在二维numpy阵列内绘制一个矩形

Question

我有一个2D numpy阵列，其中包含传感器每个像素的单个数据。图像通过相机的实时反馈显示在GUI中。我希望能够在图像上绘制一个矩形，以便区分屏幕的某个区域。绘制一个与图像边平行的矩形似乎很简单，但我最终希望能够旋转矩形。如何知道当矩形旋转时矩形覆盖哪些像素？

Answer 1

如果您不介意依赖关系，则可以使用Python Imaging Library。给定一个2D numpy的阵列data，和多边形的坐标的阵列poly（具有形状（N，2）），这将绘制在阵列中填充有值0的多边形：

img = Image.fromarray(data) 
draw = ImageDraw.Draw(img) 
draw.polygon([tuple(p) for p in poly], fill=0) 
new_data = np.asarray(img) 

这里有一个自包含的演示：

import numpy as np 
import matplotlib.pyplot as plt 

# Python Imaging Library imports 
import Image 
import ImageDraw 


def get_rect(x, y, width, height, angle): 
    rect = np.array([(0, 0), (width, 0), (width, height), (0, height), (0, 0)]) 
    theta = (np.pi/180.0) * angle 
    R = np.array([[np.cos(theta), -np.sin(theta)], 
        [np.sin(theta), np.cos(theta)]]) 
    offset = np.array([x, y]) 
    transformed_rect = np.dot(rect, R) + offset 
    return transformed_rect 


def get_data(): 
    """Make an array for the demonstration.""" 
    X, Y = np.meshgrid(np.linspace(0, np.pi, 512), np.linspace(0, 2, 512)) 
    z = (np.sin(X) + np.cos(Y)) ** 2 + 0.25 
    data = (255 * (z/z.max())).astype(int) 
    return data 


if __name__ == "__main__": 
    data = get_data() 

    # Convert the numpy array to an Image object. 
    img = Image.fromarray(data) 

    # Draw a rotated rectangle on the image. 
    draw = ImageDraw.Draw(img) 
    rect = get_rect(x=120, y=80, width=100, height=40, angle=30.0) 
    draw.polygon([tuple(p) for p in rect], fill=0) 
    # Convert the Image data to a numpy array. 
    new_data = np.asarray(img) 

    # Display the result using matplotlib. (`img.show()` could also be used.) 
    plt.imshow(new_data, cmap=plt.cm.gray) 
    plt.show() 

此脚本生成这个情节：