Hi Adrian
it took me a long time to get around this but I think now it's
completely matlab compatible. If you could test the attached file (or
the development version) and report back it would be great.
Thanks,
Carnë
## Copyright (C) 2011, 2012 Carnë Draug <carandraug+...@gmail.com>
##
## This program is free software; you can redistribute it and/or modify it under
## the terms of the GNU General Public License as published by the Free Software
## Foundation; either version 3 of the License, or (at your option) any later
## version.
##
## This program is distributed in the hope that it will be useful, but WITHOUT
## ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
## FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
## details.
##
## You should have received a copy of the GNU General Public License along with
## this program; if not, see <http://www.gnu.org/licenses/>.
## -*- texinfo -*-
## @deftypefn {Function File} {} imhist (@var{I})
## @deftypefnx {Function File} {} imhist (@var{I}, @var{n})
## @deftypefnx {Function File} {} imhist (@var{X}, @var{cmap})
## @deftypefnx {Function File} {[@var{counts}, @var{x}] =} imhist (@dots{})
## Produce histogram counts of image @var{I}.
##
## The second argument can either be @var{n}, a scalar that specifies the number
## of bins; or @var{cmap}, a colormap in which case @var{X} is expected to be
## an indexed image. If not specified, @var{n} defauls to 2 for binary images,
## and 256 for grayscale images.
##
## If output is requested, @var{counts} is the number of counts for each bin and
## @var{x} is a range for the bins so that @code{stem (@var{x}, @var{counts})} will
## show the histogram.
##
## Since a colorbar is not displayed under the histogram, calling this function
## to visualize the histogram of an indexed image may not be very helpful.
##
## @seealso{hist, histc, histeq}
## @end deftypefn
function [varargout] = imhist (img, b)
## then img can either be a "normal" or indexed image. We will need to
## check the second argument to find out
indexed = false;
if (nargin < 1 || nargin > 2)
print_usage;
elseif (nargin == 1)
if (islogical (img))
b = 2;
else
b = 256;
endif
elseif (nargin == 2)
if (iscolormap (b))
## if using a colormap, image must be an indexed image
indexed = true;
elseif (isnumeric (b) && isscalar (b) && fix(b) == b)
## do nothing, all is good
if (islogical (img) && b != 2)
error ("there can only be 2 bins when input image is binary")
endif
else
error ("second argument should either be a positive integer scalar or a colormap");
endif
endif
## check if img is good
if (indexed)
if (!isind(img))
error ("second argument is a colormap but image is not indexed");
endif
## an indexed image reads differently wether it's uint8/16 or double
## If uint8/16, index-1 is the colormap row number (there's an offset of 1)
## If double, index is the colormap row number (no offset)
## isind above already checks for double/uint8/uint16 so we can use isinteger
## and isfloat safely
if ( (isfloat (img) && max (img(:)) > rows(b) ) ||
(isinteger (img) && max (img(:)) > rows(b)-1) )
warning ("largest index in image exceeds length of colormap");
endif
endif
## prepare bins
if (indexed)
if (isinteger (img))
bins = 0:rows(b)-1;
else
bins = 1:rows(b);
endif
else
if (isinteger (img))
bins = linspace (intmin (class (img)), intmax (class (img)), b);
elseif (islogical (img))
bins = 0:1;
else
## image must be single or double
bins = linspace (0, 1, b);
endif
## we will use this bins with histc where they are the edges for each bin
## but in imhist we want them to be the center of each bin. We can't use
## hist either since values right in the middle will go to the bottom
## bin (4.5 will be placed on the bin 4 instead of 5 and this is like
## matlab, not an octave bug). So we still use histc but we decrease their
## values by half of bin width and increase it back in the end to return
## the values (if we did it on the image it would be only one step but
## would be heavier on the system since images are likely to be larger
## than bins)
if (!islogical (img))
bins -= ((bins(2) - bins(1))/2);
endif
## matlab returns bins as one column instead of a row but only for non
## indexed images
bins = bins';
endif
## if not dealing with indexed image, we may need to make sure values are
## between get bin values
if (!indexed)
## while integers could in no way have a value below the minium of their
## class, floats can have values below zero which need to be truncated
if (isfloat (img))
img(img < 0) = 0;
endif
## because we adjusted the bins edge below the max value of the class, and
## because histc will not count values outside the edges, we need to bring
## them down (no need to worry about the min because the min edge is already
## below the mininum of the class). This also adjusts floats above 1
if (max (img(:)) > bins(end))
## in case it's a integer, if we try to assign the non integer values it
## will fail so we need to make it double. But this means it takes more
## memory so let's first make sure we need to
if (fix(bins(end)) != bins(end))
img = double (img);
endif
img(img > bins(end)) = bins(end);
endif
endif
[nn] = histc (img(:), bins);
if (!indexed && !islogical(img))
bins += ((bins(2) - bins(1))/2);
endif
if (nargout != 0)
varargout{1} = nn;
varargout{2} = bins;
else
stem (bins, nn);
## would be cool if we managed to have the colormap showed under the
## histogram like matlab does. Should look into the code of waitfor and
## colormap to check how to do it
endif
endfunction
%!shared nn, bb, enn, ebb
%! [nn, bb] = imhist(logical([0 1 0 0 1]));
%!assert({nn, bb}, {[3 2]', [0 1]'})
%! [nn, bb] = imhist([0 0.2 0.4 0.9 1], 5);
%!assert({nn, bb}, {[1 1 1 0 2]', [0 0.25 0.5 0.75 1]'})
%! [nn, bb] = imhist([-2 0 0.2 0.4 0.9 1 5], 5);
%!assert({nn, bb}, {[2 1 1 0 3]', [0 0.25 0.5 0.75 1]'})
%! [nn, bb] = imhist(uint8([0 32 255]), 256);
%! enn = zeros(256, 1); enn([1, 33, 256]) = 1;
%! ebb = 0:255;
%!assert({nn, bb}, {enn, ebb'})
%! [nn, bb] = imhist(int8([-50 0 100]), 31);
%! enn = zeros(31, 1); enn([10, 16, 28]) = 1;
%! ebb = -128:8.5:127;
%!assert({nn, bb}, {enn, ebb'})
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