【opencv_python学习之二.五】如何查看opencv_python的函数说明

ゝ一纸荒年。 2021-12-22 12:27 542阅读 0赞

## 1、网上手册查询 ##

A. 打开[Welcome to opencv documentation][]

B. 在左侧输入要查询的函数, 如图1.1，假设我们要查询resize函数

![opencv\_python\_study2.5\_01.png][opencv_python_study2.5_01.png]

图 1.1

C. 点击Search按钮后可以看到结果，如图1.2

![opencv\_python\_study2.5\_02.png][opencv_python_study2.5_02.png]

图 1.2

D. 点开第一条函数说明，进去查找到resize函数，如图1.3

![opencv\_python\_study2.5\_03.png][opencv_python_study2.5_03.png]

图 1.3

从图1.3中可以看到在python中的resize函数说明为

cv2.resize(src, dsize[, dst[, fx[, fy[, interpolation]]]]) → dst

*  `[, dst[, fx[, fy[, interpolation]]]])`意味着这些参数是可选参数
 *  `→ dst`意味着函数返回dst
 *  参数说明`Parameters`可以看到参数的具体含义  
    D.A: `src – input image`, src为输入图片  
    D.B: `dst`, dst为输出图片  
    D.C: `dsize`, dsize为输出图片大小，当它为0时，要计算`dsize = Size(round(fx*src.cols), round(fy&src.rows))`，由这句话可以得出当dsize=0时，要同时输入src、fx、fy  
    D.D: `fx`, 水平缩放倍率，当它为0时则有`fx = (double)dsize.width/src.clos`  
    D.E: `fy`, 垂直缩放倍率，当它为0时则有`fy = (double)dsize.height/src.rows`  
    D.F: `interpolation`插值，主要有以下几个选项

INTER_NEAREST
    INTER_LINEAR
    INTER_AREA
    INTER_CUBIC
    INTER_LANCZOS4

*  根据D.C、D.D、D.E可知道定有dsize和fx、fy两种方式可以指定输出图片大小。

dsize方式

dsize=(180, 180)

fx、fy方式

fx=2, fy=2

如果dsize和fx、fy都存在，先计算dsize，如果dsize=None, 则输出图片大小为fx、fy，如果dsize！=None, 则为dsize。

*  阅读了上面的说明，我们知道resize可以像下面这样用

# 只指定src和dsize
    res = cv2.resize(src=img, dsize=(2*width, 2*height))
    
    # 只指定src、dsize和interpolation
    res = cv2.resize(src=img, dsize=(2*width, 2*height), interpolation = cv2.INTER_LINEAR)
    
    # 只指定src、dsize、fx、fy
    res = cv2.resize(src=img, dsize=None, fx=0.5, fy = 0.5)
    
    # 只指定src、dsize、fx、fy和interpolation
    res = cv2.resize(src=img, dsize=None, fx=0.5, fy = 0.5, interpolation = cv2.INTER_LINEAR)

## 2、使用help命令查看 ##

A. 在CMD中运行python进入python模式中

F:\QAQ\python\opencv>python
    Python 3.5.2 (v3.5.2:4def2a2901a5, Jun 25 2016, 22:18:55) [MSC v.1900 64 bit (AM
    D64)] on win32
    Type "help", "copyright", "credits" or "license" for more information.

B. 导入cv2模块

>>> import cv2

C. 使用help查看cv2.resize函数

>>> help(cv2.resize)
    Help on built-in function resize:
    
    resize(...)
        resize(src, dsize[, dst[, fx[, fy[, interpolation]]]]) -> dst
        .   @brief Resizes an image.
        .
        .   The function resize resizes the image src down to or up to the specified
     size. Note that the
        .   initial dst type or size are not taken into account. Instead, the size a
    nd type are derived from
        .   the `src`,`dsize`,`fx`, and `fy`. If you want to resize src so that it f
    its the pre-created dst,
        .   you may call the function as follows:
        .   @code
        .   // explicitly specify dsize=dst.size(); fx and fy will be computed from
    that.
        .   resize(src, dst, dst.size(), 0, 0, interpolation);
        .   @endcode
        .   If you want to decimate the image by factor of 2 in each direction, you
    can call the function this
        .   way:
        .   @code
        .   // specify fx and fy and let the function compute the destination image
    size.
        .   resize(src, dst, Size(), 0.5, 0.5, interpolation);
        .   @endcode
        .   To shrink an image, it will generally look best with cv::INTER_AREA inte
    rpolation, whereas to
        .   enlarge an image, it will generally look best with cv::INTER_CUBIC (slow
    ) or cv::INTER_LINEAR
        .   (faster but still looks OK).
        .
        .   @param src input image.
        .   @param dst output image; it has the size dsize (when it is non-zero) or
    the size computed from
        .   src.size(), fx, and fy; the type of dst is the same as of src.
        .   @param dsize output image size; if it equals zero, it is computed as:
        .   \f[\texttt{dsize = Size(round(fx*src.cols), round(fy*src.rows))}\f]
        .   Either dsize or both fx and fy must be non-zero.
        .   @param fx scale factor along the horizontal axis; when it equals 0, it i
    s computed as
        .   \f[\texttt{(double)dsize.width/src.cols}\f]
        .   @param fy scale factor along the vertical axis; when it equals 0, it is
    computed as
        .   \f[\texttt{(double)dsize.height/src.rows}\f]
        .   @param interpolation interpolation method, see cv::InterpolationFlags
        .
        .   @sa  warpAffine, warpPerspective, remap

转载于:https://www.cnblogs.com/featherw/p/7607301.html

[Welcome to opencv documentation]: http://docs.opencv.org/2.4/index.html
[opencv_python_study2.5_01.png]: /images/20211220/1ef376d2bce242848b5970fabf5a1c60.png
[opencv_python_study2.5_02.png]: /images/20211220/bdab78fde6784167ae14b299ffaf0b10.png
[opencv_python_study2.5_03.png]: /images/20211220/277a1af0ff5045f6aeaa30a0fefa9b8a.png