How to quickly determine whether a file is an image file using iPhone/iPad SDK

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How to quickly determine whether a file is an image file using iPhone/iPad SDK

If I have a (potentially largish) file on disk, and I want to determine quickly whether UIImage will be able to load it.

I don't necessarily trust the file extension to be reliable; I need to look at the actual data.

I can (of course) load it into a UIImage, but that's relatively slow and rather memory intensive. I'd rather just peek at the first chunk of the file and make a decision.

What's the fastest, most efficient way to go about this that is still fairly reliable? (Ideally, it'd be an Apple-provided API, but I didn't turn one up in my searches.) A 99.9% solution is good enough; I'm willing to have false positives in rare cases, such as when an image file has been truncated.

Are you worried about image corruption? Why not read the signature from the file and determine if its in a list of supported image formats?

CDSO1 2010-04-14 16:22:24

Worried about (a) not knowing which of the various image formats UIImage supports -- it appears to vary by platform, (b) having a reliable, exhaustive set of signatures. (By signature I assume you mean the magic bytes at the beginning.) I'm mostly worried about the variety of RAW formats, making sure I have good coverage, etc. That's why I was hoping for something official or some trick/technique using the official API or an open source project/listing that I could use.

Josh Bleecher Snyder 2010-04-14 16:45:34

I have not looked into it, but perhaps this will help:http://developer.apple.com/mac/library/samplecode/MassiveImage/Introduction/Intro.html#//apple_ref/doc/uid/DTS10004468It should provide a method to query the image information without loading the file

CDSO1 2010-04-14 17:27:16

Looked promising...but that sample code is a way to provide already decoded pixel data to a process that is going to handle it. I need the opposite -- a way to incrementally ask for decoded pixel data from an existing file. It's a good start for future investigation, though -- thanks!

Josh Bleecher Snyder 2010-04-14 19:10:14

There is no Apple API for dealing with corrupt files.

Azeem.Butt 2010-04-14 21:07:39

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How to quickly determine whether a file is an image file using iPhone/iPad SDK

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