Hiding faces on videos:

Transcription

1 Hiding faces on videos: Masks This is a mini How To to make videos during demostrations while preserving people's anonymousness. This kind of documentation comes from the experience of indymedia's videos abused by police and repressive institutions in several countries around the world...

2 First of all, you should be aware of what or who you're filming in your video.. Just a few things to keep in mind: *Your video will be probably published, so be careful on who's faces you show in it; usually it's enough to aim the camera to people's chest instead of revealing their identity during the actions. *If you have a camera that is "your weapon" in the "media war", please be careful, or enemy will use your weapon against you or people from the demostration, once the video is published. *If you've not been careful during demostration filming, let us remind you to cover picture frames that may disclose people identities, for their own security. SOFTWARE We'll try to teach you about covering faces on 4 different video editing software; unfortunately only one of these is an Open Source Software, namely the first one we're going to present: Cinelerra. At the end of this document you'll find a table with features of covering on every software we'll speak; that's a way for you to understand easily which one is right for your needs. On Cinelerra Masks select a region of the video for either displaying or hiding. Masks are also used in conjunction with another effect to isolate the effect to a certain region of the frame, for example to pixelate or to blur a subsection of a frame. Color correction may be needed in one subsection of a frame but not another. A mask can be applied to just a subsection of the color corrected track. Removal of boom microphones, airplanes, and housewives are other mask uses. Obviously first of all you have to earn the video from your camera, either with kinodv or dvgrab, then open the video file in the timeline (open as new project option). The order of the timeline affects what can be done with masks.

3 To define a mask, go into the Compositor window..and enable the mask toggle. IMPORTANT: You have to select automatic keyframes (icon of the key on the bottom left of the video in the compositor window) if you wish to move a mask over time. If you do not select automatic keyframes, the mask position will be the same even if you edit at different places on the timeline. Click drag several times in several parts of the image to create each new point of the mask. While it is not the conventional Bezier curve behavior, this masking interface performs in realtime what the effect of the mask is going to be. Creating each point of the mask expands a rubber band curve. Once points are defined, they can be moved by CTRL dragging in the vicinity of the corner. CTRL drag allows you to move existing points to new locations, thus altering the shape of the mask. This, however, does not smooth out the curve. The in out points of the Bezier curve are accessed by SHIFT dragging in the vicinity of the corner. Then SHIFT dragging near the in or out point causes the point to move. SHIFT drag activates belzier handles to create curves between mask points.

4 Finally, once you have a mask, the mask can be translated in one piece by Crtl ALT dragging the mask. Mask editing in Cinelerra is identical to how The Gimp edits masks except in this case the effect of the mask is always on. The masks have many more parameters which could not be represented with video overlays. These are represented in the tool window for masks. Selecting the question mark in the compositor window when the mask toggle is highlighted brings up the mask options. Mask options window The mode of the mask determines if the mask removes data or makes data visible. If the mode is subtractive, the mask causes video to disappear. If the mode is additive, the mask causes video to appear and everything outside the mask to disappear. Mask Mode: if you want to cover a face, choose mode "multiply alpha" and add another videotrack with the same video under the masked one.

5 The value of the mask determines how extreme the addition or subtraction is. In the subtractive mode, higher values subtract more alpha. In the additive mode, higher values make the region in the mask brighter while the region outside the mask is always hidden. Mask value The mask number determines which one of the 8 possible masks we are editing, you can edit only one by time. The previous mask is still active but only the curve overlay for the currently selected mask is visible. Once you've drawed the mask and chosen the configuration, you only have to drop an effect from resources window on the video track in the timeline window; now you've covered with that effect the parts of the video you've selected with the mask. Every mask in a single track uses the same value and mode. The feather parameter determines how many pixels to feather the mask. This creates softer edges but takes longer to render. Then click on "render" in the timeline window, then you'll find out how to render your video easily, just remember that the two video tracks must be armed (red button in the patchbay) to be rendered correctly. Note: The OpenGL mask renderer is of low quality and only suitable as a preview for initial work. For fine tuning of masks (with large feather values) OpenGL should be switched off and the software renderer be used.finally, there are parameters which affect one point on the current mask instead of the whole mask. These are Delete, x, y. The active point is defined as the last point dragged in the compositor window. Any point can be activated merely by CTRL clicking near it without moving the pointer. Once a point is activated, Delete deletes it and x, y allow repositioning by numeric entry.

6 IMOVIE The next software we'll propose will be known for osx users, imovie. This is a non free licensed software so you'll need ffpmeg2theora libraries to encode your video in a free format. Imovie has a basilar interface but it's able to andle also some compositing effect just as masks. In this case we can define a mask as a black and white image (or clip) whose value at each pixel determines it's opacity (or alpha) value. So a white pixel would indicate an opaque pixel, black a transparent one, and grey values varying degrees of transparency. You may recognize that a mask acts like a stencil. In compositing, two images (or clips) are combined in one of several ways using a mask. The most common way is to place one image (the foreground) over another (the background). Where the mask is darker, indicating transparency, the background image will show through the foreground. Where the mask is brighter, indicating opacity, the foreground image will block the background. With Imove you are not able to move the mask in anycase. 1_Import your video in imovie and then put it TWO TIMES in the timeline. The result will be two clips in timeline, now drag a blur effect to the second one. The result will be the same as the image below.

7 2_Create (with Gimp, for example) or find an image or clip to use as a mask. Ideally, the mask should be black and white. Now import the mask on imovie. 3_Place the mask in the timeline, between the two clips.

8 4_Now if the mask is a clip; trim the mask so that it is the exact same duration as the first clip in the timeline. If it is a still image, set its duration to match the first clip. (!) It is essential that the first clip and the mask be the exact same length. 5_Select the first clip in timeline.. 6_Choose ss Composite in the Effects panel.

9 7_Click the apply botton. 8_Wait for the clip to render. Try playing with the Mode slider of the effect, and notice the various ways in which the mask can combine the two clips. The first clip is clip A, the second clip is clip B. The most common modes are A over B and B over A. The other modes are used for more specialized effects. This is what we obtain.

10 FINAL CUT PRO Lets investigate how to hide child's face in this video with final cut pro. First of all we have 3 video track on timeline and our child's video clip will be repeated two times on track1 and on track3;this two video tracks must be syncronized and the second track is empty by now. Now we're going to make unrecognizable V3 video (the one on top). Choose on browser the "gaussian blur" effect (blur directory) and drop it to the clip on V3; now double click on the clip on timeline and open tab "filters" on Viewer, from there you can configure the slider "Radius" to obtain the desired blur.

11 In the Canvas window you can see that the effect has affected the whole video; this is because the v1 video clip covers (by now) the one without blur on V3. In the media generator menu below the viewer on the right choose "shapes > oval" to obtain a white oval on black background. If your mask must have different shape than use Gimp to make a black/white image of the shape you prefer. THis mask is able to make the original clip appear on the background (instead of dark) and the "blured" clip in the oval (instead of white). Because we've synchronized the clips, we'll obtain the effect of one clip with one oval shape blured that we can move as we want. Now put che "oval shape" clip on V2 and trim it to make it long as the others.

12 Now double click on V3 and choose "composite mode > travelmatte luma" This is the final effect. But is not the only effect that we can obtain with this software. Going to the Canvans windows and choosing from the top menu "View > Image+Wireframe" we can see a X on the center of the window; now double clicking to the V2 clip and moving corners of the clip on Canvas we can resize and move the oval to the position we prefer.

13 Thanks to that function we are able also to move the mask during the video using animated track motion. To start the animated track motion just click on "add motion keyframe" on canvas window after having done the mask on the first frame. Just keep playng video untill the subject goes out of the oval, than position or size of the oval to cover the face where it is. Making that operation you've created a keyframe; if your face moves other times you just have to repeate the operation; remember the clip you have to resize is V2.

14 PREMIERE Here we'll create for you a mosaic mask to oscure the face of a guy walking. Here is where we start. 1_Make a copy of the clip and put it in Video2 with "edit > copy" and "edit > paste" Make sure it is an exact copy. 2_Then apply a filter to the Video2 clip dropping it from the video filters directory called stylize to the clip in timeline.

15 We can configure the effect in the effect controls window. Now the mosainc pattern is applied to the entire clip. 3_Then we open the Title designer to create the mask; this is in order to apply the effect only to the guy's face. Keeping selection on Video2 and clicking "file > new > title" a new window will appear; here we select the ellipse tool. 4_We'll resize the ellipse and place it as we prefer.

16 5_Now we want hte mask to act as a "matte" so we have to configure in the schedule on the right the value "color" to the mask, white. 6_After saving mask as "mosaic_mask" we drop it on Video3 and resize it. 7_Now we select Video2 and going to the effect controls window we click on "trasparency setup" and select "key type matte" on color white to tell premiere to use the mask in order to limit the mosaic effect on video2 clip.

17 8_Finally we what to create the animation to keep the circle on guy's face: we'll use the filter called "transform" on filters folder "video > distort". We drop the filter to video3. 9_Now the animation is a matter of keyframes. To have a keyframe trackwe just have to click first on the triangle near the title "video3" in the timeline than in the shape on the left of the red square; for the rest of the time just click between the two black arrows and you'll have a keyframe in the frame that's in front of you in the monitor. Use the two arrows to move between keyframes.

18 10_Now we just have to move the circle on the monitor window, setting it properly to each keyframe point, the animation will be done by Premiere. So when the guy moves out of the circle, set the keyframe and then change the position of the mask. WELL DONE! Now you can publish if you're still alive ;)