deriv.m

图像对齐（inage registration）工具箱

function [di,dj] = deriv(I)

% DERIV Partial derivatives of image.
%       [di,dj] = deriv(I)
%       di, dj have the same size as I. The rims are with the last valid values.
% (c) Tom Werner Sept 1996
  

[M,N] = size(I);

if M >= 3
  di = ( I(3:M,:) - I(1:M-2,:) )/2;
  di = [ di(1,:); di; di(M-2,:) ];
else
  di = NaN * ones(M,N);
end

if N >= 3
  dj = ( I(:,3:N) - I(:,1:N-2) )/2;
  dj = [ dj(:,1) dj dj(:,N-2) ];
else
  dj = NaN * ones(M,N);
end

return