Develop Reference

Python 3.7 OpenCV - Slow processing

i'm trying to take pictures with OpenCV 4.4.0.40 and only save them if a switch, read by an Arduino, is press.
So far everything work, but it's super slow, it take about 15 seconds for the Switch value to change.
Arduino = SerialObject()
if os.path.exists(PathCouleur) and os.path.exists(PathGris):
Images = cv2.VideoCapture(Camera)
Images.set(3, 1920)
Images.set(4, 1080)
Images.set(10, Brightness)
Compte = 0
SwitchNumero = 0
while True:
Sucess, Video = Images.read()
cv2.imshow("Camera", Video)
Video = cv2.resize(Video, (Largeur, Hauteur))
Switch = Arduino.getData()
try:
if Switch[0] == "1":
blur = cv2.Laplacian(Video, cv2.CV_64F).var()
if blur < MinBlur:
cv2.imwrite(PathCouleur + ".png", Video)
cv2.imwrite(PathGris + ".png", cv2.cvtColor(Video, cv2.COLOR_BGR2GRAY))
Compte += 1
except IndexError as err:
pass
if cv2.waitKey(40) == 27:
break
Images.release()
cv2.destroyAllWindows()
else:
print("Erreur, aucun Path")
the saved images width are 640 and the height is 480 and the showimage is 1920x1080 but even without the showimage it's slow.
Can someone help me optimize this code please?

I would say that this snippet of code is responsible for the delay, since you have two major calls that depend on external devices to respond (the OpenCV calls and Arduino.getData()).
Sucess, Video = Images.read()
cv2.imshow("Camera", Video)
Video = cv2.resize(Video, (Largeur, Hauteur))
Switch = Arduino.getData()
One solution that comes to mind is to use the multithreading lib and separate the Arduino.getData() call from the main loop cycle and use it in a separate class to run in the background (you should use a sleep on the secondary thread, something like 50 or 100ms delay).
That way you should have a better response on the Switch event, when it tries to read the value on the main loop.

cam=cv2.VideoCapture(0,cv2.CAP_DSHOW)
use cv2.CAP_DSHOW it will improve the loading time of camera becasue it wil give you video feed directly

How to increase 'framerate' or text print speed? (Text-based-adventure game)

Trying to create a text-based adventure that involves interacting with a computer. So I found a way to get text to appear as though it's being typed onto the screen but it was too slow initially, so I bumped up the speed but now it's lagging a bit and several characters are appearing at a time instead of one at a time like on a computer.
I tried adding in the fps = 60, time_delta = 1./fps and upping the fps but it didn't do anything.
import time
fps = 60
time_delta = 1./fps
def delay_print(s):
for c in s:
sys.stdout.write(c)
sys.stdout.flush()
time.sleep (0.05)

You tried to change the values of fps and time_delta, but you didn't use them in your command
time.sleep (0.05)
You probably wanted
time.sleep(time_delta)

Difference in output with waitKey(0) and waitKey(1)

I've just begun using the OpenCV library for Python and came across something I didn't understand.
cap = cv2.VideoCapture(0)
while True:
ret, frame = cap.read() #returns ret and the frame
cv2.imshow('frame',frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
When I use cv2.waitKey(1), I get a continuous live video feed from my laptops webcam. However when I use cv2.waitKey(0), I get still images. Every time I close the window, another one pops up with another picture taken at the time.
Why does it not show as a continuous feed?

From the doc:
1.waitKey(0) will display the window infinitely until any keypress (it is suitable for image display).
2.waitKey(1) will display a frame for 1 ms, after which display will be automatically closed. Since the OS has a minimum time between switching threads, the function will not wait exactly 1 ms, it will wait at least 1 ms, depending on what else is running on your computer at that time.
So, if you use waitKey(0) you see a still image until you actually press something while for waitKey(1) the function will show a frame for at least 1 ms only.

waitKey(0) will pause your screen because it will wait infinitely for keyPress on your keyboard and will not refresh the frame(cap.read()) using your WebCam.
waitKey(1) will wait for keyPress for just 1 millisecond and it will continue to refresh and read frame from your webcam using cap.read().
More clearly, Use debugger in your code.When using waitKey(0) in the while loop, the debugger never crosses this statement and does not refresh the frame and hence the frame output seems stable.Does not move.
Where as with waitKey(1), the debugger will cross the code after pausing at
if cv2.waitKey(1) & 0xFF == ord('q')
for 1 milli second.

From the documentation you can see that cv2.waitKey(delay) waits for delay milliseconds if delay is positive but forever (waits for a key event infinitely) if it's zero or negative. That's why you see these differences in behavior.
In the case of cv2.waitKey(1) this is, in fact, negligible but its use provides the user the opportunity to press a key (the key might be caught in some next iteration but does not make a big difference).

Delay in milliseconds. 0 is the special value that means “forever”.
The function waitKey waits for a key event infinitely (when \texttt{delay}\leq 0 ) or for delay milliseconds, when it is positive. Since the OS has a minimum time between switching threads, the function will not wait exactly delay ms, it will wait at least delay ms, depending on what else is running on your computer at that time. It returns the code of the pressed key or -1 if no key was pressed before the specified time had elapsed.
Note: This function is the only method in HighGUI that can fetch and handle events, so it needs to be called periodically for normal event processing unless HighGUI is used within an environment that takes care of event processing.
Note: The function only works if there is at least one HighGUI window created and the window is active. If there are several HighGUI windows, any of them can be active

cv2.waitkey(1) is being used in while loop.It shows the output for 1msec but because of infinite while loop it is the sequence of images that are perceived by our brain as a single continuos video.
Hope this helped.

Indratej Reddy's answer is the only one to clearly explain why this works — and why no GUI events act until waitkey is called. Unclear how to handle menu/mouse events — e.g., ignores menu quit.
$ python3
>>> import cv2
>>> im = cv2.imread("/tmp/portrait.jpg")
>>> print("im =", im)
im = […]
>>> cv2.imshow("image", im)
>>> print("imshow called")
imshow called
>>> print("waitKey =", cv2.waitKey(0))
waitKey = 32
>>> print("destroyAllWindows =", cv2.destroyAllWindows())
destroyAllWindows = None
>>> print("Final waitKey 1ms =", cv2.waitKey(1))
Final waitKey 1ms = -1
>>>

Music player for Python not working

I want to be able to play multiple songs through a playlist using python, but it will only play the last song on the list. Please help.
from pygame import mixer # Load the required library
from os import listdir
k = listdir('C:/LOCAL')
print(k)
mixer.init()
for x in k:
y = "C:/LOCAL/" + x
print y
mixer.music.queue(y)
mixer.music.load(y)
mixer.music.play()

Your problem is that you assume that playing music with pygame will pause the program until the music is finished - which is not the case. As a result, it tries starting a song, and then it's starting another, and another, etc.
There are a few ways of trying to correct this. You could either:
Use pygame events and "tell" pygame to fire an event when the song finishes (though this requires a display surface (window) to be opened within pygame), or
Detect the length of the song, and sleep for that amount of time (which is more compatible with your current code).
I'm going to assume that you would like to do option 2, since your code works better with it.
To get the length of an MP3 file (I've not tried it with any other types), you could use the Mutagen library.
Some example code to get the length of an MP3 file (in seconds):
from mutagen.mp3 import MP3
tracklength = MP3("/path/to/song.mp3").info.length
Then you could substitute the path with y, and time.sleep for the amount of time returned, before continuing to the next iteration of the loop.
Hope that helps.
(also, you don't need to queue a file before loading it - just load and play)

Stop Winsound / Stop a thread on Python

Im writing a litle game on python using Tkinter (And by the way, i am not allowed to use any other non built in modules) and I want to play a background song when on the main window, wich is the one that holds the title, and the buttons to go to other windows and stuff...
So the thing is that I need that sound to stop when I enter to another window, but when I hit the button to go, to another window, the song keeps playing...
I'm using the winsound module, and had define a couple of functions, (That by the way, are wicked as hell) to play the song when I first run the program using threads...
So here is the deal, I want something to put in the function "killsound" so that I can add it to every button, and then when I press any button to open any other window, the sound will be killed.
I was hoping something like 'a.kill()' or 'a.stop()' but it didnt worked.
And I really don´t know how to use the SND_PURGE thing on winsound... Although I understand that SND_PURGE is no longer working on new windows OS (Got Win8.1)
Could you please help me?
Thank You! (And Sorry for the creepy english...)
def Play(nombre): #This function Is the core of the winsound function
ruta = os.path.join('Audio',nombre)
Reproducir= winsound.PlaySound(ruta,winsound.SND_FILENAME)
return Reproducir
def PlayThis():
while flag_play:
try:
return Play('prettiest weed.wav')
except:
return "Error"
def PlayThisThread():
global flag_play
flag_play= True
a=Thread(target=PlayThis, args=())
a.daemon = True
a.start()
PlayThisThread()
def killsound(): #This is the function I want, for killing sound.
global flag_play
flag_play = False

There are 2 major problems in your code:
global variable flag_play has to be placed inside the sound playback loop, in your case within the PlayThis() function
the Winsound module is aiming simple non-threaded usage. while the sound is playbacked, there is no chance to "softly" interrupt. It does not support any playback status reporting e.g. .isPlaying() nor any kind of .stop() that you need in order to kill it.
Solution:
try PyMedia package. Pymedia allows lower-level audio manipulation therefore more details have to be provided at the initialisation:
import time, wave, pymedia.audio.sound as sound
# little to do on the proper audio setup
f= wave.open( 'prettiest weed.wav', 'rb' )
sampleRate= f.getframerate() # reads framerate from the file
channels= f.getnchannels()
format= sound.AFMT_S16_LE # this sets the audio format to most common WAV with 16-bit codec PCM Linear Little Endian, use either pymedia or any external utils such as FFMPEG to check / corvert audio into a proper format.
audioBuffer = 300000 # you are able to control how much audio data is read
with the following assigment the "snd" becomes an instance of the class sound.Output and gives you bunch of useful audio methods:
snd= sound.Output( sampleRate, channels, format )
s= f.readframes( audioBuffer )
snd.play( s )
and finally your threaded playback loop might look as follows:
while snd.isPlaying():
global flag_play
if not flag_play: snd.stop() #here is where the playback gets interupted.
time.sleep( 0.05 )
f.close()
Please, let me know if you need more support on this.

I also created a 0.5 sec wavfile in Adobe Audition containing silence and attached it to the stop button, and this basically "stopped" playback of the previously played audio clip.

I found a way to do it, by adding a 0.5sec sound to a button, so that when I press the button it stops the background one to play the button one, and then stops all sounds on program.