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VideoStrobe documentation

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Screen shot

This is a screen shot showing the strobification of a video of a weight oscillating on a spring. The sine curve has been revealed by shifting each frame to the right by a constant number of pixels.

Instructions

First shoot your video.

  • Shoot in good, even light. The brighter the light the sharper the video frames.
  • Ensure there is good contrast between the subject and background. A plain background gives a more consistent look.
  • Use a tripod or sit the camera on a table or chair.
  • Don't have people moving around where they will cast shadows or get in the way of the light. Moving shadows and changing light levels will be picked up as movement.
  • Minimize the distortion caused by the projection of the image onto the camera 'film' by moving the camera as far away as possible and zooming in as tight as possible.
  • You may get better results with a manual exposure setting to avoid changes in exposure from one frame to the next.
  • VideoStrobe loads the whole video into memory, so videos more than a few seconds long or higher resolution than 640x480 may slow your computer down.

Next choose "Import video..." from the File menu.

  • Most cameras produce videos that can be imported directly into VideoStrobe. If you are unable to import your video you may need to convert it first to one of the more common formats such as mp4.
  • 'Skip frames' is useful as a way of taking only a selection of frames from a longer video. If you set 'Skip frames' to 1 then VideoStrobe will import every alternate frame. The default value of 0 imports every frame.

Finally click the "Strobify" button and then choose "Save as..." from the File menu.

  • If your video has unwanted frames at the beginning or end move through the video with the slider and use the "Start here" and "End here" buttons to limit the range of frames that are strobified.
  • Click "Reference here" to set the reference frame. The process of strobification consists of comparing the reference frame with the other frames in the video one by one. The differences between the reference frame and each other frame are retained as the strobified image. The default reference frame is the first frame in the video. (The first frame may not be the best frame to use as a reference frame because the first few frames sometimes jump around as the camera shakes when the record button is pressed.)

Advanced controls

Threshold and strength

These controls allow you to adjust the detection of differences between frames. The threshold sets the amount of difference at which background is separated from the subject, and the strength adjusts the degree of enhancement of the separation. The defaults are 25 and 25 respectively. Fiddling with these controls may allow you to make up for filming with poor light and/or contrast. (A general strategy would be to experiment with lowering the threshold and increasing the strength.)

Natural and classic

Natural uses the original image of the subject, wheras classic uses only the differences and therefore has colour artifacts. Classic sometimes gives a better look, albeit less realistic.

Blend background

A traditional strobographic photograph does not show the background. However it can be useful to include the background as a way of making the image more authentic, or a way of including a ruler in the image (useful for taking physical measurements off the image).

X shift and Y shift

For videos where the subject moves in two dimensions, such as throwing a ball in an arc, you will get best results if both X and Y shifts are left blank. However, for videos where the subject moves in one dimension, such as a ball oscillating up and down on the end of a spring, it is useful to be able to spread the frames out by applying a constant shift between frames. If a shift is used, neatest results will be obtained if the reference frame does not contain the subject at all. For example, if you are filming an oscillating spring move the spring out of view just before stopping the camera. This will give you some frames without the spring, one of which can be used as the reference frame.

Zooming and panning

You cannot zoom, pan, or crop in VideoStrobe.

  • If you need to crop your video before processing you can use Windows Movie Maker. (VideoStrobe can import wmv files.)
  • If you need to crop after processing, save your processed image and view it in a picture viewer like IrfanView.

 

Last edited by System Administrator .
Page last modified on Monday 15 of November, 2010 10:18:25 NZST.


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