python opencv 基本讀取、轉換、顯示、儲存等

檔案位置關系

filename = 'yourfilename.jpg'         #與程式碼相同位置的檔案
filename = './file/yourfilename.jpg'  #程式碼資料夾裡的資料夾中的檔案
filename = '../yourfilename.jpg'      #程式碼上一層資料夾的檔案

讀取image 及 顯示

import cv2
filename = 'yourfilename.jpg'     #與程式碼相同位置的檔案
image = cv2.imread(filename)      #讀取照片
cv2.imshow("window title", image)  #顯示照片

儲存照片

import cv2
filename = 'yourfilename.jpg'      #與程式碼相同位置的檔案
image = cv2.imread(filename)       #讀取照片
cv2.imwrite("filename.jpg", image)  #儲存照片，試過的檔案格式 .jpg .png

照片尺寸大小取得

image = cv2.imread(filename)    #讀取照片
hight = image.shape[1]
width = image.shape[0]

色彩空間轉換

這邊要注意rgb色彩空間在opencv裡排列方式是bgr

image = cv2.imread(filename)
yuv = cv2.cvtColor(image,cv2.COLOR_BGR2YUV)   #RGB to YUV
hsv = cv2.cvtColor(image,cv2.COLOR_BGR2HSV)   #RGB to HSV
gray = cv2.cvtColor(image,cv2.COLOR_BGR2GRAY) #RGB to gray
gray = cv2.cvtColor(image,cv2.COLOR_GRAY2BGR) #gray to rgb

照片三層色分離

import cv2
filename = 'yourfilename.jpg'     #與程式碼相同位置的檔案
image = cv2.imread(filename)      #讀取照片
yuv = cv2.cvtColor(image,cv2.COLOR_BGR2YUV)
imY, imU, imV = cv2.split(yuv)
cv2.imshow("image Y", imY)
cv2.imshow("image U", imU)
cv2.imshow("image V", imV)

建立水平顯示三張單色圖

import cv2
filename = 'yourfilename.jpg'     #與程式碼相同位置的檔案
image = cv2.imread(filename)      #讀取照片
yuv = cv2.cvtColor(image,cv2.COLOR_BGR2YUV)
imY, imU, imV = cv2.split(yuv)

three_img = np.zeros((yuv.shape[1],yuv.shape[0]*3), np.uint8)   ### 建立畫布
### 將gray圖水平方向拼接
three_img[:,0:width] = imY[:]
three_img[:,width:width*2] = imU[:]
three_img[:,width*2:width*3] = imV[:]
cv2.imshow('three_gray', three_img)

讀影片或webcam

import cv2
class Camera(object):
  def __init__(self, camera = 0):
    ## camera初始設定
    self.cam = cv2.VideoCapture(camera)
    self.ret = True

    if not self.cam:
      raise Exception("Camera not accessible.")

  def get_frame(self):
    ## 取得一張frame
    frame = None
    self.ret, frame = self.cam.read()
    return frame

  def get_fps(self):
    ## 取得fps
    fps = self.cam.get(cv2.CAP_PROP_FPS)
    return fps if fps != -1 else 30.0

  def get_size(self):
    ## 取得frame 的寬高
    w = int(self.cam.get(cv2.CAP_PROP_FRAME_WIDTH))
    h = int(self.cam.get(cv2.CAP_PROP_FRAME_HEIGHT))
    return (w,h)
  
  def release_camera(self):
    ## 結束camera
    self.cam.release()
    print("release_camera")
    return True

def main():
  filename = 'yourvideoname.avi'  ## 目前試過可讀mp4 avi
  cam = Camera(filename)          ## 預設0是webcam 輸入filename就讀影片檔
  
  while cam.ret:
    frame = cam.get_frame()     ## 讀一張frame
    if not cam.ret:             ## 檢查 video,camera有沒有讀完或斷線
      break

    cv2.imshow("frame", frame)  ## 顯示
    key = cv2.waitKey(10)       ## 等待??ms ,當值小於等於0 會無限等待,直到按下任意鍵
    if (key == 27) | (key == 113): #keyboard:'q' = 113, Esc = 27
      # Exit
      break
  print("close_window")
  cam.release_camera()         ## 結束camera
  cv2.destroyAllWindows()      ## 關閉所有window

if __name__=="__main__":
  main()