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• OpenCV returns an Array of All Zeros on video.read

  19 janvier 2020, par Ikechukwu Anude

  Below is the relevant code

  import cv2 as cv
  
  import numpy as np
  
  
  
  video = cv.VideoCapture(0) #tells obj to use built in camera\
  
  
  
  #create a face cascade object 
  
  face_cascade  = 
  
  cv.CascadeClassifier(r"C:\Users\xxxxxxx\AppData\Roaming\Python\Python36\site- 
  
  packages\cv2\data\haarcascade_frontalcatface.xml")
  
  
  
  a = 1
  
  #create loop to display a video
  
  while True:
  
      a = a + 1
  
      check, frame = video.read()
  
      print(frame)
  
  
  
      #converts to a gray scale img
  
      gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
  
  
  
      #create the faces
  
      faces = face_cascade.detectMultiScale(gray, scaleFactor=1.5, minNeighbors=5)
  
  
  
      for(x, y, w, h) in faces:
  
          print(x, y, w, h)
  
  
  
      #show the image
  
      cv.imshow('capturing', gray)
  
  
  
      key = cv.waitKey(1) #gen a new frame every 1ms
  
  
  
      if key == ord('q'): #once you enter 'q' the loop will be exited
  
          break
  
  
  
  print(a) #this will print the number of frames
  
  
  
  #captures the first frame
  
  video.release() #end the web cam
  
  
  
  #destroys the windows when you are not defined
  
  cv.destroyAllWindows()

  The code displays a video captured from my webcam camera. Despite that, OpevCV doesn’t seem to be processing any frames as all the frames look like this

   [[0 0 0]
  
    [0 0 0]
  
    [0 0 0]
  
    ...
  
    [0 0 0]
  
    [0 0 0]
  
    [0 0 0]]]

  which I assume means that they are empty.

  This I believe is preventing the algorithm from being able to detect my face in the frame. I have a feeling that the issue lies in the ffmpeg codec, but I’m not entirely sure how to proceed even if that is the case.

  OS : Windows 10
  Language : Python

  EDIT : The Frame is not empty but all the values in the array seem to be ’0’

  Why is the frame empty and how can I get OpenCV to detect my face in the frame ?

• Pipe PyQt Widget Images to ffmpeg

  31 octobre 2014, par throwaway17434

  I have a PyQt Window with widgets that change. I want to make a video of it. I found this Answere to be very useful, however it is does not seem to be possible to use subprocess PIPE as a target in QtGui.QPixmap’s save-method. I have the feeling that I should use the native QtProcess for this kind of work, but I don’t know how I can PIPE the images and I can’t see the errors because I can’t see the standard outpur/error either. What I want to do is something like this :

  from PyQt4 import QtGui, QtCore
  
  import random
  
  
  
  app = QtGui.QApplication([])
  
  win    = QtGui.QWidget()
  
  layout = QtGui.QGridLayout()
  
  win.setLayout(layout)
  
  
  
  #picture frame
  
  scene = QtGui.QGraphicsScene()
  
  canvas  = QtGui.QGraphicsView(scene)
  
  layout.addWidget(canvas,0,0)
  
  
  
  # start button
  
  def run():
  
      # set pen
  
      pen = QtGui.QPen(QtCore.Qt.red)
  
      size = canvas.size()
  
  
  
      # start seperate process
  
      process = QtCore.QProcess(app)
  
      process.start('ffmpeg',['-y', '-f', 'image2pipe', '-vcodec', 'mjpeg', '-r', '24',  '-i', '-', '-vcodec', 'mpeg4', '-qscale', '5', 'video.avi'])
  
      for i in range(100):
  
          x = random.randint(1, size.width()-1)
  
          y = random.randint(1, size.height()-1)        
  
          scene.addLine(x,y,x,y, pen=pen)
  
          QtGui.QPixmap.grabWidget(win).save(process, "jpeg")
  
  
  
  but_run = QtGui.QPushButton("Go!")
  
  but_run.clicked.connect(run)
  
  layout.addWidget(but_run,1,0)
  
  
  
  win.show()
  
  app.exec_()

• Pipe PyQt Widget Images to ffmpeg

  10 février 2024, par throwaway17434

  I have a PyQt Window with widgets that change. I want to make a video of it. I found this Answer to be very useful, however it is does not seem to be possible to use subprocess PIPE as a target in QtGui.QPixmap's save-method. I have the feeling that I should use the native QtProcess for this kind of work, but I don't know how I can PIPE the images and I can't see the errors because I can't see the standard outpur/error either. What I want to do is something like this :

  


  from PyQt4 import QtGui, QtCore
import random

app = QtGui.QApplication([])
win    = QtGui.QWidget()
layout = QtGui.QGridLayout()
win.setLayout(layout)

#picture frame
scene = QtGui.QGraphicsScene()
canvas  = QtGui.QGraphicsView(scene)
layout.addWidget(canvas,0,0)

# start button
def run():
    # set pen
    pen = QtGui.QPen(QtCore.Qt.red)
    size = canvas.size()
    
    # start seperate process
    process = QtCore.QProcess(app)
    process.start('ffmpeg',['-y', '-f', 'image2pipe', '-vcodec', 'mjpeg', '-r', '24',  '-i', '-', '-vcodec', 'mpeg4', '-qscale', '5', 'video.avi'])
    for i in range(100):
        x = random.randint(1, size.width()-1)
        y = random.randint(1, size.height()-1)        
        scene.addLine(x,y,x,y, pen=pen)
        QtGui.QPixmap.grabWidget(win).save(process, "jpeg")
        
but_run = QtGui.QPushButton("Go!")
but_run.clicked.connect(run)
layout.addWidget(but_run,1,0)

win.show()
app.exec_()