hough ellipse fit inaccurate?

[Kevin Keraudren]

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 at 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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