[英]render Voronoi diagram to numpy array
我想根據中心列表和圖像大小生成 Voronoi 區域。
我嘗試了下一個代碼,基於https://rosettacode.org/wiki/Voronoi_diagram
def generate_voronoi_diagram(width, height, centers_x, centers_y):
image = Image.new("RGB", (width, height))
putpixel = image.putpixel
imgx, imgy = image.size
num_cells=len(centers_x)
nx = centers_x
ny = centers_y
nr,ng,nb=[],[],[]
for i in range (num_cells):
nr.append(randint(0, 255));ng.append(randint(0, 255));nb.append(randint(0, 255));
for y in range(imgy):
for x in range(imgx):
dmin = math.hypot(imgx-1, imgy-1)
j = -1
for i in range(num_cells):
d = math.hypot(nx[i]-x, ny[i]-y)
if d < dmin:
dmin = d
j = i
putpixel((x, y), (nr[j], ng[j], nb[j]))
image.save("VoronoiDiagram.png", "PNG")
image.show()
我有所需的輸出:
但是生成輸出需要太多時間。
我也試過https://stackoverflow.com/a/20678647它很快,但我沒有找到將其轉換為 img_width X img_height 的 numpy 數組的方法。 大多數情況下,因為我不知道如何為 scipy Voronoi class提供圖像大小參數。
有沒有更快的方法來獲得這個輸出? 不需要中心或多邊形邊
提前致謝
2018-12-11 編輯:使用@tel “快速解決方案”
代碼執行速度更快,似乎中心已經轉換。 可能這種方法是為圖像添加邊距
以下是如何將基於scipy.spatial.Voronoi
的快速解決方案的輸出轉換為任意寬度和高度的 Numpy 數組。 給定一組regions, vertices
您從鏈接代碼中的voronoi_finite_polygons_2d
函數獲得的regions, vertices
,這里有一個輔助函數,可以將該輸出轉換為數組:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.backends.backend_agg import FigureCanvasAgg as FigureCanvas
def vorarr(regions, vertices, width, height, dpi=100):
fig = plt.Figure(figsize=(width/dpi, height/dpi), dpi=dpi)
canvas = FigureCanvas(fig)
ax = fig.add_axes([0,0,1,1])
# colorize
for region in regions:
polygon = vertices[region]
ax.fill(*zip(*polygon), alpha=0.4)
ax.plot(points[:,0], points[:,1], 'ko')
ax.set_xlim(vor.min_bound[0] - 0.1, vor.max_bound[0] + 0.1)
ax.set_ylim(vor.min_bound[1] - 0.1, vor.max_bound[1] + 0.1)
canvas.draw()
return np.frombuffer(canvas.tostring_rgb(), dtype='uint8').reshape(height, width, 3)
這是一個完整的vorarr
示例:
from scipy.spatial import Voronoi
# get random points
np.random.seed(1234)
points = np.random.rand(15, 2)
# compute Voronoi tesselation
vor = Voronoi(points)
# voronoi_finite_polygons_2d function from https://stackoverflow.com/a/20678647/425458
regions, vertices = voronoi_finite_polygons_2d(vor)
# convert plotting data to numpy array
arr = vorarr(regions, vertices, width=1000, height=1000)
# plot the numpy array
plt.imshow(arr)
輸出:
如您所見,生成的 Numpy 數組確實具有(1000, 1000)
的形狀,如對vorarr
的調用中所指定。
以下是如何更改當前代碼以使用/返回 Numpy 數組:
import math
import matplotlib.pyplot as plt
import numpy as np
def generate_voronoi_diagram(width, height, centers_x, centers_y):
arr = np.zeros((width, height, 3), dtype=int)
imgx,imgy = width, height
num_cells=len(centers_x)
nx = centers_x
ny = centers_y
randcolors = np.random.randint(0, 255, size=(num_cells, 3))
for y in range(imgy):
for x in range(imgx):
dmin = math.hypot(imgx-1, imgy-1)
j = -1
for i in range(num_cells):
d = math.hypot(nx[i]-x, ny[i]-y)
if d < dmin:
dmin = d
j = i
arr[x, y, :] = randcolors[j]
plt.imshow(arr.transpose(1, 0, 2))
plt.scatter(cx, cy, c='w', edgecolors='k')
plt.show()
return arr
用法示例:
np.random.seed(1234)
width = 500
cx = np.random.rand(15)*width
height = 300
cy = np.random.rand(15)*height
arr = generate_voronoi_diagram(width, height, cx, cy)
示例輸出:
不使用 matplotlib 的快速解決方案也是可能的。 您的解決方案很慢,因為您要遍歷所有像素,這會在 Python 中產生大量開銷。 對此的一個簡單解決方案是在單個 numpy 操作中計算所有距離,並在另一個單個操作中分配所有顏色。
def generate_voronoi_diagram_fast(width, height, centers_x, centers_y):
# Create grid containing all pixel locations in image
x, y = np.meshgrid(np.arange(width), np.arange(height))
# Find squared distance of each pixel location from each center: the (i, j, k)th
# entry in this array is the squared distance from pixel (i, j) to the kth center.
squared_dist = (x[:, :, np.newaxis] - centers_x[np.newaxis, np.newaxis, :]) ** 2 + \
(y[:, :, np.newaxis] - centers_y[np.newaxis, np.newaxis, :]) ** 2
# Find closest center to each pixel location
indices = np.argmin(squared_dist, axis=2) # Array containing index of closest center
# Convert the previous 2D array to a 3D array where the extra dimension is a one-hot
# encoding of the index
one_hot_indices = indices[:, :, np.newaxis, np.newaxis] == np.arange(centers_x.size)[np.newaxis, np.newaxis, :, np.newaxis]
# Create a random color for each center
colors = np.random.randint(0, 255, (centers_x.size, 3))
# Return an image where each pixel has a color chosen from `colors` by its
# closest center
return (one_hot_indices * colors[np.newaxis, np.newaxis, :, :]).sum(axis=2)
在我的機器上運行此函數可以獲得相對於原始迭代解決方案的約 10 倍加速(不考慮繪圖並將結果保存到磁盤)。 我確信還有很多其他的調整可以進一步加速我的解決方案。
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