| Re: distribution of colors for an image [message #41492 is a reply to message #41366] |
Wed, 27 October 2004 06:57   |
R.Bauer
Messages: 1424
Registered: November 1998
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Senior Member |
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David Fanning wrote:
> Reimar Bauer writes:
>
>
>> fine, I have seen a lot of instruction on your marvellous web page.
>>
>> But I don't understand the result I got. Lets show an example.
>>
>> a=dist(20)
>> h=histogram(a)
>> print,max(a),max(h)
>> 14.1421 56
>>
>>
>> u=uniq(a,sort(a))
>> help,u,h
>> U LONG = Array[61]
>> H LONG = Array[15]
>>
>> Why could be h higher as a?
>> Why doesn't I got a vector length of 61 as uniq tells?
>
>
> You asked about color distribution in an image. A histogram
> will tell you (with a byte scaled image, of course) how many
> pixels in the image have a particular color. It will even
> tell you which pixels those are, but that is another story,
> best explained with JD's Histogram Tutorial.
>
> In your case H is fifteen elements long, because your data
> had values between 0 and 15, and you used a bin size of 1,
> by default. The *numbers* returned from histogram, told you
> the pixel distribution of those 15 "colors". In one bin, for
> example, you had 56 pixels values that fell into that bin.
>
> You had 61 unique numbers in your data, but all 61 of them fell
> into one of the 15 bins you set up.
>
> To see your color distribution, you want to plot the histogram
> of your data:
>
> data = dist(200)
> Plot, Histogram(data), XStyle=1, $
> XTitle='Color Distribution', YTitle='Number of Pixels'
>
> Does that help?
>
Yes, this is very good explained.
Now it is clear and I know why I was so irritated of the result I got.
I have used a circular clipping of an image and have missed that's
histogram uses always rectangular input. The background color which
clips the data to invisible is count highest. If I don't use max_value I
see nothing on the plot.
Thanks for all help
Reimar
> Cheers,
>
> David
>
--
Reimar Bauer
Institut fuer Stratosphaerische Chemie (ICG-I)
Forschungszentrum Juelich
email: R.Bauer@fz-juelich.de
------------------------------------------------------------ -------
a IDL library at ForschungsZentrum Juelich
http://www.fz-juelich.de/icg/icg-i/idl_icglib/idl_lib_intro. html
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