Add support for DICOM (aka Supp 145) #157

[Benjamin Gilbert]

On Fri, Oct 07, 2016 at 08:14:57AM +0200, Mathieu Malaterre via openslide-users wrote:
> On Fri, Oct 7, 2016 at 5:58 AM, Benjamin Gilbert via openslide-users
> <openslide-users at lists.andrew.cmu.edu> wrote:
> >
> > As I understand the spec, all tiles from a given level, Z-plane, and
> > wavelength must be stored in a single image object, and thus in a single
> > file.  (I think that's also what David is saying?)  Am I misunderstanding
> > the spec, or is there another reason that there could be a large number of
> > files?
> 
> There is no requirement for the the tiles of a given level to be
> stored in a single file.

The part I had missed, I think, is that the frames of a multi-frame image
can be divided among multiple objects in a concatenation.

> > To be clear: you're saying that GDCM and DCMTK need to load all of the image
> > *data* into RAM, not just the metadata?
> 
> Correct. Keep in mind that DICOM really is just like XML. You need a
> properly defined DTD and specifically tailored parser if you want to
> do anything smart.

Ouch.  Custom parser it is, then.

> I'll return to the review page and address your remaining comments.
> Pay attention that we are close to Debian freeze, so it's my turn to
> being drag onto other shiny things.

OK.  I'm clearly not in any position to complain about delays.  :-)

--Benjamin Gilbert