Merge pull request #21224 from UncleLLD:fix-cvtColor-error

fix cvtColor-error

* fix gray image channel error

* fix gray image channel error

* fix cvtColor error after the video end

* fix cvtColor error after the video end and change next variable

* fix cvtColor error after the video end

* reset next variable

* fix cvtColor error after the video end

* fix cvtColor error after the video end

samples/python/tutorial_code/video/optical_flow/optical_flow.py

@@ -17,12 +17,12 @@ feature_params = dict( maxCorners = 100,
                        blockSize = 7 )
 
 # Parameters for lucas kanade optical flow
-lk_params = dict( winSize  = (15,15),
+lk_params = dict( winSize  = (15, 15),
                   maxLevel = 2,
                   criteria = (cv.TERM_CRITERIA_EPS | cv.TERM_CRITERIA_COUNT, 10, 0.03))
 
 # Create some random colors
-color = np.random.randint(0,255,(100,3))
+color = np.random.randint(0, 255, (100, 3))
 
 # Take first frame and find corners in it
 ret, old_frame = cap.read()
@@ -33,7 +33,11 @@ p0 = cv.goodFeaturesToTrack(old_gray, mask = None, **feature_params)
 mask = np.zeros_like(old_frame)
 
 while(1):
-    ret,frame = cap.read()
+    ret, frame = cap.read()
+    if not ret:
+        print('No frames grabbed!')
+        break
+
     frame_gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
 
     # calculate optical flow
@@ -45,18 +49,20 @@ while(1):
         good_old = p0[st==1]
 
     # draw the tracks
-    for i,(new,old) in enumerate(zip(good_new, good_old)):
-        a,b = new.ravel()
-        c,d = old.ravel()
-        mask = cv.line(mask, (int(a),int(b)),(int(c),int(d)), color[i].tolist(), 2)
-        frame = cv.circle(frame,(int(a),int(b)),5,color[i].tolist(),-1)
-    img = cv.add(frame,mask)
-
-    cv.imshow('frame',img)
+    for i, (new, old) in enumerate(zip(good_new, good_old)):
+        a, b = new.ravel()
+        c, d = old.ravel()
+        mask = cv.line(mask, (int(a), int(b)), (int(c), int(d)), color[i].tolist(), 2)
+        frame = cv.circle(frame, (int(a), int(b)), 5, color[i].tolist(), -1)
+    img = cv.add(frame, mask)
+
+    cv.imshow('frame', img)
     k = cv.waitKey(30) & 0xff
     if k == 27:
         break
 
     # Now update the previous frame and previous points
     old_gray = frame_gray.copy()
-    p0 = good_new.reshape(-1,1,2)
+    p0 = good_new.reshape(-1, 1, 2)
+
+cv.destroyAllWindows()

samples/python/tutorial_code/video/optical_flow/optical_flow_dense.py

@@ -2,22 +2,28 @@ import numpy as np
 import cv2 as cv
 cap = cv.VideoCapture(cv.samples.findFile("vtest.avi"))
 ret, frame1 = cap.read()
-prvs = cv.cvtColor(frame1,cv.COLOR_BGR2GRAY)
+prvs = cv.cvtColor(frame1, cv.COLOR_BGR2GRAY)
 hsv = np.zeros_like(frame1)
-hsv[...,1] = 255
+hsv[..., 1] = 255
 while(1):
     ret, frame2 = cap.read()
-    next = cv.cvtColor(frame2,cv.COLOR_BGR2GRAY)
-    flow = cv.calcOpticalFlowFarneback(prvs,next, None, 0.5, 3, 15, 3, 5, 1.2, 0)
-    mag, ang = cv.cartToPolar(flow[...,0], flow[...,1])
-    hsv[...,0] = ang*180/np.pi/2
-    hsv[...,2] = cv.normalize(mag,None,0,255,cv.NORM_MINMAX)
-    bgr = cv.cvtColor(hsv,cv.COLOR_HSV2BGR)
-    cv.imshow('frame2',bgr)
+    if not ret:
+        print('No frames grabbed!')
+        break
+
+    next = cv.cvtColor(frame2, cv.COLOR_BGR2GRAY)
+    flow = cv.calcOpticalFlowFarneback(prvs, next, None, 0.5, 3, 15, 3, 5, 1.2, 0)
+    mag, ang = cv.cartToPolar(flow[..., 0], flow[..., 1])
+    hsv[..., 0] = ang*180/np.pi/2
+    hsv[..., 2] = cv.normalize(mag, None, 0, 255, cv.NORM_MINMAX)
+    bgr = cv.cvtColor(hsv, cv.COLOR_HSV2BGR)
+    cv.imshow('frame2', bgr)
     k = cv.waitKey(30) & 0xff
     if k == 27:
         break
     elif k == ord('s'):
-        cv.imwrite('opticalfb.png',frame2)
-        cv.imwrite('opticalhsv.png',bgr)
+        cv.imwrite('opticalfb.png', frame2)
+        cv.imwrite('opticalhsv.png', bgr)
     prvs = next
+
+cv.destroyAllWindows()