>Psychtoolbox>PsychGLImageProcessing

Add2DConvolutionToGLOperator(gloperator, kernel [, opname] [, nrinputchannels] [, nroutchannels] [, debug] [, shadertype])

Add a non-separable 2D convolution kernel to GL operator ‘gloperator’.

‘kernel’ is a simple 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 matrix is used as a weight factor for the
convolution.

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.

‘opname’ is the optional name of the convolution operation, meant as
debugging aid.

‘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.