Transformation from log-polar to Cartesian

edit

I have one simple (and perhaps stupid) question. I am using OpenCV 2.1.

• I transform the original image (320 x 240) to a log-polar image of resolution (200 x 200) by using CvLogPolar function with the magnitude parameter 40, and center of the image set as the center of transformation.
• I perform some processing, and obtain a single point (centroid of the blob) in the log polar coordinates.

-My question: How to transform coordinate values of the point from log-polar to Cartesian frame, i.e. to the coordinates of the original image? (I just need to transform the computed values, not the whole image)?

Thanks.