[Qgis-developer] raster visualization

[Tim Sutton]

Hi

On Fri, Apr 20, 2012 at 2:17 PM, Marco Hugentobler
<marco.hugentobler at sourcepole.ch> wrote:
> Hi
>
>
>>BTW Freak out will go after resampler branch is merged....
>
> I've managed to convert freakout style to singleband pseudocolor in the
> project file / qml conversion to the new format :-)
>
>> - visualizing monoband rasters could be improved:
>>
>> - why not loading it with a greyscale by default? or with a colour ramp?
>> - why not adding a dtm colour table (we can take the one
>
>
> I'd like to improve selecting colorramps in the raster resampler branch
> (that would even allow us to add a freakout color ramp for trips down memory
> lane).
>
> Default style: I'm not sure what would be a good default, since we don't
> know the value range at the beginning (at least not without doing a time
> consuming value scan). Do you have any ideas (maybe a partial raster scan to
> speed things up?).
>

Yes - Julien had a really nice suggestion to implement the following logic:

- on initial load of a raster, generate a quicklook that is the larger
of 1/4 screen resolution or 500x500 pixels by sampling every nth pixel
- generate a histogram from the quicklook
- calculate clipped 2% - 96% range min max for each band
- apply a histogram stretch based on the above
- the histogram could be used for generating the graph in raster
props, and the quicklook could be used to create thumbs and previews
etc
- ideally we should cache these quicklooks and only regenerate them if
the underlying dataset has changed

I believe if we do this we will have fast initial load and the images
(grayscale and rgb) will 'look right' when first loaded (i.e with good
contrast) and it would not be necessary to assign any color value to
grayscales by default.

Regards

Tim


> Regards,
> Marco
>
>
> On 20.04.2012 11:10, Tim Sutton wrote:
>>
>> Hi
>>
>> On Fri, Apr 20, 2012 at 10:47 AM, Giovanni Manghi
>> <giovanni.manghi at gmail.com>  wrote:
>>>
>>> On Fri, 2012-04-20 at 10:19 +0200, Paolo Cavallini wrote:
>>>>
>>>> Hi all.
>>>> Visualizing monoband rasters could be improved:
>>>> - why not loading it with a greyscale by default? or with a colour ramp?
>>>> - why not adding a dtm colour table (we can take the one
>>>> in/usr/lib/grass64/etc/colors/terrain), possibly replacing the Freak out
>>>> one?
>>>
>>> +100
>>> much needed improvements
>>>
>> All good ideas but we are feature frozen so lets first focus on
>> releasing 1.8 and then we can do these.
>>
>> BTW Freak out will go after resampler branch is merged....
>>
>> Regards
>>
>> Tim
>>
>>> -- Giovanni --
>>>
>>>
>>>
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>>
>>
>>
>
>
> --
> Dr. Marco Hugentobler
> Sourcepole -  Linux&  Open Source Solutions
> Churerstrasse 22, CH-8808 Pfäffikon SZ, Switzerland
> marco.hugentobler at sourcepole.ch http://www.sourcepole.ch
> Technical Advisor QGIS Project Steering Committee
>
>
> _______________________________________________
> Qgis-developer mailing list
> Qgis-developer at lists.osgeo.org
> http://lists.osgeo.org/mailman/listinfo/qgis-developer



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Tim Sutton - QGIS Project Steering Committee Member (Release  Manager)
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