["python","opencv"]
imread returns None, violating assertion !_src.empty() in function 'cvtColor' error

I am trying to do a basic colour conversion in python however I can't seem to get past the below error. I have re-installed python, opencv and tried on both python 3.4.3 (latest) and python 2.7 (which is on my Mac). I installed opencv using python's package manager opencv-python. Here is the code that fails: frame = cv2.imread('frames/frame%d.tiff' % count) frame_HSV= cv2.cvtColor(frame,cv2.COLOR_RGB2HSV) This is the error message: cv2.error: OpenCV(3.4.3) /Users/travis/build/skvark/opencv-python/opencv/modules/imgproc/src/color.cpp:181: error: (-215:Assertion failed) !_src.empty() in function 'cvtColor'
This error happened because the image didn't load properly. So you have a problem with the previous line cv2.imread. My suggestion is : check if the image exists in the path you give check if the count variable has a valid number