this has to be easy but i am being a bit slow !
(i guess I could just raw some black rects in place, but it makes changing the sf more complex)
Cheers
Try setting the GratingStim color='black'. If you want more help, it would be helpful if you could update your question with:
Then we can solve instead of guessing 
Hi , thanks for the response,
I thought i posted in the ‘coder’ forum, but i see that it’s ‘coding’
I am using coder - just to write a feasibility demo
color = black gives the inverse, (black background and white opaque) just need to invert it! see screenshot
colour=white give an all white screen.
the code is trivial, posted below…
from psychopy import core, visual, event
from psychopy.tools.arraytools import createXYs
import numpy as np
myWin = visual.Window((1024,1000), allowGUI=False, color=1, monitor='testMonitor', winType='pyglet', units='pix')
image = visual.ImageStim(myWin, image='bottle.png', mask=None, pos=(-450, 0) )
myMask = np.array([
[-1,1,-1,1,-1,0,-1],
])
myStim = visual.GratingStim(myWin, tex=None, mask=myMask, size=1024)
while True:
image.pos += (1, 0)
image.draw()
myStim.draw()
myWin.flip()
if event.getKeys(keyList=['escape','q']):
print myWin.fps()
myWin.close()
core.quit()
event.clearEvents('mouse')#only really needed for pygame windows
also note the jaggy image (from png) looks fine on preview etc.
Hmmm, I don’t think that there’s a way to do this, i.e. a “Color to alpha” function. You can do it if the mask is a visual.ShapeStim, but that would be the solution you already conceptually mentioned: draw a series of vertical black rectangles.
Just for future users, here’s a function that does the trick:
from psychopy import visual, core
window_size = [800, 600] # set this to something appropriate
# Set up stimuli
win = visual.Window(window_size, units='pix')
bar = visual.Rect(win, height=window_size[1], fillColor='black', lineColor=None) # set the height to your window height (or higher)
def draw_bars(sf):
""" Draw bars with a certain spatial frequency (sf).
Simply moves an existing ShapeStim and draws it a the appropriate locations."""
bar.width = window_size[0] / sf / 2
for i in range(sf): # a loop for each bar to draw
x = -win.size[0]/2 + bar.width/2 + i*bar.width*2 # calculate x-position of this bar
bar.pos = (x, 0) # set it
bar.draw() # and draw (OBS: no flipping, this function simply draws)
# Demo it
draw_bars(10)
win.flip()
core.wait(3)
This is reasonably fast. draw_bars(100) takes 10 ms on my laptop and draw_bars(10) is around 1.5 ms.
thanks for that, thought i was missing something as it seemed ‘obvious’ but im not familiar with the internals (i did go and have a look at opacity but see its all buried in pyglet so dont really want to go there !)
thats plenty fast enough for what i need to do for the demo (or indeed anything else!)
thanks again
You can set the colour of the GratingStim (mask) to be black and set the colour of the window (background) to be white. Doesn’t that do exactly what you were asking?
As for the jagginess of the image:
What @jon said! To be specific:
from psychopy import visual, core
import numpy as np
# Set up stimuli
win = visual.Window(units='pix', color='white')
image = visual.Circle(win, fillColor='red', radius=200) # just to demo it. You want to use an image here.
myMask = np.array([[-1,1,-1,1,-1,0,-1],])
bars = visual.GratingStim(win, tex=None, color='black', mask=myMask, size=1024)
# Show it
image.draw()
bars.draw()
win.flip()
core.wait(2)
(Actually, what Jon said is what I tried to write in my first reply. I just mistyped “image” instead of “GratingStim” - now corrected for future users)
whoop ! thanks Jon I should have written down all the combinations for the black and white and worked through it.
the jagginess occurred to me last night, but one drink too many to correct it…
I postulated the image being rotated very very slightly so i checked the code
(ripped off from a demo as i just wanted to show someone) and ori=1 !
Now the hard part is to work out what the path is he want to move the image along, I dont think it’s
describable mathematically so ill have to have either something external (which would be cool as
could put that easily under user control) or a constant list of points…
thaks both…
Cheers
here’s the final demo for anyone thats intersted,
it creates a spline from some x,y points and moves
the image along that path behind the mask
stimuli (bottle.png)
code.
from psychopy import core, visual, event
from psychopy.tools.arraytools import createXYs
import numpy as np
import scipy as sp
from scipy.interpolate import interp1d
win_width = 1050
win_height = 1000
path_length = win_width
myWin = visual.Window((win_width,win_height), color='white', monitor='testMonitor', units='pix')
# An image using ImageStim. and a mask
image = visual.ImageStim(myWin, mask=None,image='bottle.png')
myMask = np.array([[-1,1,-1,1,-1,1,-1],])
myStim = visual.GratingStim(myWin, tex=None, mask=myMask, color='black', size=win_width)
left_edge = (myWin.size[0] - image.size[0] ) / 2
# 0,0 is middle of left margin 1024,0 is middle right
x0 = [-50, 75, 225, 460, 470, 480, 490, 550, 650, 750, 850, 950, 1040]
y1 = [0, -10, 350, -100, -150, -190, -210, -200, -100, 0, 100, 150, 50]
x1 = [x-left_edge for x in x0]
new_x = np.linspace(min(x1), max(x1), path_length)
new_y = sp.interpolate.interp1d(x1, y1, kind='cubic')(new_x)
path_points = zip(new_x, new_y)
i=0
while True:
image.pos = path_points[i]
image.draw()
myStim.draw()
myWin.flip()
i = (i + 1) % path_length #; print i, path_points[i]
if event.getKeys(keyList=['escape','q']):
print 'fps:', myWin.fps()
myWin.close()
core.quit()
event.clearEvents('mouse')Nice spline! 
Glad you got it all working