How to operate OpenCV4.X Slider Bar
How to carry out OpenCV4.X slider operation, many novices are not very clear about this, in order to help you solve this problem, the following small series will explain in detail for everyone, people who have this need can learn, I hope you can gain something.
I. Slider bar
createTrackbar(trackbarName, windowName, value, count, onChange): Create slider
getTrackbarPos(trackbarname, winname): Get the slider value
trackbarName: slider name windowName: window name value: default value of parameter count: maximum value of parameter onChange: callback function executed apply one
Create an application that displays the specified colors: there is a window that displays colors and three sliding track bars for specifying B, G, R color values. You can slide the track bar and change the color. The initial color is set to black.
code
import numpy as np
import cv2
def nothing(x):
Pass #do nothing.
#Create initial black image and window
img = np.zeros((300,512,3), np.uint8)
cv2.namedWindow('image')
#Create R, G, B sliders
cv2.createTrackbar('R', 'image', 0, 255, nothing)
cv2.createTrackbar('G', 'image', 0, 255, nothing)
cv2.createTrackbar('B', 'image', 0, 255, nothing)
#Create switches via slider bar, simulate buttons
#Another important application of the track bar is to use it as a button or switch. By default,
# OpenCV has no button functionality. Therefore, tracking bars can be used to obtain such functionality.
#In our app, a switch was created where the app only works when the switch is open
#Valid, otherwise the screen is always black
switch = '0 : OFF \n1 : ON'
cv2.createTrackbar(switch, 'image', 0, 1, nothing)
while True:
cv2.imshow('image',img)
k = cv2.waitKey(1) & 0xFF
if k == 27:
break
#Get slider position set RGB values
r = cv2.getTrackbarPos('R','image')
g = cv2.getTrackbarPos('G','image')
b = cv2.getTrackbarPos('B','image')
s = cv2.getTrackbarPos(switch,'image')
if s == 0:
img[:] = 0
else:
img[:] = [b, g, r]
cv2.destroyAllWindows()
2. application two
Slider bar controls video playback progress
code
import cv2
def nothing(emp):
pass
video = 'input.mp4'
cv2.namedWindow('video')
cap = cv2.VideoCapture(video)
frames = int(cap.get(cv2.CAP_PROP_FRAME_COUNT))
loop_flag = 0
pos = 1
cv2.createTrackbar('time', 'video', 0, frames, nothing)
while 1:
if loop_flag == pos:
loop_flag = loop_flag + 1
cv2.setTrackbarPos('time', 'video', loop_flag)
else:
pos = cv2.getTrackbarPos('time', 'video')
loop_flag = pos
cap.set(cv2.CAP_PROP_POS_FRAMES, pos)
ret, img = cap.read()
cv2.imshow('video', img)
if cv2.waitKey(1) & loop_flag == frames:
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