Add a way to get the format of an image

[bu6n]

This library seems to do every possible thing with images but one simple thing: get the format of an image. In the introspection functions, I would love to see a function named sth. like type that would return "png" or "jpeg" or "heis", etc.
It seems that you already parse the magic numbers in the open functions. Would you consider extracting the magic numbers to be able to just check if an image file is of a given type? Given the scope of this library it does not feel right to add another library to my project just to check for that.

[kipcole9]

It seems that you already parse the magic numbers in the open functions. Would you consider extracting the magic numbers to be able to just check if an image file is of a given type?

That's a possibility. The implementation for matching file types is far from complete or exhaustive but it wouldn't be too hard to generalise is and add something to the API. The api would need to support pathnames and binaries so that in-memory images can be processed.

I'm curious what the use case is? Related to MIME types maybe?

[bu6n]

The use case is that I'm accepting image uploads and I need to verify they are of the correct format (and then proceed to some transformations). It's just that the scope of your library seems so big, so it's interesting that it does not do this one small thing. I'm ok with going with another library just for that if you don't plan to add that here.

[kipcole9]

Ah, ok, that makes sense. I’ll work on adding the basic capability to identify the image type of a binary. I’m on the road at the moment so it may take a week or so to have something to try.

[bu6n]

Thanks, I have no stress!

[kipcole9]

I've caught up with the slack conversation now. Overall, it seems to me that https://github.com/Group4Layers/ex_image_info does a really good job of this. I'd be happier to contribute a PR to detect heif/heic image detection than duplicate that code in image. It's a small library and appears well written so I wouldn't be hesitant about using it.

[bu6n]

@kipcole9 In the meantime, I have opened a PR in Group4Layers/ex_image_info#13, if you want to check it out or make comments.

[kipcole9]

I'll work on this for the next release (likely 0.54) over the next couple of weeks. I also want to investigate whether I can include some image safety aspects as well.

[bu6n]

That's nice to know thanks!