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How to remove background in video

Users often need to remove background in video and to replace it with the needed one. Our videoeditor enables to remove background by mask and by chosen color (chromakey). We recommend touse removal by chromakey to remove background in video, because the first method requires a lot ofcomputer power. Let’s review example of removing background in video which was shot at home inpoor lightning.

First of all you need to place a video on the scene:

After it you need to add background remover effect "Video effects­>Transparent­>Backgroundremover". For this purpose you need to open effects editing mode of the added video by clicking theobject on the scene or choosing a tab with object name on timeline.

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Then you need to set the added effect the way to remove the bluebackground. For this purpose set "Mode" parameter in "By chromakeycolor" and set color of removed background. In order to set color you’dbetter use eyedropper tool which enables to get the needed color directlyfrom the scene – click "Get the color from scene" in effect properties andchoose a color from the scene.

If you chose a color incorrectly, image will be partially removed from the scene – it is the consequenceof poor lightning and shadows on it:

You may re­chose a color or set parameters which determine color difference in video fromchromakey: "Min. brightness threshold", "Min. chromaticityU threshold" and "Min. chromaticityVthreshold". These parameters set difference in brightness and chromacity in color space YUV from thesought, i.e. set subspace of possible colors. This condition strictly sets if the color will be displayed ornot. But you can lighten the condition by selecting "Adaptive alfa" parameter which enables to settranslucency for the colors located on the border of the two subspaces. The following parameters ­"Max. brightness threshold", "Max. chromaticityU threshold" and "Max. chromaticityV threshold" set thesecond subspace, and starting from the second subspace translucency is calculated for the image.

Therefore if vector of difference in color is located in the first subspace, this color will remain; but if it isalso located in the second subspace, a translucency coefficient will be calculated for it; in case it is notlocated either in the first or in the second subspaces, the color will be replaced by the transparent one.

Translucency coefficient is calculated as follows:

R=((AlfaFactor*VLen)/64)+AlfaOffset

Where "Alfa factor", "Alfa offset" are parameters to be set,

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VLen is a length of difference vector between chromakey and color at a point in UV space, i.e.brightness of the point is not considered.

Varying these parameters we obtain the following result:

Now we need to add any image or video file to the background. For this purpose you may add anyobject to the scene for our edited video:

Recommendations for creating similar video:

Try not to amend size of original video, because in this case neighboring colors may be mixed; usesize mode without color mixing. After background was removed (in case of unoriginal resolution ofvideo file), objects will have the color tone of the removed background. For example in our case weused video which was automatically sized by iPhone:

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Try to use well lightened background without shadows, because in this case the best chromakeywill be selected.

Removed background and remaining image should have a maximum contrast. For instance in thegiven example you should not use red, orange and other neighboring colors as a background,because color of clothes will be blended with the background.

You can remove borders in video in case if background in these regions is not intercrossed withthe image which you would like to leave. It enables to increase performance by reducing workableregion.

This software can be downloaded from Free Video Editor description page.

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