在2D numpy数组中绘制一个矩形

Question

我有一个2D numpy数组，其中包含来自传感器每个像素的单个数据。图像显示在GUI中，带有来自摄像头的实时信息源。我希望能够在图像上绘制一个矩形，以区分屏幕区域。绘制一个与图像侧面平行的矩形似乎很简单但我最终希望能够旋转矩形。如何知道矩形在旋转时所覆盖的像素？

Answer 1

如果您不介意依赖，可以使用Python Imaging Library。给定2D numpy数组data和多边形坐标数组poly（带形状（n，2）），这将绘制一个填充数组中值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)

这是一个独立的演示：

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()

此脚本生成此图：