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Re: [OctDev] New imrotate
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From: Etienne G. <et...@cs...> - 2004-10-27 12:07:43
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Hi all,
I have just tested imrotate briefly and commited it on octave-forge
cvs. Thanks for your contribution,
Etienne
On Tue, Oct 26, 2004 at 09:50:41AM +0200, Justus H. Piater wrote:
# OK, here's my proposed replacement for imrotate, with fixes applied,
# humbly submitted for inclusion in octave-forge.
#=20
# Justus
#=20
#=20
# Stefan van der Walt <st...@su...> wrote on Thu, 21 Oct 2004
# 11:49:51 +0200:
#=20
# > Hi Justin
# >
# > The script works well. If you want it to be incorporated into
# > octave-forge
#=20
# ## Copyright (C) 2004 Justus Piater
# ##
# ## 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 2
# ## 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, write to the Free Software
# ## Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-130=
7, USA.
#=20
# ## -*- texinfo -*-
# ## @deftypefn {Function File} {}=20
# ## imrotate(@var{imgPre}, @var{theta}, @var{method}, @var{bb=
ox})
# ## Rotation of a 2D matrix about its center.
# ##
# ## Input parameters:
# ##
# ## @var{imgPre} an input image matrix
# ##
# ## @var{theta} the rotation angle in degrees counterclockwise
# ##
# ## @var{method} "nearest" neighbor (default; faster, but produces
# ## aliasing effects) or "bilinear" interpolation
# ## (preferred; does anti-aliasing)
# ##
# ## @var{bbox} "loose" (default) or "crop"
# ##
# ## Output parameters:
# ##
# ## @var{imgPos}t the rotated image matrix
# ##
# ## @var{H} the homography mapping original to rotated pixel
# ## coordinates. To map a coordinate vector c =3D [x;y=
] to its
# ## rotated location, compute round((@var{H} * [c; 1])(1:2)).
# ## @end deftypefn
#=20
# ## Author: Justus H. Piater <Jus...@UL...>
# ## Created: 2004-10-18
# ## Version: 0.1
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# function [imgPost, H] =3D imrotate(imgPre, theta, method, bbox)
# if (nargin < 2)
# help("imrotate");
# return;
# endif
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# theta =3D theta * pi/180;
#=20
# sizePre =3D size(imgPre);
#=20
# ## We think in x,y coordinates here (rather than row,column).
#=20
# R =3D [cos(theta) sin(theta); -sin(theta) cos(theta)];
#=20
# if (nargin =3D=3D 4 && strcmp(bbox, "crop"))
# sizePost =3D sizePre;
# else
# ## Compute new size by projecting image corners through the rotatio=
n:
# corners =3D [0, 0;
# (R * [sizePre(2); 1])';
# (R * [sizePre(2); sizePre(1)])';
# (R * [1; sizePre(1)])' ];
# sizePost(2) =3D ceil(max(corners(:,1))) - floor(min(corners(:,1)));
# sizePost(1) =3D ceil(max(corners(:,2))) - floor(min(corners(:,2)));
# endif
#=20
# ## Compute the translation part of the homography:
# oPre =3D ([sizePre(2) ; sizePre(1) ] + 1) / 2;
# oPost =3D ([sizePost(2); sizePost(1)] + 1) / 2;
# T =3D oPost - R * oPre;
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# ## And here is the homography mapping old to new coordinates:
# H =3D [[R; 0 0] [T; 1]];
#=20
# Hinv =3D inv(H);
#=20
# ## "Pre" variables hold pre -rotation values;
# ## "Post" variables hold post-rotation values.
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# ## Target coordinates:
# [xPost, yPost] =3D meshgrid(1:(sizePost(2)), 1:(sizePost(1)));
#=20
# ## Compute corresponding source coordinates:
# xPre =3D Hinv(1,1) * xPost + Hinv(1,2) * yPost + Hinv(1,3);
# yPre =3D Hinv(2,1) * xPost + Hinv(2,2) * yPost + Hinv(2,3);
# ## zPre is guaranteed to be 1, since the last row of H (and thus of
# ## Hinv) is [0 0 1].
#=20
# ## Now map the image, either by nearest neighbor or by bilinear
# ## interpolation:
# if (nargin < 3 || !size(method) || strcmp(method, "nearest"))
# ## nearest-neighbor: simply round Pre coordinates
# xPre =3D round(xPre);
# yPre =3D round(yPre);
# valid =3D find(1 <=3D xPre & xPre <=3D sizePre(2) &
# 1 <=3D yPre & yPre <=3D sizePre(1) );
# iPre =3D sub2ind(sizePre , yPre (valid), xPre (valid));
# iPost =3D sub2ind(sizePost, yPost(valid), xPost(valid));
#=20
# imgPost =3D zeros(sizePost);
# imgPost(iPost) =3D imgPre(iPre);
# else
# ## bilinear interpolation between the four floor and ceiling coordi=
nates
# xPreFloor =3D floor(xPre);
# xPreCeil =3D ceil (xPre);
# yPreFloor =3D floor(yPre);
# yPreCeil =3D ceil (yPre);
#=20
# valid =3D find(1 <=3D xPreFloor & xPreCeil <=3D sizePre(2) &
# 1 <=3D yPreFloor & yPreCeil <=3D sizePre(1) );
#=20
# xPreFloor =3D xPreFloor(valid);
# xPreCeil =3D xPreCeil (valid);
# yPreFloor =3D yPreFloor(valid);
# yPreCeil =3D yPreCeil (valid);
#=20
# ## In the following, FC =3D floor(x), ceil(y), etc.
# iPreFF =3D sub2ind(sizePre, yPreFloor, xPreFloor);
# iPreCF =3D sub2ind(sizePre, yPreFloor, xPreCeil );
# iPreCC =3D sub2ind(sizePre, yPreCeil , xPreCeil );
# iPreFC =3D sub2ind(sizePre, yPreCeil , xPreFloor);
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# ## We'll have to weight by the fractional part of the coordinates:
# xPreFrac =3D xPre(valid) - xPreFloor;
# yPreFrac =3D yPre(valid) - yPreFloor;
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# iPost =3D sub2ind(sizePost, yPost(valid), xPost(valid));
#=20
# imgPost =3D zeros(sizePost);
# imgPost(iPost) =3D ...
# round(imgPre(iPreFF) .* (1 - xPreFrac) .* (1 - yPreFrac) + ...
# imgPre(iPreCF) .* xPreFrac .* (1 - yPreFrac) + ...
# imgPre(iPreCC) .* xPreFrac .* yPreFrac + ...
# imgPre(iPreFC) .* (1 - xPreFrac) .* yPreFrac );
# endif
# endfunction
#=20
# --=20
# Justus H. Piater, Ph.D. http://www.montefiore.ulg.ac.be/~piater=
/
# Institut Montefiore, B28 Phone: +32-4-366-2279
# Universit=E9 de Li=E8ge, Belgium Fax: +32-4-366-2620
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Etienne Grossmann ------ http://www.cs.uky.edu/~etienne
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