[Qgis-developer] Slow raster loading

[Giovanni Manghi]

Hi all,

On Mon, 2012-01-30 at 13:16 +0100, Paolo Cavallini wrote:
> Hi all.
> Currently, loading coloured rasters with stretching to minmax on is extremely slow
> (almost unusable):
> http://hub.qgis.org/issues/4421
> E.g. I could load a large RasterLite in <1 sec instead of minutes (!).
> The trick, from the user point of view, is to disable stretching by default, and
> enable it only for rasters where the option makes sense (e.g. a monoband, greyscale).
> Obviously we could do it better, disabling the stretch for the rasters where it does
> not make sense.
> In addition, Giovanni noticed several other small bugs.


my notes are in the ticket.

There a few bugs (see ticket) and a couple of things need to be changed:

*) computing of stats takes a long time, it is easy to see that also
with not that big rasters it takes a lot, especially if multi-band,
hurting the user experience. The proposal is to make computing of stats
optional.

*) in the raster properties there are two properties ("contrast
enhancement" and "standard deviation") that have a button to save the
option in a way to allow the setting be persistent among qgis sessions.
This obviously should be moved to the general options, allowing to
override at a layer level.

cheers

-- Giovanni --