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• Copy a rectangular area from AVFrame - ffmpeg

  5 février 2013, par Marty

  I am trying to pull out a rectangular area of an AVFrame and have started on a function that will do so. I'm only interested in using AVFrames that are format PIX_FMT_RGB24. I may be reinventing the wheel a bit here too, so please jump in if there is already a function to do this. So far my function looks like this :

  AVFrame * getRGBsection(AVFrame *pFrameRGB, const int start_x, const int start_y, const int w, const int h) {
  
  
  
  AVFrame *pFrameSect;
  
  int numBytes;
  
  uint8_t *mb_buffer;
  
  
  
  pFrameSect = avcodec_alloc_frame();
  
  numBytes = avpicture_get_size(PIX_FMT_RGB24, w, h);
  
  mb_buffer = (uint8_t *) av_malloc(numBytes * sizeof(uint8_t));
  
  avpicture_fill((AVPicture *) pFrameSect, mb_buffer, PIX_FMT_RGB24, w, h);
  
  
  
  int curY, curX, i = 0;
  
  for (curY = start_y ; curY < (start_y + h); curY++) {
  
  
  
      for (curX = start_x; curX < (start_x + w); curX++) {
  
  
  
          int curIndex = curX * 3 + curY * pFrameRGB->linesize[0];
  
  
  
          pFrameSect->data[0][i] = pFrameRGB->data[0][curIndex];
  
          pFrameSect->data[0][i + 1] = pFrameRGB->data[0][curIndex + 1];
  
          pFrameSect->data[0][i + 2] = pFrameRGB->data[0][curIndex + 2];
  
  
  
          i += 3;
  
  
  
      }
  
  
  
  }
  
  
  
  return pFrameSect;
  
  
  
  }

  The function seems to work when I start at (0,0) (I think) but when I move elsewhere in the image it outputs colors similar to what should be there but isn't right. I think I am very close here, can anyone offer guidance ?

• Saving scatterplot animations with matplotlib produces blank video file

  1er avril 2013, par user2175850

  I am having a very similar problem to this question

  but the suggested solution doesn't work for me.

  I have set up an animated scatter plot using the matplotlib animation module. This works fine when it is displaying live. I would like to save it to an avi file or something similar. The code I have written to do this does not error out but the video it produces just shows a blank set of axes or a black screen. I've done several checks and the data is being run and figure updated it's just not getting saved to video...

  I tried removing "animated=True" and "blit=True" as suggested in this question but that did not fix the problem.

  I have placed the relevant code below but can provide more if necessary. Could anyone suggest what I should do to get this working ?

  def initAnimation(self):
  
          rs, cfgs = next(self.jumpingDataStreamIterator)     
  
          #self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], marker='o')
  
          self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], marker='o', animated=True)
  
          return self.scat,
  
  
  
  
  
  def updateAnimation(self, i):
  
      """Update the scatter plot."""
  
      rs, cfgs = next(self.jumpingDataStreamIterator)
  
      # Set x and y data...
  
      self.scat.set_offsets(rs[:2,].transpose()) 
  
      #self.scat = self.axAnimation.scatter(rs[0], rs[1], c=cfgs[0], animated=True)
  
      # Set sizes...
  
      #self.scat._sizes = 300 * abs(data[2])**1.5 + 100
  
      # Set colors..
  
      #self.scat.set_array(cfgs[0])
  
      # We need to return the updated artist for FuncAnimation to draw..
  
      # Note that it expects a sequence of artists, thus the trailing comma.
  
      matplotlib.pyplot.draw()
  
      return self.scat,
  
  
  
  def animate2d(self, steps=None, showEvery=50, size = 25):
  
      self.figAnimation, self.axAnimation = matplotlib.pyplot.subplots()
  
      self.axAnimation.set_aspect("equal")
  
      self.axAnimation.axis([-size, size, -size, size])
  
      self.jumpingDataStreamIterator = self.jumpingDataStream(showEvery)
  
  
  
      self.univeseAnimation = matplotlib.animation.FuncAnimation(self.figAnimation, 
  
                              self.updateAnimation, init_func=self.initAnimation,
  
                              blit=True)
  
      matplotlib.pyplot.show()
  
  
  
  def animate2dVideo(self,fileName=None, steps=10000, showEvery=50, size=25):
  
      self.figAnimation, self.axAnimation = matplotlib.pyplot.subplots()
  
      self.axAnimation.set_aspect("equal")
  
      self.axAnimation.axis([-size, size, -size, size])
  
      self.Writer = matplotlib.animation.writers['ffmpeg']
  
      self.writer = self.Writer(fps=1, metadata=dict(artist='Universe Simulation'))
  
      self.jumpingDataStreamIterator = self.jumpingDataStream(showEvery)
  
  
  
      self.universeAnimation = matplotlib.animation.FuncAnimation(self.figAnimation, 
  
                              self.updateAnimation, scipy.arange(1, 25), init_func=self.initAnimation)
  
  
  
      self.universeAnimation.save('C:/universeAnimation.mp4', writer = self.writer)

• YUV420p to other formats, color shift problems

  1er juin 2013, par Sam

  So I'm writing a color detection application using an AR Drone. The drone sends my python/opencv socket server an image from its camera in YUV420p format.

  What I do to access the image as an opencv IPLImage is the following (and yes this is inefficient but I didn't / don't want to have to write new conversion tools myself) :

  1. Save the yuv image to a file (some_image.yuv)
  2. subprocess.call(insert ffmpeg call here)
  3. Read the resultant file (bmp, png, it doesn't matter) back in using cv.LoadImage

  My problem right now is a very noticable color shift. I'm waving a red felt sheet in these pictures. The first one shows a heavy yellow tint. The second isn't as bad but is very rare — mostly when I have the red sheet it's heavily tinted.

  • Tinted image : http://i.stack.imgur.com/BQikM.png
  • Less-tinted image : http://i.stack.imgur.com/ezHyy.png

  I'm wondering both of these things :

  1. if there's either a better way to do this
  2. If the color tinting issue can be resolved

  My ffmpeg conversion line looks something like

  ffmpeg -s 640x480 -vcodec rawvideo -f rawvideo -pix_fmt yuv420p -i image.yuv -vcodec bmp -f image2 output.bmp

  I've also tried :

  ffmpeg -f rawvideo -s 640x480 -pix_fmt yuv420p -vf colormatrix=bt709:bt601 -i image.yuv -f image -vcodec png output.png

  The color shift is always there, unfortunately !

  The color shift is my big problem right now as I later convert the image to HSV and use thresholding to choose a color range that works for me.