Fun Photoshop File Format Facts
Paul Ford

I was one of the developers for PhotoCaster (a Photoshop to Macromedia Director plugin ) and SiteGrinder (a Photoshop to web tool) and worked intimately with the internals of the Photoshop file formats for over a decade. The specification available at any given time was always behind. If memory serves, we had to reverse engineer three different methods for how Photoshop stored text layers. I don’t believe any of them ever appeared in the spec. Similarly, layer masks had a vast array of encodings and interpretations, none of which were documented. And image metadata was stored repeatedly throughout the .psd file, in many different representations, with no indication of which was canonical. Good times.