Clash Royale CLAN TAG#URR8PPP

Tranform HSV mask into a set of points

I created a HSV mask from the image. The result is like the following:

I hope that this mask can be represented by a set of points. My original idea was to use Skimage Skeletonize to create a line and then use the sliding window to calculate the local mean for point creation.

However, skeletonize takes too long. It requires 0.4s for each frame. This is not a good idea for video processing.

2 Answers
2

Do you want the points of all True elements of the mask, or do you just want a skeleton? If the former..

import skimage as ski
from skimage import io
import numpy as np
mask = ski.io.imread('./mask.png')[:,:,0]/255
mask = mask.astype('bool')

s0,s1 = mask.shape # dimensions of mask
a0,a1 = np.arange(s0),np.arange(s1) # make two 1d coordinate arrays
coords = np.array(np.meshgrid(a0,a1)).T # cartesian product into a coordinate matrix
coords = coords[mask] # mask out the points of interest


If the latter, you can get the start and end points (from left to right) of the object in the mask in a fast way with something like

start_mat = np.stack((np.roll(mask,1,axis=1),mask),-1)
start_mask = np.fromiter(map(lambda p: np.alltrue(p==np.array([False,True])),start_mat[mask]),dtype=bool)
starts = coords[start_mask]

end_mat = np.stack((np.roll(mask,-1,axis=1),mask),-1)
end_mask = np.fromiter(map(lambda p: np.alltrue(p==np.array([False,True])),end_mat[mask]),dtype=bool)
ends = coords[end_mask]


This will give you a rough outline of the object. Outline points will be missing anywhere that the slope of the figure is 0. You may have to think of a vertical difference scheme for those areas. The same idea would work with np.roll(...,axis=0). You could just concatenate the unique points from rolling over rows to the points from rolling over columns to get the full outline.

np.roll(...,axis=0)

Averaging the correct pairs to get the skeleton isn't so easy.

Here's a resultant outline. You can definitely make this faster than 0.4s:

Couldn't a simple For loop work?

Scan each "across" line of your bitmap looking for...

X pos where from Black meets White = new start point.

from Black

White

start point

Also in same scanned line now look for a new X-pos:
where from White meets Black = new end point.

from White

Black

end point

Either put dots at start/end points for "outline" effect,
or else put dots in "center" effect by dot.x = (end_point - start_point) / 2

dot.x = (end_point - start_point) / 2

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