OpenCV needs Python 2.7
Basic GUI
import cv2 as cv
import numpy as np
load image (wrong path do not throw error), show image, write image
img = cv.read('test.jpg', -1) # -1 color, 0 gray, 1 including alpha
cv.show('title', img)
cv.waitKey(0) # wait for keyboard interrupt in millisec, 0 forever
cv.destroyAllWindows() # close image
cv.imwrite('image_name.jpg', img)
little tip for key interrupt
k = cv.waitKey(0)
if k == 27: # wait for ESC key to exit
cv.destroyAllWindows()
elif k == ord('s'): # wait for 's' key to save and exit
cv.imwrite('messigray.png',img)
cv.destroyAllWindows()
capture the video, convert to gray and play
cap = cv.VideoCapture(0)
while(True):
ret, frame = cap.read()
gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
cv.imshow('frame',gray)
if cv.waitKey(1) & 0xFF == ord('q'):
break
cap.release()
cv.destroyAllWindows()
draw
# Create a black image
img = np.zeros((512,512,3), np.uint8)
# blue line with thickness of 5 px
cv.line(img,(0,0),(511,511),(255,0,0),5)
# rectangle (top-left, bottom right)
cv.rectangle(img,(384,0),(510,128),(0,255,0),3)
# circle (center, radius)
cv.circle(img,(447,63), 63, (0,0,255), -1)
cv.circle(img,(447,63), 63, (0,0,255), -1)
# add text to the image
font = cv.FONT_HERSHEY_SIMPLEX
cv.putText(img,'title',(10,500), font, 4,(255,255,255),2,cv.LINE_AA)
# title, font, size, color, thickness, linetype
mouse event, use following code to show available events
import cv2 as cv
events = [i for i in dir(cv) if 'EVENT' in i]
print( events )
example, when double click, draw a circle
# mouse callback function
def draw_circle(event,x,y,flags,param):
if event == cv.EVENT_LBUTTONDBLCLK:
cv.circle(img,(x,y),100,(255,0,0),-1)
# Create a black image, a window and bind the function to window
img = np.zeros((512,512,3), np.uint8)
cv.namedWindow('image')
cv.setMouseCallback('image',draw_circle)
while(1):
cv.imshow('image',img)
if cv.waitKey(20) & 0xFF == 27:
break
cv.destroyAllWindows()
Image Process
access pixel
px = img[100,100] # pixel position
print ( px ) # result is [b,g,r]
blue = img[100,100,0] # access blue channel
img[100,100] = [0,0,0] # change it to black
# for individual pixel, following is faster
px = img.item(100,100,0)
use img.shape,img.size,img.dtype
to see image properties
select a region
ball = img[280:340, 330:390]
channel split and merge
b,g,r = cv.split(img)
img = cv.merge((b,g,r))
add
cv.add(img1,img2)
cv.addWeighted(img1,0.7, img2,0.3, 0) # w1, w2, b
also bitwise operations omitted here
Measurement
can use following code, can also use time.time()
e1 = cv.getTickCount()
e2 = cv.getTickCount()
t = (e2 - e1)/cv.getTickFrequency()
print (t)
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