opencv 常用图片操作函数备忘

图像翻转函数flip 

Flips a 2D array around vertical, horizontal, or both axes.

• C++: void flip(InputArraysrc, OutputArraydst, int flipCode)
  

• C:   void cvFlip(const CvArr*src, CvArr*dst=NULL, intflip_mode=0)

Parameters:

• src - input array
• dst - output array of the same size and type as src.
• flipCode -  a flag to specify how to flip the array; 0 means flipping around the x-axis and positive value (for example, 1) means flipping around y-axis. Negative value (for example, -1) means flipping around both axes (see the discussion below for the formulas).

The function flip flips the array in one of three different ways (row and column indices are 0-based):

The example scenarios of using the function are the following:

• Vertical flipping of the image (flipCode==0) to switch between top-left and bottom-left image origin. This is a typical operation in video processing on Microsoft Windows* OS.
• Horizontal flipping of the image with the subsequent horizontal shift and absolute difference calculation to check for a vertical-axis symmetry (flipCode>0).
• Simultaneous horizontal and vertical flipping of the image with the subsequent shift and absolute difference calculation to check for a central symmetry (flipCode<0).
• Reversing the order of point arrays (flipCode>0 orflipCode==0).

灰度直方图均衡化

equalizeHist

Equalizes the histogram of a grayscale image.

C++: void equalizeHist(InputArray src, OutputArray dst)

Python: cv2.equalizeHist(src[, dst]) → dst

C: void cvEqualizeHist(const CvArr* src, CvArr* dst)

Parameters:

• src – Source 8-bit single channel image.
• dst – Destination image of the same size and type as src .

The function equalizes the histogram of the input image using the following algorithm:

1. Calculate the histogram  for src .

2. Normalize the histogram so that the sum of histogram bins is 255.

3. Compute the integral of the histogram:

   

4. Transform the image using  as a look-up table: 

The algorithm normalizes the brightness and increases the contrast of the image.

颜色空间变换cvtColor

Converts an image from one color space to another.

C++: void cvtColor(InputArray src, OutputArray dst, int code, int dstCn=0 )

Python: cv2.cvtColor(src, code[, dst[, dstCn]]) → dst

C: void cvCvtColor(const CvArr* src, CvArr* dst, int code)

Python: cv.CvtColor(src, dst, code) → None

Parameters:

• src – Source image: 8-bit unsigned, 16-bit unsigned ( CV_16UC... ), or single-precision floating-point.
• dst – Destination image of the same size and depth as src .
• code – Color space conversion code. See the description below.
• dstCn – Number of channels in the destination image. If the parameter is 0, the number of the channels is derived automatically from src and code .