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Re: Reading images from internal char string

From: Pantxo
Subject: Re: Reading images from internal char string
Date: Thu, 21 Jul 2016 05:40:46 -0700 (PDT)

PhilipNienhuis wrote
> Hi,
> AFAIK (pls correct me if I'm wrong) Octave can only read images from file
> (or URL, essentially a file as well).
> I'd like to find a way to read images directly from a char string ("text
> file"). 
> For some assignment I need to process a long series of rain radar images
> in PNG format. 
> I haul them in using urlread() in "raw" (compressed) form, IOW the very
> same format in memory as it would be on disk.  To make an image out of
> them I haven't found a better way yet than to first write them in raw form
> to to disk (fopen, fwrite, fclose), only then to be able turn them into an
> image using imread() to read them back in as an image.  
> It would be a lot faster, and save disk space, if the output from
> urlread() could directly be interpreted and turned into an image while the
> "raw" image is still in memory, skipping disk I/O altogether.
> Is this possible at all?
> Stepping through imread.m I see that control finally passes to binary
> module __magickread__. All the way through there I only see references to
> real files.
> I saw the url option in imageIO.m but that also results in a file on disk
> that is fed to __magickread__ in the end.
> Thanks,
> Philip

Hi Phillip,

AFAIU Octave never has to deal with raw image headers/data, we rely on
graphics magick to obtain image data in the form of RGB or indexed matrix.

To do the job, you'd have to either implement a png reader your self or use
libpng from an oct file.


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