On Thu, Dec 06, 2012 at 09:25:02AM -0200, holgermw wrote: > I have a series of stm images taken at the same coordinates. By > following a feature on several stm images I want to correct the drift > based on the assumption of a constant drift velocity. Assuming the > distorted image would have to be transformed by X' = X - Vd * t(x,y) , > where X' is the corrected image, X is the distorted image, Vd is the > calculated drift velocity and t(x,y) is the time for each data point. > The solution will result in a polynomial equation. Its coefficients > calculated from coordinate ranges [0,1] i want to put in the polynomial > distortion dialog ( Data Process → Correct Data → Polynomial Distortion > ). Now i have two questions. > > Am i doing this correctly? Probably this is a rather simple method but > my images don't seem to improve as expected.
It seems that you might be doing it the other way round, depending on what exactly X means. The transformation entered to Polynomial Distortion is from result to source. I.e. take coordinates of a pixel in the result and obtain coordinates in the source image. It is mapped this way because only this way is is unique. If you entered the inverse transformation then a single pixel in the result could correspond to multiple locations in the source. But note I described the transformation in terms of coordinates, I did not say what happens to the image because that is the *inverse* transformation. If coordinates are scaled up twice the image becomes scaled down twice. > The undistorted image is only partially visible on the window due to the > transformation. Is there a way to see the whole image? Unfortunately, this is not possible in general because the area occupied by the source image in the result can be unbound. Suppose you entered transformation x≡0, y≡0. Then the entire infinite xy plane in the result image is then occupied by the origin of the source image. Even if infnitities were handled, such option would still lead to all kinds of strange results. What can be done instead is extending the image beforehand, i.e. adding some borders filled for instance with the mean value. Such function is not yet in Gwyddion but it is not difficult to implement. Regards, Yeti ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Gwyddion-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/gwyddion-users
