opencv版本3. * HogDescriptor最多接受1个参数(给定5个) [英] opencv version 3.* HogDescriptor takes at most 1 argument (5 given)

问题描述

我正在尝试使用HogDescriptor，但出现此错误.我在文档中看到，构造函数可以接受一个以上的参数.我正在python 3.6和opencv 3.2中工作

I am trying to use HogDescriptor and I am getting this error. I saw in the document that the constructor can take more then one argument. I am working in python 3.6 and opencv 3.2

这是我的代码:

def _extract_feature(X):
    """Performs feature extraction

        :param X:       data (rows=images, cols=pixels)
        :param feature: which feature to extract
                        - "hog":  HOG features
        :returns:       X (rows=samples, cols=features)
    """

    X = [cv2.cvtColor(x, cv2.COLOR_BGR2GRAY) for x in X]

    # operate on smaller image
    small_size = (32, 32)
    X = [cv2.resize(x, small_size) for x in X]

    # histogram of gradients
    block_size = (small_size[0] / 2, small_size[1] / 2)
    block_stride = (small_size[0] / 4, small_size[1] / 4)
    cell_size = block_stride
    num_bins = 9
    hog = cv2.HOGDescriptor(small_size, block_size, block_stride,
                            cell_size, num_bins)
    X = [hog.compute(x) for x in X]

    X = [x.flatten() for x in X]
    return X

那我为什么会收到错误消息:

So why am I getting the error:

TypeError: HogDescriptor takes at most 1 argument (5 given)

---

更新:我安装了python 2.7并对其进行了尝试.

---

Update: I installed python 2.7 and tried it and it works.

推荐答案

您所观察到的问题是由于多种因素共同导致的:

The issue you're observing is due to combination of several factors:

• PEP-238 –更改除法运算符
• 映射到Python并分派重载的C ++函数(在OpenCV中完成)

• PEP-238 – Changing the Division Operator
• Mapping to Python and dispatching of overloaded C++ functions (as done in OpenCV)

在Python 2.x和Python 3.x之间，运算符/的含义已更改.

The meaning of operator / has changed between Python 2.x and Python 3.x.

从PEP-238:

• 经典除法将保留为Python 2.x的默认设置 系列;真正的划分将是Python 3.0中的标准

• Classic division will remain the default in the Python 2.x series; true division will be standard in Python 3.0

例如，在Python 2.x中，您拥有

For example, in Python 2.x you have

>>> small_size = (32, 32)
>>> block_size = (small_size[0] / 2, small_size[1] / 2)
>>> print(block_size)
(16, 16)

在Python 3.x中，您拥有

And in Python 3.x you have

>>> small_size = (32, 32)
>>> block_size = (small_size[0] / 2, small_size[1] / 2)
>>> print(block_size)
(16.0, 16.0)

为了获得相同的结果，您的Python 3.x代码将需要使用运算符//

In order to get the same result, your Python 3.x code would need to use operator //

>>> small_size = (32, 32)
>>> block_size = (small_size[0] // 2, small_size[1] // 2)
>>> print(block_size)
(16, 16)

过载的映射和处理

在不详细介绍(这将需要一个单独的问题)的情况下，重载解决方案取决于参数的类型.类型的匹配非常严格，例如您不能将浮点数传递给整数参数.

Mapping and Handling of Overloads

Without going into detail (that would warrant a separate question), the overload resolution depends on the types of arguments. The matching of types is quite strict, e.g. you may not pass a floating point number to an integer argument.

所讨论的构造函数的C ++签名(仅被截断为相关参数)是

The C++ signature of the constructor in question (truncated to only the relevant arguments) is

HOGDescriptor (Size _winSize
    , Size _blockSize
    , Size _blockStride
    , Size _cellSize
    , int _nbins, ...)

cv::Size是一个类，其中包含两个整数.在Python API中，它表示为包含两个整数的元组.

cv::Size is a class that contains two integers. In the Python API, it is represented as a tuple containing two integers.

因此，要在Python中调用此重载，我们需要提供:

Therefore, to call this overload in Python, we need to provide:

• 4x一个包含两个整数(对于_winSize，_blockSize，_blockStride和_cellSize)的元组
• 1x整数(用于_nbins)

• 4x a tuple containing two integers (for _winSize, _blockSize, _blockStride, and _cellSize)
• 1x an integer (for _nbins)

我们可以在Python解释器中对此进行测试.

We can test this out in the Python interpreter.

>>> import cv2
>>> cv2.HOGDescriptor((1,1),(1,1),(1,1),(1,1),1)
<HOGDescriptor 0393D0F0>

这符合我们的期望.让我们尝试其他选择.

This matches our expectations. Let's try some other options.

>>> cv2.HOGDescriptor((1,1,1),(1,1),(1,1),(1,1),1)
TypeError: HOGDescriptor() takes at most 1 argument (5 given)
>>> cv2.HOGDescriptor((1,),(1,1),(1,1),(1,1),1)
TypeError: HOGDescriptor() takes at most 1 argument (5 given)

我们看到元组需要有2个值，不多也不少.

We see the tuples need to have 2 values, no more, no less.

>>> cv2.HOGDescriptor([1,1],(1,1),(1,1),(1,1),1)
TypeError: HOGDescriptor() takes at most 1 argument (5 given)

列表不会，它必须是一个元组.

Lists won't do, it has to be a tuple.

>>> cv2.HOGDescriptor((1.0,1.0),(1,1),(1,1),(1,1),1)
TypeError: HOGDescriptor() takes at most 1 argument (5 given)

成千上万个浮标也不起作用.

Tuples of floats won't work either.

>>> cv2.HOGDescriptor((1,1),(1,1),(1,1),(1,1),1.0)
TypeError: HOGDescriptor() takes at most 1 argument (5 given)

我们也不能用浮点数代替整数.

Nor can we substitute an float for an integer.

考虑到上述情况，就您通过构造函数传递的值而言，两个变体是:

Considering the above, in terms of the values you pass the constructor, the two variants are:

• Python 2.x:cv2.HOGDescriptor((32,32),(16,16),(8,8),(8,8),9)
• Python 3.x:cv2.HOGDescriptor((32,32),(16.0,16.0),(8.0,8.0),(8.0,8.0),9)

• Python 2.x: cv2.HOGDescriptor((32,32),(16,16),(8,8),(8,8),9)
• Python 3.x: cv2.HOGDescriptor((32,32),(16.0,16.0),(8.0,8.0),(8.0,8.0),9)

我们可以清楚地看到Python 3.x中的参数不满足重载的要求.

We can clearly see that the parameters in Python 3.x don't satisfy the requirements of the overload.

关于为什么我们得到误导性错误消息，这似乎是另一个需要单独解决的问题，而我还没有做所有必要的研究来回答这个问题.

As to why we get the misleading error message, that seems like another topic warranting a separate question, and I haven't done all the research necessary to answer this authoritatively.

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