width and height should be allowed to be excluded (no defaults)

[crisog]

I've been using pdf-image but switched to this library as the former only supports writing to the file system.

I've encountered an issue with this library regarding its default settings for width and height. These default values interfere with the behavior of the underlying library which already does a good job when these options are not specified.

I think there should be a way to omit specifying width and height when invoking GraphicsMagick, thus leveraging its native capabilities for better results.

Kind of related to #88

[mskec]

Hi @crisog, you can set width and height to undefined and allow the underling library to set aspect ratio. You can find some examples -> #88 (comment)