[Qgis-developer] Feedback for contrast enhancement ... enhancements ?

G. Allegri giohappy at gmail.com
Fri Sep 2 04:50:38 PDT 2016


I would also make min/max the default option, because I've has many users
(mostly newcomers) were struggling too find out why some pixels were not
displaying as expected. It was because the statistics weren't including
some, few, important pixels.
Anyway I know that, generally, cutting the tails provide a better visual


Il 02/set/2016 12:39, "Even Rouault" <even.rouault at spatialys.com> ha

> Hi,
> There has been interest expressed to improve the usability of the contrast
> enhancement function. Basically there are workflows where you want the
> min/max
> values used by contrast enhancement to be updated each time you pan or zoom
> the canvas. From what I've seen, here's what currently exists:
> - a long method (6 clicks): through the Style tab of the layer properties
> - a faster method (2 clicks): through the "Strech using current extent" of
> the
> contextual menu of the layer panel.
> When you have several rasters loaded, even the 2-click method is
> inconvenient,
> so there's a need for a 0-click solution (once the layers have been
> configured)
> Another shortcoming in the current implementation is that the settings of
> the
> "Load min/max values" foldable group are not persistant, which requires re-
> setting them if you're not happy with the default Cumlative count cut
> method.
> And if you use the "Strech using current extent" menu item, the genuine
> min/max values are used (not the 2-98% cumulative count cut)
> So I was thinking to something along the following lines:
> - make the min/max settings persistant
> - remove the "Load" button and "Clip extent to canvas" checkbox, and
> replace
> them by 3 radio buttons to determine the scope of statistics : "Whole
> raster",
> "Current canvas" and "Updated canvas". See the attached
> proposal_min_max.png.
> The function of the Load button would be replaced by the general Apply / OK
> buttons.
> - when the user manually enters the min/max values, the 2 groups of radio
> buttons (method to compute min/max and scope of statistics) would be
> unchecked
> so that is is clear that they don't come from computed statistics. I also
> think that when you select "Current canvas", once the Apply/OK buttons have
> been pushed, the checked state of Current canvas shouldn't be saved. This
> way
> when you display the layer properties you have a good idea of where the
> current min/max values come from.
> - make the "Strech using current extent" method honour the way min/max are
> computed in the min/max settings instead of using systematically the
> min/max.
> So when "Updated canvas" would be selected, it would have no (extra)
> effect as
> expected.
> Any opinions ?
> Even
> --
> Spatialys - Geospatial professional services
> http://www.spatialys.com
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