Kdenlive: Technique to hide a person’s face using layer blending modes

Some time ago I already did a tutorial in which I touched on the topic of creating masks and we saw various techniques.

In this tutorial I am going to explain a new technique to create this type of mask to hide people or objects. I will assume that the application is known, if not, I recommend consulting the entries that deal with:

Annotation about the new version 19.04

I have done this practice with version 18.12.1 as it is the most stable today. Kdenlive 19.04 still gives too many errors to recommend it to work.

In this practice I use the effect of “Position and zoom, (Position and zoom)” but could well have used the “Transform”.

In the new version 19.04 this practice can be carried out perfectly. What I recommend to use the “Transform” effect to be more handy. The “Position and zoom” is still available, but by default they are hidden and to be able to see it we must activate the filter so that it only shows the video effects (see point 1 of the following image).

In point two we have to choose one of the two effects.

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Create a mask using layer blending modes in Kdenlive

In this case we need 3 tracks to make the mask with this technique.

  1. In the upper track we have a title clip with a box that will cover the face to be hidden.
  2. In the middle track we have exactly the same clip as in the track below, a perfect copy of this clip and perfectly synchronized.
  3. As I mentioned in point 2 in this third track we have the same clip as the one in the center.

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In the previous image we see the final layout of the tracks, with the effects used in each one and the layer blending mode between the two above, that of the title clip with the duplicate of the video. I omit the audio tracks because they are not relevant to the practice that we are going to do.

The clip to cover is a girl from an animated short film that is useful for this example. She runs jumping down a corridor towards the camera.

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So we will have to make a dynamic mask so that it continues its journey. We do this with a title clip.

We put the video clip in its initial frame and open the wizard to create a title clip. This is done from the project folder with the option “Add title clip”.

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We activate the box to show the background (located at the bottom of the wizard) and insert a rectangle over the girl’s face (which is what we intend to hide in this scene). The rectangle color is indifferent.

Now we have this configuration in the hints section:

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With this result:

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In other words, the title clip covering the girl’s face.

Now to the title clip we insert the “Position and zoom” effect of the “Crop and transform” family to be able to animate this clip so that the square follows the girl and, as she gets closer, that she also scales to hide his face at all times.

Once the effect is inserted, we advance the clip and by means of keyframes we animate the position and, when necessary, the size of the rectangle so that it keeps the girl hidden.

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The first step is to move forward in the timeline and, when the girl leaves the square that covers her face, insert a keyframe in the effect (see previous image, the one highlighted in red) and then move the clip so that it covers the face following the movement of the girl: we can do this from the project monitor, for this we must have the edit mode activated on the monitor (see next image).

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Now we must repeat these steps until the end of the clip so that the green square always covers the girl’s face.

In the following images we see the keyframes that I have inserted to cover the girl until she comes out flat and what this looks like in the project monitor.

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It is observed that the manipulation crosshead leaves the visible frame of the screen; to zoom in the display space we can use the key combination “Ctrl + Shift + Mouse Wheel”.

This is the most laborious part of this process: making the animation so that the rectangle of the title clip follows the object or person to be covered.

Once the previous animation is done, we only have to insert the “Alphain” transition of the layer blending modes between the title clip track (the one above) and the one that is just below this video clip (the one in middle, “Video 2”) we insert the “Pixelize” effect from the “Distort” family.

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By means of this mask and the alphain transition, the result is that of the “Video 2” track we only see the portion that occupies the square of the title clip located in Video 3, and when inserting a pixelize effect in the video clip, this portion it is distorted with the aforementioned effect.

In the following image, the track “Video 1” that is the background is deactivated.

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When adding the clip of the track below (Video 1) we obtain the following result:

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We can also animate the pixelization effect so that as the girl gets closer to the camera the size of the pixel increases. In the following image you can see the parameters that I have used and how I have animated them.

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Note about the new version 19.04

The Pixelate effect is now in the “Image Adjustment” family

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And its animation mode has improved to frame key line effects type.

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Result of practice

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As we can see, creating skins in Kdenlive is a simple task.

It is true that Kdenlive has an effect called automatic mask, but it fails a lot, so to ensure a good result we have this option seen here and the different techniques that we saw in the previous tutorial on concealment masks.

Regarding the new version of KDEnlive, to mention that despite the changes in the timeline and the improvements, anything learned in previous versions is done exactly the same way. Of course, to work without errors with the new version 19.04 we must have the most current version that we can of our GNU / Linux operating system for library compatibility and today it is still very unstable and full of errors; I don’t know what is happening with the Kdenlive development team but, for now, I recommend working with version 18.12 because it is one of the most stable versions and that it is giving fewer errors.

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