Maybe I missed something on the methodology, but I have a question regarding justification of designing a complete new tool.

The article mentions "ImageMagick is slow because it does a lot more than just extract image size". So we implemented a complete new solution.

How about: "We added to ImageMagick a new command to just extract image size". So we published a small patch to Imagemagick, and got it done much faster than creating a complete new tool. On top of that, reusing tested Imagemagick data structure would probably reduce a lot maintenance cost.

Maybe I did not see some subtleties ?