## OrientationBandpass

##### >Psychtoolbox>PsychSignal

w=orientationBandpass(size,oLow,oHigh) returns a “window”, i.e. a matrix

meant to be used as a band-pass filter. The matrix size is mxn if “size”

is [m,n], and nxn if “size” is n. The matrix elements represent gain at

each freq, uniformly spaced from about -1 to 1 of Nyquist frequency (see

FREQSPACE). oLow and oHigh are the cut-off orientations in degrees (e.g.

0 to 360). The interval will include all angles from oLow up to but not

including orientation oHigh. oHigh must be in the range [oLow,oLow+180].

Setting oHigh=oLow+180 will produce an all-pass filter. The filter has

gain 1 in the orientation intervals [oLow,oHigh) and

[oLow+180,oHigh+180), and gain 0 outside those intervals. Note the

asymmetry: oLow is included and oHigh is excluded. Frequency zero, which

has no orientation, is always passed with gain 1. The logical OR

of filters for several contiguous bands, e.g. 0 to 20 and 20 to 40 will

equal the filter for the composite band, 0 to 40. oLow can be any finite

value, but only the range 0 to 180 is unique. o+180 is equivalent to o.

Here’s a typical use, to produce orientation-bandpass noise:

noise=randn(n,n);

filter=OrientationBandpass(n,oLow,oHigh);

if any(any(filter~=1)) % skip all-pass filter

ft=filter.*fftshift(fft2(noise));

noise=real(ifft2(ifftshift(ft)));

end

Also see Bandpass2, Bandpass, FREQSPACE.

`Psychtoolbox/PsychSignal/OrientationBandpass.m`