php opening a psd file

I apologize that this isn't so much a programming question as it is a general information question.

I do know C and C++ as well as my web languages, but I ran across a php class that extracted a .psd image. And I thought to myself, as a somewhat inexperienced programmer, I would have no idea where to ev开发者_StackOverflow中文版en start there. How does one discover how a particular type of file is structured? How would you find how to process the bytes of the file? Because really my only idea would be to call Adobe.

Thanks for your help and advice!

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Get the SDK and read the documentation. If the file format is documented, you can read the documentation / specification. This is the most common way. Otherwise you have to reverse engineer it.