no decode delegate for this image format `PNG'

Question

I'm writing a django/python application and I need to convert PDF files uploaded by the user to JPEGs (files are scans)

I'm trying to use wand, with an ImageMagick backend (on OSX) and I keep getting the following error:

MissingDelegateError at /user_docs/upload/certificate/
no decode delegate for this image format `PNG' @ error/constitute.c/ReadImage/501

My current test code is as simple as:

with wandImage(filename='/Users/username/Pictures/telechargement.pdf') as img:
    img.format = 'jpeg'
    img.save(filename='/Users/username/Pictures/bzzz.jpeg')

Some information:

1. The file exists (I verify with os.path.exists)
2. I can convert the file from PDF to JPG on the command line using convert
3. I tried to set DYLD_LIBRARY_PATH to include the ImageMagick lib directory
4. identify -list configure | grep DELEGATES returns

DELEGATES bzlib fftw fontconfig freetype gs jpeg jng lcms2 lzma mpeg png tiff x11 xml zlib

Anyone has an idea?

Thanks

Answer 1

OK, Found it! As always the key is RTFM:

http://docs.wand-py.org/en/0.4.0/guide/install.html#install-imagemagick-on-mac

I was missing the:

$ export MAGICK_HOME=/opt/local