Images appearing as black boxes after many trials

Comments

• sebastiaan

  July 2016

  Hi,

  However I am running into a problem consistently after (about) 900 trials: the image appears as a black box.

  This is a problem with PsychoPy that I've experienced myself as well on a few occasions. I don't think that there's anything you can do about it, although you could ask around on the PsychoPy users group. I think it's a memory corruption of sorts.

  I have tried switching the backend from PsychoPy to xpyriment | legacy, but with the later two I immediately get an AttributeError 'pygame.Surface object has no attribute 'units'.

  That's because you are using PsychoPy code directly, in which case you must use the psycho backend. But there's nothing in your code that couldn't be done just as easily using OpenSesame's native Python libraries, which are backend-independent, or Expyriment, which requires the xpyriment backend.

  • http://osdoc.cogsci.nl/3.1/manual/python/canvas
  • http://docs.expyriment.org/

  Is there any particular reason that you need PsychoPy?

  Cheers!
  Sebastiaan

  
  
  Check out SigmundAI.eu for our OpenSesame AI assistant!
  
• sageboe

  July 2016 edited July 2016

  Hi Sebastiaan,

  thanks for the fast response!

  It is quite unfortunate that PsychoPy shows this issue! I will definately raise it in the users group and see what people think.

  About using canvas(): I agree that it would be no problem to draw the stimuli with it, but I am a bit unsure/confused about drawing the mask and making it mouse contingent.

  First, it seems to be disagreeing with the maskimage I am feeding it:
  <PIL.Image.Image image mode=RGBA size=256x256 at 0x61ECF30>' is not a supported image format

  Second, it seems that I can't really set a size of the canvas, like I do here in PsychoPy: mask.setSize((max(win.size)*2,max(win.size)*2))

  Do you have any quick suggestions about how to best implement the mask with canvas()?

  Thanks!!!
• sebastiaan

  July 2016 edited July 2016

  Hi,

  I actually misread your code: I thought you were just showing an image at the gaze location. But even a gaze-contingent window can be done in pure PyGame. It's maybe even easier than in PsychoPy, or at least the way you're doing it now.

  Here's an example of a mouse-contingent window, which you can easily modify to a gaze-contingent window. This requires the legacy backend or the xpyriment backend with OpenGL set to 'no.'

  import numpy as np
  import pygame
  from pygame.locals import *
  
  radius = 100
  source_img = 'image.jpg'
  xc = var.width/2
  yc = var.height/2
  white = pygame.Color('white')
  black = pygame.Color('black')
  my_mouse = mouse(timeout=0)
  
  # Load the image and create a mask, which is also an image
  img = pygame.image.load(pool[source_img])
  mask = pygame.Surface( (var.width, var.height) )
  
  time_list = []
  
  while True:
      # Loop until a button is clicked.
      button, pos, time = my_mouse.get_click()
      if button is not None:
          break
      # Keep track of time so that we can determine the framerate
      time_list.append(time)
      # Get the cursor position, and draw a white circle on an otherwise black
      # mask image. The coordinate transformation is necessary to go from
      # (0,0) = center to (0,0) = top-left.
      (x, y), time = my_mouse.get_pos()
      x = int(x+xc)
      y = int(y+yc)
      mask.fill(black)
      pygame.draw.circle(mask, white, (x, y), radius) 
      # Create a copy of the original image, and combine with the mask so that the
      # lowest color is copied (BLEND_MIN). In other words, wherever the mask
      # image is black, the copied image will become black as well. This gives you
      # a mouse-contingent window!
      win_img = img.copy()    
      win_img.blit(mask, (0,0), special_flags=BLEND_MIN)
      # Show the copied image!
      win.blit(win_img, (0,0))
      pygame.display.flip()
  
  # Check if the frame duration is short enough
  time_array = np.array(time_list)
  dur_array = time_array[1:] - time_array[:-1]
  print('Mean frame duration: %.2f' % (dur_array.mean()))
  

  Another simple solution would just be to run your experiment in two shorter sessions, so that the memory corruption issue in PsychoPy doesn't come up.

  Cheers!
  Sebastiaan

  
  
  Check out SigmundAI.eu for our OpenSesame AI assistant!
  
• sageboe

  July 2016

  Hi Sebastiaan,

  thanks for the detailed answer and code!

  I did think about spliting my experiments into 2 sessions, but this would really only be my last choice!

  I played around with your code today, but the fact that the pygame servers were down and I could not get a hand on their documentation pretty much limited my efforts!
  I get a mask which only covers the object, rather than the whole screen, when using your code, even though this is set: mask = pygame.Surface( (var.width, var.height) ).
  If I want to add distractors to the screen, can I then just draw them to win?

  I hope you have some suggestions! pygame being offline makes this blit method a bit mysterious!

  Thanks!
• sebastiaan

  July 2016

  I get a mask which only covers the object, rather than the whole screen, when using your code, even though this is set: mask = pygame.Surface( (var.width, var.height) ).

  What do you mean exactly? My script shows a mouse-contingent window (to be adapted for gaze). That's what you want, right?

  If I want to add distractors to the screen, can I then just draw them to win?

  That would probably work, but it would be more common to blit the distractors to win_img and then blit win_img to win.

  I played around with your code today, but the fact that the pygame servers were down and I could not get a hand on their documentation pretty much limited my efforts!

  Look what I found after 1 microsecond of Googling!

  • https://media.readthedocs.org/pdf/pygame/latest/pygame.pdf

  
  
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