Re: Raw JPEG Data Size

<nozisles_2000@xxxxxxxxx> wrote in message
news:1136833978.124058.79510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>I have a raw stream of data, part of which contains a JPEG (possibly
> not in its entirity). I am attempting to extract (just extract, not
> interpret) the image. Currently I detect the JPEG (JFIF) signature,
> then walk through the image for as long as possible by detecting valid
> headers and their size. Unfortunately, once I reach the start of a
> scan (M_SOS) I am lost as to how to detect the correct/appropriate
> size.

I think you have to decode it.

> I could attempt to scan for M_EOI however, this is extremely
> unreliable as a) it may occur in data (?)

Not legally. Any image data that looks like a valid marker has a 0x00
inserted in the middle.

> and b) there is the
> possiblity it will not be there at all and my extraction will never
> end. I am not very versed in the ways of JPEG and any help on this
> matter will be great. I have looked over IJG's code on the subject and
> it seems rather advanced for what I am trying to do. Is there any
> simple calculations I can use to get the size of the scan or the
> distance from any unique marker to M_EOI?

If your codestream is complete, looking for the FFD9 should work.
If it's truncated, I think you need to decode till you can decode no more
(assuming I've understood your question correctly).


.

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