opencv installation not detected about astrowidgets HOT 7 CLOSED

Solution appears to be to upgrade freetype library (installed by conda) to version 2.10.0. Apparently the opencv installation in conda doesn't have this pre-requiste set properly.

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I think there is still an issue here: conda install open can is not requiring the right version of free type. It may be that the best we can do here is clearly document how to get opencv working.

Let’s keep this open at least until a doc update I’m planning for later today.

Will also try to look at the opencv conda package. @JuanCab — can you check where your opencv is coming from: conda list opencv

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opencv itself isn't a Python library, right? Updating with conda like you did seems like the right way to go. Seems like it is solved on your end. I don't think we should force users to install it, as in the future, Ginga will not be the only backend that AstroImage would support. Please close the issue if there is nothing else that needs to be fixed in this regard. Thanks!

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I don't want to close this yet. The cause is not an astrowidgets issue, but the clarity of the error message is. I have already posted to the conda-forge opencv github issues page about the problem with the bad freetype dependency. In a nutshell, I updated opencv to the conda-forge version (which was 4.1.0) from the default channel version (3.4.2) and it didn't catch that freetype needed to be updated as well.

A clearer error message might make sense (at least echo back the error message from the import cv2 command).

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Nice sleuthing over at conda-forge/opencv-feedstock#174, @JuanCab! I think for now I'll add a note to the documentation about installing opencv. The only reason I'm hesitant to make opencv a hard requirement is that install with pip looks a little painful (there is a package called opencv-python that provides binary wheels but it isn't quite the same as installing opencv from source or from conda-forge).

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@JuanCab -- can you https://github.com/astropy/astrowidgets/pull/91/files#diff-62c330cd8da31d476bb63b51bb8b1307 take a look at https://github.com/astropy/astrowidgets/pull/91/files#diff-62c330cd8da31d476bb63b51bb8b1307 and let me know if you think it is adequate for now?

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closed by #91

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