Random Noise Patch Element

Modified on 2018/07/16 02:36 by Administrator — Categorized as: Elements, Stimulus generators

Summary

Element Icon Random Noise Patch
Info
Category: Stimulus Generators AddIn: Visual Kernels
Creator: OkazoLab Scope: Parent event
Owns Snippets: None Usage: Stimulus screen

Properties

NameDescription                              ConstraintsTypeOn
runtime
change
Settings
Patch Type        Defines a type of the random dot patch        
Normal..
        		enRand..         
Random Distribution        Defines a type of the random dot distribution        
Normal..
        		enRand..         
Luminance Range        Defines the normalized range, 0..1, for the dot luminance. The full range, 0..1, corresponds to 0..255 in the RGB space. The range does not affects the color hues        
Normal..
        		clRange         
Patch Shape        Defines a shape of the generated patch        
Normal..
        		GaborP..         
Random Seed        Defines a seed value for the random noise patch. If the value is equal zero, a random seed value is automatically selected. Assigning a new value regenerates the patch.        
Normal..
        		Int32         
Runtime Status
Current Seed        Returns the current random seed of the dot pattern, when the seed selection is randomized (Random Seed value is zero). If the seed is assigned manually via Random Seed, this property mirrors the assigned value.        
Status..
        		Int32         
Regenerate Patch Now        Runtime command regenerating the patch. Use as 'RegeneratePatchNow=true;' in snippets        
Runtime Command..
        		Boolean         
Visual Appearance
Alpha Masking        Defines, whether the visual content is used to create an opacity mask on the event surface. If masking is on, the content's pixel luminance (or, its inverse) defines transparency within element's viewport. The alpha masking allows, for example, create transparent holes on the event surface.        
Design Time..
        		Int32         
AntiAliasing        if true, the rendered content will be antialiased for smoother visual appeariance. If false, rendering will be authentic to its source, e.g. a bitmap.        
Normal..
        		Boolean         
Position        Defines a position of the rendering viewport on the screen        
Normal..
        		clPoint         
Size        Defines a size of the element's rendering viewport on the screen        
Normal..
        		clSize         
Z Order        Indicates Z Order of the element on the given event        
Status..
        		Int32         
Pivot Point        Defines alignment of the pivot point (or, element's position) relative to element's rendering area. The pivot point sets the center of element's rotation and scale directions.        
Normal..
        		stAlig..         
Visible        Defines whether the element is visible        
Normal..
        		Boolean         
Rotation        Rotation angle in degrees        
Normal..
        		Double         
Effects
Transparent Color        The color of the original pixels of rendered content that will be set as transparent        
Normal..
        		stColor         
Transparent Tolerance        Tolerance ratio for choosing colors that become transparent. Zero means that effect is not applied, 1 denotes that all colors will become trasparent        
Normal..
        		Int32         
Color Mask        Produces a multiplicative combination of the original pixels and the selected mask color (except the alpha channel).  The effect emulates a look through a colored glass.  White or transparent mask color dont change the original pixels        
Normal..
        		stColor         
Opacity        Opacity of the rendered content        
Normal..
        		Int32         
Contrast        Contrast of the rendered content        
Normal..
        		Int32         
Brightness        Brightness the rendered content        
Normal..
        		Int32         
Saturation        Saturation of the rendered content        
Normal..
        		Double         
Pixelation        Pixelation of the rendered content        
Normal..
        		Int32         
Blurring        The radius used in the gaussian blur of rendered content, as a pixel-based factor. The default is 0 which means no blurring.        
Normal..
        		Int32         
Scrambling                
Normal..
        		Double         
Scrambling Grid Size        Defines a size of the scrambling grid        
Normal..
        		clSize         
Positional Jitter
Reset Jitter Now        Runtime command that resets the positional jitter.        
Runtime Command..
        		Boolean         
Current Jitter        Returns the current jitter        
Status..
        		clPoint         
Jitter Range        Defines a possible range for the random jitter. The range is centered to the position of the element.        
Normal..
        		clSize         
Test Jitter        Click to test the current jitter        
Design Time..
        		Boolean         
Control
Is Enabled        If set to false the element is completely omitted when the experiment is run        
Design Time..
        		Boolean         
Title        Title of the element        
Design Time..
        		String         

Random Noise Patch Element is capable of generating random dot patterns in real-time. The patterns are composed of pixels with random gray luminance or combinations of random color and luminance. The randomization is based on the fast Multiply-with-Carry algorithm (Marsaglia and Zaman, 1991). The element is a recommended replacement for the old Random Dots element.


Description

The random noise patch element can generate and render 2D noise patches controlled by several input parameters. The element employs hardware-accelerated graphics and fast randomization algorithm allowing generation of the noise stimuli in real-time.

Snapshots

The examples of rendered element with three available random dots types (the insets show zoomed patterns):

Random luminance surface

Random luminance surface

Random luminance&color surface

Random luminance&color surface

Random color surface

Random color surface


Practical Use

Generation of random dots surfaces via the graphics hardware implies certain limitations on type of a randomization algorithm. Our algorithm requires a relatively slow initialization where the random seed map is created by a standard random number generator. Later this seed map is used for generation of new random surfaces by ultra-fast shuffling of the original pixel positions.

There are two major ways of using the element for generation of multiple random dots surfaces (e.g., one per trial). Every surface generated by the element is defined by the index of the seed map and index of the surface itself. You may choose how to control these indexes in experiment.

If you need to present an incidental random dots surface (for example, for introducing a random noise to stimuli), you can setup the automatic time-dependent indexes. For this purpose, set two index properties [Seed map] and [Surface] to zero. Then the element will automatically generate the seed map and random dot surface with indexes that are random themselves. If you want to log these indexes, anytime you can read them in the statistical properties [Current Map] and [Current Surface]. In order to generate a new incidental surface at runtime you should initiate one of runtime actions in your code snippets: [Update Seed Map] or [Update Surface]. The runtime action is initiated by assigning TRUE to the property in a snippet.

If you need to present a deterministic random dots surface then you have to set the indexes manually, at design-time or in code snippets at runtime. You can do by assigning a certain positive integer value to the [Seed map index] or [Surface Index] properties which causes immediate regeneration of the surface. Thus, for the "deterministic" scenario you don't need to initiate the runtime actions [Update Seed Map] or [Update Surface].

In most cases the regeneration of the seed map is not necessary, since there are 2,147,483,648 unique random surfaces can be created with a single seed map.

By default, the seed map is generated with the same dimensions as a current size of the random dot element. If you change the size of the element in runtime, it might be a good practice to initiate regeneration of the seed map in parallel by the runtime action [Update Seed Map] - it will guarantee a correct randomization process.

Evaluation of the randomization algorithm

Our randomization algorithm of reshuffling the pixel positions has an important gain for many experimental scenarios – it allows keeping the overall luminance intensity of each generated surface nearly constant. The graph below demonstrates the frequency distribution of the RGB luminance for 10000 random dots surfaces (1024x768) generated by the random dots element. Notice that the entire distribution falls within a single RGB step.

Image

The algorithm has been also tested for cross-correlation of two randomly selected pixels in a sequence of the generated surfaces. The results are shown below on the scatter plot. The cross-correlation has been found to be not significant after 10000 runs and r is -0.02. The red line shows the "zero" correlation trend with confidence intervals.

Image

Our randomization algorithm has been designed to produce a continuous uniform distribution of random values for every pixel. For luminance the distribution falls within the standard gray RGB range, 0..255, by default. We evaluated the goodness of the produced uniform distribution by comparing it with the distribution of pixel sampling by the standard random number generator in the C# programming language. Below are three graphs showing frequency distributions of the RGB luminance for two pixels (coordinates are randomly selected) and the standard random numbers generated in ~ 10000 passes.

Image
Image
Image

We assesses the most common statistical measures of all the obtained distributions and did not find significant differences in results between our and standard randomization algorithms. Notice the Kurtosis values in the table below, the negative values are indicative for the uniform distributions.

GeneratorNMeanSumMinimumMaximumVarianceStd. Dev.Std. ErrorKurtosis
Pixel A10000126.976013789590.00255.00005446.43573.799970.708176-1.18102
Pixel B10000128.808513988600.00255.00005457.43673.874460.708891-1.18804
Standard10000126.824513773140.00255.00005365.27273.248020.702880-1.17682

Notes

1. If you need a random dots surface with individual dots larger than the screen pixel (like as a grid with large cells of random colors), the best way is to simply apply the pixelation effect with the selected ratio to the element. The pixelation effect would zoom the generated pixel pattern such that a color of the central pixel in each cell would define the color of the cell itself. Then the element can be rendered as on the example below.

Image
The random dot surface, 1024x768, is rendered with the pixelation effect (pixilation ratio=86%)

2. You can enable different visual effects on the random dots element in order to obtain various rendering outputs, useful in real scenarios. One example below demonstrates the random dots surface made of only black and white pixels. The result is obtained with the contrasts visual effect set to +100%.

Image
The element with the contrast filter (+100%) applied produces the surface that contains only black and white dots.

3. Another example below shows a monochromatic random dots surface made of combination of the gray random dots and the "orange" color filter effect.

Image
The element with a monochromatic random dots surface made of combination of the gray random dots and the orange color filter effect.