psd file format

Question

I am attempting to find documentation of the psd file format so I can read in a .psd and then save out the individual layers as files, along with do other modifications. Does anyone know of any document in on the .psd file format? (Just for reference, I will be writing this in C++)

If there are any code examples of loading a .psd file in C++ then I would appreciate them being linked.

(Please not turn this into a "just use XXX software". This is not homework, or anything related to that. I am doing this because I think it will be a fun project to work on. I will ask for posts to be down voted if this happens.)

Answer 1

There's also some Objective-C code on GitHub (should be easily understandable for anyone with a C++ background), also source of this gem, which appears to sum it up nicely:

At this point, I'd like to take a moment to speak to you about the Adobe PSD format. PSD is not a good format. PSD is not even a bad format. Calling it such would be an insult to other bad formats, such as PCX or JPEG. No, PSD is an abysmal format. Having worked on this code for several weeks now, my hate for PSD has grown to a raging fire that burns with the fierce passion of a million suns.
If there are two different ways of doing something, PSD will do both, in different places. It will then make up three more ways no sane human would think of, and do those too. PSD makes inconsistency an art form. Why, for instance, did it suddenly decide that these particular chunks should be aligned to four bytes, and that this alignement should not be included in the size? Other chunks in other places are either unaligned, or aligned with the alignment included in the size. Here, though, it is not included. Either one of these three behaviours would be fine. A sane format would pick one. PSD, of course, uses all three, and more.
Trying to get data out of a PSD file is like trying to find something in the attic of your eccentric old uncle who died in a freak freshwater shark attack on his 58th birthday. That last detail may not be important for the purposes of the simile, but at this point I am spending a lot of time imagining amusing fates for the people responsible for this Rube Goldberg of a file format.
Earlier, I tried to get a hold of the latest specs for the PSD file format. To do this, I had to apply to them for permission to apply to them to have them consider sending me this sacred tome. This would have involved faxing them a copy of some document or other, probably signed in blood. I can only imagine that they make this process so difficult because they are intensely ashamed of having created this abomination. I was naturally not gullible enough to go through with this procedure, but if I had done so, I would have printed out every single page of the spec, and set them all on fire. Were it within my power, I would gather every single copy of those specs, and launch them on a spaceship directly into the sun.

PSD is not my favourite file format.

Just so you are warned. :)

Answer 2

This will not be a fun project, the .psd format is big. It incorporates every feature Adobe has put into Photoshop over many years.

I believe the specification can be had from Adobe, but they don't just hand it out to the public. You'll have to contact them and jump through some hoops first.