Real time plotting of average hue taken from webcam

[siemovit]

Hello,

I am new in Python and working on a project where I need to display in real time the average hue a picture taken by a camera. For the moment, I use my webcam, for simplicity reasons. I have read many articles and topics, especially http://forum.arduino.cc/index.php?topic=137635.15;wap2 and https://groups.google.com/d/msg/pyqtgraph/haiJsGhxTaQ/sTtMa195dHsJ and my code comes directly from these examples. However, for some reason, the graph doesn't want to plot. 

As I said, I am very beginner and I don't understand exactly what I am doing with the threads, but I have to use it and not the timer approach because the final camera will need such implementation. 

Here is the code I have :

########################

import cv2

import numpy as np

import pyqtgraph as pg

from pyqtgraph.Qt import QtGui, QtCore

import time

import sys

cap = cv2.VideoCapture(0)

frames = 10

app = QtGui.QApplication([])

average_hue_array = np.empty(frames)

win = pg.GraphicsWindow()

win.setWindowTitle('Real time plotting of the average hue of an image')

p1 = win.addPlot()

plt = pg.plot()

def update(average_hue_array):

    plt.plot(average_hue_array, clear=True)

    

class Reader(pg.QtCore.QThread):

    

    newData = pg.QtCore.Signal(object)

    

    def run(self):

        

        for i in range(0,frames):

            global avghue

            # Take each frame

            _, frame = cap.read()

            # Convert BGR to HSV

            imghsv = cv2.cvtColor(frame, cv2.COLOR_BGR2HSV)

            average_color_per_row = np.average(imghsv, axis=0)

            average_color = np.average(average_color_per_row, axis=0)

            avghue = average_color.item(0)

            average_hue_array[i] = avghue

            self.newData.emit(average_hue_array)

            time.sleep(0.05)

            print("average hue = {}".format(avghue))

                  

            k = cv2.waitKey(1) & 0xFF

                  

            if k == 27 or k == 'q':

                cap.release()

                cv2.destroyAllWindows()

                sys.exit(0)

        

            

thread1 = Reader()

thread1.newData.connect(update)

thread1.start()

########################             

I guess it is quite easy to solve and I probably miss something obvious.

Siemovit