| Re: setting histogram bin sizes? [message #61604] |
Tue, 22 July 2008 10:18  |
Juggernaut
Messages: 83
Registered: June 2008
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Member |
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On Jul 22, 12:59 pm, Bennett <juggernau...@gmail.com> wrote:
> On Jul 22, 11:52 am, "Jeff N." <jeffnettles4...@gmail.com> wrote:
>
>
>
>> Hi folks,
>
>> I'm looking for suggestions for a way to set bin sizes for a histogram
>> when I don't know much about the data before calculating the
>> histogram. Here's my situation: I'm putting together some code that
>> takes a hyperspectral image cube and extracts a series of one-band
>> parameters from the cube (band depth at a certain wavelength, etc.).
>> In trying to assess which of these parameters is most useful for our
>> particular application i thought about calculating a histogram for
>> each parameter. The problem is that these parameter images (one band,
>> floating point images per parameter) will not necessarily fall into
>> the same range. Many have possible values of 0 - 1, but they won't
>> necessarily take up that entire range. Some however, will not have
>> possible values of 0 - 1, but could instead have numbers in the 10s or
>> even hundreds. Some parameters have values that are actually in log
>> space.
>
>> I know that I could simply set the NBINS keyword to HISTOGRAM(), but
>> then the question would become how many bins to use? I did some quick
>> searching, and there are a few attempts at calculating bin sizes or
>> the number of bins on Wikipedia (http://en.wikipedia.org/wiki/
>> Histogram). Short of any other information, i am going to use an
>> equation from that page that is at least based on the standard
>> deviation of the data. But, since I don't have a lot to go on, I
>> would very much like to have input from anyone on this newsgroup who
>> might have any suggestions for me.
>
>> Thanks,
>> Jeff
>
> I'd have to say if I was going to approach this and this is definitely
> not a very fun problem is to do the following.
> nels = n_elements(data)
> range = max(data) - min(data)
> IF range/median(data) GT 10 THEN nbins = 10 ELSE nbins = round(range/
> median(data))
> nbins = nbins < nels/10 ;- Make sure you don't have way too many bins
> This is just off the top of my head and working with some random
> data...
> I'm sure there are special cases that require some serious thought.
>
> Hope it helps a bit....somehow....someway
The GT should be a LT by the way...sorry for the confusion
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| Re: setting histogram bin sizes? [message #61605 is a reply to message #61604] |
Tue, 22 July 2008 09:59  |
Juggernaut
Messages: 83
Registered: June 2008
|
Member |
|
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On Jul 22, 11:52 am, "Jeff N." <jeffnettles4...@gmail.com> wrote:
> Hi folks,
>
> I'm looking for suggestions for a way to set bin sizes for a histogram
> when I don't know much about the data before calculating the
> histogram. Here's my situation: I'm putting together some code that
> takes a hyperspectral image cube and extracts a series of one-band
> parameters from the cube (band depth at a certain wavelength, etc.).
> In trying to assess which of these parameters is most useful for our
> particular application i thought about calculating a histogram for
> each parameter. The problem is that these parameter images (one band,
> floating point images per parameter) will not necessarily fall into
> the same range. Many have possible values of 0 - 1, but they won't
> necessarily take up that entire range. Some however, will not have
> possible values of 0 - 1, but could instead have numbers in the 10s or
> even hundreds. Some parameters have values that are actually in log
> space.
>
> I know that I could simply set the NBINS keyword to HISTOGRAM(), but
> then the question would become how many bins to use? I did some quick
> searching, and there are a few attempts at calculating bin sizes or
> the number of bins on Wikipedia (http://en.wikipedia.org/wiki/
> Histogram). Short of any other information, i am going to use an
> equation from that page that is at least based on the standard
> deviation of the data. But, since I don't have a lot to go on, I
> would very much like to have input from anyone on this newsgroup who
> might have any suggestions for me.
>
> Thanks,
> Jeff
I'd have to say if I was going to approach this and this is definitely
not a very fun problem is to do the following.
nels = n_elements(data)
range = max(data) - min(data)
IF range/median(data) GT 10 THEN nbins = 10 ELSE nbins = round(range/
median(data))
nbins = nbins < nels/10 ;- Make sure you don't have way too many bins
This is just off the top of my head and working with some random
data...
I'm sure there are special cases that require some serious thought.
Hope it helps a bit....somehow....someway
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| Re: setting histogram bin sizes? [message #61660 is a reply to message #61604] |
Thu, 24 July 2008 06:23 |
humanumbrella
Messages: 52
Registered: June 2008
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Member |
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On Jul 22, 1:18 pm, Bennett <juggernau...@gmail.com> wrote:
> On Jul 22, 12:59 pm, Bennett <juggernau...@gmail.com> wrote:
>
>
>
>> On Jul 22, 11:52 am, "Jeff N." <jeffnettles4...@gmail.com> wrote:
>
>>> Hi folks,
>
>>> I'm looking for suggestions for a way to set bin sizes for a histogram
>>> when I don't know much about the data before calculating the
>>> histogram. Here's my situation: I'm putting together some code that
>>> takes a hyperspectral image cube and extracts a series of one-band
>>> parameters from the cube (band depth at a certain wavelength, etc.).
>>> In trying to assess which of these parameters is most useful for our
>>> particular application i thought about calculating a histogram for
>>> each parameter. The problem is that these parameter images (one band,
>>> floating point images per parameter) will not necessarily fall into
>>> the same range. Many have possible values of 0 - 1, but they won't
>>> necessarily take up that entire range. Some however, will not have
>>> possible values of 0 - 1, but could instead have numbers in the 10s or
>>> even hundreds. Some parameters have values that are actually in log
>>> space.
>
>>> I know that I could simply set the NBINS keyword to HISTOGRAM(), but
>>> then the question would become how many bins to use? I did some quick
>>> searching, and there are a few attempts at calculating bin sizes or
>>> the number of bins on Wikipedia (http://en.wikipedia.org/wiki/
>>> Histogram). Short of any other information, i am going to use an
>>> equation from that page that is at least based on the standard
>>> deviation of the data. But, since I don't have a lot to go on, I
>>> would very much like to have input from anyone on this newsgroup who
>>> might have any suggestions for me.
>
>>> Thanks,
>>> Jeff
>
>> I'd have to say if I was going to approach this and this is definitely
>> not a very fun problem is to do the following.
>> nels = n_elements(data)
>> range = max(data) - min(data)
>> IF range/median(data) GT 10 THEN nbins = 10 ELSE nbins = round(range/
>> median(data))
>> nbins = nbins < nels/10 ;- Make sure you don't have way too many bins
>> This is just off the top of my head and working with some random
>> data...
>> I'm sure there are special cases that require some serious thought.
>
>> Hope it helps a bit....somehow....someway
>
> The GT should be a LT by the way...sorry for the confusion
David Fanning's article here: http://www.dfanning.com/tips/histogram_tutorial.html
might help.
Cheers,
--Justin
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