Python 从 Numpy 数组的图像中裁剪边界框
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Crop a Bounding Box from an Image which is a Numpy Array
提问by Abhik
So I have an Image which is of shape (224,244,3) as an ndarray. I have a bounding box annotation for the image that looks like this
所以我有一个形状为 (224,244,3) 的图像作为 ndarray。我有一个看起来像这样的图像的边界框注释
{
annotations: [
{
class: "rect",
height: 172,
width: 341,
x: 282,
y: 165
},
{
class: "rect",
height: 172,
width: 353,
x: 592,
y: 90
}
],
class: "image",
filename: "img_05974.jpg"
}
How do I crop the numpy array so that it gives me an image like the above bounding rectangles ?
我如何裁剪 numpy 数组，以便它给我一个像上面的边界矩形这样的图像？
回答by ImportanceOfBeingErnest
In principle cropping is easily done simply by slicing the correct part out of the array. E.g. image[100:200, 50:100, :]slices the part between pixels 100 and 200 in y (vertical) direction, and the part between pixels 50 and 100 in x (horizontal) direction.
原则上，只需从数组中切出正确的部分，即可轻松完成裁剪。例如image[100:200, 50:100, :]，在 y（垂直）方向上对像素 100 和 200 之间的部分进行切片，在 x（水平）方向上对像素 50 和 100 之间的部分进行切片。
See this working example:
请参阅此工作示例：
import matplotlib.pyplot as plt
mydic = {
"annotations": [
{
"class": "rect",
"height": 98,
"width": 113,
"x": 177,
"y": 12
},
{
"class": "rect",
"height": 80,
"width": 87,
"x": 373,
"y": 43
}
],
"class": "image",
"filename": "https://i.stack.imgur.com/9qe6z.png"
}
def crop(dic, i):
image = plt.imread(dic["filename"])
x0 = dic["annotations"][i]["x"]
y0 = dic["annotations"][i]["y"]
width = dic["annotations"][i]["width"]
height = dic["annotations"][i]["height"]
return image[y0:y0+height , x0:x0+width, :]
fig = plt.figure()
ax = fig.add_subplot(121)
ax.imshow(plt.imread(mydic["filename"]))
ax1 = fig.add_subplot(222)
ax1.imshow(crop(mydic, 0))
ax2 = fig.add_subplot(224)
ax2.imshow(crop(mydic, 1))
plt.show()
