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GratingStim

Attributes

GratingStim(win[, tex, mask, units, pos, ...]) Stimulus object for drawing arbitrary bitmaps that can repeat (cycle) in either dimension.
GratingStim.win The Window object in which the stimulus will be rendered by default.
GratingStim.tex Texture to used on the stimulus as a grating (aka carrier)
GratingStim.mask The alpha mask (forming the shape of the image)
GratingStim.units None, ‘norm’, ‘cm’, ‘deg’, ‘degFlat’, ‘degFlatPos’, or ‘pix’
GratingStim.sf Spatial frequency of the grating texture
GratingStim.pos The position of the center of the stimulus in the stimulus
GratingStim.ori The orientation of the stimulus (in degrees).
GratingStim.size The size (width, height) of the stimulus in the stimulus
GratingStim.contrast A value that is simply multiplied by the color
GratingStim.color Color of the stimulus
GratingStim.colorSpace The name of the color space currently being used
GratingStim.opacity Determines how visible the stimulus is relative to background
GratingStim.interpolate Whether to interpolate (linearly) the texture in the stimulus
GratingStim.texRes Power-of-two int.
GratingStim.name String or None.
GratingStim.autoLog Whether every change in this stimulus should be auto logged.
GratingStim.draw([win]) Draw the stimulus in its relevant window.
GratingStim.autoDraw Determines whether the stimulus should be automatically drawn on every frame flip.

Details

class psychopy.visual.GratingStim(win, tex='sin', mask='none', units='', pos=(0.0, 0.0), size=None, sf=None, ori=0.0, phase=(0.0, 0.0), texRes=128, rgb=None, dkl=None, lms=None, color=(1.0, 1.0, 1.0), colorSpace='rgb', contrast=1.0, opacity=1.0, depth=0, rgbPedestal=(0.0, 0.0, 0.0), interpolate=False, name=None, autoLog=None, autoDraw=False, maskParams=None)

Stimulus object for drawing arbitrary bitmaps that can repeat (cycle) in either dimension.

One of the main stimuli for PsychoPy.

Formally GratingStim is just a texture behind an optional transparency mask (an ‘alpha mask’). Both the texture and mask can be arbitrary bitmaps and their combination allows an enormous variety of stimuli to be drawn in realtime.

Examples:

myGrat = GratingStim(win, tex='sin', mask='circle')  # gives a circular patch of grating
myGabor = GratingStim(win, tex='sin', mask='gauss')  # gives a 'Gabor'

A GratingStim can be rotated scaled and shifted in position, its texture can be drifted in X and/or Y and it can have a spatial frequency in X and/or Y (for an image file that simply draws multiple copies in the patch).

Also since transparency can be controlled two GratingStims can combine e.g. to form a plaid.

Using GratingStim with images from disk (jpg, tif, png, ...)

Ideally texture images to be rendered should be square with ‘power-of-2’ dimensions e.g. 16 x 16, 128 x 128. Any image that is not will be upscaled (with linear interpolation) to the nearest such texture by PsychoPy. The size of the stimulus should be specified in the normal way using the appropriate units (deg, pix, cm, ...). Be sure to get the aspect ratio the same as the image (if you don’t want it stretched!).

autoDraw

Determines whether the stimulus should be automatically drawn on every frame flip.

Value should be: True or False. You do NOT need to set this on every frame flip!

autoLog

Whether every change in this stimulus should be auto logged.

Value should be: True or False. Set to False if your stimulus is updating frequently (e.g. updating its position every

frame) and you want to avoid swamping the log file with

messages that aren’t likely to be useful.

clearTextures()

Clear all textures associated with the stimulus.

As of v1.61.00 this is called automatically during garbage collection of your stimulus, so doesn’t need calling explicitly by the user.

color

Color of the stimulus

Value should be one of:

When color is specified using numbers, it is interpreted with respect to the stimulus’ current colorSpace. If color is given as a single value (scalar) then this will be applied to all 3 channels.

Examples::

# ... for whatever stim you have: stim.color = ‘white’ stim.color = ‘RoyalBlue’ # (the case is actually ignored) stim.color = ‘#DDA0DD’ # DDA0DD is hexadecimal for plum stim.color = [1.0, -1.0, -1.0] # if stim.colorSpace=’rgb’:

# a red color in rgb space
stim.color = [0.0, 45.0, 1.0] # if stim.colorSpace=’dkl’:
# DKL space with elev=0, azimuth=45
stim.color = [0, 0, 255] # if stim.colorSpace=’rgb255’:
# a blue stimulus using rgb255 space
stim.color = 255 # interpreted as (255, 255, 255)
# which is white in rgb255.

Operations work as normal for all numeric colorSpaces (e.g. ‘rgb’, ‘hsv’ and ‘rgb255’) but not for strings, like named and hex. For example, assuming that colorSpace=’rgb’:

stim.color += [1, 1, 1]  # increment all guns by 1 value
stim.color *= -1  # multiply the color by -1 (which in this
                    # space inverts the contrast)
stim.color *= [0.5, 0, 1]  # decrease red, remove green, keep blue

You can use setColor if you want to set color and colorSpace in one line. These two are equivalent:

stim.setColor((0, 128, 255), 'rgb255')
# ... is equivalent to
stim.colorSpace = 'rgb255'
stim.color = (0, 128, 255)
colorSpace

The name of the color space currently being used

Value should be: a string or None

For strings and hex values this is not needed. If None the default colorSpace for the stimulus is used (defined during initialisation).

Please note that changing colorSpace does not change stimulus parameters. Thus you usually want to specify colorSpace before setting the color. Example:

# A light green text
stim = visual.TextStim(win, 'Color me!',
                       color=(0, 1, 0), colorSpace='rgb')

# An almost-black text
stim.colorSpace = 'rgb255'

# Make it light green again
stim.color = (128, 255, 128)
contains(x, y=None, units=None)

Returns True if a point x,y is inside the stimulus’ border.

Can accept variety of input options:
  • two separate args, x and y

  • one arg (list, tuple or array) containing two vals (x,y)

  • an object with a getPos() method that returns x,y, such

    as a Mouse.

Returns True if the point is within the area defined either by its border attribute (if one defined), or its vertices attribute if there is no .border. This method handles complex shapes, including concavities and self-crossings.

Note that, if your stimulus uses a mask (such as a Gaussian) then this is not accounted for by the contains method; the extent of the stimulus is determined purely by the size, position (pos), and orientation (ori) settings (and by the vertices for shape stimuli).

See Coder demos: shapeContains.py

contrast

A value that is simply multiplied by the color

Value should be: a float between -1 (negative) and 1 (unchanged).
Operations supported.

Set the contrast of the stimulus, i.e. scales how far the stimulus deviates from the middle grey. You can also use the stimulus opacity to control contrast, but that cannot be negative.

Examples:

stim.contrast =  1.0  # unchanged contrast
stim.contrast =  0.5  # decrease contrast
stim.contrast =  0.0  # uniform, no contrast
stim.contrast = -0.5  # slightly inverted
stim.contrast = -1.0  # totally inverted

Setting contrast outside range -1 to 1 is permitted, but may produce strange results if color values exceeds the monitor limits.:

stim.contrast =  1.2  # increases contrast
stim.contrast = -1.2  # inverts with increased contrast
depth

DEPRECATED. Depth is now controlled simply by drawing order.

draw(win=None)

Draw the stimulus in its relevant window. You must call this method after every MyWin.flip() if you want the stimulus to appear on that frame and then update the screen again.

interpolate

Whether to interpolate (linearly) the texture in the stimulus

If set to False then nearest neighbour will be used when needed, otherwise some form of interpolation will be used.

mask

The alpha mask (forming the shape of the image)

This can be one of various options:
  • ‘circle’, ‘gauss’, ‘raisedCos’, ‘cross’
  • None (resets to default)
  • the name of an image file (most formats supported)
  • a numpy array (1xN or NxN) ranging -1:1
maskParams

Various types of input. Default to None.

This is used to pass additional parameters to the mask if those are needed.

  • For ‘gauss’ mask, pass dict {‘sd’: 5} to control

    standard deviation.

  • For the ‘raisedCos’ mask, pass a dict: {‘fringeWidth’:0.2},

    where ‘fringeWidth’ is a parameter (float, 0-1), determining the proportion of the patch that will be blurred by the raised cosine edge.

name

String or None. The name of the object to be using during logged messages about this stim. If you have multiple stimuli in your experiment this really helps to make sense of log files!

If name = None your stimulus will be called “unnamed <type>”, e.g. visual.TextStim(win) will be called “unnamed TextStim” in the logs.

opacity

Determines how visible the stimulus is relative to background

The value should be a single float ranging 1.0 (opaque) to 0.0 (transparent). Operations are supported. Precisely how this is used depends on the Blend Mode.

ori

The orientation of the stimulus (in degrees).

Should be a single value (scalar). Operations are supported.

Orientation convention is like a clock: 0 is vertical, and positive values rotate clockwise. Beyond 360 and below zero values wrap appropriately.

overlaps(polygon)

Returns True if this stimulus intersects another one.

If polygon is another stimulus instance, then the vertices and location of that stimulus will be used as the polygon. Overlap detection is typically very good, but it can fail with very pointy shapes in a crossed-swords configuration.

Note that, if your stimulus uses a mask (such as a Gaussian blob) then this is not accounted for by the overlaps method; the extent of the stimulus is determined purely by the size, pos, and orientation settings (and by the vertices for shape stimuli).

See coder demo, shapeContains.py

phase

Phase of the stimulus in each dimension of the texture.

Should be an x,y-pair or scalar

NB phase has modulus 1 (rather than 360 or 2*pi) This is a little unconventional but has the nice effect that setting phase=t*n drifts a stimulus at n Hz

pos

The position of the center of the stimulus in the stimulus units

value should be an x,y-pair. Operations are also supported.

Example:

stim.pos = (0.5, 0)  # Set slightly to the right of center
stim.pos += (0.5, -1)  # Increment pos rightwards and upwards.
    Is now (1.0, -1.0)
stim.pos *= 0.2  # Move stim towards the center.
    Is now (0.2, -0.2)

Tip: If you need the position of stim in pixels, you can obtain it like this:

from psychopy.tools.monitorunittools import posToPix posPix = posToPix(stim)
setAutoDraw(value, log=None)

Sets autoDraw. Usually you can use ‘stim.attribute = value’ syntax instead, but use this method to suppress the log message.

setAutoLog(value=True, log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message.

setColor(color, colorSpace=None, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message and/or set colorSpace simultaneously.

setContrast(newContrast, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

setDKL(newDKL, operation='')

DEPRECATED since v1.60.05: Please use the color attribute

setDepth(newDepth, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

setLMS(newLMS, operation='')

DEPRECATED since v1.60.05: Please use the color attribute

setMask(value, log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message.

setOpacity(newOpacity, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

setOri(newOri, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

setPhase(value, operation='', log=None)

DEPRECATED. Use ‘stim.parameter = value’ syntax instead

setPos(newPos, operation='', log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message.

setRGB(newRGB, operation='', log=None)

DEPRECATED since v1.60.05: Please use the color attribute

setSF(value, operation='', log=None)

DEPRECATED. Use ‘stim.parameter = value’ syntax instead

setSize(newSize, operation='', units=None, log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

setTex(value, log=None)

DEPRECATED. Use ‘stim.parameter = value’ syntax instead

setUseShaders(value=True, log=None)

Usually you can use ‘stim.attribute = value’ syntax instead, but use this method if you need to suppress the log message

sf

Spatial frequency of the grating texture

Should be a x,y-pair or scalar or None. If units == ‘deg’ or ‘cm’ units are in

cycles per deg or cm as appropriate.
If units == ‘norm’ then sf units are in cycles per stimulus
(and so SF scales with stimulus size).
If texture is an image loaded from a file then sf=None
defaults to 1/stimSize to give one cycle of the image.
size

The size (width, height) of the stimulus in the stimulus units

Value should be x,y-pair, scalar (applies to both dimensions) or None (resets to default). Operations are supported.

Sizes can be negative (causing a mirror-image reversal) and can extend beyond the window.

Example:

stim.size = 0.8  # Set size to (xsize, ysize) = (0.8, 0.8)
print(stim.size)  # Outputs array([0.8, 0.8])
stim.size += (0.5, -0.5)  # make wider and flatter: (1.3, 0.3)

Tip: if you can see the actual pixel range this corresponds to by looking at stim._sizeRendered

tex

Texture to used on the stimulus as a grating (aka carrier)

This can be one of various options:
  • ‘sin’,’sqr’, ‘saw’, ‘tri’, None (resets to default)
  • the name of an image file (most formats supported)
  • a numpy array (1xN or NxN) ranging -1:1

If specifying your own texture using an image or numpy array you should ensure that the image has square power-of-two dimesnions (e.g. 256 x 256). If not then PsychoPy will upsample your stimulus to the next larger power of two.

texRes

Power-of-two int. Sets the resolution of the mask and texture. texRes is overridden if an array or image is provided as mask.

Operations supported.

units

None, ‘norm’, ‘cm’, ‘deg’, ‘degFlat’, ‘degFlatPos’, or ‘pix’

If None then the current units of the Window will be used. See Units for the window and stimuli for explanation of other options.

Note that when you change units, you don’t change the stimulus parameters and it is likely to change appearance. Example:

# This stimulus is 20% wide and 50% tall with respect to window
stim = visual.PatchStim(win, units='norm', size=(0.2, 0.5)

# This stimulus is 0.2 degrees wide and 0.5 degrees tall.
stim.units = 'deg'
useShaders

Should shaders be used to render the stimulus (typically leave as True)

If the system support the use of OpenGL shader language then leaving this set to True is highly recommended. If shaders cannot be used then various operations will be slower (notably, changes to stimulus color or contrast)

verticesPix

This determines the coordinates of the vertices for the current stimulus in pixels, accounting for size, ori, pos and units

win
The Window object in which the
stimulus will be rendered by default. (required)

Example, drawing same stimulus in two different windows and display simultaneously. Assuming that you have two windows and a stimulus (win1, win2 and stim):

   stim.win = win1  # stimulus will be drawn in win1
   stim.draw()  # stimulus is now drawn to win1
   stim.win = win2  # stimulus will be drawn in win2
   stim.draw()  # it is now drawn in win2
   win1.flip(waitBlanking=False)  # do not wait for next
                # monitor update
   win2.flip()  # wait for vertical blanking.

Note that this just changes **default** window for stimulus.
You could also specify window-to-draw-to when drawing::

   stim.draw(win1)
   stim.draw(win2)