[Image-SIG] Help needed in Image Rectification.

[Narendra Sisodiya]

    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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