OpenCV Python save jpg specifying quality; gives SystemError

Question

I just installed the newest OpenCV 2.4 on windows 7 (32bit)/ Python 2.7.3,
but I still get the same error I got using the beta version:

>>> import cv2
>>> a = cv2.imread(r"DMap.jpg")
>>> a.shape
(1080, 1920, 3)
>>> cv2.imwrite('img_CV2_90.jpg', a, [cv2.IMWRITE_JPEG_QUALITY, 90])
Traceback (most recent call last):
  File "<input>", line 1, in <module>
SystemError: error return without exception set

Any ideas ? Using tuple instead of list, or adding a trailing 0 to the sequence does not help - same error.

Thanks - Sebastian Haase

Answer 1

It is probably due to some wrong wrapping of the imwrite() parameters from Python to C, cv2.IMWRITE_JPEG_QUALITY (which is of type "long"), and causes some weird problems. You should try to convert this constant to "int" type:

cv2.imwrite('img_CV2_90.jpg', a, [int(cv2.IMWRITE_JPEG_QUALITY), 90])

for me it solved the problem (python 2.7.2, opencv 2.4.1)