A second source of inaccuracy comes from your input ellipse: it is not a perfect ellipse because you drew it using anti-aliasing. On Thu, Mar 5, 2015 at 12:21 AM, Kevin Keraudren < kevin.keraudren@googlemail.com> wrote:

Hi Arno,

The first source of inaccuracy comes from your code, you need to round the values instead of truncating them:

#yc = int(best[1])

#xc = int(best[2])

#a = int(best[3])

#b = int(best[4])

yc = int(round(best[1]))

xc = int(round(best[2]))

a = int(round(best[3]))

b = int(round(best[4]))

See resulting image attached.

Kind regards,

Kevin

On Wed, Mar 4, 2015 at 11:49 PM, Arno Dietz <arnodietz86@googlemail.com> wrote:

...

Ok sorry. Here is my code:

from skimage import color

...

from skimage.filter import canny from skimage.transform import hough_ellipse from skimage.draw import ellipse_perimeter from skimage import io from skimage.viewer import ImageViewer # load image img = io.imread('ellipse.png') cimg = color.gray2rgb(img) # edges and ellipse fit edges = canny(img, sigma=0.1, low_threshold=0.55, high_threshold=0.8) result = hough_ellipse(edges, accuracy=4, threshold=25, min_size=47, max_size=60) result.sort(order='accumulator') # Estimated parameters for the ellipse best = result[-1] yc = int(best[1]) xc = int(best[2]) a = int(best[3]) b = int(best[4]) orientation = best[5] # Draw the ellipse on the original image cy, cx = ellipse_perimeter(yc, xc, a, b, orientation) cimg[cy, cx] = (0, 0, 255) # Draw the edge (white) and the resulting ellipse (red) edges = color.gray2rgb(edges) edges[cy, cx] = (250, 0, 0) viewer = ImageViewer(edges) viewer.show()

I noticed, that the ellipse center is detected only in half pixel accuracy. Maybe this is the Problem? Is there a possibility to get the ellipse center with sub-pixel accuracy?

regards Arno

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