Skip to main content

Remove static objects from an image sequence


Is it possible to remove static objects/pixels from a sequence of images?


Lets say I have a black square in the middle of my white picture (white background) and a black circle is orbiting around it. The result would be that my images will only contain the moving black circle from frame to frame and that the static black square would be colored white and though "removed".


My example would be something like this:


Manipulate[Graphics[{
   Opacity[0], Rectangle[{-1.1, -1.1}, {1.1, 1.1}],
   Opacity[1], Rectangle[{-.5, -.5}],
   Disk[{Cos[p], Sin[p]}, .1]
   }], {p, 0, 2 Pi}]


Which gives this image sequence


enter image description here


My first thoughts were going to something like that "put a circle around a cell"-thing with which one could identify not moving cells by looking at the static positions of the targeted cells positions. But I don't have enough expertise in that to manage this problem by myself right now.


Another thing that I came up now was the possibility to create a table with all images of my sequence, turn the images into tables with ImageData and calculate the Mean of each pixels RGB value which then gives me the information if the pixel was black or white all time or if it wasn't. But that explodes my RAM. Maybe there is a better solution?



Answer



Essentially you want to find all pixels that are black in all images. I turned the color around so that the goal became to find the pixels that are white in all images. Now 0x0=0, 1x0=0 and 1x1=1, so what I would propose is to multiply all images in the animation with each other. Afterwards I use ColorNegate to get back your configuration with a white background and black foreground.


img[p_] := Graphics[{
   White, Rectangle[{-.5, -.5}],
   Disk[{Cos[p], Sin[p]}, .1]
   },

  Background -> Black,
  PlotRange -> {{-1.1, 1.1}, {-1.1, 1.1}}
  ]

ColorNegate@Fold[ImageMultiply[#, img@#2] &, img[0], Range[0.05, 2 Pi, 0.05]]

Now that we have the background we can use ImageSubtract to remove it. You mentioned problems with memory which is why I generate each frame only when I need it, so only one image is in the memory at a time. You should know however that this is probably a lot slower than to generate all images first; ImageMultiply can work on an arbitrary number of images simutaneously and will work much faster if you let it. You should at least consider if you can multiply the images in batches.


Comments

Post a Comment

Popular posts from this blog

plotting - Filling between two spheres in SphericalPlot3D

Manipulate[ SphericalPlot3D[{1, 2 - n}, {θ, 0, Pi}, {ϕ, 0, 1.5 Pi}, Mesh -> None, PlotPoints -> 15, PlotRange -> {-2.2, 2.2}], {n, 0, 1}] I cant' seem to be able to make a filling between two spheres. I've already tried the obvious Filling -> {1 -> {2}} but Mathematica doesn't seem to like that option. Is there any easy way around this or ... Answer There is no built-in filling in SphericalPlot3D . One option is to use ParametricPlot3D to draw the surfaces between the two shells: Manipulate[ Show[SphericalPlot3D[{1, 2 - n}, {θ, 0, Pi}, {ϕ, 0, 1.5 Pi}, PlotPoints -> 15, PlotRange -> {-2.2, 2.2}], ParametricPlot3D[{ r {Sin[t] Cos[1.5 Pi], Sin[t] Sin[1.5 Pi], Cos[t]}, r {Sin[t] Cos[0 Pi], Sin[t] Sin[0 Pi], Cos[t]}}, {r, 1, 2 - n}, {t, 0, Pi}, PlotStyle -> Yellow, Mesh -> {2, 15}]], {n, 0, 1}]
Post a Comment
Read more

plotting - Plot 4D data with color as 4th dimension

I have a list of 4D data (x position, y position, amplitude, wavelength). I want to plot x, y, and amplitude on a 3D plot and have the color of the points correspond to the wavelength. I have seen many examples using functions to define color but my wavelength cannot be expressed by an analytic function. Is there a simple way to do this? Answer Here a another possible way to visualize 4D data: data = Flatten[Table[{x, y, x^2 + y^2, Sin[x - y]}, {x, -Pi, Pi,Pi/10}, {y,-Pi,Pi, Pi/10}], 1]; You can use the function Point along with VertexColors . Now the points are places using the first three elements and the color is determined by the fourth. In this case I used Hue, but you can use whatever you prefer. Graphics3D[ Point[data[[All, 1 ;; 3]], VertexColors -> Hue /@ data[[All, 4]]], Axes -> True, BoxRatios -> {1, 1, 1/GoldenRatio}]
Post a Comment
Read more

plotting - Mathematica: 3D plot based on combined 2D graphs

I have several sigmoidal fits to 3 different datasets, with mean fit predictions plus the 95% confidence limits (not symmetrical around the mean) and the actual data. I would now like to show these different 2D plots projected in 3D as in but then using proper perspective. In the link here they give some solutions to combine the plots using isometric perspective, but I would like to use proper 3 point perspective. Any thoughts? Also any way to show the mean points per time point for each series plus or minus the standard error on the mean would be cool too, either using points+vertical bars, or using spheres plus tubes. Below are some test data and the fit function I am using. Note that I am working on a logit(proportion) scale and that the final vertical scale is Log10(percentage). (* some test data *) data = Table[Null, {i, 4}]; data[[1]] = {{1, -5.8}, {2, -5.4}, {3, -0.8}, {4, -0.2}, {5, 4.6}, {1, -6.4}, {2, -5.6}, {3, -0.7}, {4, 0.04}, {5, 1.0}, {1, -6.8}, {2, -4.7}, {3, -1.
Post a Comment
Read more