Comments on: Spatial transformations: maketform, tformfwd, and tforminv http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/ Steve Eddins manages the Image & Geospatial development team at The MathWorks and coauthored Digital Image Processing Using MATLAB. He writes here about image processing concepts, algorithm implementations, and MATLAB. Sat, 11 Feb 2012 18:27:50 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Steve http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-24416 Steve Wed, 17 Aug 2011 02:12:22 +0000 http://blogs.mathworks.com/steve/?p=37#comment-24416 Lawaller—You can use imtransform for that. Lawaller—You can use imtransform for that.

]]> By: lawaller http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-24364 lawaller Wed, 27 Jul 2011 22:00:17 +0000 http://blogs.mathworks.com/steve/?p=37#comment-24364 Hi, i'd like to do a 2D shear on a 4D matrix. so i have the affine tform matrix T and the input 4D matrix. which function should i use to get the output 4D matrix that has been operated on by T?? thanks! Hi,

i’d like to do a 2D shear on a 4D matrix. so i have the affine tform matrix T and the input 4D matrix. which function should i use to get the output 4D matrix that has been operated on by T?? thanks!

]]> By: Steve http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-24199 Steve Fri, 13 May 2011 13:46:36 +0000 http://blogs.mathworks.com/steve/?p=37#comment-24199 Sundar—Close, but it actually works in the opposite direction. Start with a pixel location in the <strong>output image</strong>. Rotate that pixel location to find the corresponding location in the input image. In general, the input-image location won't be integer valued. Round the input-image location. Grab the input-image pixel value at the rounded location and use that value for the corresponding output image pixel. Sundar—Close, but it actually works in the opposite direction. Start with a pixel location in the output image. Rotate that pixel location to find the corresponding location in the input image. In general, the input-image location won’t be integer valued. Round the input-image location. Grab the input-image pixel value at the rounded location and use that value for the corresponding output image pixel.

]]> By: Sundar http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-23980 Sundar Tue, 22 Feb 2011 09:15:04 +0000 http://blogs.mathworks.com/steve/?p=37#comment-23980 Hi Steve, I have a question on nearest neighbor interpolation (NNI) when I do image rotation. I am comfortable with using imtransform but I would like to know a bit more on NNI. Say, I rotate an image by a certain degree using NNI and let us consider a single point (30,30) in the image. When rotated, say (30,30) in the new image is at (35.25,45.4). Does NNI round up this co-ordinate to (35,45) and then fill up this position with the pixel value of (30,30)? Thanks Sundar Hi Steve,
I have a question on nearest neighbor interpolation (NNI) when I do image rotation. I am comfortable with using imtransform but I would like to know a bit more on NNI. Say, I rotate an image by a certain degree using NNI and let us consider a single point (30,30) in the image. When rotated, say (30,30) in the new image is at (35.25,45.4). Does NNI round up this co-ordinate to (35,45) and then fill up this position with the pixel value of (30,30)?

Thanks
Sundar

]]> By: Alex http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-23773 Alex Fri, 10 Dec 2010 14:28:24 +0000 http://blogs.mathworks.com/steve/?p=37#comment-23773 Hi Steve, I do have a question regarding calculation of homography matrix to compensate the distortion in a picture, unfortunately I could not find any suitable example regarding this case. I have checked the following link as as a m file that computes the 3x3 2D homography of 4 or more points in a plane. This code follows the normalised direct linear transformation algorithm given by Hartley and Zisserman. http://www.csse.uwa.edu.au/~pk/Research/MatlabFns/Projective/homography2d.m but i did not figure out how should I get the x1 and x2 points. I have posted my picture here: http://i53.tinypic.com/qsje4n.jpg please help me the solution Hi Steve,

I do have a question regarding calculation of homography matrix to compensate the distortion in a picture, unfortunately I could not find any suitable example regarding this case. I have checked the following link as as a m file that computes the 3×3 2D homography of 4 or more points in a plane. This code follows the normalised direct linear transformation algorithm given by Hartley and Zisserman.

http://www.csse.uwa.edu.au/~pk/Research/MatlabFns/Projective/homography2d.m

but i did not figure out how should I get the x1 and x2 points. I have posted my picture here:
http://i53.tinypic.com/qsje4n.jpg

please help me the solution

]]> By: Steve http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-23011 Steve Mon, 19 Apr 2010 18:38:59 +0000 http://blogs.mathworks.com/steve/?p=37#comment-23011 Helen—After you call <tt>load</tt>, do you have the variables <tt>x</tt> and <tt>y</tt> in your workspace? Helen—After you call load, do you have the variables x and y in your workspace?

]]> By: Helen http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-22950 Helen Fri, 02 Apr 2010 08:29:33 +0000 http://blogs.mathworks.com/steve/?p=37#comment-22950 <pre> % http://blogs.mathworks.com/images/steve/37/george.mat load george plot(x,y), axis ij, axis equal, axis([-1 1 -1 1]), grid on ??? Undefined function or variable 'x'. </pre> could you help me solve this problem? I am a beginning student ,please forgive me for my question % http://blogs.mathworks.com/images/steve/37/george.mat load george plot(x,y), axis ij, axis equal, axis([-1 1 -1 1]), grid on ??? Undefined function or variable 'x'.

could you help me solve this problem? I am a beginning student ,please forgive me for my question

]]> By: Steve http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-22924 Steve Fri, 26 Mar 2010 20:17:45 +0000 http://blogs.mathworks.com/steve/?p=37#comment-22924 Esther—How the inference problems are formulated and solved for the different types are pretty well documented in code comments inside the function cp2tform.m. See the code comments associated with the different subfunctions inside. Esther—How the inference problems are formulated and solved for the different types are pretty well documented in code comments inside the function cp2tform.m. See the code comments associated with the different subfunctions inside.

]]> By: Esther http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-22923 Esther Fri, 26 Mar 2010 17:03:10 +0000 http://blogs.mathworks.com/steve/?p=37#comment-22923 Hi Steve, I would like to know how Matlab performs linear conformal mapping for 2 and more than 2 control point pairs (for the registration of a pair of images) under the function cp2tform. Is it using some kind of least square solutions? Can you suggest any reference for this? Thanks. Hi Steve,

I would like to know how Matlab performs linear conformal mapping for 2 and more than 2 control point pairs (for the registration of a pair of images) under the function cp2tform. Is it using some kind of least square solutions?

Can you suggest any reference for this? Thanks.

]]> By: Steve http://blogs.mathworks.com/steve/2006/02/14/spatial-transformations-maketform-tformfwd-and-tforminv/#comment-22919 Steve Fri, 26 Mar 2010 13:01:34 +0000 http://blogs.mathworks.com/steve/?p=37#comment-22919 Esther—Can you be more specific about what you want to know? Esther—Can you be more specific about what you want to know?

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