On Mar 4, 2015, at 7:24 PM, Kevin Keraudren <kevin.keraudren@googlemail.com> wrote:
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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