1) The specs are now much more publicly accessible than they used to be, and frankly the spec does a fairly reasonable job describing a tricky format relatively compactly. It requires a fair bit of knowledge of Photoshop to read and understand, but it’s mostly fairly explicit. Much better than many other proprietary document formats.

2) For someone with relatively extensive knowledge of photoshop, the format is fairly comprehensible, albeit complicated. The biggest part of the problem here is, as you say, that Photoshop just has a ton of features to support, so that becoming enough of a Photoshop expert to understand it all is a difficult undertaking by itself.

3) The code this comment is taken from only interacts with a small fraction of PSD features, and is frankly pretty awful code: hacky, ad-hoc, not modular at all, etc.

All that said, if someone was to redesign PSD format today, I’m sure it would be organized quite a bit differently, and would have much better re-use of a smaller number of features. (The same goes for Photoshop itself.)

Whenever I need to write a binary serialization format, I usually copy .mov's tree of structs format, it's ridiculously fast, extensible, and keeps people away from C++ terrible stream operators/Java's BinaryReaderWhateverFactoryErrorProneOneIntAtATimeReader.

No.

He will think of the "serialization format" as an interchange format between two different instances of his program. One process first writes the data file and another process later will read it. He also knows that sooner or later the "serialization format" needs to talk with different versions of his program, not just different running instances.

AFAIK, the Word .doc also started (and unfortunately continued) as basically a not-so-designed memory dump of the in-memory OLE data model. It's a format that more often than not has infamously stumped its own implementation as well. (Over time, OpenOffice has saved quite a lot of .doc files of Office users.)

I like how you embodied your point in the unsyntax of that very sentence. ;)

And that's the basic design flaw - it is a data interchange format despite not being designed as one, and the terrible job that it apparently does at it. The people who wrote it didn't recognise that they were going to be filling that need. There's a lesson in there somewhere.

Now, Word docs are xml format. Pretty extensible.

care to elaborate?

The only oddity I can recall is that Photoshop does something odd with the alpha channel - I think it was the alpha channel? - by sometimes storing it with the summary image rather than the layer to which it's related. (Don't ask me for more details than that - I don't remember.) I thought at the time that this looked like somebody's attempt to make newer data work tolerably with older revisions. That part WAS annoying, because the documentation didn't mention that, and it took about a week before somebody managed to create a photoshop file that was arranged this way.

The file format overall bore many of the hallmarks of one that had grown rather than being planned, but it looks like they'd started to clamp down on things at some point because the newer data chunks looked a lot better-designed than the old ones. These things happen. It could be worse. BMP is worse. TGA is worse. They aren't even chunk-based.

It is actually padded to 2-byte boundaries. The 68000 had an external 16 bit data interface. That's the only thing I would fix about IFF if I redid it today. (And I would add a 64-bit length extension, and a "reserved chunkid" designation, e.g. anything that starts with a '$' must be registered in some central registry)

  #define TRUE FALSE //Happy debugging suckers

PS: I wish Jeff hadn't shut down the thread.

try {

} finally { // should never happen

}

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So that Google code link is the original source today, but it might not be tomorrow.