[GRASSLIST:2332] i.his.rgb

Hi all, I have a problem that I can't quite figure out with i.his.rgb. I have
been manipulating landsat 7 data using the method described in the GRASS book.
I am trying to add in band 8. So far I can get this to work, in a number of
different ways. The way I have found to be the most successful (for retaining
the colors that I want) is to enhance the contrast of all 4 bands using
r.rescale, converting to his (i.rgb.his), and converting back to rgb (i.his.rgb
with band 8 as intensity). The problem is that a lot of "holes" appear in the
final rgb files. Single pixels seem to be converted to a value of zero, even
though the same pixels (in space) are not zeros or nulls in the original files
(pre i.rgb.his > i.his.rgb). I have posted a specific example here.

www.uweb.ucsb.edu/~ian_macmillan/hisrgb.jpg

Band1x is the i.his.rgb converted blue file, while bands 1,2,3,8 are the
original rescaled files. The black dots are clearly visible scattered
throughout the image. They each have a value of zero.

Anybody have any ideas what is going on?

thanks, Ian

On Thu, Jan 22, 2004 at 12:22:20PM -0800, Ian Macmillan wrote:

Hi all, I have a problem that I can't quite figure out with i.his.rgb. I have
been manipulating landsat 7 data using the method described in the GRASS book.
I am trying to add in band 8. So far I can get this to work, in a number of
different ways. The way I have found to be the most successful (for retaining
the colors that I want) is to enhance the contrast of all 4 bands using
r.rescale, converting to his (i.rgb.his), and converting back to rgb (i.his.rgb
with band 8 as intensity). The problem is that a lot of "holes" appear in the
final rgb files.

I don't think that the usage of r.rescale is a good idea. Like that
you are manipulating the pixels instead of the color table.

Why not applying the HIS/RGB procedure and then using r.colors on
the resulting 3 channels?

Single pixels seem to be converted to a value of zero, even
though the same pixels (in space) are not zeros or nulls in the original files
(pre i.rgb.his > i.his.rgb). I have posted a specific example here.

Yes - probably due to r.rescale usage.

www.uweb.ucsb.edu/~ian_macmillan/hisrgb.jpg

Band1x is the i.his.rgb converted blue file, while bands 1,2,3,8 are the
original rescaled files. The black dots are clearly visible scattered
throughout the image. They each have a value of zero.

Anybody have any ideas what is going on?

It's not the procedure proposed in the book (there r.colors is recommended).
IMHO pixel values should not be touched.

Cheers

Markus

--
Markus Neteler <neteler itc it> http://mpa.itc.it
ITC-irst - Centro per la Ricerca Scientifica e Tecnologica
MPBA - Predictive Models for Biol. & Environ. Data Analysis
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