Home>>Engines>>Extracter

Extracter Help
This is a detailed help screen for background removal

What is background removal?

As shown in the picture above background removal is where the software removes the background of an object and makes that background blue.  This isolates the moving subject against a blue background.

What videos are required for an Extracter?

To remove the background the software requires a picture of what the background is. This picture is a short video of background, exactly how it should look without the subject (in this case a golfer). The other video is one of the background and the golfer.

Can the camera move?

No, the background and subject videos must be with the camera completely the same, pixel by pixel. If the camera is moved or position has changed then a new background must be captured.

Can the background be the same video as the subject video?

Yes, actually it is suggested that the same video be used, Lighting conditions can change over time, (overhead clouds, and sun position), by using the same video segment these effects can be reduced. 

The software has not problem with having the same file open twice, you can choose where is the video the background image is. This is what the position selector is for in the extraction and freezer engines. Note that the background processor does use more than one frame to build a model of the background image. It will use the frame before and the frame after the selected frame.

How does the process work?

The process details are proprietary, and use complex statistical algorithms, but in general, the program compares the pixels of the subject video and the background video. If the pixels are the same color then that pixel is made blue. If there is a difference than that pixel retains its current color.

What is important for good results?

In general, the more contrast the better. If you have, a subject (golfer) wearing grass green pants on a grass background there is a good chance that the software will not detect a difference in color and make the pants blue. 

More light helps support more contrast. Sunny days will provide the best results. In addition, with more light exposure time can be reduced. With shorter exposure times, the fast moving parts in the video (club heads) are crisp and clear. With long exposure, times the club head get blurred which allows some background to feed through to the foreground.  This makes the difference less, which causes some, clubs heads to be cleared.

Exposure time is the amount of time that the camera is open for light to pass onto the detection electronics. The shorter the amount of time, the less distance a fast moving object will blur the picture.  Always try to get the fastest exposure time.

Also, beware of windy days and trees. In the wind trees move around, these trees will appear in the video because they are moving around and creating a difference between background and subject videos.

Does the background and subject video need to be the same size?

No, there can be a difference is size. It is suggested that they be that same size (format) for example 320x240 pixels, but the extraction a freeze engines can compensate for the different formats. If this must be the case then it is suggested that background video be a larger format then the subject.

Shadows do they show up?

Yes, shadows show up, and they are a big problem in early and later day video capture. Shadows do appear as a different color to the algorithms, therefore capture model videos during periods when shadows can be reduced to a minimum.