#774: i.rgb.his, i.his.rgb, d.his support for >8 bit
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Reporter: hamish | Owner: grass-dev@…
Type: enhancement | Status: new
Priority: normal | Milestone: 7.0.5
Component: Raster | Version: svn-develbranch6
Resolution: | Keywords: i.rgb.his, i.his.rgb, d.his
CPU: All | Platform: All
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Comment (by nikosa):
The attached diff works for me, for bitnesses >8-bit. The outputs hue,
saturation and intensity are in their expected range, as per the HSL/HSV
color space model. There is still an issue on how to instruct the output
to be DCELL and not FCELL. Accordingly, I'd like to modify i.his.rgb.
Source for the math of concern are:
- https://en.wikipedia.org/wiki/HSL_and_HSV#Hue_and_chroma
- https://en.wikipedia.org/wiki/HSL_and_HSV#From_HSL
The current/old implementation is identical to the one documented at
[http://www.gis.usu.edu/manuals/labbook/erdas/manuals/FieldGuide.pdf
ERDAS' field guide]. I think, however, it was meant to deal/avoid the case
when hue is undefined (this being the case when the max and min values of
a band/image are identical) and, perhaps, other issues with floating point
math(?).
See also:
- http://arxiv.org/abs/1107.3348
--
Ticket URL: <https://trac.osgeo.org/grass/ticket/774#comment:9>
GRASS GIS <https://grass.osgeo.org>
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