% 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 2005

function [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)));