使用 OpenCV 在 Python 中反转图像
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inverting image in Python with OpenCV
提问by Mansueli
I want to load a color image, convert it to grayscale, and then invert the data in the file.
我想加载一个彩色图像，将其转换为灰度，然后反转文件中的数据。
What I need: to iterate over the array in OpenCV and change every single value with this formula (it might be wrong but it seems reasonable for me):
我需要的是：在 OpenCV 中迭代数组并使用此公式更改每个值（这可能是错误的，但对我来说似乎是合理的）：
img[x,y] = abs(img[x,y] - 255)
but I don't understand why doesn't it works:
但我不明白为什么它不起作用：
def inverte(imagem, name):
imagem = abs(imagem - 255)
cv2.imwrite(name, imagem)
def inverte2(imagem, name):
for x in np.nditer(imagem, op_flags=['readwrite']):
x = abs(x - 255)
cv2.imwrite(name, imagem)
if __name__ == '__main__':
nome = str(sys.argv[1])
image = cv2.imread(nome)
gs_imagem = cv2.cvtColor(image, cv2.COLOR_BGR2GRAY)
inverte(gs_imagem, "invertida.png")
inverte2(gs_imagem, "invertida2.png")
I don't want to do an explicit loop (I am trying to be more pythonic). I can see that in one image that got a white background it turned black, but only this it doesn't looks like the other colors are having much (if any) change.
我不想做一个显式循环（我试图变得更加 Pythonic）。我可以看到，在一张白色背景的图像中，它变成了黑色，但仅此而已，其他颜色看起来并没有太多（如果有）变化。
采纳答案by Saullo G. P. Castro
You almost did it. You were tricked by the fact that abs(imagem-255)will give a wrong result since your dtypeis an unsigned integer. You have to do (255-imagem)in order to keep the integers unsigned:
你几乎做到了。你被一个事实欺骗了，abs(imagem-255)因为你dtype是一个无符号整数，所以会给出错误的结果。(255-imagem)为了保持整数无符号，您必须这样做：
def inverte(imagem, name):
imagem = (255-imagem)
cv2.imwrite(name, imagem)
You can also invert the image using the bitwise_notfunction of OpenCV:
您还可以使用bitwise_notOpenCV的功能反转图像：
imagem = cv2.bitwise_not(imagem)
回答by Eric Olmon
Alternatively, you could invert the image using the bitwise_notfunction of OpenCV:
或者，您可以使用bitwise_notOpenCV的功能反转图像：
imagem = cv2.bitwise_not(imagem)
I liked the example at: https://www.learnopencv.com/filling-holes-in-an-image-using-opencv-python-c/
我喜欢这个例子：https: //www.learnopencv.com/filling-holes-in-an-image-using-opencv-python-c/
回答by Diroallu
You can use "tilde" operator to do it:
您可以使用“波浪号”运算符来做到这一点：
import cv2
image = cv2.imread("img.png")
image = ~image
cv2.imwrite("img_inv.png",image)
This is because the "tilde" operator (also known as unary operator) works doing a complement dependent on the type of object
这是因为“波浪号”运算符（也称为一元运算符）根据对象的类型进行补码
for example for integers, its formula is:
例如对于整数，它的公式是：
x + (~x) = -1
x + (~x) = -1
but in this case, opencv use an "uint8 numpy array object" for its images so its range is from 0 to 255
但在这种情况下，opencv 对其图像使用“uint8 numpy 数组对象”，因此其范围是从 0 到 255
so if we apply this operator to an "uint8 numpy array object" like this:
因此，如果我们将此运算符应用于“uint8 numpy 数组对象”，如下所示：
import numpy as np
x1 = np.array([25,255,10], np.uint8) #for example
x2 = ~x1
print (x2)
we will have as a result:
结果是：
[230 0 245]
because its formula is:
因为它的公式是：
x2 = 255 - x1
x2 = 255 - x1
and that is exactly what we want to do to solve the problem.
而这正是我们想要解决的问题。
