% RIDGEFREQ - Calculates a ridge frequency image%% Function to estimate the fingerprint ridge frequency across a% fingerprint image. This is done by considering blocks of the image and% determining a ridgecount within each block by a call to FREQEST.%% Usage:%  [freqim, medianfreq] =  ridgefreq(im, mask, orientim, blksze, windsze, ...%                                    minWaveLength, maxWaveLength)%% Arguments:%         im       - Image to be processed.%         mask     - Mask defining ridge regions (obtained from RIDGESEGMENT)%         orientim - Ridge orientation image (obtained from RIDGORIENT)%         blksze   - Size of image block to use (say 32) %         windsze  - Window length used to identify peaks. This should be%                    an odd integer, say 3 or 5.%         minWaveLength,  maxWaveLength - Minimum and maximum ridge%                     wavelengths, in pixels, considered acceptable.% % Returns:%         freqim     - An image  the same size as im with  values set to%                      the estimated ridge spatial frequency within each%                      image block.  If a  ridge frequency cannot be%                      found within a block, or cannot be found within the%                      limits set by min and max Wavlength freqim is set%                      to zeros within that block.%         medianfreq - Median frequency value evaluated over all the%                      valid regions of the image.%% Suggested parameters for a 500dpi fingerprint image%   [freqim, medianfreq] = ridgefreq(im,orientim, 32, 5, 5, 15);%% I seem to find that the median frequency value is more useful as an% input to RIDGEFILTER than the more detailed freqim.  This is possibly% due to deficiencies in FREQEST.%% See also: RIDGEORIENT, FREQEST, RIDGESEGMENT% Reference: % Hong, L., Wan, Y., and Jain, A. K. Fingerprint image enhancement:% Algorithm and performance evaluation. IEEE Transactions on Pattern% Analysis and Machine Intelligence 20, 8 (1998), 777 789.% Peter Kovesi  % School of Computer Science & Software Engineering% The University of Western Australia% pk at csse uwa edu au% http://www.csse.uwa.edu.au/~pk%% January 2005function [freq, medianfreq] = ridgefreq(im, mask, orient, blksze, windsze, ...                                        minWaveLength, maxWaveLength)             [rows, cols] = size(im);    freq = zeros(size(im));        for r = 1:blksze:rows-blksze        for c = 1:blksze:cols-blksze          blkim = im(r:r+blksze-1, c:c+blksze-1);              blkor = orient(r:r+blksze-1, c:c+blksze-1);                           freq(r:r+blksze-1,c:c+blksze-1) =  ...              freqest(blkim, blkor, windsze, minWaveLength, maxWaveLength);        end    end    % Mask out frequencies calculated for non ridge regions    freq = freq.*mask;        % Find median freqency over all the valid regions of the image.    medianfreq = median(freq(find(freq>0)));