% detransrot.m                                      Steve Mann, 1993
% (x-b)/a group image desampling for testing Peleg algorithm.
%
% This function will un-rotate and un-translate an image at subpixel resolution.
% An additional feature (for future use) is that it can un-scale an image.
%
% Note the group is the reverse mapping y=g((x-b)/a) and not ax+b
%      so rot, trans, etc in usual sense: g(x-1) gives incr. along real axis
%
% Use: Y = detransrot(a,X,b)
%          a is dilation: angle(a) is rotation      to act on X
%          X is input image
%          b is translation (real part is downward axis, imag part, right axis)
%
% Examples: tv(detransrot(exp(i*30*o),red)) % 30o rotated counterclockwise
%           tv(detransrot(1,red,3+4*i))     % translated 3 pixels down, 4 right
%           tv(detransrot(2,red) % displays function Y=red(X/2) which is bigger
%
% detransrot(2,red,100) is red((x-100)/2) = red(x/2-50); so 100 pel shift right
%
% detransrot(a,red,b,interp_order)  uses something other than default bilinear
% detransrot(a,red,b,interp_order,antialias_method) uses other than default = -1
% See also: detransrotxy, retransrotxy

function Y = desamplerforPeleg(a,X,b, interp_order, antialias_method,myNaN)

if nargin < 6
  disp('detransrot: setting myNaN=NaN (default background grey level)')
  myNaN=NaN;  % default NaN
end%if

if nargin < 5
  disp('detransrot: antialias method not specified; setting it to -1')
  antialias_method = -1;
end%if

if nargin < 4
  disp('detransrot: interp_order not specified; setting it to 1 (bilinear)')
  interp_order = 1;
end%if

if nargin == 2
  disp('detransrot: you did not specify b so I am setting it to 0')
  b=0;
end%if

if nargin == 1
  disp('--------------------------------------------')
  disp('detransrot: you MUST specify an input image, X')
  disp('--------------------------------------------')
  return
end%if

if nargin == 0
  disp('---------------------------------------------------------------------')
  disp('detransrot: you MUST specify the dilation parameter,a, and the image X')
  disp('---------------------------------------------------------------------')
  return
end%if

Y = retransrot(1/a,X,-b/a, interp_order, antialias_method,myNaN);