Mirax slides png tiles

[ajwood at mta.ca]

Hi All,

I've been wondering about Mirax downsampling for some time and this seems like
an alright place to ask. I've noticed that downsampling layer N to half its
size with Image Magick makes for a different image than layer N+1. Does anyone
know details about where the Mirax layers come from?

Thanks,
Andrew



Quoting Benjamin Gilbert <bgilbert at cs.cmu.edu>:

> On Fri, November 11, 2011 4:18 am, Konstantin Kozlov wrote:
> > But if I try to get the region
> >
> > openslide-write-png 256 256 <layer> 100 100 file.png
> >
> > I get a 100 by 100 pixels file but its origin is not at the point
> > (256,256). For one file and one of the layers I've determined
> > experimentally that I have to multiply the coordinates of the desired
> > origin on 204.8, of course approximately.
> >
> > So do I need to find some correct factor for each layer and each file
> > or it is a bug?
>
> Hello Konstantin,
>
> The parameters to openslide-write-png have the same semantics as those to
> openslide_read_region(): x and y are always coordinates in layer 0.  In
> the C API, you can use openslide_get_layer_downsample() to get the
> downsampling factor for each layer.  Unfortunately, these values are not
> included in the output of openslide-show-properties.
>
> However, for Mirax, each layer should be exactly a factor of 2 downsample
> from the previous layer, so I can't explain your 204.8 value.
>
> --Benjamin Gilbert
>
>
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