| Re: user-selected ROIs [message #72024] |
Wed, 04 August 2010 11:46  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Emily writes:
> The XROI procedure is the first thing I tried, but I don't understand
> how to get the actual values I've already calculated in the histogram.
I don't understand what you mean by "actual values" in the histogram.
A histogram tells you how many values fall into a particular bin of
the histogram. And you can use the reverse indices to tell you which
of the data values contributed to that count, but there are no "values"
per se. You could, of course, use the indices retrieved with
REVERSE_INDICES to go back to the data and obtain the data values.
Is this what you mean?
> This is why I started doing it in a different way. If I just send the
> image, I get the occurrences over 0-255 and if I send the actual data,
> which is an array, I just get a little image that I can't really even
> see.
I think you are confusing the *display* of your image with
the image itself. They are really two completely different
things. The "values" of the image are completely divorced
from the "values" in which the image is displayed, except that
a very small subset of display values (0 to 255) are used to
represent an infinite number of real (image) values. You
are very rarely interested in the display values. In fact,
you may not even know what they are!
> If I send the array of masses, the latitude array, and longitude
> array, I just get three tiny images.
Three tiny images where?
> Do you know how I send XROI the
> real values of the pixels (n-g/m3, not 0-255) and still have it
> displayed as a map?
What does "displayed as a map" mean in this context? Does
it mean you have map grid lines and continental boundaries
on it? XROI doesn't care what you pass it, as long as it
is an 8-bit or 24-bit image. What you are going to get
back from XROI is not the information you are looking
for. Rather, it is the information you need to *retrieve*
the values you are looking for from the original image
data. In other words, what you are looking for is a mask
that you can use to either select the image values you
are interested in, or to select the image values you
are not interested in. Your goal here is to obtain a
mask that you can apply to your real image data that
allows you to work with the right pixels.
I think if you read the first article a couple of times,
and maybe work through the example, you will see what
I mean.
Cheers,
David
P.S. Do you see how the REVERSE_INDICES from the Histogram
are a type of mask to select pixels you are interested in?
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")
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