Nothing wrong with using PNG only for (rare) edge tiles. This is the
approach in Google Earth PhotoOverlay tile pyramids:
http://code.google.com/apis/kml/documentation/photos.html
For (rectangular) photos one might suggest that JPEG tiles of lesser
dimensions than 256x256 might be better, but orthorectified imagery
will, in general, have diagonal edges, so a PNG with transparent parts
seems ideal to me.
- L
On 11 Nov 2009, at 15:42, Keith Jenkins wrote:
Image tiles should be 256x256 pixels in 8- or 24-bit compressed
PNG format
I understand the desire for transparency, but I'm not entirely sure
how we see it being used.
I agree that JPEG makes more sense for imagery. My guess is that the
transparency info would be needed in order to merge tiles from
different layers into a global layer. For example, one layer might
only cover half the tile. Maybe there is another way to address this
problem without depending on PNG transparency... perhaps by using the
bounding box metadata?
Keith
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