Benjamin Gilbert bgilbert at cs.cmu.edu
Thu Jul 5 18:32:58 EDT 2012

On 07/05/2012 05:30 PM, Agelos Pappas wrote:
> My question here is: Would it be safe / acceptable to assume that the
> first tag always refers to the the thumbnail IFDs and the second to the
> main image?

I'd rather not if we can avoid it.  It looks as though there are a few 
things you could use to distinguish the images:

1a. The <view> coordinates for the slide image describe a rectangle 
inside the view for the thumbnail.

1b. The <view> for the thumbnail has its origin at (0, 0).

2. The <pixels> width and height are larger for the slide.

3. The <objective> is lower for the thumbnail.

It's a judgment call.  #3 is probably too obscure.  The paranoid 
approach would be to check all of #1a, #1b, and #2, and fail the open if 
we find any inconsistencies.  (OpenSlide should always fail the open 
when it gets confused, because that way we'll get a bug report that will 
help us better understand the format.)

Also, a slide could contain more than two images, e.g. two completely 
separate slide pyramids from different regions of the slide.  Your 
sanity checks should catch this.

--Benjamin Gilbert

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