OpenCV Main Function Description

Open CV Main Function Description

1.OpenCV Api searching

(https://docs.opencv.org/master/)

2.Load Video file

cv2.imread(filename, flags=None) -> retval

• filename : the name loading video (literal)
• flags : the option flag loading video

function	description
cv2.IMREAD_COLOR	Read as BGR color video shape = (rows,cols,3)
cv2.IMREAD_GRAYSCALE	Read as Gray scale shape = (rows,cols)
cv2.IMREAD_UNCHANGED	Read as original video property (e.g) transparent file shape = (rows,cols,4)

• retval : the video data loaded (numpy.ndarray)

3.Save Video file

cv2.imwrite(filename, img, params=None) -> retval

• filename : the name to save video (literal)
• img : image data to be saved (numpy.ndarray)
• params : select option to save file ( integer of attribute & value )
  e.g) [cv.IMWRITE_JPEG_QUALITY,90] : specify the compression ratio as 90%

-retval : If save is successful, it is True. If save is fail, it is False.

4.Open the new window

cv2.namedWindow(winname, flags=None) -> None

• winname : the name of window (literal)
• flag : select the flag of window attibute

cv2.WINDOW_NORMAL	specify the video size to fit the window size
cv2.WINDOW_AUTOSIZE	translate the window size to fit the video size

5.CLose the widdow

cv2.destroyWindow(winname) -> None
cv2.destroyAllWindows() -> None

• winname : the name of window you want to close

** cv2.destroyWindow() just close a window,
cv2.destroyAllWindows() close all window.

6.Move the window

cv2.moveWindow(winname,x,y) -> None

• winname : the name of window
• x,y : the position coordinate to move

7.Resize the window

cv2.resizeWindow(winname,width,height) -> None

• winname : the name of window
• width : the horizontal size of window to change
• height : the vertical size of window to change

8.Show the window

cv2.imshow(winname,mat) -> None

• winname : the name of window
• mat : the data to show video data (numpy,ndarray)
  ** Note
  
  • If the case is unit16, int32,divide the matrix element value by 255 and print them out.
  • If the case is float32, float64,multiply the matrix element value by 255 and print them out.
  • Actually, the image appears on screen only when cv2.waitKey() function is called.

9.Wait Keyboard input

cv2.waitKey(delay=None) -> retval

• delay : the waiting time (e.g) delay <= 0, wait forever. delfault value is 0
• retval : pressed key value. (if not, the value is -1)
  ** Note
  

  • Main special key code : 27(ESC) , 13(ENTER), 9(TAB)

  • Use ord() function to check the input of specific key

      while True:
      if cv.waitKey() == ord('q'):
          break