moviepy: ImageMagick not detected by moviepy while using SubtitlesClip

ubuntu 16.04 python3.6

• Install apt-get -y install ffmpeg imagemagick

export FFMPEG_BINARY=‘/usr/bin/ffmpeg’ export IMAGEMAGICK_BINARY=‘/usr/bin/convert’

from moviepy.video.tools.subtitles import TextClip,SubtitlesClip

font="ArialUnicode"
color='white'
generator = lambda txt: TextClip(txt, font=font, fontsize=40, color=color)

subtitles = SubtitlesClip("big3.srt",generator)

• Error

[MoviePy] This command returned an error !--------------------------------------------------------
OSError                Traceback (most recent call last)
/usr/local/lib/python3.6/dist-packages/moviepy/video/VideoClip.py in __init__(self, txt, filename, size, color, bg_color, fontsize, font, stroke_color, stroke_width, method, kerning, align, interline, tempfilename, temptxt, transparent, remove_temp, print_cmd)
   1219         try:
-> 1220             subprocess_call(cmd, verbose=False )
   1221         except (IOError,OSError) as err:

/usr/local/lib/python3.6/dist-packages/moviepy/tools.py in subprocess_call(cmd, verbose, errorprint)
     48         verbose_print(errorprint, "\n[MoviePy] This command returned an error !")
---> 49         raise IOError(err.decode('utf8'))
     50     else:

OSError: convert: not authorized `@/tmp/tmpatq66tt_.txt' @ error/property.c/InterpretImageProperties/3405.
convert: no images defined `PNG32:/tmp/tmp4uy8drq2.png' @ error/convert.c/ConvertImageCommand/3210.


During handling of the above exception, another exception occurred:

OSError                Traceback (most recent call last)
<ipython-input-3-923a31c238ba> in <module>()
----> 1 subtitles = SubtitlesClip("big3.srt",generator)

/usr/local/lib/python3.6/dist-packages/moviepy/video/tools/subtitles.py in __init__(self, subtitles, make_textclip)
     84
     85         self.make_frame = make_frame
---> 86         hasmask = (self.make_textclip('T').mask is not None)
     87         self.mask = (VideoClip(make_mask_frame, ismask=True) if hasmask else None)
     88

<ipython-input-2-31100183c052> in <lambda>(txt)
      1 font="ArialUnicode"
      2 color='white'
----> 3 generator = lambda txt: TextClip(txt, font=font, fontsize=40, color=color)

/usr/local/lib/python3.6/dist-packages/moviepy/video/VideoClip.py in __init__(self, txt, filename, size, color, bg_color, fontsize, font, stroke_color, stroke_width, method, kerning, align, interline, tempfilename, temptxt, transparent, remove_temp, print_cmd)
   1227                     "path to the ImageMagick binary in file conf.py, or."
   1228                     "that the path you specified is incorrect" ))
-> 1229             raise IOError(error)
   1230
   1231         ImageClip.__init__(self, tempfilename, transparent=transparent)

OSError: MoviePy Error: creation of None failed because of the following error:

convert: not authorized `@/tmp/tmpatq66tt_.txt' @ error/property.c/InterpretImageProperties/3405.
convert: no images defined `PNG32:/tmp/tmp4uy8drq2.png' @ error/convert.c/ConvertImageCommand/3210.
.

.This error can be due to the fact that ImageMagick is not installed on your computer, or (for Windows users) that you didn't specify the path to the ImageMagick binary in file conf.py, or.that the path you specified is incorrect

What should I do ?