Comments on: Spatial transformations: Forward mapping http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/ 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/2006/04/28/spatial-transforms-forward-mapping/#comment-23012 Steve Mon, 19 Apr 2010 18:40:48 +0000 http://blogs.mathworks.com/steve/?p=53#comment-23012 Shre—I can't offer consulting on individual projects or on reading and interpreting journal papers. It sounds like you should use on of the locally varying transform types offered by the function <tt>cpselect</tt>. Shre—I can’t offer consulting on individual projects or on reading and interpreting journal papers. It sounds like you should use on of the locally varying transform types offered by the function cpselect.

]]> By: Shre http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22953 Shre Mon, 05 Apr 2010 19:37:05 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22953 In the above mentioned comment I would like to add that only those control points selected by the user by clicking with the mouse need to be warped to target pixel position In the above mentioned comment I would like to add that only those control points selected by the user by clicking with the mouse need to be warped to target pixel position

]]> By: Shre http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22952 Shre Mon, 05 Apr 2010 19:35:16 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22952 Hi Steve, I'm doing a facial aging project at the undergraduate level.I wanted the user to click on certain control points on the 20 year old image and then wanted the program to to warp certain features downward to show geometrical facial changes.The displacement will be embedded into the code already. Which transformation should I use?..Can I find MATLAB code for it which I can modify(add displacement values, etc) to fit my purpose. Most of the codes available warp/morph one photo into another...in this case i dont have my resultant image(its to be predicted)...so i cant use those codes and i dont know how to modify them....It's very very urgent! I'll appreciate if you reply to this ASAP heres the link of the paper that Im trying to implement http://www.dca.fee.unicamp.br/~leopini/private/pubs/Greyce-2007WesternNYImageProcessingWorksop.pdf Thanks! Hi Steve,

I’m doing a facial aging project at the undergraduate level.I wanted the user to click on certain control points on the 20 year old image and then wanted the program to to warp certain features downward to show geometrical facial changes.The displacement will be embedded into the code already. Which transformation should I use?..Can I find MATLAB code for it which I can modify(add displacement values, etc) to fit my purpose. Most of the codes available warp/morph one photo into another…in this case i dont have my resultant image(its to be predicted)…so i cant use those codes and i dont know how to modify them….It’s very very urgent! I’ll appreciate if you reply to this ASAP

heres the link of the paper that Im trying to implement

http://www.dca.fee.unicamp.br/~leopini/private/pubs/Greyce-2007WesternNYImageProcessingWorksop.pdf

Thanks!

]]> By: Steve http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22815 Steve Mon, 08 Mar 2010 16:26:03 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22815 Jie—No, there is no forward-mapping spatial image transformation function. I'm sorry, but I don't have any references. Jie—No, there is no forward-mapping spatial image transformation function. I’m sorry, but I don’t have any references.

]]> By: Jie Shi http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22802 Jie Shi Fri, 05 Mar 2010 07:33:26 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22802 Hello, Steve. In my recent research, I have to spatially warp an image using a vector field. After the forward mapping, some of the image coordinates will be mapped to floating-point values. I think this problem can be addressed by the rectangle-to-quadrilateral method you mentioned here. But I am wondering whether there is a function in Matlab to do so, or if I need to implement the algorithm myself? In the latter case, do you have some references for this algorithm's details? Thanks. Hello, Steve. In my recent research, I have to spatially warp an image using a vector field. After the forward mapping, some of the image coordinates will be mapped to floating-point values. I think this problem can be addressed by the rectangle-to-quadrilateral method you mentioned here. But I am wondering whether there is a function in Matlab to do so, or if I need to implement the algorithm myself? In the latter case, do you have some references for this algorithm’s details? Thanks.

]]> By: Steve http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22148 Steve Tue, 22 Sep 2009 12:30:10 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22148 Douglas—Use <tt>cp2tform</tt> to infer a spatial transformation from your point set. One of the spatially varying ones might be best. Then use <tt>imtransform</tt> to warp your image. Douglas—Use cp2tform to infer a spatial transformation from your point set. One of the spatially varying ones might be best. Then use imtransform to warp your image.

]]> By: douglas http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22147 douglas Tue, 22 Sep 2009 06:10:27 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22147 Could you tell how to apply the grid points (data points from the transformation grid) in the transformation ? <em>[Points edited out for space.]</em> Could you tell how to apply the grid points (data points from the transformation grid) in the transformation ?

[Points edited out for space.]

]]> By: Rudolph http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22076 Rudolph Fri, 28 Aug 2009 08:05:13 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22076 I managed to overcome the idea of linear indexing which imtransform use to determine the custom spatial transform. Thanks I managed to overcome the idea of linear indexing which imtransform use to determine the custom spatial transform. Thanks

]]> By: Rudolph http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-22072 Rudolph Fri, 21 Aug 2009 09:23:06 +0000 http://blogs.mathworks.com/steve/?p=53#comment-22072 Hi Steve, I need to perform lense calibration on an image taken with specific camera. The lense coefficients are available. The distortions on the lense are radial distortion, decentering of the principal point and some affinity. According to me I'll have to calculate the (subpixel units) distance which I have to move each pixel in the x and y direction. So each pixel will have it's own resulting transformation. I went through most of your blogs and I want to create a custom tform struct which I can implement on bulk images. Now I can't see how I will be able to do this with inverse mapping, true? Will imtransform deal with the overlapping and gaps for me automatically with chosen interpolation? How do I deal with a pixel that moves 0.166 pixels up for instance? How will matlab save the info on output space? Any guidence would be appreciated. Hi Steve,

I need to perform lense calibration on an image taken with specific camera. The lense coefficients are available.

The distortions on the lense are radial distortion, decentering of the principal point and some affinity. According to me I’ll have to calculate the (subpixel units) distance which I have to move each pixel in the x and y direction. So each pixel will have it’s own resulting transformation. I went through most of your blogs and I want to create a custom tform struct which I can implement on bulk images.

Now I can’t see how I will be able to do this with inverse mapping, true? Will imtransform deal with the overlapping and gaps for me automatically with chosen interpolation? How do I deal with a pixel that moves 0.166 pixels up for instance? How will matlab save the info on output space?

Any guidence would be appreciated.

]]> By: Steve http://blogs.mathworks.com/steve/2006/04/28/spatial-transforms-forward-mapping/#comment-20560 Steve Sat, 05 Apr 2008 02:49:02 +0000 http://blogs.mathworks.com/steve/?p=53#comment-20560 Leonardo—Sounds like you could use <tt>cp2tform</tt> to estimate a spatial transform fitting your points. Leonardo—Sounds like you could use cp2tform to estimate a spatial transform fitting your points.

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