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Re: Follow point in AVI

  • To: mathgroup at smc.vnet.net
  • Subject: [mg123936] Re: Follow point in AVI
  • From: Mark McClure <mcmcclur at unca.edu>
  • Date: Mon, 2 Jan 2012 02:39:20 -0500 (EST)
  • Delivered-to: l-mathgroup@mail-archive0.wolfram.com
  • References: <201112301206.HAA08399@smc.vnet.net>

On Fri, Dec 30, 2011 at 7:06 AM, nlko <niko at homebound.de> wrote:

> I want to follow a horizontal movement of a black object on white
> background in an AVI.


It just so happens that I need to solve a similar question.  Here's a
very short clip of a flying saucer from The Day the Earth Stood Still.

movie = Import["http://facstaff.unca.edu/mcmcclur/Saucer.mov";,
   "GraphicsList"];
ListAnimate[Image /@ movie]


We can find the location of the ship using Binarize.  In this case,
we've got to block out the bottom since the white building has a color
similar to the ship.  This is accomplished using ImageMultiply with a
black bottomed image.

marker = Image[Join[Table[1, {100}, {480}],
    Table[0, {260}, {480}], 1]];
binaryMovie = Table[Binarize[ImageMultiply[frame, marker], 0.9],
   {frame, movie}];


Let's check how it worked.

ListAnimate[binaryMovie]


If you need something like a center of mass, I guess you do to the following.

locations = Table[
   Mean[N[Position[ImageData[frame], 1]]],
   {frame, binaryMovie}];
locations = {#[[2]], 360 - #[[1]]} & /@ locations;


Here's a look.

ListAnimate[Image /@ Table[Graphics[Point[loc],
    PlotRange -> {{0, 480}, {0, 360}}],
   {loc, locations}]]


Mark McClure



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