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
C. 点击Search按钮后可以看到结果，如图1.2
D. 点开第一条函数说明，进去查找到resize函数，如图1.3
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:QAQpythonopencv>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[ exttt{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[ exttt{(double)dsize.width/src.cols}f]
. @param fy scale factor along the vertical axis; when it equals 0, it is
computed as
. f[ exttt{(double)dsize.height/src.rows}f]
. @param interpolation interpolation method, see cv::InterpolationFlags
.
. @sa warpAffine, warpPerspective, remap