Python OpenCV / PIL COLOR_BGR2RGB 错误

Question

I've written some Python code that takes frames from a video and puts several of them into rows/columns in jpegs. For the most part, it works, except for the end. So I assume this error has something to do with indexing out-of-range in an array.

import cv2, Image, os


name = raw_input('Video File (With Extension): ')
x_res = int(raw_input('Image Width (Pixels): '))
y_res = int(raw_input('Image Height (Pixels): '))
rows = int(raw_input('Number of Rows: '))
columns = int(raw_input('Number of Columns: '))


vidcap = cv2.VideoCapture(name)
_,im = vidcap.read()
frames = int(vidcap.get(cv2.CAP_PROP_FRAME_COUNT))
new_im = Image.new('RGB', (x_res, y_res))
x_cntr = 0
y_cntr = 0


if not os.path.exists('./' + name + ' Output/'):
    os.makedirs('./' + name + ' Output/')


for x in xrange(0,frames,1):
    if x%(rows*columns) == 0:
        new_im.save('./' + name + ' Output/' + str(x) + '.jpg')
        new_im = Image.new('RGB', (x_res,y_res))
        y_cntr = 0
        x_cntr = 0
        print str(round(100*(float(x)/frames), 1)) + "% Complete"
    elif x%rows == 0:
        x_cntr = 0
        y_cntr = y_cntr + y_res/columns
    elif x%1 == 0:
        x_cntr = x_cntr + x_res/rows
    _,cv2_im = vidcap.read()
    cv2_im = cv2.cvtColor(cv2_im,cv2.COLOR_BGR2RGB)
    im = Image.fromarray(cv2_im)
    im = im.resize((x_res/rows + x_res%rows, y_res/columns + y_res%columns), Image.ANTIALIAS)
    new_im.paste(im, (x_cntr, y_cntr))

It returns this when it is going to make the last image:

Traceback (most recent call last):
  File "C:/Users/Cameron/Downloads/JPG/IMG2.py", line 36, in <module>
    cv2_im = cv2.cvtColor(cv2_im,cv2.COLOR_BGR2RGB)
error: C:\builds\master_PackSlaveAddon-win32-vc12-static\opencv\modules\imgproc\src\color.cpp:7349: error: (-215) scn == 3 || scn == 4 in function cv::cvtColor

Answer 1

This error suggests that your image cv2_im is not BGR format so it cannot convert to RGB. It must already be RGB format or might be GRAY format. The error represents format mismatch.

Use this code

cv2_im = cv2.cvtColor(cv2_im, cv2.COLOR_GRAY2RGB)

Answer 2

So basically, it was trying to save a non-existent frame to the end. So if I chose 5 rows and 5 columns, when there were 132 frames, it wouldn't divide equally (132 % 25 ≠ 0) and it would try to index something out of range of the video. So I basically added an "if success == True" then process normally, else "if success == False" then save what it has and stop. So here is the working code.

import cv2, Image, os


name = raw_input('Video File (With Extension): ')
x_res = int(raw_input('Image Width (Pixels): '))
y_res = int(raw_input('Image Height (Pixels): '))
rows = int(raw_input('Number of Rows: '))
columns = int(raw_input('Number of Columns: '))


vidcap = cv2.VideoCapture(name)
success,im = vidcap.read()
frames = int(vidcap.get(cv2.CAP_PROP_FRAME_COUNT))
print frames
new_im = Image.new('RGB', (x_res, y_res))
x_cntr = 0
y_cntr = 0


if not os.path.exists('./' + name + ' Output/'):
    os.makedirs('./' + name + ' Output/')


for x in xrange(0,frames,1):
    if x%(rows*columns) == 0:
        new_im.save('./' + name + ' Output/' + str(x) + '.jpg')
        new_im = Image.new('RGB', (x_res,y_res))
        y_cntr = 0
        x_cntr = 0
        print str(round(100*(float(x)/frames), 1)) + "% Complete"
    elif x%rows == 0:
        x_cntr = 0
        y_cntr = y_cntr + y_res/columns
    elif x%1 == 0:
        x_cntr = x_cntr + x_res/rows
    success,cv2_im = vidcap.read()
    if success == True:
        cv2_im = cv2.cvtColor(cv2_im,cv2.COLOR_BGR2RGB)
        im = Image.fromarray(cv2_im)
        im = im.resize((x_res/rows + x_res%rows, y_res/columns + y_res%columns), Image.ANTIALIAS)
        new_im.paste(im, (x_cntr, y_cntr))
    elif success == False:
        new_im.save('./' + name + ' Output/' + str(x) + '.jpg')