Python Image Stimulus

Description

An image stimulus whose content is generated dynamically by Python code.

Every time the stimulus draws, it evaluates the Python expression provided in pixel_buffer_expr. The result of evaluating the expression must be a bytes-like object, typically a bytes object or a C-style, contiguous NumPy array. The raw bytes associated with the object must contain the image data, whose layout is specified by pixel_buffer_format, pixel_buffer_width, and pixel_buffer_height.

For information on the modules and functions available to your Python code, see Run Python File.

Note: To preserve the image’s aspect ratio on screen, x_size and y_size must be equal. When drawn, the larger dimension spans the full specified size, while the smaller dimension is scaled to maintain the aspect ratio.

Signature

stimulus/python_image

Required Parameters

pixel_buffer_format

Options

RGB8

sRGB8

RGBA8

sRGBA8

RGBA16F

Pixel buffer format.

The specified format determines how the stimulus interprets the data obtained by evaluating pixel_buffer_expr. The format name indicates the number and order of each pixel’s color components. R, G, and B refer to the pixel’s red, green, and blue components, respectively, while A denotes the pixel’s alpha channel, if any. The following table provides details on each supported format:

Format	Number of components	Bytes per component	Component data type
RGB8	3	1	Unsigned integer
sRGB8	3	1	Unsigned integer
RGBA8	4	1	Unsigned integer
sRGBA8	4	1	Unsigned integer
RGBA16F	4	2	Floating point

The total size, in bytes, of the data buffer provided by pixel_buffer_expr must be equal to the product of pixel_buffer_width, pixel_buffer_height, the number of components per pixel, and the number of bytes per component. For example, if the format is RGBA16F, the width is 400, and the height is 300, then the buffer size in bytes must be 400 * 300 * 4 * 2 = 960,000.

1-byte, unsigned integer components must have values between 0 and 255, inclusive. The values of floating-point components must lie between 0.0 and 1.0, inclusive. Multi-byte component values must be in native byte order.

A leading s in the format name indicates that the red, green, and blue component values are specified in the sRGB color space. Before these component values are used to draw the image, they are converted from sRGB’s non-linear gamma to linear gamma. Such formats should be preferred when using integer-valued pixels with color management enabled(see #mainScreenInfo). When using integer-valued pixels with color management disabled, the non-s formats should be used. Floating-point-valued pixels may be used with or without color management enabled.

pixel_buffer_width

Example

512

Width of generated image in pixels

pixel_buffer_height

Example

512

Height of generated image in pixels

pixel_buffer_expr

Examples

render_scene()

img.update()

Pixel buffer expression.

Must evaluate to either a bytes-like object containing the current image data or None. If None, the most recently provided image data is reused.

Optional Parameters

elapsed_time

Name of a variable in which to store the elapsed time (in microseconds) since the stimulus started playing (either implicitly due to autoplay being YES or via an explicit Play Dynamic Stimulus action).

If the stimulus has been paused (e.g. via Pause Dynamic Stimulus or Pause Experiment), the time elapsed while paused is excluded from the reported elapsed time.

autoplay

Default

YES

If YES, the stimulus will start playing automatically (as if by an implicit Play Dynamic Stimulus action) after it has been queued and Update Stimulus Display has been invoked. It will also stop playing automatically (as if by an implicit Stop Dynamic Stimulus action) after it has been dequeued and Update Stimulus Display is invoked.

alpha_multiplier

Default

1.0

By default, the alpha multiplier controls the transparency of the stimulus. 1.0 is fully opaque, while 0.0 is fully tranparent.

Changes to the parameters source_blend_factor and dest_blend_factor can alter how (or if) the alpha multiplier is used.

Note: If the image contains an alpha channel, the embedded alpha value for each pixel is multiplied by the value of this parameter.

source_blend_factor

Options

zero

one

source_color

one_minus_source_color

dest_color

one_minus_dest_color

source_alpha

one_minus_source_alpha

dest_alpha

one_minus_dest_alpha

Default

source_alpha

Source blending factor.

The parameters source_blend_factor, dest_blend_factor, source_alpha_blend_factor, and dest_alpha_blend_factor provide detailed control over how the color components and alpha multiplier of each fragment of the stimulus (the “source”) are combined with the color and alpha values already present in the framebuffer (the “destination”), which in turn result from blending the stimulus display background with any stimuli drawn beneath the source stimulus. These parameters correspond directly to the four arguments of the OpenGL function glBlendFuncSeparate. Please refer to that function’s reference page for explanations of the different blend factor options.

Note: Irrespective of the blend factors used, the blend equation is always GL_FUNC_ADD.

dest_blend_factor

Default

one_minus_source_alpha

Destination blending factor. Accepts the same values as source_blend_factor.

source_alpha_blend_factor

Source alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of source_blend_factor is used.

dest_alpha_blend_factor

Destination alpha blending factor. Accepts the same values as source_blend_factor.

If omitted, the value of dest_blend_factor is used.

x_size

Example

5.0

Horizontal size (degrees).

If omitted, the value of y_size is used. It is an error to omit both x_size and y_size (unless fullscreen is YES).

y_size

Example

5.0

Vertical size (degrees).

If omitted, the value of x_size is used. It is an error to omit both x_size and y_size (unless fullscreen is YES).

x_position

Default

0.0

Horizontal center position (degrees)

y_position

Default

0.0

Vertical center position (degrees)

rotation

Default

0.0

Rotation (degrees)

fullscreen

Default

NO

If YES, the stimulus is sized to fill the display. In this mode, x_size, y_size, x_position, y_position, and rotation are ignored.

deferred

Options

no

yes

explicit

Default

no

Controls when the stimulus is loaded. If no, the stimulus is loaded at experiment load time. If yes, the stimulus is loaded the first time it is queued. If explicit, the stimulus must be loaded explictly with Load Stimulus.

Placement

Allowed at top level:	Yes
Allowed parent:	Folder, Frame List Stimulus, Layer Stimulus, List Replicator, Movie Stimulus, Range Replicator, Stimulus Group