function im_out=imsharpen(im,C,VERBOSITY);

% IMSHARPEN Image sharpening.

% CMP Vision Algorithms http://visionbook.felk.cvut.cz

% Tomas Svoboda, Petr Nemecek, 2006-2007



% Function imsharpen sharpens an image by emphasizing places

% with high gradient: 

% sharpening is computed by subtracting 

% a weighted Laplacian from the blurred image. 

% Usage: im_out = imsharpen(im,C,VERBOSITY)

% Inputs:

%   im  [m x n]  Input image, gray scale images assumed.

%   C   1x1  Multiplicative coefficient: (0.3--1.5) is a reasonable range.

%   VERBOSITY  (default 0)
%              Verbosity of the function, if >0 displays

%             images of the gradients.
% Outputs:

%   im_out  [m x n]  Sharpened image.

% See also: gradient.



% History:

% $Id: imsharpen_decor.m 1074 2007-08-14 09:45:42Z kybic $

%

% 2006-01 Petr Nemecek created

% 2007-03-12 Tomas Svoboda (TS), decorated and pedagogically enhanced

% 2007-05-02 TS: new decor

% 2007-05-24 VZ: typo

% 2007-08-09 TS: refinement for better looking of m-files





if nargin<3

  VERBOSITY=0;

end



if C<=0

    warning('Incorrect input value of parameter C. Parameter C has to be greater than zero.');

end



% First, convert the input image to double precision, integers cause errors in

% gradient computation. 

im = double(im);



% Compute the first derivatives: 

[gradX,gradY] = gradient(im);

% Compute the second derivatives:

sqgradX = gradient(gradX);

sqgradY = gradient(gradY')';

% Compute the Laplacian

Laplacian = sqgradX + sqgradY;



% and sharpen the image:

im_out = im - C*Laplacian;



% Truncate values smaller than 0 and higher than 255.

% An alternative post-processing may be

% to re-map the new range to the range (0,...,255), see

% hist_equal or imagesc.

% 

im_out(im_out>255) = 255;

im_out(im_out<0) = 0;

im_out = uint8(im_out);



if VERBOSITY>0

  figure;

  subplot(2,2,1), imagesc(gradX), axis image, colormap(gray(256)); title('x-gradient \it \partial I/\partial x')

  subplot(2,2,2), imagesc(gradY), axis image, colormap(gray(256)); title('y-gradient \it \partial I/\partial y')

  subplot(2,2,3), imagesc(sqgradX), axis image, colormap(gray(256)); title('\it \partial^2 I/\partial x^2')

  subplot(2,2,4), imagesc(sqgradY), axis image, colormap(gray(256)); title('\it \partial^2 I/\partial y^2')

  figure;

  imagesc(Laplacian), axis image, colormap(gray(256)); 

  title('Laplacian: \it \nabla = \partial^2 I/\partial x^2 + \partial^2 I/\partial y^2')

end





return; % end of imsharpen