python - 通过输入uint8数组将图像读取到OpenCV(Numpy)

Question

我正在尝试开发一个使用一些Javascript代码上传图像的应用程序。 Javascript代码向我返回了一个大小等于其大小的数组。因此，如果我有一个4k大小的jpg图像，它将返回给我(大约)4,000字节类型为unit8的图像数据。这是如下所示的python列表。

[137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 50, 0, 0, 0, 50, 8, 6, 0, 0, 0, 30, 63, 136, 177, 0, 0, 0, 1, 115, 82, 71, 66, 1, 217, 201, 44, 127, 0, 0, 0, 9, 112, 72, 89, 115, 0, 0, 11,
19, 0, 0, 11, 19, 1, 0, 154, 156, 24, 0, 0, 12, 76, 73, 68, 65, 84, 120, 156, 205, 90, 9, 116, 84, 85, 18, 125, 85, 191, 155, 69, 136, 6, 81, 143, 204, 184, 224, 130, 251, 58, 234, 168, 227, 56, 42, 46, 99, 0, 145
, 221, 153, 1, 68, 22, 9, 4, 18, 72, 128, 132, 64, 22, 146, 16, 18, 8, 4, 8, 73, 200, 0, 178, 4, 68, 86, 89, 195, 190, 139, 130, 65, 16, 5, 113, 1, 4, 21, 20, 16, 81, 32, 64, 72, 250, 85, 205, 253, 29, 228, 140, 1
03, 28, 108, 9, 33, 212, 57, 117, 222, 79, 247, 239, 247, 235, 190, 170, 186, 85, 245, 193, 152, 75, 64, 236, 60, 67, 190, 5, 166, 186, 46, 50, 84, 174, 141, 36, 147, 59, 74, 180, 39, 167, 180, 11, 229, 74, 123, 2
06, 181, 221, 157, 116, 219, 143, 250, 105, 154, 19, 103, 211, 169, 124, 155, 159, 235, 185, 83, 13, 233, 108, 122, 192, 206, 50, 233, 50, 139, 18, 101, 9, 215, 214, 105...]

现在我有了上面的字节数组，我想知道如何在OpenCV或使用Numpy中读取上面的数组？
我已经通过 imdecode和 imread编写了一些代码，但是它们都无法正常工作。

import cv2
img = cv2.imdecode(np.asarray(image_array), cv2.IMREAD_UNCHANGED)

上面的代码总是返回空图像。通过使用上述数组，可以在OpenCV中读取图像吗？

Answer 1

如果查看列表的前几个元素，您会发现它是经典的PNG file signature(魔术数字)，或者用十六进制表示:

89 50 4e 47 0d 0a 1a 0a

其中 50是ASCII P， 4e是ASCII N， 47是 G-拼写 PNG。这意味着您的Javascript已向您发送了PNG编码的图像。
因此，您需要以下内容:

import cv2
import numpy as np

L = [137, 80, 78, 71, 13, 10, 26, 10, 0, 0, 0, 13, 73, 72, 68, 82, 0, 0, 0, 64, 0, 0, 0, 64, 8, 2, 0, 0, 0, 37, 11, 230, 137, 0, 0, 0, 4, 103, 65, 77, 65, 0, 0, 177, 143, 11, 252, 97, 5, 0, 0, 0, 32, 99, 72, 82, 77, 0, 0, 122, 38, 0, 0, 128, 132, 0, 0, 250, 0, 0, 0, 128, 232, 0, 0, 117, 48, 0, 0, 234, 96, 0, 0, 58, 152, 0, 0, 23, 112, 156, 186, 81, 60, 0, 0, 0, 6, 98, 75, 71, 68, 0, 255, 0, 255, 0, 255, 160, 189, 167, 147, 0, 0, 0, 7, 116, 73, 77, 69, 7, 228, 9, 3, 7, 16, 45, 84, 246, 102, 10, 0, 0, 0, 112, 73, 68, 65, 84, 104, 222, 237, 215, 177, 9, 192, 64, 12, 4, 65, 25, 222, 253, 151, 108, 23, 241, 193, 34, 152, 173, 224, 6, 69, 154, 89, 222, 115, 230, 212, 27, 174, 58, 0, 0, 0, 0, 0, 0, 155, 59, 239, 188, 245, 134, 59, 192, 250, 11, 0, 0, 0, 0, 0, 0, 108, 14, 160, 14, 160, 14, 160, 14, 160, 14, 160, 206, 83, 95, 7, 80, 7, 80, 7, 80, 7, 80, 7, 80, 7, 80, 7, 80, 7, 80, 7, 80, 183, 31, 224, 169, 7, 0, 0, 0, 0, 216, 220, 122, 192, 243, 205, 87, 111, 184, 234, 7, 229, 134, 4, 235, 125, 72, 121, 243, 0, 0, 0, 37, 116, 69, 88, 116, 100, 97, 116, 101, 58, 99, 114, 101, 97, 116, 101, 0, 50, 48, 50, 48, 45, 48, 57, 45, 48, 51, 84, 48, 55, 58, 49, 54, 58, 52, 53, 43, 48, 48, 58, 48, 48, 156, 134, 199, 95, 0, 0, 0, 37, 116, 69, 88, 116, 100, 97, 116, 101, 58, 109, 111, 100, 105, 102, 121, 0, 50, 48, 50, 48, 45, 48, 57, 45, 48, 51, 84, 48, 55, 58, 49, 54, 58, 52, 53, 43, 48, 48, 58, 48, 48, 237, 219, 127, 227, 0, 0, 0, 0, 73, 69, 78, 68, 174, 66, 96, 130]

# Decode the PNG-encoded image
im = cv2.imdecode(np.array(L, dtype=np.uint8), cv2.IMREAD_UNCHANGED)

由于您没有提供列表，因此我做了以下操作来复制您的起始位置...
首先，使用 ImageMagick 制作一个小的PNG图片:

magick -size 64x64 gradient:black-magenta PNG24:a.png

然后，从PNG编​​码的文件中提取所有字节，并将它们放入列表中:

with open('a.png', 'rb') as image:
    data = image.read()
L = list(data)

关键字:Python。图像处理，OpenCV，解码，编码，Javascript，图像。