Comments on: Spatial transformations: Controlling the input and output grids with imtransform http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/ Steve Eddins manages the Image & Geospatial development team at <a href="http://www.mathworks.com/">The MathWorks</a> and coauthored <a href="http://www.mathworks.com/support/books/book5291.html?category=-1&language=-1">Digital Image Processing Using MATLAB</a>. He writes here about image processing concepts, algorithm implementations, and MATLAB.<br><br><img> Mon, 23 Nov 2009 01:00:41 +0000 http://wordpress.org/?v=2.3.1 By: Vitaliy http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21856 Vitaliy Fri, 12 Jun 2009 10:29:26 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21856 I thank! Probably it will help to solve a problem. I thank! Probably it will help to solve a problem.

]]> By: Steve http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21837 Steve Mon, 08 Jun 2009 14:13:25 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21837 Vitaliy—I'm not familiar with techniques for doing that. I did come across an article that might be helpful to you: "Decomposing a Matrix into Simple Transformation," by Spencer W. Thomas, in Graphics Gems II, edited by James Arvo, Morgan Kaufman, 1991. Vitaliy—I’m not familiar with techniques for doing that. I did come across an article that might be helpful to you: “Decomposing a Matrix into Simple Transformation,” by Spencer W. Thomas, in Graphics Gems II, edited by James Arvo, Morgan Kaufman, 1991.

]]> By: Vitaliy http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21819 Vitaliy Mon, 01 Jun 2009 21:24:37 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21819 Hi, Steve! I have such quastion: how to recover scale, rotation, shear from projective t-matrix? For example: 0.1038 -0.1363 -0.0007 0.0270 0.6553 0.0001 292.3112 70.3536 1.0000 Thank you Vitaliy Hi, Steve!

I have such quastion: how to recover scale, rotation, shear from projective t-matrix? For example:
0.1038 -0.1363 -0.0007
0.0270 0.6553 0.0001
292.3112 70.3536 1.0000

Thank you
Vitaliy

]]> By: Steve http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21344 Steve Mon, 29 Dec 2008 16:08:08 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21344 Adrian—Basically, <tt>imtransform</tt> uses inverse mapping to find the input-space location corresponding to each output-space pixel, and then uses interpolation in input space. My <a href="http://blogs.mathworks.com/steve/category/spatial-transforms/" rel="nofollow">spatial transforms series</a> includes some algorithm information. Adrian—Basically, imtransform uses inverse mapping to find the input-space location corresponding to each output-space pixel, and then uses interpolation in input space. My spatial transforms series includes some algorithm information.

]]> By: adrian david http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21343 adrian david Sun, 28 Dec 2008 13:35:53 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-21343 Hello! I am trying to find the algorithm inside imtrasform! I need an algorithm which rotates a colour image around its center with any angle, but without using predefined matlab functions(imtransform).Can you help me, please?..thanks Hello!
I am trying to find the algorithm inside imtrasform! I need an algorithm which rotates a colour image around its center with any angle, but without using predefined matlab functions(imtransform).Can you help me, please?..thanks

]]> By: Steve http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20778 Steve Thu, 05 Jun 2008 19:01:24 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20778 Sara—You shuold take a close look at your transformation. Using <tt>tformfwd</tt>, I can see that your transformation maps the point (1,1) to (-0.004209131281674, -0.004605571052168), and it maps the point (256,256) to (-0.004192049430379, -0.004589211830939). Given that, it's not too surprising that your output image is very small! Sara—You shuold take a close look at your transformation. Using tformfwd, I can see that your transformation maps the point (1,1) to (-0.004209131281674, -0.004605571052168), and it maps the point (256,256) to (-0.004192049430379, -0.004589211830939). Given that, it’s not too surprising that your output image is very small!

]]> By: Sara http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20776 Sara Thu, 05 Jun 2008 14:37:07 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20776 Thanks steve, but we tried this and the result was a Black image and the image became so small this is our code Homog = -0.5909 -0.0619 126.8663 0.0030 -0.5817 13.3776 -0.0003 -0.0000 -0.5001 t_proj = maketform('projective',Homog); I_projective = imtransform(I,t_proj,'FillValues',.3); subplot(334); imshow(I_projective); title('projective'); Thanks steve, but we tried this and the result was a Black image and the image became so small
this is our code
Homog =

-0.5909 -0.0619 126.8663
0.0030 -0.5817 13.3776
-0.0003 -0.0000 -0.5001

t_proj = maketform(’projective’,Homog);
I_projective = imtransform(I,t_proj,’FillValues’,.3);
subplot(334);
imshow(I_projective);
title(’projective’);

]]> By: Steve http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20775 Steve Thu, 05 Jun 2008 12:53:53 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20775 Sara—<tt>maketform</tt> and <tt>imtransform</tt>. Sara—maketform and imtransform.

]]> By: Sara http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20774 Sara Thu, 05 Jun 2008 12:28:41 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20774 Dear Steve, if we already have a 3x3 homography transformation matrix and we want to transform an image using this matrix,can you tell me which function to use that takes this homography matrix and applies it to a specific image?? thanks in advance Dear Steve,
if we already have a 3×3 homography transformation matrix and we want to transform an image using this matrix,can you tell me which function to use that takes this homography matrix and applies it to a specific image??
thanks in advance

]]> By: Steve http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20526 Steve Thu, 27 Mar 2008 21:16:59 +0000 http://blogs.mathworks.com/steve/2006/08/01/spatial-transformations-controlling-the-input-and-output-grids-with-imtransform/#comment-20526 Yuan-Lian—I didn't remember this, but there's code in <tt>imtransform</tt> that modifies the width and height of the output pixels to cut down on the output image size, unless you specify the XYScale parameter explicitly. I see that our documentation is incorrect on this point, since it currently says that the scale of the input pixels is used for XYScale. You can get the result you expect by passing in ..., 'XYScale', 1, ... in your input argument list, and I'll request that the doc be corrected. Yuan-Lian—I didn’t remember this, but there’s code in imtransform that modifies the width and height of the output pixels to cut down on the output image size, unless you specify the XYScale parameter explicitly. I see that our documentation is incorrect on this point, since it currently says that the scale of the input pixels is used for XYScale. You can get the result you expect by passing in …, ‘XYScale’, 1, … in your input argument list, and I’ll request that the doc be corrected.

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