images were taken on a cloudy day: too much Sun, in fact, makes some objects excessively bright, and provides strange shapes to the shadows (in general, noon is a good option because they are seen less shadows). The trees, then, create considerable difficulties: their leaves, moving, cause a slight glow that is difficult to eliminate. It is much simpler if the shot we took only includes buildings. Better, therefore, images taken in the city rather than in the countryside.
Prepare the original video clip
We place the clip and two color effects that will serve shortly
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In shades of blue
Let’s give the image the classic night blue tone
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We turn off the light, we turn on the stars
We insert the starry sky into the movie and make the image darker
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Different brightness according to the distance
We use the rotoscope to give less distant objects less brightness
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