Found this one on Hacker News and really liked it :
// 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.
Credit : https://code.google.com/p/xee/source/browse/XeePhotoshopLoader.m?r=f16763d221dfca6253983824b470adf553a19e06#108