Mercurial > hg > octave-image
changeset 773:dffca76f1a22
histeq.m: restored, was broken after change to gray2ind; added tests block.
| author | Cristian Versari <cristian.versari@lifl.fr> |
|---|---|
| date | Fri, 09 Aug 2013 15:17:07 +0200 |
| parents | ab0ac77d350b |
| children | ba3b6e94ae58 |
| files | inst/histeq.m |
| diffstat | 1 files changed, 77 insertions(+), 18 deletions(-) [+] |
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--- a/inst/histeq.m +++ b/inst/histeq.m @@ -15,29 +15,88 @@ ## this program; if not, see <http://www.gnu.org/licenses/>. ## -*- texinfo -*- -## @deftypefn {Function File} @var{J} = histeq (@var{I}, @var{n}) -## Histogram equalization of a gray-scale image. The histogram contains +## @deftypefn {Function File} {@var{J} =} histeq (@var{I}, @var{n}) +## Equalize histogram of grayscale image. +## +## The histogram contains ## @var{n} bins, which defaults to 64. ## -## @var{I}: Image in double format, with values from 0.0 to 1.0 +## @var{I}: Image in double format, with values from 0.0 to 1.0. +## +## @var{J}: Returned image, in double format as well. ## -## @var{J}: Returned image, in double format as well -## @seealso{imhist} +## Note that the algorithm used for histogram equalization gives results +## qualitatively comparable but numerically different from @sc{matlab} +## implementation. +## +## @seealso{imhist, mat2gray, brighten} ## @end deftypefn -function J = histeq (I, n) - if (nargin == 0) - print_usage(); - elseif (nargin == 1) - n = 64; +function J = histeq (I, n = 64) + + if (nargin < 1 || nargin > 3) + print_usage (); + endif + + if (isempty (I)) + J = []; + return endif - [r,c] = size(I); - I = mat2gray(I); - [X,map] = gray2ind(I, n); - [nn,xx] = imhist(I, n); - Icdf = 1 / prod(size(I)) * cumsum(nn); - J = reshape(Icdf(X),r,c); - plot(Icdf,'b'); - legend( 'Image Cumulative Density Function'); + [r, c] = size (I); + I = mat2gray (I); + [X, map] = gray2ind (I, n); + [nn, xx] = imhist (I, n); + Icdf = 1 / prod (size (I)) * cumsum (nn); + J = reshape (Icdf(X + 1), r, c); endfunction + +## FIXME: the method we are using is different from Matlab so our results +## are slightly different. The following xtest show the Matlab +## results that we should be aiming at. + +%!assert (histeq ([]), []); + +## One value +%!assert (histeq (0), 1); +%!assert (histeq (1), 1); +%!assert (histeq (1.5), 1); +%!assert (histeq (zeros (100, 200)), ones (100, 200)); # matrix + +## Two values +%!xtest assert (histeq ([0 1]), [0.4920634921 1], 10^-8); +%!xtest assert (histeq ([0 1]'), [0.4920634921 1]', 10^-8); # column array +%!xtest assert (histeq ([0 255]), [0.4920634921 1], 10^-8); +%!xtest assert (histeq (uint8 ([0 1])), [ 125 190]); # uint8 +%!xtest assert (histeq (uint8 ([0 255])), [ 125 255]); +%!xtest assert (histeq (uint16 ([0 1])), [65535 65535]); # uint16 +%!xtest assert (histeq (uint16 ([0 255])), [32247 48891]); +%!xtest assert (histeq (uint16 ([0 256])), [32247 48891]); +%!xtest assert (histeq (uint16 ([0 65535])), [32247 65535]); + +## Three values +%!test assert (histeq ([0 1 1] ), [ 1/3 1 1] , 10^-8); +%!test assert (histeq ([0 0 1]'), [ 2/3 2/3 1]', 10^-8); +%!xtest assert (histeq ([0 1 2] ), [ 1/3 1 1] , 10^-8); +%!xtest assert (histeq (uint8 ([0 1 2])), [ 85 125 215]); +%!xtest assert (histeq (uint16 ([0 1 2])), [65535 65535 65535]); +%!xtest assert (histeq (uint16 ([0 100 200])), [43690 43690 55133]); + +## Many values +%!xtest +%! J = [20 32 57 81 105 125 150 174 198 223 247]; +%! assert (histeq (uint8 (0:10:100)), J); + +%!xtest +%! J = [0.0793650794 +%! 0.1269841270 +%! 0.2222222222 +%! 0.3174603175 +%! 0.4126984127 +%! 0.4920634921 +%! 0.5873015873 +%! 0.6825396825 +%! 0.7777777778 +%! 0.8730158730 +%! 1.0000000000]; +%! assert (histeq (0:0.1:1), J', 10^-8);