Drawing circles in a numpy array
Hi all, I have this problem: Given some point draw a circle centered in this point with radius r. I'm doing that using numpy this way (Snippet code from here [1]):
# Create the initial black and white image import numpy as np from scipy import ndimage a = np.zeros((512, 512)).astype(uint8) #unsigned integer type needed by watershed y, x = np.ogrid[0:512, 0:512] m1 = ((y-200)**2 + (x-100)**2 < 30**2) m2 = ((y-350)**2 + (x-400)**2 < 20**2) m3 = ((y-260)**2 + (x-200)**2 < 20**2) a[m1+m2+m3]=1 imshow(a, cmap = cm.gray)# left plot in the image above
The problem is that it have to evaluate all values from 0 to image size (in snippet, from 0 to 512 in X and Y dimensions). There is a faster way of doing that? Without evaluate all that values? For example: only evaluate from 0 to 30, in a circle centered in (0, 0) with radius 30. Thanks! Thiago Franco de Moraes [1] - http://www.scipy.org/Cookbook/Watershed
On Mon, Jan 10, 2011 at 11:53 AM, totonixsame@gmail.com <totonixsame@gmail.com> wrote:
Hi all,
I have this problem: Given some point draw a circle centered in this point with radius r. I'm doing that using numpy this way (Snippet code from here [1]):
# Create the initial black and white image import numpy as np from scipy import ndimage a = np.zeros((512, 512)).astype(uint8) #unsigned integer type needed by watershed y, x = np.ogrid[0:512, 0:512] m1 = ((y-200)**2 + (x-100)**2 < 30**2) m2 = ((y-350)**2 + (x-400)**2 < 20**2) m3 = ((y-260)**2 + (x-200)**2 < 20**2) a[m1+m2+m3]=1 imshow(a, cmap = cm.gray)# left plot in the image above
The problem is that it have to evaluate all values from 0 to image size (in snippet, from 0 to 512 in X and Y dimensions). There is a faster way of doing that? Without evaluate all that values? For example: only evaluate from 0 to 30, in a circle centered in (0, 0) with radius 30.
Thanks! Thiago Franco de Moraes
Hi, I've just seen I can do something like this:
radius = 10 a = np.zeros((512, 512)).astype('uint8') cx, cy = 100, 100 # The center of circle y, x = np.ogrid[-radius: radius, -radius: radius] index = x**2 + y**2 <= radius**2 a[cy-radius:cy+radius, cx-radius:cx+radius][index] = 255
Numpy is very cool! Is there other way of doing that? Only to know ... Thanks! Thiago Franco de Moraes
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