[shader configstring] = EXPCreateStatic2DConvolutionShader(kernel [, nrinputchannels=3][, nroutchannels=3][, debug][, shadertype])

Creates a GLSL fragment shader for 2D convolution of textures with
the 2D or 1D convolution kernel ‘kernel’ and returns a handle ‘shader’
to it, as well as a blitter config options string as needed by the
PTB imaging pipeline.

Usually you won’t call this routine directly, but use
Add2DConvolutionToGLOperator() instead. It allows convenient setup of
convolution operators of arbitrary size and complexity to GLOperators
for use with Screen(‘TransformTexture’); and for use with the stimulus
post-processing pipeline. Only if you want to create small convolution
kernels for single-pass convolution of textures, you’ll use this routine
directly and use the returned ‘shader’ as argument to Screen(‘DrawTexture’)
or Screen(‘MakeTexture’) as ‘textureShader’ argument.

If you call this function directly, the generated shader may only work with
the onscreen window that is active at the time you call the function. To make
sure that the shader works with the onscreen window ‘win’ of your choice, call
Screen(‘GetWindowInfo’, win); first, to activate the window ‘win’.


‘kernel’ is a simple 2D m-by-n matrix of floating point numbers with m and
n being odd numbers, e.g., 1x1, 3x3, 5x5, 7x7, 9x9,…, 1x3, 1x9, 7x1 …
Each entry in the kernel is used as a weight factor.

The simplest way to get a 2D kernel is to use the function
kernel = fspecial(…); fspecial is part of the Matlab image
processing toolbox, see “help fspecial” for more information.

‘nrinputchannels’ = The number of image channels to use as input for the
convolution. Possible values are: 3 = Red, Green and Blue color channels are
provided as part of a true-color image, don’t use the alpha channel (if
any) for convolution but just pass it through unmodified. 1 = The image
only defines a luminance channel for convolution, an (optional) alpha
channel is passed through unmodified. 4 = Use all four channels (Red,
green, blue, alpha) for convolution.

‘nroutchannels’ = The number of channels to convolve as output: 3 =
Convolve each of the three color channels red, green and blue separately
by the same kernel. An (optional) alpha channel is passed through unmodified.
1 = Output a filtered luminance channel, and an (optional) unmodified
alpha channel. If input is a 3 channel RGB image, then the RGB image will
get converted to luminance before convolution. 4 = Filter all four
channels independently.

Typical settings:

Filter a RGB(A) image: nrinputchannels = 3, nroutchannels = 3.
Filter a RGB(A) image into grayscale: nrinputchannels = 3, nroutchannels = 1.
Filter a luminance(A) image: inputchannels = 1, filteredoutchannels = 1.
Generic filtering of 4-channel data: nrinputchannels = 4, nroutchannels = 4.

‘debug’ Optional debug flag: If set to non-zero, will output some debug
info about the shader.

‘shadertype’ (Optional) The type of internal implementation to choose for
the operator. This parameter is best left alone, unless you really know
what you are doing.


This feature is in early alpha stage. It may fail on your system and its
future implementation may change significantly! Don’t trust its results
without validation against a known good reference implementation!

NOTES: Filtermode 2 and 3 not fully implemented for the general case!
—> No separable 1D kernels, no support for all input->output mappings

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