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| GeoCommunity Mailing List |
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| Subject: | [gislist] Summary of Raster Woes responses |
| Date: |
12/15/2003 12:20:01 PM |
| From: |
Michele Mattix |
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Hi Everyone,
I want to summarize the responses I received for my question about how to
remove the black collar from raster images (using ArcGIS 8.3). Thanks to
all who wrote: Robert Lega, Fernando Gil, Jordan Chamberlin, Todd Clausen,
Jim Cueno, Emily Smith, Margaret Gooding, Mike Juvrud, Travis Smith,
Cynthia True, Doug Culbert, and Gwen Wolph.
Most everyone had the same suggestion:
Here is what I do to make the background disappear:
Right click on the raster layer --> properties --> symbology tab -->
select stretched --> check the box: "Display Background Value:" -->
Enter the value of the background (in my case it is 255 because I have
inverted the high/low values...it is probably 0 in your case) --> click
the dropdown box next to the value you entered --> select "No Color" at
the top of the color selector that pops up --> click apply. If you still
see the background...try the other extreme value in your raster layer.
Basically, that is what worked for me. I clicked the symbology tab, saw
that a color ramp was chosen by default, clicked on the very first item
which was a black box with nothing written beside it (null), then clicked
the removed button. It went bye-bye and with my problem.
Additionally, here are some other suggestions from some responders:
* Now, if you've got a lot of images, you might want to go through each
one, group them, and then save the group as a layer file so you won't need
to re-symbolize every time.
* There are 3 items in the ArcMap help:
Contents: ArcMap --> Working with rasters --> removing the background
area of a raster layer. They are all basically saying the same
thing...just depending on what kind of symbology you are using.
* if you want to permanently remove this void data, you can do this in
a variety of ways including, deleting that particular black signature
value,
clipping each scene, or merging the scenes, etc...
* I wrote this AML awhile back to make the black areas NODATA. It gets rid
of black collars around images, and should work for this. You can modify
it for your needs, but the basic commands are in the ArcInfo help docs
(ArcDocs). Here are the basic steps from my AML (and the full thing is
attached):
/* First turn the image into a grid
arc: imagegrid %in_image% %outgrid%
/* Set all of the "black" cells to NODATA
grid: %nulloutgrid% = setnull(%outgrid% eq 0,%outgrid%) /* Keep in
mind that if your image turns into a gridstack,
/* you have to run this command for every band that is in the
stack
/* Repeat the above steps until ALL of your images have been processed
/* Now merge all of the grids. If you have gridstacks, then merge each
band. For example, merge all of the %outgrid%c1 grids. Then all of the
%outgrid%c2, and so on.
grid: %mergedgrid% = merge(%nulloutgrid%)
/* If you were working with gridstacks, now you need to create a stack from
the merged bands
grid: makestack %finalgrid% list %mergedgridband1% %mergedgridband2%
/* only use this "addtostack" if there was more than 2 bands in the image
grid: addtostack %finalgrid% %mergedbandn%
/* Convert the merged grid back to an image
arc: gridimage %finalgrid% # %outimage% TIFF /* or whatever kind of
image you want
Thanks again to all who came to my rescue. You guys ROCK!
Happy Holidays,
Michele Mattix
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