## bbfbp

This function is not yet fully documented. This is a transcript of
the text-formatted help.

bbfbp Create black-box for Filtered Back-Projection
[BB,DIM2]=bbfbp(DIM1) creates an operator that approximately invert
the Radon transform using Filtered Back Projection (FBP). This is
a linear operator, and can therefore be represented as a black-box.
The operator converts a sinogram of dimension DIM1=[SAMP,K] to an
image of dimension DIM2. The image dimension may be specified using
the syntax BB=bbfbp(DIM1,DIM2). The default image is DIM2=[N,N] where
N=2*floor(SAMP/sqrt(8)).
The angles in the projection are assumed to be THETA=(0:K-1)*(180/K).
Options may be passed in the same way as bbradon, and the options
'len', 'roi', and 'notol' have the same meaning.
The FBP algorithm is based on a filter to undo the Radon transform,
but also amplifies noise. To reduce the noise, a cut-off frequency
may be set as bbfbp(...,'cut',D), where 0<D<=1 is normalized to
the Nyquist frequency, i.e. the highest possible frequency allowed
by the discretization (default: D=1).
To alleviate the effect of the sharp cut-off, which can result in
"ringing", the filter may also be multiplied by a window:
'ramp': Ramp-filter, no window (default)
AKA: 'ram-lak', 'rect', or 'none'
'triangular': Triangular window (AKA 'bartlett')
'hamming': Hamming window
'hanning': Hanning window (AKA 'hann')
'blackman': Blackman window
Example:
I0=bbphantom([150,150],'restest');
figure(1); imagesc(I0); axis image; colormap(gray);
[bb,dim2,opt]=bbradon(size(I0),0:5:175,'notol');
S=reshape(bb*I0(:),dim2);
figure(2); imagesc(S); colormap(gray);
[bbi,dim3]=bbfbp(dim2,'cut',.75,'hamming','notol');
I1=reshape(bbi*S(:),dim3);
figure(3); imagesc(I1); axis image; colormap(gray);
See also bbradon, bbempoisson, (image toolbox).

bbeyebbflipdim