[Geopackage] WEBP extension

Pepijn Van Eeckhoudt pepijn.vaneeckhoudt at luciad.com
Tue Dec 2 10:12:13 EST 2014


The wording of the tile encoding format requirements is a bit convoluted 
indeed. I'm not sure why it's phrased the way it is.

Basically the set of allowed image formats in the base spec is
{ png, jpeg }

The webp extension extends this set to
{ png, jpeg, webp }

WebP was added to provide a format that supports lossy compression 
combined with an alpha mask. The alternative to using WebP is to mix 
jpeg and png where png is only used if transparent pixels are present.

Pepijn

On 02/12/14 15:19, Even Rouault wrote:
> Hi,
>
> "Annex P: Tiles Encoding WebP Extension (Normative)"  mentions
> "The MIME type of values of the tile_data column in tile pyramid user data
> tables SHALL be image/x-webp"
>
> whereas "3.2.2.2. WEBP MIME Type" mentions :
> "A GeoPackage that contains a tile pyramid user data table that contains tile
> data MAY store tile_data in MIME type image/x-webp"
>
> The first seems to imply that a tile pyramid user data declared with gpkg_webp
> extension should store ONLY webp tiles, wheras the latter could be interpreted
> as allowing mix of jpeg, png and webp tiles within the same tile pyramid user
> data.
>
> Which interpretation is the correct one : first one (only webp) ?
>
> Best regards,
>
> Even
>

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