Develop Reference

NameError: name 'showimg' is not defined - this error is always showing even though it seems to be defined?? have i missed something?

I am a complete beginner with coding and needed to code a few lines of code for getting pictures from a USB camera for a research project that i am responsible for. admittingly i took help of a few source codes from a few blogs online, they did show a couple of errors but most of them were resolved except this one that keeps popping up no matter what i do. does anyone have any idea where exactly the problem could be arising from? all the errors in the previous lines of code seem to be dealt with. I really need to get this right as this project decides my bacheklor thesis
the following was the code that i used, even though i am really really dumb with this stuff:
`
#new camera code
import cv2
import imutils
import time
#loop for taking picture and saving
cap = cv2.VideoCapture(0)
frame = cap.read()
def takePicture():
global showimg
(frame) = cap.read()
showimg=frame
return image
cv2.imshow('image', img)
cv2.imshow('img1',showimg) # display the captured image
cv2.waitKey(1)
time.sleep(0.3) # Wait 300 miliseconds
image ='C:/Users/whale/Desktop/REMOVE/capture.png'
cv2.imwrite(image, frame)
img = cv2.imread('no-such-file.jpg', 0)
cap.release()
print(takePicture())
`

There are a few issues with your code:
The takePicture() function is not returning anything. It needs to return showimg instead of image.
The line global showimg (frame) = cap.read() should be changed to global showimg, frame; frame = cap.read().
The line img = cv2.imread('no-such-file.jpg', 0) should be removed as it is not being used and it may cause confusion.
The line print(takePicture()) should be changed to takePicture() as the function already displays the image.
Here's the correct code:
#new camera code
import cv2
import imutils
import time
#loop for taking picture and saving
cap = cv2.VideoCapture(0)
def takePicture():
global showimg, frame
frame = cap.read()
showimg = frame
cv2.imshow('image', showimg) # display the captured image
cv2.waitKey(1)
time.sleep(0.3) # Wait 300 miliseconds
image ='C:/Users/whale/Desktop/REMOVE/capture.png'
cv2.imwrite(image, frame)
return showimg
takePicture()
cap.release()

OpenCV taking single camera frame while camera still running

I wrote a script for an image processing. I need to take a frame from camera and then make some operations. I can do this but the time when script is initializing the camera is very long. Is there any solution that I will run my script and camera will be working all the time and for example when I will press a button it will save a frame?
This is my code for now:
import cv2
cap = cv2.VideoCapture(1)
cap.set(3, 640)
cap.set(4, 480)
while True:
_, img = cap.read()
cv2.imshow('Output', img)
if cv2.waitKey(1) & 0xFF==ord('s'):
print('DO IMAGE PROCESSING...')
elif cv2.waitKey(1) & 0xFF==ord('q'):
break
cap.release()
cv2.destroyAllWindows()
The problem is that when I am pressing "q" sometimes it doesn't stop. Can you give me an advice which loop or maybe which lib should I use for that?
Thanks!

Python Opencv control (increase/decrease) the video playback speed as custom

I'm writing a program to control the video playback speed as custom rate.
Is there is anyway to achieve that?
What code should be added to control the playback speed?
import cv2
cap = cv2.VideoCapture('video.mp4')
while(cap.isOpened()):
ret, frame = cap.read()
cv2.imshow('frame',frame)
if cv2.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()

In the docs it is stated:
Note
This function should be followed by waitKey function which displays
the image for specified milliseconds. Otherwise, it won’t display the
image. For example, waitKey(0) will display the window infinitely
until any keypress (it is suitable for image display). waitKey(25)
will display a frame for 25 ms, after which display will be
automatically closed. (If you put it in a loop to read videos, it will
display the video frame-by-frame)
In cv2.waitKey(X) function X means the number of milliseconds for an image to be displayed on the screen. In your case it is set to 1, so theoretically you are able to achieve 1000 fps (frames per seconds). But frame decoding takes time in VideoCapture object and limits your framerate. To change the playback speed you need to declare variable and use it as a parameter in waitKey function.
import cv2
cap = cv2.VideoCapture('video.mp4')
frameTime = 10 # time of each frame in ms, you can add logic to change this value.
while(cap.isOpened()):
ret, frame = cap.read()
cv2.imshow('frame',frame)
if cv2.waitKey(frameTime) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()
Alternatively, as frame decoding is the most time consuming task you can move it to the second thread and use a queue of decoded frames. See this link for details.
The third approach is to separate grabbing and decoding process and simply decode every nth frame. That will result in displaying only a subset of frames from the source video but from the user perspective the video will be played faster.
import cv2
cap = cv2.VideoCapture('video.mp4')
i=0 #frame counter
frameTime = 1 # time of each frame in ms, you can add logic to change this value.
while(cap.isOpened()):
ret = cap.grab() #grab frame
i=i+1 #increment counter
if i % 3 == 0: # display only one third of the frames, you can change this parameter according to your needs
ret, frame = cap.retrieve() #decode frame
cv2.imshow('frame',frame)
if cv2.waitKey(frameTime) & 0xFF == ord('q'):
break
cap.release()
cv2.destroyAllWindows()

You can use ffmpeg to speed up (or slow down) your video like fast forwarding by using "presentation time stamps".
For speed up an example would be:
ffmpeg -i YOUR_INPUT_MOVIE.mp4 -vf "setpts=0.20*PTS" YOUR_OUTPUT_MOVIE.mp4
which will speed up your movie by 5x.
For slow down an example would be:
ffmpeg -i YOUR_INPUT_MOVIE.mp4 -vf "setpts=5*PTS" YOUR_OUTPUT_MOVIE.mp4
which will slow down your movie by 5x.
Note: this method will drop frames.

OpenCV show err.message at camera lunch

I would like to lunch a usb-camera at my raspberry pi, but when I try to start python code (opencv), it shows this message and stop a lunch
ASSERT: "false" in file qasciikey.cpp, line 501
Aborted
Can someone please explain me, what error is this?
It doesnt work even with another codes as well... But camera works fine, when I open it in programs like Camorama webcam viewer. I read that this part makes a problem
cv2.waitKey(20)
So it makes in another code (when i uncomment it, it lunch the code but dont show camera output) But in this code, even if I uncomment it, the code themself doesn't work: show upper error message
Here is the code
import numpy as np
import cv2
cap = cv2.VideoCapture(0)
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Our operations on the frame come here
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
# Display the resulting frame
cv2.imshow('frame',frame)
cv2.imshow('gray',gray)
if cv2.waitKey(20) & 0xFF == ord('q'): # HERE
break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

oh are you Japanese yes bro computers are little racist do not press any japanese letter while your code runing. for waitKey you can use esc or number keys:
if cv2.waitKey(20) & 0xFF == ord('0'):
break

load Video Using OpenCV in python

Here is my code which is running...but I didnt understood why we used:
if cv2.waitKey(1000) & 0xFF == ord('q'):
break
in the code......under display the resulting frame comment:
import numpy as np
import cv2
cap = cv2.VideoCapture('C:\\Users\\KRK\\Desktop\\Dec17thVideo.mp4')
while(True):
# Capture frame-by-frame
ret, frame = cap.read()
# Our operations on the frame come here
gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
# Display the resulting frame
cv2.imshow('frame',gray)
if cv2.waitKey(1000) & 0xFF == ord('q'):
break
# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()

waitkey displays the image for the specified number of milliseconds. Without it, you actually wouldn't be able to see anything. Then 0xFF == ord('q') detects when the keystroke q is pressed on the keyboard.
Think of waitkey as a pause function. After the code has been executed; at lightning speed :), waitkey says, pause for 1000 milliseconds to display the frame. Within this, detect if the user pressed q. If q is pressed, then get outside of my infinite while loop. When this happens, then the window won't be shown anymore.
Their documentation is a good resource as well.