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

[Nyall Dawson]

On 2 September 2016 at 21:50, G. Allegri <giohappy at gmail.com> wrote:
> +1
>
> 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.

Yes please! There's so many users on stackexchange who get confused
with this same issue.

Nyall

> Anyway I know that, generally, cutting the tails provide a better visual
> result.
>
> giovanni
>
>
> Il 02/set/2016 12:39, "Even Rouault" <even.rouault at spatialys.com> ha
> scritto:
>>
>> 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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>
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