[Geopackage] Mixing JPEG and PNG tiles ?
even.rouault at spatialys.com
Tue Nov 4 04:38:18 EST 2014
TLDR: Can someone confirm if it is allowed to have both JPEG and PNG tiles in
the same "Tile Pyramid User Data Table" ?
I've read requirements 35 and 36 multiple times, and I'd think so, but
honestly their language is a bit too convoluted for me to be absolutely
"In a GeoPackage that contains a tile pyramid user data table that contains
tile data that is not MIME type image/jpeg, by default SHALL store that tile
data in MIME type image/png"
Imagine a user table with 2 tiles: one PNG, one JPEG. That table contains
tiledata that is not MIME type image/jpeg (the PNG one). And that tile data is
of MIME type image/png. So requirement satisfied ? But what does the "by
default" means (="if you don't use the webp extension or a custom one") ?
But I've add a look at the test case
and/opt/tiles/tiles_encoding/data/mime_type_png and I'm even more confused.
Looking at the test method as it is currently written, it would seem that you
cannot pass it if you have a mix of formats. Worse, my understanding is that
you cannot satisfy both /opt/tiles/tiles_encoding/data/mime_type_jpeg
and/opt/tiles/tiles_encoding/data/mime_type_png as soon as you have tile_data
content. Step 3b of mime_type_png (resp. mime_type_jpeg) should rather be "For
each row tile_data from step a THAT IS NOT MIME TYPE IMAGE/JPEG (resp THAT IS
NOT MIME TYPE IMAGE/PNG)", shouldn't it ?
I've found an old draft of the spec (v0.2.0, 2012-11-15,
http://portal.opengeospatial.org/files/?artifact_id=51391), that had a very
clear statement :
"NOTE: Images of multiple MIME types may be stored in given table. For
example, in a tiles table, image/png format tiles without compression could be
used for transparency where there is no data on the tile edges, and image/jpeg
format tiles with compression could be used for storage efficiency where there
is image data for all pixels. Images of multiple bit depths of the same MIME
type may also be stored in a given table, for example image/png tiles in both
8 and 24 bit depths."
Does this still apply to the 1.0 version ?
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