[Qgis-developer] 'cubic' resambling for "zoomed in" (scale > 100%) rasters creates undesired visual glitches

[Mathieu Pellerin]

Steps to reproduce visual glitches:

1. Load a raster; for the sake of this example, please use 1:10m ocean
bottom available @
http://www.naturalearthdata.com/downloads/10m-raster-data/10m-ocean-bottom/as
it shows this issue quite well
2. In the layer property window, retrieve the min/max values of RGB bands
with these settings:
(*) cumulative count cut 2 - 98%
(*) Full (extend)
(*) Estimate (faster) (accurary)
3. Set contrast enhancement to "Stretch to MinMax"
4. Set zoomed in resampling to "Cubic"
5. Apply the change, then zoom in (raster zoom scale must be > 100% to
activate cubic resampling) a region of the raster (if using the above ocean
bottom raster, glitches easily to spot in southern china sea, among other
places)

You'll notice weird visual glitches which are not there if using the two
other types of resambling. I'm attaching a screenshot of the problem [1].

[1]
http://hub.qgis.org/attachments/5005/qgis-raster-resampling-visualglitch.jpg
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