| Re: user-selected ROIs [message #72153 is a reply to message #72024] |
Thu, 05 August 2010 06:01  |
geogal34
Messages: 6
Registered: August 2010
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Junior Member |
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On Aug 4, 2:46 pm, David Fanning <n...@dfanning.com> wrote:
> 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.")
Thanks, David. I've managed to get the mask and indices from the
PolyFillV procedure, now I just have to figure out how to work with
them. I'm not really clear on how to use the REVERSE_INDICES yet, but
I'm playing with it. I always find it hard to translate what I'm doing
on the screen to my actual data (the retrieving part). It's just not
always intuitive to me. Thanks again!
Emily
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