Coherent Backscattering from Multiple Scattering Systems - KOPS ...

Evaluation of the small angle data
Evaluation of the small angle data
The following MATLAB code is a very simplified version of the evaluation program for the
small angle setup; it will not work with all data. The script finds the backscattering direction
θ = 0 in the CCD image and calculates either an azimuthal average or a radial profile section
of the backscattering cone.
The signals of the CCD chip and their errors (se = standard error) are stored in two uint16
binary files. Depending on the preprocessing the numbers can have big (ieee-be) or little
(ieee-le) endian.
function small_angle_evaluation
%% Open file
endian = ’ieee-be’ ;
% alternative: ’ieee-le’
fid = fopen (’C:\Examples\example.i16’, ’r’) ;
matrix = fread (fid, [2048,2048], ’uint16’, 0, endian) ;
fclose (fid) ;
fid = fopen (’C:\Examples\example_se.i16’, ’r’) ;
errormatrix = fread (fid, [2048,2048], ’uint16’, 0, endian) ;
fclose (fid) ;
%% Find peak
% the image has to be scaled to have intensities in [0,1] by dividing by the
% largest possible intensity (i.e. 65535)
dummy = matrix / 65535 ;
% turn matrix into black-and-white picture (conetip forms white blob,
% everything else is black)
n = 5 ;
dummy = medfilt2 (dummy, [n,n]) ;
maximum = max ( max (dummy) ) ;
level = 0.95 * maximum ;
bwimage = im2bw (dummy, level) ;
% smooth picture so that fluctuations do
% not disturb the search for the cone
% find center of the blob => scattering angle theta = 0
dummy = bwlabel (bwimage) ; % label connected components in binary image
regions = regionprops (dummy, ’Area’, ’Centroid’) ; % measure properties
% of image regions
[area,index] = max ( [ regions.Area ] ) ;
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