We simulate an old slide projector with Kdenlive, using the overlay modes and playing with the brightness of the scene. The perfect solution for a teacher or scientist role.
When making a video to explain something, it can be a good idea to fall into the clichĂ© of a slide show. It is a great way to appear teachers in a school, or professors at the university, or more generally people who explain something with some authority. It is also a clear sign reminiscent of the 90s, despite the fact that the projectors are still in circulation. In short, a scene with a projector is perfect for immersing viewers in a specific environment. It is a symbol so iconic that it does not require explanations. The only problem is that today the projectors are not very easily found, and above all it is not easy to produce slides. Printing services still exist, but they are very expensive because it is a niche technology. You could simulate a slide projector with a digital video projector, but even these are not so common and have a certain cost. In addition, giving the images of a digital projector the appearance of a slide projector is not that simple. It is, however, much easier to do everything in post production, using Kdenlive to make the slides appear as we want. The starting set must obviously be a fairly dark scene, with a light source that simulates the projector, aimed at a white background such as a wall or a curtain. Then, with GIMP, we will produce a version of the background that is in complete shadow. We could also actually do this, simply by turning off the light and taking a photo of the unlit background. But, should it not be simple, just use GIMP to create the “dark” version of the background. In Kdenlive we can then improve the luminous halo of the projector by obtaining the classic rectangle with shaded edges, since the projectors never have a round shape. Then, you can use it in Multiply mode to superimpose the image we want to use as a slide on the illuminated background. Using this mode, in fact, you get a result very similar to that of an actual slide, with lighter tones that tend to transparency and therefore to take the color of the background and the light beam. Then you have to recreate the classic movement of a slide: it enters from above and always comes out towards the top. Using the keyframes of Kdenlive’s transitions, 4 steps are enough to create the animation. Obviously, the work must then be finished by covering the part of the background that is located above the luminous rectangle, to avoid that the image of the slide may appear there during the entrance or exit animation. This completes the effect, especially if combined with the recognizable sound of the projector trolley that moves to make a new slide enter and exit. To add a further note of realism, just dim the light at the moment of the slide change. You can superimpose the image of the dark background created with GIMP, making it appear only for a few frames between the end of the exit animation of a slide and the entry animation of the next slide. This flashing helps the eye to understand that an exchange of the slides is taking place. As always, you can see the example video at the following address: https://www.youtube.com/watch?v=GueRVbAIhuw
Simulate a projector with light
How to illuminate a scene with a fake slide projector? First, you need to simulate the projector. The best thing to do is to get a torch that projects a fairly small beam of light. Eventually, you can take a fairly powerful light source and cover it with a piece of cardboard that has only one small hole. Then, however, you also need to illuminate the actor, and normally when making a slide presentation the speaker is not too bright: the room is always in the dark, otherwise the slides would not be seen. The solution consists in illuminating only the speaker with a light diffused enough not to look like a reflector, just do not point it directly towards the actor, but only in a smear, with the center part of the light beam falling out of the frame (better if on white reflective material for filling light).
Prepare the unlit background
We modify a frame to obtain the background without projector light
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Projector light
We create a rectangular light area, like in real projectors
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Here is the slide
We draw an animation for entry and exit of the slide
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Retouching the image
We add the top edge and a darkening in the slide change
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