[solved] image display speed

Comments

• sebastiaan

  October 2013 edited 1:56PM

  Hi Dror,

  I see. In principle your approach is fine: Simply draw a series of frames that scale the image differently. But your implementation may be too slow, which is why it jumps. The easiest way to make the process faster is to construct all canvas objects first, and then show them one after another. That way the animation won't be slowed down by the canvas preparation time. For example:

  import numpy as np
  from openexp.canvas import canvas
  
  # Create an array (numpy list) of scaling factors
  # from 0.5 to 1 in 20 steps.
  scale_array = np.linspace(0.5, 1, 20)
  
  # The full path to the image in the file pool
  my_image = exp.get_file('image.png')
  
  # Create a list of canvas objects with differently
  # scaled images.
  canvas_list = []
  for scale in scale_array:
      my_canvas = canvas(exp)
      my_canvas.image(my_image, scale=scale)
      canvas_list.append(my_canvas)
  
  # Show the canvas objects one after another!
  for my_canvas in canvas_list:
      my_canvas.show()
  

  Alternatively, you can directly use the PsychoPy or Expyriment functions, which allow you to scale images as well. This will probably be even more efficient, but I doubt that it will be necessary in this case:

  • http://www.psychopy.org/api/visual/imagestim.html
  • http://docs.expyriment.org/expyriment.stimuli.Picture.html#expyriment.stimuli.Picture.scale

  Cheers!
  Sebastiaan

  
  
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• drorgarbi

  October 2013 edited 1:56PM

  hi
  I used the array and it works better(the animation itself)
  but.
  every trail is a different stim and it takes 5-8 seconds before every trail starts
  is there a way to speed things up
  I have a fixation of 1 second before every animation and scaling procedure after every stim in every trail
  dror
• sebastiaan

  October 2013 edited 1:56PM

  As I mentioned, an alternative would be to use PsychoPy directly. PsychoPy allows you to change the size of the object on the fly, without requiring you to prepare each frame separately. The downside is (or could be) that you are tied to the psycho back-end when you use this approach:

  from psychopy.visual import ImageStim
  import numpy as np
  from scipy.misc import imread
  
  # Create an array (numpy list) of scaling factors
  # from 0.5 to 1 in 10 steps.
  scale_array = np.linspace(0.5, 1, 100)
  
  # The full path to the image in the file pool
  my_image = exp.get_file('image.png')
  
  # Get the size of the image by reading into a numpy array
  # and getting the shape of the array
  height, width = imread(my_image, flatten=True).shape
  
  # Create an ImageStim object
  img = ImageStim(win, image=my_image)
  
  # Repeatedly show the image and change the size on each
  # showing
  for scale in scale_array:
      img.setSize( (width*scale, height*scale) )
      img.draw()
      win.flip()
  

  
  
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• drorgarbi

  October 2013 edited 1:56PM

  works like a charm/
  thank you/