Help needed in Image Rectification.

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Help needed in Image Rectification.

narendra sisodiya-3
    I want your guidance in following problem.

I have a Rectangle with a known height and width. (aspect ration is fixed) It has a plane surface. Something like cardboard. Or Rectangle Drawn on wall.
I am now taking image of this rectangle from webcam.
After taking image of this rectangle from webcam, rectangle occupy small area on image and that is in a form of quadrilateral inside image. I can calculate the XY location of Rectangle from image , So I have Following Matrix

Co-ordinate on image -> Actual real world co-ordinate
_______________________________________
X1 Y1                         -> 0 , 0
X2 Y2                         -> width, 0
X3 Y3                         -> 0, height
X4 Y4                         -> width, height
________________________________________

width and height of rectangle is known because I can measure this real object
X1 Y1 to X4 Y4 are 4 co-ordinate of this object in image. Because it is a projective transformation, this will be in a shaped of quadrilateral.


Now I want to know a matrix operation or any formula, by which I can convert a given X Y of image into corresponding co-ordinate on rectangle.
I think, this is known as homography. seeing on web, i can find complex description and formulas which i am unable to understand.

May you give me exact formula for how to do it.

Thanks !

--
┌─────────────────────────┐
│    Narendra Sisodiya
│    http://narendrasisodiya.com
└─────────────────────────┘

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Re: Help needed in Image Rectification.

narendra sisodiya-3


On Sat, Jan 8, 2011 at 12:24 PM, Narendra Sisodiya <[hidden email]> wrote:
    I want your guidance in following problem.

I have a Rectangle with a known height and width. (aspect ration is fixed) It has a plane surface. Something like cardboard. Or Rectangle Drawn on wall.
I am now taking image of this rectangle from webcam.
After taking image of this rectangle from webcam, rectangle occupy small area on image and that is in a form of quadrilateral inside image. I can calculate the XY location of Rectangle from image , So I have Following Matrix

Co-ordinate on image -> Actual real world co-ordinate
_______________________________________
X1 Y1                         -> 0 , 0
X2 Y2                         -> width, 0
X3 Y3                         -> 0, height
X4 Y4                         -> width, height
________________________________________

width and height of rectangle is known because I can measure this real object
X1 Y1 to X4 Y4 are 4 co-ordinate of this object in image. Because it is a projective transformation, this will be in a shaped of quadrilateral.


Now I want to know a matrix operation or any formula, by which I can convert a given X Y of image into corresponding co-ordinate on rectangle.
I think, this is known as homography. seeing on web, i can find complex description and formulas which i am unable to understand.

May you give me exact formula for how to do it.

Thanks !



Also - This code will be useful - I am unable to understand it fully - But i guess , this is doing exactly what i want.
 http://wiiwhiteboard.cvs.sourceforge.net/viewvc/wiiwhiteboard/source/linux/perspective.py?view=markup

_______________________________________________
Image-SIG maillist  -  [hidden email]
http://mail.python.org/mailman/listinfo/image-sig