如何用Python选择图像的一部分？

Question

我正在处理卫星图像，我需要从图像中选择一部分进行操作。我该怎么做呢？Im.crop似乎不太管用。那我是不是应该用Resize？

谢谢！

Answer 1

要从一张大图中得到一张小图，只需要用数组的索引就可以了。

subImage=Image[ miny:maxy, minx:maxx ]

在这里，你可以在图片上画一个矩形，这样就能把它裁剪掉了。

import numpy as np
import cv2
import matplotlib.pyplot as plt


def downloadImage(URL):
    """Downloads the image on the URL, and convers to cv2 BGR format"""
    from io import BytesIO
    from PIL import Image as PIL_Image
    import requests

    response = requests.get(URL)
    image = PIL_Image.open(BytesIO(response.content))
    return cv2.cvtColor(np.array(image), cv2.COLOR_BGR2RGB)


fig, ax = plt.subplots()

URL = "https://www.godan.info/sites/default/files/old/2015/04/Satellite.jpg"
img = downloadImage(URL)[:, :, ::-1]  # BGR->RGB
plt.imshow(img)

selectedRectangle = None
# Capture mouse-drawing-rectangle event
def line_select_callback(eclick, erelease):
    x1, y1 = eclick.xdata, eclick.ydata
    x2, y2 = erelease.xdata, erelease.ydata

    selectedRectangle = plt.Rectangle(
        (min(x1, x2), min(y1, y2)),
        np.abs(x1 - x2),
        np.abs(y1 - y2),
        color="r",
        fill=False,
    )
    ax.add_patch(selectedRectangle)

    imgOnRectangle = img[
        int(min(y1, y2)) : int(max(y1, y2)), int(min(x1, x2)) : int(max(x1, x2))
    ]
    plt.figure()
    plt.imshow(imgOnRectangle)
    plt.show()


from matplotlib.widgets import RectangleSelector

rs = RectangleSelector(
    ax,
    line_select_callback,
    drawtype="box",
    useblit=False,
    button=[1],
    minspanx=5,
    minspany=5,
    spancoords="pixels",
    interactive=True,
)

plt.show()

Answer 2

from PIL import Image
im = Image.open("test.jpg")

crop_rectangle = (50, 50, 200, 200)
cropped_im = im.crop(crop_rectangle)

cropped_im.show()

请注意，裁剪区域需要用四个数字来表示，分别是左边、上边、右边和下边。

更多详细信息可以查看这里使用图像类

如何用Python选择图像的一部分？

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